Grow-out Stage Research Articles

Comparative analysis on growth performance, survival and harvest traits between offspring from wild and mass-selected populations of Crassostrea nippona

Crassostrea nippona has recently been recognized as a preferred alternative to C. gigas in summer due to its firm flesh and high glycogen content. To promote industrial development, the mass selective breeding program was initiated to improve growth performance of C. nippona in 2014. Although a steady genetic gain of approximately 10% for growth traits was achieved in each of the first three generations of the selected strains, little is known about the cumulative genetic progress in desired traits contributed by the selective breeding in the genetic improvement program. In this study, the aquaculture performance of the selected population was comprehensively evaluated by comparing the production performance and reproductive traits of the progeny (WF1 and SF4) from the wild population and the third-generation selected line in commercial farming environments. The results showed that the diameters of eggs from both populations were at similar levels, but the fertilization and hatching rates of the progeny from the selected lines were significantly higher than those of the wild population (P < 0.05). At larval stages, the shell height and cumulative survival rate (CSR) of individuals from SF4 were consistently superior to that of WF1, especially on day 6 post-fertilization, in which CSR of the improved C. nippona was increased by 25.08% compared to that of wild oysters. Meanwhile, a significant 12.10% enhancement in the metamorphosis rate was observed in SF4 when compared with WF1. During the grow-out stage, SF4 displayed distinct advantages in growth performance and survival compared to the wild strain, with 23.19, 33.48, 34.18 and 79.11% improvement in shell height, body weight, CSR and final yield at harvest on day 800, respectively. Meanwhile, relative brood amount (RBA) associated with initial development of offspring was found to be significantly higher in SF4 compared with WF1 (P < 0.05). Remarkably, the gonadal development, sex ratios and biochemical composition of oysters from both populations were at similar levels at final harvest, implying that high-intensity artificial selection had no significant effect on reproductive characteristics and nutritional quality of C. nippona. The encouraging results in the present study suggest that the overall genetic progress contributed by genetic breeding is considerable in the fast-growing strain of C. nippona, and such gains are expected to continue to increase with further selective breeding.

Effects of dietary L-tryptophan supplementation on agonistic behavior, feeding behavior, growth performance, and nutritional composition of the Chinese mitten crab (Eriocheir sinensis)

In the pond culture of Chinese mitten crabs (Eriocheir sinensis), high stocking densities usually increase the frequency of agonistic behavior, which can directly impact crab integrity, survival, and growth and result in economic losses. We hoped to reduce agonistic behavior by adding additives to feed. In this study, we first observed the agonistic behavior of E. sinensis in 5 molting periods (from first molting to puberty molting) during the adult grow-out stage. Then, we assessed the effects of L-TRP as a feed additive on the agonistic behavior of juvenile, precocious, subadult, and adult crabs. Finally, we performed 106 days of cage culture to assess the effects of L-TRP on feeding behavior, animal vitality, growth performance, and nutritional composition. The results showed that the intensity of agonistic behavior was significantly higher after puberty molting than in other molting periods during the adult grow-out stage. Moreover, L-TRP supplementation inhibited the agonistic behavior of juvenile, subadult, and adult crabs, but it did not affect the precocious crabs. During cage culture, L-TRP significantly improved crab vitality after 3 weeks but not after 6 and 9 weeks, but it reduced the ingestion rate after 9 weeks. Moreover, the L-TRP group showed a significant increase in the weight gain rate and specific growth rate after the fourth molting. After 106 days of culture, the content of proline and fatty acids in the muscle decreased significantly after L-TRP diet supplementation. Some long-chain polyunsaturated fatty acids also decreased significantly in the hepatopancreas. However, we must focus on the adverse effects of L-TRP on Pro and fatty acid composition. Further research is required on the balance between inhibition of agonistic behavior and effects of L-TRP on the nutritional quality of E. sinensis.

Growth, survival, and morphometric relationships of Crassostrea corteziensis cultivated during the nursery stage in oyster bags at different tidal levels, in Boca de Camichín, Nayarit, Mexico

The optimal tide height at which the intertidal oyster bed system (IOBS) should be installed to cultivate Crassostrea corteziensis in Boca de Camichín (BC), Nayarit, Mexico, during the intermediate grow-out stage (39.3–60.2 mm in shell length) was determined. Temperature, salinity, chlorophyll a (Chla), and turbidity were recorded 3 times a day. A trophic state index (TSI) was calculated with Chla and turbidity data. Three treatments corresponding to tide levels were tested: (1) high level (14 cm above mean sea level [MSL], emersion time [ET] = 56.4% of the total duration of the experiment), (2) intermediate level (MSL, ET = 48.6%), and (3) low level (41 cm below MSL, ET = 32.1%). Gross growth rates and absolute and relative monthly growth rates were calculated to identify periods with highest growth relative to environmental conditions. Finally, the effect of the treatments on the dimensions and weight of the oysters was studied. The results indicate that BC water was mesotrophic in April–June and eutrophic in July–August. The low tide level was the best for IOBS operation, with growth rates of 0.15, 0.10, and 0.07 mm·d–1 in shell length, width, and thickness, respectively, and 0.204 g·d–1 wet weight. Cumulative mortality was lower in the low (18.5%) and intermediate (16.4%) treatments. Shell thickness was significant reduced (P &lt; 0.05) in the high treatment and total wet weight was reduced in the high and intermediate treatments. The results of this study offer a viable and different alternative to the cultivation of C. corteziensis in strings that is currently carried out in Boca de Camichín, Nayarit, Mexico.

The growth performance of pond-reared common carp (Cyprinus carpio) larvae propagated using cryopreserved sperm.

The aim of our study was to determine the efficacy of utilizing cryopreserved common carp sperm (in comparison to fresh sperm) for propagation at a Hungarian aquaculture facility. The sperm was frozen in 5mL straws using an extender method that was previously tested in common carp. Sperm motility was monitored using a computer-assisted sperm analysis system. The hatching and malformation rates among the specimens were recorded before the stocking of larvae in both groups. The growth (body weight, total length) and survival rates of the fish were measured during the pre-nursing (from May to June: between 1 and 26days post hatching) and grow-out periods (from June to October: between 26 and 105days post hatching) of the same year. The fresh sperm, which was collected and pooled prior to fertilization, showed high MOT (97%), pMOT (92%), VCL (106µms-1), LIN (75%), and ALH (1.84µm). Prior to the fertilization trial of the cryopreserved sperm, low MOT (34%), pMOT (14%), and VCL (61µms-1) values were observed in frozen-thawed sperm. A significantly higher hatching rate was measured in the fresh sperm group (87%) when compared to the cryopreserved sperm group (42%). No significant difference in the overall malformation rate was observed in larvae originating from either the fresh or frozen sperm. A significant difference between the two test groups was observed in the incidence of deformed tails (fresh: 20%, cryopreserved: 55%). Except for one sampling period, no significant difference in the body weight and total length of the fish larvae was found between the two groups throughout the pre-nursing and grow-out periods. A significantly higher larvae survival rate was noted in the fresh sperm (72%) as compared to the cryopreserved group (43%) by the end of the pre-nursing stage. However, no significant difference in survival rate was observed for the cryopreserved sperm (96%) in comparison to the fresh sperm (95%) by the end of the grow-out stage. The results of this study showed, for the first time in large-scale pond culturing, an equal growth and viability in larvae propagated from cryopreserved sperm when compared to fresh sperm (despite the limited available rearing ponds provided by the commercial company).

Effect of Lysine and Poultry Slaughterhouse by Product Meal on Growth Performance, Feed Efficiency, and Blood Profile of Sangkuriang Catfish (Clarias gariepinus var. Sangkuriang)

The increasing demand for livestock and poultry feeds results in the lack of fish meals (FM). Poultry slaughterhouse by-product (PSB) is one promising strategy due to its high protein content despite the limited content of lysine. Thus, supplementing lysine in dietary fish feed is necessary. The present study aimed to investigate how different lysine doses in feed with PSB and FM as animal protein sources affected protein digestibility, feed utilization, growth, hematology, and body composition of Sangkuriang catfish (Clarias gariepinus var. Sangkuriang). Sangkuriang catfish at the grow-out stage (15.54±0.17 g/fish) were used. The fish were fed six experimental diets with similar protein and energy content but different lysine levels at 1.25%, 1.75%, 2.25%, 2.75%, 3.25%, and 3.75%/kg (treatments 1 to 6). The addition of lysine to feed had a significant (P&lt;0.05) effect on protein digestibility (ADCp), efficiency of feed utilization (EFU), and relative growth rate (RGR) of Sangkuriang catfish at a grow-out stage but had no significant (P&gt;0.05) effect on survival rate, hematology, and nutrient content. The optimal doses of dietary lysine with PSB and FM to improve ADCp, EFU, and RGR of Sangkuriang catfish were 2.59%, 2.63%, and 2.62%/kg diet, respectively. However, the supplementation of PSB in experimental diets had no significant effect on glucose, triglyceride, total protein, urea, calcium, magnesium, albumin, globulin, hemoglobin, hematocrit, phosphorous, and mean corpuscular hemoglobin concentration (MCHC). The lysine addition in feed formulated with PSB and FM could improve the growth performance and increase the feed digestibility of Sangkuriang catfish at the grow-out stage.

Compensatory growth and production economics of Silver pompano, Trachinotus blochii (Lacepede, 1801), fingerlings stunted by feed and space deprivation

The effect of stunting by feed and space deprivation on compensatory growth (CG) in Silver pompano,Trachinotus blochii, was investigated. A commercial pellet feed (45% protein and 10% fat) was fed two times a day, throughout the entire experiment. The 270-day experiment consisted of an initial 60-day stunting phase and a 60-day post-stunting phase carried out in 4 × 2 × 2 m3galvanized iron (GI) rectangular cages, and a 150-day grow-out phase carried out in 3-m diameter circular GI cages. During the stunting phase, the normal fish (in triplicates) were stocked at lower stocking density (17 fish/m3) and fed at 10% of body weight (BW), while stunted fish (one replication) were stocked at about three times higher stocking density (56 fish/m3) and fed at a three times lower feeding rate (3% of BW). The stunted and normal fish were reared in triplicates during the post-stunting phase, at uniform stocking density (15 fish/m3) with feeding at a higher rate (10% of BW) for stunted fish and normal feeding rate (8% of BW) was adopted for normal fish. During the grow-out stage, each replication from the post-stunting phase was shifted to 3-m circular cages with the same feeding rates. The lag in growth in stunted fish (5.56 g against 9.43 ± 0.13 g of normal) during the stunting phase was compensated during the post-stunting phase (36.88 ± 2.23 g against 38.13 ± 1.48 g of normal) by higher feeding rate. There were no significant (p&amp;gt; 0.05) differences in final harvest, biometry, morphometry, dressing yield, carcass nutritional composition, and serum biochemical markers at the end of grow-out stage. Because of the significant difference (p&amp;lt; 0.05) in the total feed provided (5.2 kg for stunted fish against 22.8 kg for normal fish) and the lesser unit cost for the production of stunted fingerling (USD 0.087 for stunted fish against USD 0.106 for normal), the farming of stunted fish brought about a higher net operational revenue and benefit:cost ratio.

Comparative estimation of the lysine requirements in two generations of improved strain of Nile tilapia (Oreochromis niloticus) at the grow-out stage

A 3 × 2 factorial experiment was conducted to investigate the effects of dietary lysine on growth performance, body indices, feed intake, feed efficiency, whole body nutrient composition and amino acid deposition in two successive generations (16th and 17th) of GIFT (Oreochromis niloticus). Three diets containing different levels of lysine at 1.16%, 1.56% and 2.41% were prepared for the feeding trial. Triplicate groups of fish with an initial body weight of 155 g were fed to apparent satiation for 10 weeks in a recirculating aquaculture system. Apparent digestibility coefficients (ADC) of dry matter, crude protein, crude lipids, and total carbohydrates were measured in the experimental diets. At the end of the experiment, no interactions between dietary lysine levels in diet and fish generation were observed on all parameters except for the condition factor (CF) and ADC of crude protein. However, dietary lysine level significantly affected the final weight, weight gain, thermal unit growth coefficient (TGC), protein efficiency ratio (PER) and ADC of dry matter regardless of the fish generation. Final weight, weight gain and TGC of fish were the highest in fish fed 2.41% dietary lysine in diet or 6.52% lysine in the protein. PER was the lowest in fish fed 1.16% dietary lysine. The final weight and the body's accumulation of isoleucine, phenylalanine, and alanine were significantly affected by the fish generation, with the 17th generation having the best performance. Increase growth and higher lysine requirement observed in the improved generation (17th) compared to the (16th) generation at grow out phase indicating that genetic improvement may have changed the dietary lysine requirement.

Net cleaning impacts Atlantic salmon gill health through microbiome dysbiosis

IntroductionNet biofouling has a significant impact for the global salmon industry in the seawater grow-out stage in terms of its management. Current mitigation strategies occur primarily through the regular removal of biofouling using in situ cleaning. While in situ net cleaning is effective there is uncertainty as to whether the equipment or dispersed material has an impact upon the fish in the cages. Through direct contact with the environment, the significant surface area of the gill including its microbiome is directly exposed to the acute environmental changes generated by net cleaning. This study aimed to provide a detailed understanding of the impact of in situ net cleaning on Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) gill health.MethodsThree field trials were conducted on commercial fish farms in western Norway. Fouling organisms on net pens and flushed particles during in situ cleaning were identified and screened for major fish pathogens. Hydrographic profile measurements were performed to measure the impact on water quality. Gill samples were examined for histopathological changes, immune gene expression, and the prevalence of major pathogens. 16S rRNA amplicon sequencing was employed to explore the impact of net cleaning on gill microbiome.Results and discussionData obtained from these trials identified a diversity of fouling species including hydroids, algae, skeleton shrimps, and filter feeders on net pens, a direct impact on measured water quality indicators, a moderate change in gill inflammatory and antigen presentation activity at the level of mRNA, and a large significant change in gill microbiome. Observed changes in gill microbial community involved a decrease in bacterial richness coupled to an increase in identified bacterial genera related to negative health consequences. Parallel analyses for pathogens load in biofouling organisms and flushed particles highlighted the presence of several fish bacteria and parasites. However, minor changes were detected in salmon gill pathogen diversity and loading. Our results suggest that biofouling organisms may act as transient reservoirs for some fish pathogens but not viruses and that gill microbial dysbiosis could be related to the host stress response during and post net cleaning.

Growth, survival and color segregation of F2 hybrids between selected “Haida no.1” and Orange-shell lines of the Pacific oyster

In aquatic breeding work, much attention has been paid to the performance of the F1 hybrids. However, fewer studies have been conducted on the characteristics of F2 and Fn hybrids, especially in the intraspecific hybridization of the Pacific oyster Crassostrea gigas. In this study, the two purebreds, F1 hybrid families and F2 hybrid families was developed utilizing “Haida No.1” line (HH), Orange-shell line (OO) and their reciprocal hybrids (HO and OH) of C. gigas as the parents. The growth (shell height and wet weight), survival and shell color traits of the six groups were systematically investigated. Our results demonstrated the two F1 hybrid families exhibited significantly heterosis in shell height and wet weight compared to the purebred groups, with mid-parental heterosis at 9.85–36.49% and − 16.50–50.07%, respectively. Moreover, the traits of two F2 hybrid families were gradually inferior to F1 hybrid families from 6th month. Two F2 hybrid families exhibited inbreeding depression in wet weight compared to F1 hybrid families through the whole grow-out stage, with the values from −13.13% to −7.34%. However, the growth and survival advantages were existed in F2 hybrid families compared to their two parental counterparts. Meanwhile, the survival rate of the F2 hybrid families were greater than those of the parental groups during the grow-out stage, with superiority rate of 1.55–19.59%. Furthermore, some orange-shell and purple-shell individuals were detected in the F2 hybrid families. The rates of orange-shell individuals to non-orange shell individuals and purple-shell individuals to non-purple shell individuals were both 1:3. Surprisingly, the growth traits of orange-shell and purple-shell individuals in the F2 hybrid families were significantly superior than those of their corresponding controls (Orange-shell line and wild population). Through this comprehensively comparison analysis, we confirmed that F2 hybrids of C. gigas had obvious advantages in terms of shell height, wet weight and survival rate compared to the purebred lines, and the orange and purple individuals obtained from the F2 hybrid families have great potential to be used for the development for new strains.

Heterosis and genetic diversity of intraspecific hybrids crosses between two selected lines of the Pacific oyster Crassostrea gigas

For aquatic species, long-term intense artificial selection inevitably leads to decreased genetic diversity and increased genotypic purity in the population, which may lead to a reduction in the adaptation of populations to their environment. Consequently, how to restore a high level of population genetic diversity becomes a critical issue in the breeding process. In this study, a complete diallel crosses was performed utilizing “Haida No. 1”, which had been selected for 10 generations, and the Orange-shell line of the Pacific oyster (Crassostrea gigas), which had been selected for 8 generations. The growth and survival traits of the crossed and self-crossed groups were systematically evaluated during the larval and grow-out stages. Meanwhile, the population genetic diversity of the four combinations was also assessed using 18 microsatellite loci and mitochondrial cytochrome oxidase I sequences (mtCOI). The growth and survival of two reciprocal groups were significantly larger than those of two parental lines. Meanwhile, the average allelic richness (Ar), observed heterozygosity (Ho), expected heterozygosity (He) and number of alleles (Na) of the hybrids was considerably larger than two purebreds. Moreover, significant reduction in average inbreeding coefficient Fis was detected in hybrids when compared to purebreds. The results indicate that crossbreeding between selected lines could not only obtain phenotypically superior descendants, but also increase the genetic diversity of C. gigas.

Oregon shellfish farmers: Perceptions of stressors, adaptive strategies, and policy linkages

In the United States, domestic oyster aquaculture production is insufficient to meet national demand, thus creating a reliance on international oyster imports for consumption. West coast shellfish farmers are threatened by climate change, including ocean acidification as well as socioeconomic challenges such as labor availability. To expand and enhance United States oyster production, and support domestic food security and livelihoods, a better understanding of the limitations that oyster farmers’ experience, and corresponding pathways forward for adaptation is needed. Through semi-structured interviews conducted with commercial Oregon shellfish farmers, we assess the environmental, economic, social and regulatory stressors impacting oyster growing operations, and the corresponding adaptive strategies employed or envisioned by aquaculture farmers. We find farmers are most impacted by environmental stressors (nuisance species that interact with oysters or oyster habitat negatively), followed by regulatory and economic stressors (permitting and regulations and labor availability). Farmers perceived ocean acidification as a risk, but primarily at the oyster larva stage rather than the juvenile or adult grow-out stage. Examples of farmer-identified adaptive strategies included streamlining permitting and regulations, incentivizing employee retention, and having flexibility in culture type to avoid nuisance species and other environmental stressors. An increase in targeted outreach related to aquaculture policies and engagement with industry, scientists, managers, and policy-makers could facilitate policies that support these and other adaptive strategies.

Divergent Carry-Over Effects of Hypoxia during the Early Development of Abalone

After being exposed to environmental stimuli during early developmental stages, some organisms may gain or weaken physiological regulating abilities, which would have long-lasting effects on their performance. Environmental hypoxia events can have significant effects on marine organisms, but for breeding programs and other practical applications, it is important to further explore the long-term physiological effects of early hypoxia exposure in economically significant species. In this study, the Pacific abalone Haliotis discus hannai was exposed to moderate hypoxia (∼4 mg/L) from zygote to trochophora, and the assessments of hypoxia tolerance were conducted on the grow-out stage. The results revealed that juvenile abalones exposed to hypoxia at the early development stages were more hypoxia-tolerant but with slower weight growth, a phenomenon called the trade-off between growth and survival. These phenotypic effects driven by the hypoxia exposure were explained by strong selection of genes involved in signal transduction, autophagy, apoptosis, and hormone regulation. Moreover, long non-coding RNA regulation plays an important role modulating carry-over effects by controlling DNA replication and repair, signal transduction, myocardial activity, and hormone regulation. This study revealed that the ability to create favorable phenotypic differentiation through genetic selection and/or epigenetic regulation is important for the survival and development of aquatic animals in the face of rapidly changing environmental conditions.

Low Salinity Application to Improve Biofloc System in Early Grow-Out Stage of White Shrimp (Litopenaeus vannamei)

Extreme time for the failure of white shrimp culture often occurs at the beginning of rearing, especially during disease attacks and environmental degradation, where high salinity is also a trigger. This research aimed to examine the robustness of shrimp culture with environmental design at low salinity at the beginning of rearing. Methodology: this study was conducted in two plastic ponds (900 m2), each with a seed stocking density (PL-8) of 250 indv/m2, where treatment A (control/initial salinity 27 ppt), while treatment B (low initial salinity 15 ppt) with rearing for 80 days. According to the results from both regimens, salinity changed from the beginning of stocking until the day of 43(27-28 ppt). There began to be similarities, where the addition of water always used normal seawater (33 ppt) until the end. Vibrio harveyii disease attack in DOC 41 occurred in treatment A (control) which was marked by luminescence light from the water rearing, this was different in treatment B which was clean from the luminescence light of pond water. This is also thought to cause the survival rate of control to be lower. It appears that the survival rate (SR) calculation is different, whereas, in treatment A (control), it is only 86%, while in treatment B is 98%. The average body weight in treatment A averaged 8.19±1,36 g/indv, while treatment B averaged 8.69±1,55 g/indv. The results of the FCR calculation in treatment A (control) was around 1.57, while treatment B was 1.42 with total biomass on A 1.402 kg and for treatment B 1.624 kg. The implementation of a low salinity environmental design at the start of rearing can boost the white shrimp culture biofloc system’s robustness, it can be concluded.

Comparative analysis of growth, survival and sex proportion among tetraploid-based autotriploid (Crassostrea gigas and C. angulata) and their allotriploid oysters

Triploid is widely cultivated in China and many other oyster-producing countries for the advantages of fast growth, favorable infertility and better meat quality. However, triploid Crassostrea gigas is found to have disadvantages of slow growth in later grow-out stage and high summer mortality, while the triploid C. angulata has the disadvantages of fragile shells and a relatively high ratio of developed gonads in population, and therefore, both of them have space for further improvement. Due to the limitations of poor fertility and low survival of offspring, triploid genetic improvement cannot be carried out directly. Hybridization between species is a useful method for indirect genetic improvement of triploids, and natural crosses between tetraploid males and diploid females have proven to be the best method for commercial promotion of triploids. The growth, survival and gonad development of autotriploids (DGTG-diploid C. gigas ♀ × tetraploid C. gigas ♂, DATA-diploid C. angulata ♀ × tetraploid C. angulata ♂) and allotriploids (DATG-diploid C. angulata ♀ × tetraploid C. gigas ♂, DGTA-diploid C. gigas ♀ × tetraploid C. angulata ♂) were investigated in this study. It is showed that the fertilization rates of autotriploids were significantly higher than that of allotriploids, and DATG larvae grew significantly faster than the other three groups (P < 0.05). DGTA had significant shell height, whole weight and survival advantages at Laizhou site (P < 0.05), while DATG exhibited significantly fastest growth and highest survival at Zhangpu site (P < 0.05), but both DATG and DATA showed significantly faster growth and higher survival at Beihai site (P < 0.05), with no significant difference between them (P > 0.05). Sites, genotypes and their interaction always presented significant effects on shell height and whole weight from the 90th to 360th day, but not on survival with the 180th day as an exception. Gonad examination confirmed that the proportions of fertile individuals in the groups with maternal C. gigas (DGTG and DGTA) were lower than that in the groups with maternal C. angulata (DATA and DATG), and DATA always had the highest rate of developed gonad at three sites. These results indicate that DGTA has advantages in growth, survival and infertility in northern China while DATG performs best in southern China, which exhibits that there is a significant maternal effect of hybridization in allotriploids, and promise a guidance for their commercial production.

Feasibility of interspecific hybridization between Iwagaki oyster, Crassostrea nippona and Portuguese oyster, Crassostrea angulata

Iwagaki oyster, Crassostrea nippnoa is famous for its unique flavor and delicacy, while the Portuguese oyster, C. angulata has become an important oyster species in aquaculture because of its high growth rate and high market demand. For the first time, 2 × 2 factorial hybridization between them was performed, forming four groups, including C. nippona♀ × C. nippona♂ (NN), C. nippona♀ × C. angulata♂ (NA), C. angulata♀ × C. nippona♂ (AN), C. angulata♀ × C. angulata♂ (AA). The results showed that fertilization only occurred in NA, not in AN. The cleaved rate, D larvae rate and larvae survival level of NA were remarkably lower than those of the two pure parent groups, but the survival rate of NA and NN was comparable during the grow out stage. NA has no growth heterosis in larval stage, but has obvious growth heterosis in growth stage. On 360th day, the mid-heterosis of NA was 10.76 for shell height, and 26.60 for wet weight, respectively. Like the progenies of pure parents, the gonads of NA hybrids develop normally and can produce gametes. The shell morphology of NA was similar to that of NN and has a strong maternal effect. These results demonstrate that the eggs of C. nippona can be fertilized with the sperm of C. angulata through one way fertilization, and can produce viable hybrids with growth heterosis at the grow-out stage. NA hybrids have good application potential in aquaculture.

Insight into selective breeding for robustness based on field survival records: New genetic evaluation of survival traits in pacific white shrimp (Penaeus vannamei) breeding line.

Survival can be considered a relatively ‘old’ trait in animal breeding, yet commonly neglected in aquaculture breeding because of the simple binary records and generally low heritability estimates. Developing routine genetic evaluation systems for survival traits however, will be important for breeding robust strains based on valuable field survival data. In the current study, linear multivariate animal model (LMA) was used for the genetic analysis of survival records from 2-year classes (BL2019 and BL2020) of pacific white shrimp (Penaeus vannamei) breeding lines with data collection of 52, 248 individuals from 481 fullsib families. During grow-out test period, 10 days intervals of survival data were considered as separate traits. Two survival definitions, binary survivability (S) and continuous survival in days (SL), were used for the genetic analysis of survival records to investigate; 1) whether adding more survival time information could improve estimation of genetic parameters; 2) the trajectory of survival heritability across time, and 3) patterns of genetic correlations of survival traits across time. Levels of heritability estimates for both S and SL were low (0.005–0.076), while heritability for survival day number was found to be similar with that of binary records at each observation time and were highly genetically correlated (r g > 0.8). Heritability estimates of body weight (BW) for BL2019 and BL2020 were 0.486 and 0.373, respectively. Trajectories of survival heritability showed a gradual increase across the grow-out test period but slowed or reached a plateau during the later grow-out test period. Genetic correlations among survival traits in the grow-out tests were moderate to high, and the closer the times were between estimates, the higher were their genetic correlations. In contrast, genetic correlations between both survival traits and body weight were low but positive. Here we provide the first report on the trajectory of heritability estimates for survival traits across grow-out stage in aquaculture. Results will be useful for developing robust improved pacific white shrimp culture strains in selective breeding programs based on field survival data.

Response to selection for growth in successive mass selected generations of Iwagaki oyster Crassostrea nippona

The Iwagaki oyster (Crassostrea nippona) is a potential aquaculture species with delicious taste and edibility in summer when the Pacific oyster (Crassostrea gigas) suffer from low meat quality. Although there is an increasing interest in hatchery mass production and field grow-out among farmers, large-scale expansion of C. nippona aquaculture has been compromised by unimproved growth performance. To improve the growth rate of C. nippona, we initiated the mass selective breeding program for fast growth in 2014 and estimated the genetic parameters of growth traits in the first three successive mass-selected generations. Each selected line exhibited better growth performance than the corresponding control group at all sampling dates. At grow-out stage, the average selection response (SR), realized heritability (hR2) and genetic gain (GG) for shell height was 0.45–0.56, 0.27–0.42 and 9.20–11.12% in the three mass selected lines, respectively. A significant increase in GG for shell height was observed in the third-generation selected line compared with that in the first-generation (P < 0.05). Meanwhile, the average SR (0.44–0.49) and GG (11.07–12.46%) for body weight of C. nippona were observed in the selective breeding program after three successive generations of mass selection. The encouraging results obtained in this study suggest that genetic variances still remain at a relatively high level in the breeding populations of C. nippona, and demonstrate the feasibility of improving the growth traits by selective breeding for C. nippona.

Growth, survival and gonad development of two new types of reciprocal triploid hybrids between Crassostrea gigas and C. angulata

The allotriploid technology has been widely applied to aquaculture worldwide. To overcome the deficiency of low growth, poor taste and high mortality of diploid hybrids between Crassostrea gigas and C. angulata in summer, two new types of triploid hybrids were produced by inhibiting the polar body II using cytochalasin B. The growth, survival and gonad traits of triploid hybrids (TGA – C. gigas ♀ × C. angulata ♂ and TAG – C. angulata ♀ × C. gigas ♂), diploid hybrids (GA – C. gigas ♀ × C. angulata ♂ and AG – C. angulata ♀ × C. gigas ♂) and purebred crosses (GG – C. gigas ♀ × C. gigas ♂ and AA – C. angulata ♀ × C. angulata ♂) were evaluated. A high triploidy induction rate (> 95%) was found by ploidy analysis. The fertilization and hatch rates of triploid hybrids were significantly (P < 0.05) lower than that of diploid crosses. During the larval stage, the triploid advantage (TA) was positive in growth, despite was negative in survival. The triploid hybrids exhibited superior performance during the grow-out stage. Across three culture environments (Rongcheng, Rushan and Huangdao), triploid hybrids performed better than diploid hybrids in growth with an increasing value of TA over time. The incremental survival rates of triploid hybrids, especially that of TGA, were significantly (P < 0.05) higher than that of diploid hybrids at Rushan and Huangdao in summer. The TA in cumulative survival rate ranged from 13.80% to 36.04% among environments. A positive yield advantage for diploid and triploid hybrids was observed at Rongcheng (mid-parent heterosis H: 114.11%; TA: 35.76%), Rushan (H: 148.22%; TA: 48.78%) and Huangdao (H: 138.96%; TA: 60.22%). Additionally, most of the triploid hybrids exhibited high sterility during reproduction phase. These findings demonstrated that triploid hybrids between C. gigas × C. angulata had obvious advantage in growth, survival and yield, which have important application value for commercial oyster cultivation in northern China.

Strain‐specific effects of broodstock size on fecundity and offspring performance in bighead catfish ( Clarias macrocephalus Günther, 1864)

This study investigated the relationships among parental body weight, egg size and number, and offspring performance at the larval, juvenile and grow-out stages of bighead catfish (Clarias macrocephalus) in Mekong domesticated (Can Tho; CT) and wild (Ca Mau; CM) strains. One-year-old broodstock from each strain were separated into two size groups, with those in the large (L) group having, on average, approximately double the body weight of those in the small (S) group. Both strains exhibited a strong linear increase in absolute fecundity (slope = 58.8, p < 0.01 for CT and slope = 52.3, p < 0.01 for CM) and a slight increase in egg diameter associated with increasing female body weight (slope = 0.0002, p = 0.03 for CT and slope = 0.0003, p = 0.06 for CM). However, there were no linear correlations between female body weight and yolk-sac volume or larval body length at hatching (p > 0.05). Despite similar fecundities, the CM wild strain had larger eggs and more favourable larval properties than the CT domesticated strain (p < 0.01). However, these advantages did not result in better growth and survival of CM offspring at any stage. The CT strain showed improved growth in offspring with parents in the L group compared to those with parents in the S group across the three stages (35.7%, 50.0% and 43.9% respectively), while there was no significant increase in growth in the CM wild strain (p > 0.05). Parental body weight and strain had no effects on survival and feed conversion ratios (FCRs), with the exception that juveniles of the CM S group had the lowest SR (38.8 ± 6.0%) and FCR (1.09 ± 0.08) due to disease infection. The CT L group grew fastest and consumed the highest amount of food with similar feed efficiency to the other groups in juvenile and grow-out stages (p < 0.05). These results indicated that the pertinence of ‘the bigger the better’ paradigm varied between growth stages in the two bighead catfish strains.

Mutations in Growth-Related Genes Induced by EMS Treatment in Scallops.

Background: The goal of genetic breeding is to select variants with mutations that are related to expected traits, such as fast growth. Artificial induction has been widely used to obtain strains with more mutations for further selection. Ethylmethylsulfone (EMS) is one of the most commonly used chemical mutagens in plant and microorganism breeding. However, the application of EMS mutagenesis in shellfish has not been reported. The aim of this study is to evaluate the potential use of EMS as a mutagen in scallop breeding, especially in characterization of mutations in growth-related genes. Results: Our results indicated that hatching of about 50% of fertilized eggs was blocked by treatment with 20 mM EMS for 3 h and the resulted larvae developed normally into adult stages. We then evaluated the mutagenic effects of EMS by sequencing the genomes of 4 adult scallops from the control group and 12 from the treatment group at 8 months after fertilization. On average, after removing shared types of mutations, there were 1,151,380 ± 258,188 SNPs (Single Nucleotide Polymorphisms) and 229,256 ± 51,714 InDels (insertion-deletion) in each animal in the EMS treatment group, while there were only134841 ± 10,115 SNPs and 42,605 ± 5,136 InDels in the control group. The average mutation rate in the genome of the EMS treatment group (0.0137 ± 0.0013%) was about 9 times that of the control group (0.0015 ± 0.0002%). GO (Gene Ontology) annotation and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analyses revealed that mutations induced by EMS occurred evenly in most biological processes, cellular components and functions, as well in most pathways. However, significant lower percentage of mutations were found in the exonic region, in non-synonymous or Stopgain/Stoploss SNPs and in coding domains, suggesting apparent DNA repair or selection during grow-out stage. Analyses of the growth-related genes with mutations indicated that mutations in MFS (Major Facilitator Superfamily) and Tubulin were only found in the large-sized group (Five largest scallops: Treated-1, Treated-2, Treated-3, Treated-4, and Treated-5) and Homeobox and Socs (Suppressor of cytokine signaling) only in the small group (Two smallest scallops: Treated-11 and Treated-12). These results suggested that these genes may be involved in the regulation of growth in these animals, although further verification is certainly warranted. Conclusion: Treatment of fertilized eggs with 20 mM EMS for 3 h induced 9 times more mutations in scallop genomes. We found that mutations in MFS and Tubulin may be related to fast growth in the large-sized group and those mutations in Homeobox and SOCs may be involved in the slow growth in the small-sized scallops. EMS can be used to accelerate selection of economically important traits in molluscs.