Hatchery Practices Research Articles

The applicability of large-scale sperm cryopreservation in wels catfish (Silurus glanis) optimized for hatchery practice

In the presented study, effects of sperm cryopreservation methods (Polystyrene box-P. box vs a controlled-rate freezer-CRF) and various semen confection methods during freezing (5 mL straw vs. 10 mL cryotube) on sperm motility parameters and fertilization capacity of wels catfish (Silurus glanis) were tested. In general, pMOT (Control: 89 ± 3%, Straw P. box: 50 ± 9%, Straw CRF: 53 ± 12%, Cryotube: 52 ± 7%) and BCF (Control: 30 ± 1 Hz, Straw P. box: 27 ± 1 Hz, Straw CRF: 26 ± 1 Hz, Cryotube: 27 ± 1 Hz) showed significant reduction following thawing. ALH reduced significantly in the case of the straw frozen with P. box (1.2 ± 0.2 μm) compared to the fresh control (1.5 ± 0.1 μm). However, VCL (Control: 108 ± 6 μm/s, Straw P. box: 107 ± 5 μm/s, Straw CRF: 108 ± 8 μm/s, Cryotube: 109 ± 7 μm/s) and VSL (Control: 94 ± 6 μm/s, Straw P. box: 99 ± 4 μm/s, Straw CRF: 99 ± 9 μm/s, Cryotube: 99 ± 7 μm/s) did not decrease. A significantly higher LIN was measured using the straw cryopreserved in the P. box (92 ± 2%) and the CRF (91 ± 2%) in comparison with the fresh control (86 ± 1%). No significant difference in the fertilization capacity when eggs were fertilized by frozen/thawed (Straw P. box: 75 ± 5%, Straw CRF: 72 ± 3%, Cryotube: 66 ± 6%) or fresh (control, 68 ± 4%) semen was observed (P > .05). As well, no significant correlation between none of sperm motility parameters tested and the fertilization rate were recorded (P > .05). All tested sperm cryopreservation showed a similar high efficiency in the hatchery practice of wels catfis.

Artificial seminal plasma improves motility and fertilisation capacity of common carp Cyprinus carpio L. sperm during one hour of storage

The quality of fish sperm is characterized by relatively high individual variation. Moreover, under artificial conditions, the collected sperm loses its motility and viability very rapidly, which may decrease fertilisation success. Therefore, techniques able to secure and maintain a high biological value of collected fish sperm are needed in hatchery practice. Herein, we used previously composed artificial seminal plasma (ASP) containing 2 mM CaCl2, 1 mM Mg2SO4, 20 mM Tris, 110 mM NaCl and 40 mM KCl (pH 7.5 and 310 mOsm kg−1) to dilute common carp sperm samples for 1 h storage prior to fertilisation. Sperm was collected from mature males and, after checking its motility (MOT) using the CASA system, was divided into high (range 55–65%) and low (range 5–10%) quality. Samples of both sperm qualities (high/low) were diluted tenfold (1: 9; sperm: extender) in ASP and stored for 24 h at 10 °C. Motility (MOT, PRG) and velocity (VCL, VSL) of low- and high-quality sperm diluted in ASP increased after 1 h of storage compared to undiluted sperm. Moreover, the fertilisation capacity of low-quality sperm (previously diluted and stored for 1 h in ASP) increased three times compared to undiluted sperm of the same quality. Prolonging the time of sperm storage in ASP to 24 h results in the further increase of MOT, PRG and VCL in the low quality samples and PRG in the high quality samples. The results of the presented study confirm the possibility of common carp sperm revitalisation using ASP. The utilisation of such sperm in hatchery practice is possible since the fertilisation capacity of sperm, previously diluted and stored for 1 h in ASP, was over 90% regardless of the initial sperm quality (high/low).

Predation on wild and hatchery salmon by non‐native brown trout (Salmo trutta) in the Trinity River, California

AbstractNon‐native predators may interfere with conservation efforts for native species. For example, fisheries managers have recently become concerned that non‐native brown trout may impede efforts to restore native salmon and trout in California's Trinity River. However, the extent of brown trout predation on these species is unknown. We quantified brown trout predation on wild and hatchery‐produced salmon and trout in the Trinity River in 2015. We first estimated the total biomass of prey consumed annually by brown trout using a bioenergetics model and measurements of brown trout growth and abundance over a 64‐km study reach. Then, we used stable isotope analysis and gastric lavage to allocate total consumption to specific prey taxa. Although hatchery‐produced fish are primarily released in the spring, hatchery fish accounted for most of the annual consumption by large, piscivorous brown trout (>40 cm long). In all, the 1579 (95% CI 1,279–1,878) brown trout >20 cm long in the study reach ate 5,930 kg (95% CI 3,800–8,805 kg) of hatchery fish in 2015. Brown trout predation on hatchery fish was ca. 7% of the total biomass released from the hatchery. Brown trout only ate 924 kg (95% CI 60–3,526 kg) of wild fish in 2015, but this was potentially a large proportion of wild salmon production because wild fish were relatively small. As large brown trout rely heavily on hatchery‐produced fish, modifying hatchery practices to minimise predation may enhance survival of hatchery fish and potentially reduce the abundance of predatory brown trout.

Hatching and post-hatching performances of Indonesian native chicken eggs infused saline solution

An experiment was conducted to determine the effects of infusing sterilized physiological saline on the hatching and post-hatching performances of the eggs of Indonesian native hen aged 60 weeks reared in the University Farm, which included hatchability, weight of newly hatched, hatching time and growth of the chicken up to 8 weeks of age. In accordance with a Completely Randomized Design (2 treatments, with 3 different times of incubation as replication – 20 eggs per treatment per replication), a total of 120 fertile eggs of approximately the same weight (46.53 ± 2.87 g) with live embryos which resulted from candling at d 7 of incubation was used, and 60 eggs were subject for the saline infusion. All eggs were sterilized using 70% ethanol, numbered and weighed before incubation, then incubated according to standard hatchery practices. The saline solution was infused through a small hole made manually at a little bit above the narrow end of the egg. The results indicated that infusing saline was significantly reduced hatchability of the egg from 84.83 ± 1.89 to 79.68 ± 2.71%. Despite the weight (g) of newly hatched chick was not significantly affected by infusing saline, the relative weight of hatched chick (%) was significantly increased from 70.69 ± 1.09 to 73.81 ± 1.18. Infusing saline into the albumin resulted in a shorter time required for hatching processes; even though it mostly occurred between d 20 and d 21 of incubation. Growth performance was indicated by a significantly heavier body weight of male chicken, in particular, resulted from the treated eggs (896.25 ± 30.14 vs 985.62 ± 47.61 g). In conclusion, the present results demonstrate that infusion of sterilized physiological saline into the eggs of the Indonesian native chicken improved hatching and post-hatching performances.

Effects of incubation temperature on the embryonic viability and hatching time in Russian sturgeon (Acipenser gueldenstaedtii)

BackgroundRussian sturgeon (Acipenser gueldenstaedtii) is an emerging candidate species in the Korean aquaculture domain owing to its highly valued caviar. Although the embryonic development of this species was previously described, the complete image data on the morphological differentiation of developing embryos have not been yet fully available. Further, with the viewpoint of larval production in hatchery, the effects of temperature on embryonic viability and the temporal window of hatching event have not been extensively studied. Hence, the objective of this study was to provide a complete set of photographic image data on the embryogenesis and also to examine the effects of incubation temperatures on embryonic viability and hatching event in farm-bred Russian sturgeon.ResultsTypical characteristics of embryonic development including uneven, holoblastic cleavages with unequal blastomeres, followed by the formation of germ layer, neurulation, and organogenesis until hatching, were documented. Under different temperature conditions (12, 16, or 20 °C), viability of embryos incubated at 12 °C was significantly lower as relative to those of 16 and 20 °C incubated embryos. Hatchability of embryos was higher, and the timing of hatching event was more synchronized at 20 °C than at 12 and 16 °C.ConclusionData from this study suggest that the incubation of Russian sturgeon embryos at 20 °C would be desirable in the hatchery practice with respect to the good hatchability of embryos and the synchronization of hatching events. Additionally, the updated image data for complete embryonic development could be a useful reference guide for not only developmental researches but also artificial propagation of Russian sturgeon in farms.

Comparative analysis of sperm freezability of sex-reversed female brook trout and sex-reversed female rainbow trout semen

The aim of our study was to compare quality of fresh and cryopreserved semen of sex-reversed female rainbow trout and sex-reversed female brook trout. The effect of different final sperm concentrations in straws with a constant extender concentration and final glucose concentration on the sperm motility parameters of cryopreserved semen was tested. Furthermore, we examined the effect of post-thaw storage time on sperm motility parameters at optimal sperm and glucose concentrations. The effects of semen cryopreservation from sex-reversed female rainbow trout and sex-reversed female brook trout on sperm fertilizing ability at the sperm-to-egg ratios 500,000:1 and 1,000,000:1 after 0 and 60 min of post-thaw storage of semen were investigated. We have demonstrated that final sperm concentrations in straws as well as final glucose concentrations in extended semen influenced post-thaw sperm motility parameters in both species. The high post-thaw sperm motility was recorded for sperm concentrations within the range of 1.0–4.0 × 109 spermatozoa ml−1 for both species. Furthermore, the glucose concentration appeared to be very important for cryopreservation success and its effect was species-specific. The final glucose concentrations of 0.15 M and 0.19 M, for sex-reversed female rainbow trout and sex-reversed female brook trout, respectively, produced the highest results for sperm motility after cryopreservation. The post-thaw sperm motility was unaffected by 60 and 360 min after thawing for sex-reversed female rainbow trout and sex-reversed female brook trout, respectively. The fertilization rates of cryopreserved semen of sex-reversed female rainbow trout were high and did not differ between the investigated sperm:egg ratios after 0 and 60 min of post-thaw storage. However, fertilization rates of cryopreserved semen of sex-reversed females brook trout were lower and decreased after 60 min of post-thaw storage of semen at sperm: egg ratio 1,000,000:1. In conclusion, our results demonstrated differences in freezability between the semen of sex-reversed female rainbow trout and sex-reversed female brook trout. The semen of both species can be cryopreserved at the final sperm concentration of 3.0 × 109 spermatozoa ml−1. However, the influence of final glucose concentration on cryopreservation success, as well as the duration of post-thaw storage time and fertilization rates, are species-specific. In our opinion, standardizing the procedure of semen cryopreservation presented in this study is a prerequisite for the development of repeatable procedures and the future implementation of cryopreserved semen from sex-reversed females into hatchery practice.

Standardized cryopreservation protocol of European perch (Perca fluviatilis) semen allows to obtain high fertilization rates with the use of frozen/thawed semen

The general aim of this study was to develop an efficient and standardized cryopreservation procedure for European perch semen. The specific aims of this study were: to test the effects of (i) final glucose concentration, (ii) final sperm concentration in the extended semen and (iii) the storage time of post-thaw semen on sperm motility parameters. Moreover, the effects of cryopreservation of semen on fertilization rates were tested at sperm:egg ratios ranging between 50,000:1 and 500,000:1 (iv), as well as the fertilization of 25 g portions of eggs (v). The range of optimal sperm concentrations in straws with high post-thaw sperm motility (66–73%) was quite wide, from 1.0 to 6.0 × 109 spermatozoa ml−1. The final glucose concentration of 0.30–0.34 M in 7.5% methanol produced the highest results of sperm motility (76 ± 5%) after cryopreservation. Storage time of post-thaw semen negatively influenced sperm motility parameters. The fertilization rates while using cryopreserved semen were high (79%) and did not differ from fresh semen (85%). Similar results (73–77%) were obtained between sperm:egg ratio ranged from 50,000:1 to 500,000:1. Moreover, cryopreserved semen was successfully used for fertilization as much as 12,500 eggs (25 g). However, semen has to be used for fertilization within 2 min after thawing. In our opinion, standardizing the procedure of semen cryopreservation presented in this study is a prerequisite for the development of repeatable procedures and the future implementation of cryopreserved semen in hatchery practice. Further studies should focus on extension of time of post-thaw sperm motility, determination of optimal sperm:egg ratio at the conditions of large-scale fertilization and scaling up procedure to fertilize 50–150 g of eggs (one ribbon) at single application.

Consequences of captive breeding: Fitness implications for wild-origin, hatchery-spawned Atlantic salmon kelts upon their return to the wild

Broodstock collection and enhancement programs are a widely-used management practice within the Atlantic salmon's (Salmo salar) native range. Wild-origin adult salmon captured as part of these programs experience multiple stressors during their time in hatcheries. However, no studies have assessed the potential consequences of hatchery practices on the physiology (stress and immune states), migratory behaviour, and long-term survival of hatchery-spawned kelts that are subsequently released back to their natal river. To address these knowledge gaps, we obtained blood samples from, and acoustically tagged 30 hatchery-spawned kelts and 31 wild-spawned kelts, originating from endangered populations native to a UNESCO Biosphere Reserve in Canada during the autumns of 2014 and 2015. We then tracked individuals for up to two years through their downstream river migration, estuarine residence, ocean entry, and subsequent return as repeat-spawners. Our results indicated that hatchery-spawned kelts showed significantly higher stress levels (elevated plasma cortisol and glucose), as well as potentially altered immune states (increased circulating prostaglandin E2) in comparison to wild-spawned individuals. Behaviourally, hatchery-spawned kelts exited freshwater prematurely (~66 days earlier on average) compared to wild-spawned counterparts, which was associated with a marked increase in estuarine mortality. Furthermore, survival to repeat-spawning was 0% (0/30) for hatchery-spawned kelts and 6.5% (2/31) for wild-spawned. Given that female repeat-spawners are generally larger and have increased fecundity, our findings suggest that a reduction in the fitness of post-spawners and likelihood of repeat-spawning as a result of hatchery stressors could have population-level consequences. Such impacts should be considered in conservation and management planning.

Morphological, biochemical and histological analysis of mud crab ovary and hepatopancreas at different stages of development

This study describes the fatty acids, total carotenoids, and cell diameter characteristics of the female ovary and hepatopancreas of the mud crab, Scylla olivacea, with comparisons at different ovarian maturation stages. Seventy-one S. olivacea individuals at all stages of ovarian maturation were sampled from the Setiu wetlands, Terengganu, Malaysia. The ovary and hepatopancreas of each crab were used for morphological studies, histological and biochemical analyses (fatty acid composition and total carotenoids). Morphological observations indicated there was an increase in ovarian gonado-somatic index (GSI), with color changes from translucent to dark red; however, a relatively consistent hepato-somatic index (HSI) in the hepatopancreas, with the color ranging from yellow to yellowish-brown. Histological analysis indicated that oocyte diameter was positively correlated with GSI. Hepatopancreatic tubules had a relatively constant diameter from Stage 2 to 4, with increased proportions of R- and B-cells. Biochemical analysis indicated there was a significant increase in total carotenoids in the ovary during maturation. The hepatopancreas, however, had relatively consistent total carotenoid concentrations that were greater than those of the ovary. Overall, the lipid analysis results indicated there were lesser concentrations of fatty acids in the hepatopancreas, while in the ovary there were increasing concentrations during maturation. The lesser concentrations of fatty acids in the hepatopancreas than ovary suggested that energy was transferred to the ovary for future embryonic and larval development. The relationship between the hepatopancreas and the ovary in nutrient content is an important finding in providing a baseline to formulate an optimal diet for improved mud crab hatchery practices.

Effect of carp pituitary homogenate (CPH) and sGnRHa (Ovaprim) on northern pike (Esox lucius) spermiation stimulation and its effect on quantity and quality of sperm

The effect of carp pituitary homogenate (CPH, n = 7) at a dose of 2.0 mg kg−1 and (D-Arg6, Pro9NET)-sGnRH + domperidone (Ovaprim, n = 7) at a dose of 0.5 ml kg−1 in northern pike (Esox lucius) sperm maturation under controlled conditions was examined. On the control group, 0.9% NaCl at a dose of 1.0 ml kg−1 (n = 7) was used. Sperm was collected 48 h following injection. Sperm quantity (total sperm volume, total sperm production and sperm concentration), sperm motility using the Computer-assisted sperm analysis (CASA) system and sperm and seminal plasma quality (sperm pH, seminal plasma osmotic pressure and seminal plasma pH) were determined for each male separately in each group. The results of the present study demonstrate that hormonal treatment had a positive effect on sperm maturation in northern pike, regardless of the hormonal preparation used. However, even though no differences were found in total sperm volume and total sperm production between fish injected with either CPH or Ovaprim, it should be highlighted that the highest progressive motile sperm (PRG), straight-linear velocity (VSL) and movement linearity (LIN) was noted in fish treated with Ovaprim. It was also found that it is possible to collect sperm from non-hormonally manipulated fish. However, in such a case, only a small sperm volume (around 0.1 ml) characterised by lowered PRG (below 40%) was noted. Considering the fact that only after Ovaprim application sperm motility with progressive movement of sperm above 50% was observed, the hatchery practice of collection of sperm 48 h after its application (at a dose of 0.5 ml kg−1) may be recommended.

Response of antioxidant enzymes and digestive enzymes to temperature stress in Lates calcarifer larvae

Acute temperature stress in 15-day post-hatch (DPH) Lates calcarifer larvae was studied using the semi-static bioassay method to understand the physical response of fish larvae to low temperature. In this study, 20oC, 22oC, 24oC, and 26oC were tested and 28oC was the control. Antioxidant enzyme activity including superoxide dismutase (SOD), peroxidase (POD), catalase, acid phosphatase (ACP), glutathione peroxidase (GSH-Px) and digestive enzymes including lipase, amylase, trypsin, pepsin were used as the physical indicators. SOD activities were elevated to scavenge excess reactive oxygen species (ROS) after exposure to lower temperatures, and their activities increased dramatically in relation to the increasing residue time. POD enzyme activity maintained a low level in the early stage of cold exposure and increased to a high level in relation to exposure time. Catalase, GSH-Px, and ACP activities were elevated in fish after exposure to lower temperatures compared to those in fish maintained at 28oC. Lipase activity decreased after exposure to lower temperatures and modestly elevated over time. The highest amylase activity was observed in the control group. However, trypsin and pepsin activity was elevated with the decrease of environmental temperature. Our results indicate that lower temperature significantly affects activity of antioxidant enzymes and digestive enzymes in barramundi larvae. Barramundi larvae exhibited a certain tolerance of low temperature for a short period. Results from the present study will improve our understanding of the physical response of warm water fish to low temperatures and can therefore guide hatchery practices for Lates calcarifer.

Effect of Acute Ammonia Stress on Antioxidant Enzymes and Digestive Enzymes in Barramundi Lates calcarifer Larvae

The acute toxicity of ammonia to barramundi Lates calcarifer larvae (15 days post-hatching, DPH) was studied with a semi-static bioassay method to understand the physical response of fish larvae to ammonia stress. In this study, 15 and 20 mg/L ammonia were tested, and 0 mg/L ammonia (control) was used as control. The activity of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), acid phosphatase (ACP), glutathione peroxidase (GSH-Px), and digestive enzymes lipase (LPS), amylase (AMS), trypsin (TRYP) were used as biochemical indicators. With the increase of residue time, the SOD activity in barramundi was elevated at 15 mg/L ammonia and decreased at 20 mg/L ammonia. CAT activity was lower at 20 mg/L ammonia. GSH- PX activity was elevated at the low ammonia concentration and decreased at the high ammonia concentration. ACP activity was elevated after exposure to ammonia. LPS and AMS activities in the control were significantly higher than those of the other groups (P<0.05). TRYP activity was elevated after exposure to ammonia. The results indicate that acute ammonia stress significantly affects antioxidant capacity and digestive capacity, and barramundi exhibited a certain tolerance of ammonia in a short time (<6h). Results from the present study will improve our understanding of the physical response of fish to ammonia and may guide hatchery practice for Lates calcarifer.

Optimal sperm concentration in straws and final glucose concentration in extender are crucial for improving the cryopreservation protocol of salmonid spermatozoa

Ensuring the precise conditions during cryopreservation relies on constant sperm concentration in straws with constant cryoprotectant concentrations, which are essential for standardizing cryopreservation protocols. The aim of our study was to test the effect of different sperm concentrations in straws with constant extender concentration on sperm motility parameters of cryopreserved semen of brown trout (Salmo trutta m. fario), sea trout (Salmo trutta m. trutta), brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar). At the same time, the usefulness of different straw sizes (0.25 and 0.5ml) for cryopreservation of the semen of these species was examined. Additionally, the effect of the final glucose concentration at a constant sperm concentration on post-thaw sperm motility was evaluated. The final sperm concentration in straws at a constant cryoprotectant concentration influenced the post-thaw sperm motility parameters of salmonids. The optimal sperm concentration with high post-thaw sperm motility was 2.0×109 spermatozoa ml−1 for brook trout, 3.0×109 spermatozoa ml−1 for brown trout and sea trout and 4.0×109 spermatozoa ml−1 for Atlantic salmon. The use of 0.5ml straws led to higher or similar values of post-thaw sperm motility than the 0.25ml straws. The final glucose concentration of 0.15M produced the highest results of sperm motility after cryopreservation for all tested species. Our results demonstrated that the influence of sperm concentration in straws on cryopreservation success is species-specific within salmonids. On the other hand, the effect of glucose concentration did not appear to be species-specific. In our opinion, standardization of the semen cryopreservation protocol presented in this study is a prerequisite for the development of a repeatable procedure and hence the future implementation of cryopreserved semen in hatchery practice.

Penerapan Cara Pembenihan Ikan yang Baik dalam Meningkatkan Kinerja UMKM Pembenihan Udang di Kabupaten Barru, Provinsi Sulawesi Selatan

Shrimp is one of the leading commodity of fishery sector in Indonesia because the number of export increasing the foreign exchange for this country. In globalization era, business has fierce competition, so that the quality is a keyword to succeed. Therefore, shrimp hatcheries must be certified. The objectives are to: (1) study the related Good Hatchery Practices (GHP) regulation, (2) Analyze the relationship of application of GHP on shrimp hatchery performances, (3) measure the performance of shrimp hatcheries, (4) identify the Gap of the application of GHP. Content analysis, multiple regression analysis and important-performance analysis (IPA) was used to process the data. Result of content analysis showed that there were no regulation contain the obligation that every farmer must be certified in order to control the seed shrimp quality. Result of multiple regression analysis revealed that the application of GHP had positive impact on shrimp hatchery performances and the most influence factors were food safety and environment. Important-performance analysis showed that the best performance was the availability of adequate production equipment. Average production after applied the GHP principles showed that production increased by 19%. Level of concordance between expectation and performance on hatcheries to meet customer satisfaction and consistency of GHP implementation showed a negative gap value by -1.118, overall performance on hatcheries have not meet customer satisfaction and inconsistent implementing GHP principles

Large-scale Dam Removals and Nearshore Ecological Restoration: Lessons Learned from the Elwha Dam Removals

Large dam removals are emerging as an important ecosystem restoration tool, and they often have direct influence on the marine nearshore zone, but dam removal plans give little consideration to nearshore restoration. We provide an overview of the relationship between large-scale dam removals and nearshore restoration, using the Elwha dam removal project, in Washington State, United States, as a basis. The following steps are essential for incorporating nearshore restoration planning into future dam removals: 1) Conceptual and technical modeling of nearshore physical and ecological processes at the drift cell scale to define nearshore priorities and geographic areas to be conserved or restored; 2) Acquiring seasonal field data to inform models, including: water quality; sediment delivery volumes, timing, trajectory and composition; and basic fish community data such as abundance, size, species composition, and trophic components; 3) Mapping nearshore habitat areal extent and ecological function prior to, during, and after dam removal, including vegetation composition and invertebrate community composition; 4) Defining and addressing the implications of habitat barriers and fish management actions for nearshore ecosystem function prior to dam removal. Structures and hatchery practices that conflict with nearshore ecosystem function for wild species prior to, during, and after dam removal should be identified and eliminated; 5) Anticipating nearshore invasive species colonization as a result of dam removal; 6) Developing and implementing long-term adaptive management plans to ensure nearshore restoration goals are identified and met. These steps must begin as early as possible in the planning process.

Contrasting patterns in growth and survival of Central Valley fall run Chinook salmon related to hatchery and ocean conditions

The objective of this study was to determine important ocean and hatchery covariates influencing early growth and survival of Central Valley fall run Chinook salmon. We used a dataset of recaptured coded wire tagged hatchery Chinook salmon to estimate early growth and cohort survival. Ocean conditions during the period of early ocean entry were based on output from a coupled physical-biogeochemical model configured for the broader California Current region. We built generalized additive and generalized linear models to describe growth and survival and used Akaike Information Criterion (AICc) model selection to determine which hatchery and ocean covariates related best to response variables. With regards to hatchery covariates, growth was best explained by release location, while survival was best explained by release weight and hatchery of origin. The ocean conditions included in the best models for both growth and survival included diatoms, predatory zooplankton, temperature, and currents. We observed the highest rates of salmon survival when in situ physical ocean conditions were indicative of relaxation events. For all four ocean covariates, the response curves illustrated opposite patterns between growth and survival models. This result implies that during periods of low survival, juvenile salmon were either 1) growing at a faster rate, or 2) growth appeared to increase because smaller fish had a higher mortality rate than larger fish. The first explanation would imply density-dependence, whereas the second explanation would imply size-selective mortality. These alternatives have implications on hatchery practices including salmon size at release and number of salmon in release groups.

Genetic markers provide insight on origins of immature green turtles Chelonia mydas with biased sex ratios at foraging grounds in Sabah, Malaysia

An understanding of population dynamics is needed to assess the viability of migra- tory species. Monitoring of marine turtles at foraging grounds may detect changes in population trends that would take decades to be seen at nesting beaches. Mixed Stock Analysis using molec- ular markers provides a tool for estimating the origin of turtles sampled at foraging grounds. Here, we analysed mitochondrial DNA sequences of 90 immature green turtles at 2 foraging grounds in northwestern Sabah, Malaysia. We used data from 30 Indo-Pacific green turtle rookeries as the baseline for tracing the origin of turtles at the 2 foraging grounds. The inferred origins of turtles at the 2 locations were not different and indicated that the majority originated from 3 major popula- tions in Southeast Asia, the Turtle Islands of Sarawak in northwestern Borneo (29%), the Turtle Islands Heritage Protected Area (TIHPA) (28%) and Peninsular Malaysia (25%). Previous analy- ses indicated a 1:4 female-biased sex ratio at the foraging grounds, and based on our results, this largely reflects the use of unshaded beach hatcheries at some of the source rookeries for decades, which resulted in mostly female hatchlings. This result is supported by differences in the origins of male and female turtles. The result suggests a greater proportion of males originating from Peninsular Malaysia and fewer males originating from Sarawak and possibly the TIHPA com- pared to females. We discuss the implications of hatchery practices that influence sex ratios of hatchlings and recommend future research to improve the management of marine turtles in the region.

Critical Dissolved Oxygen Tolerances of Whirling Disease‐Resistant Rainbow Trout

AbstractA low concentration of dissolved oxygen (DO) is commonly the limiting factor in fish culture systems. Hypoxia tolerance in Rainbow Trout Oncorhynchus mykiss can be affected by both history of domestication and growth rate. As such, selecting strains for specific characteristics such as growth rate or disease resistance could potentially affect DO tolerance, making culture difficult. Here we used two experiments to examine the differences in tolerance to lower DO concentrations among four Rainbow Trout strains and crosses selected for resistance to whirling disease Myxobolus cerebralis. The first experiment examined differences in critical DO concentrations of fry (≥73 mm total length [TL]) when exposed to rapid decreases in DO at 30, 60, 90, and 120 d postswim‐up. In addition, since formalin is a common chemical used in aquaculture to treat for external parasites, the effect of exposure to formalin on tolerance to low DO was evaluated. The second experiment evaluated critical DO concentrations among four strains and crosses exposed to a prolonged decrease in DO at age 7 months (averaging 178 mm TL). Formalin exposure had an effect on low‐DO tolerance, with DO concentrations that resulted in a loss of equilibrium decreasing with an increase in formalin concentration. In addition, low‐DO tolerances were diminished with an increase in fish size, with larger fish losing equilibrium at higher DO concentrations. Differences in DO concentrations resulting in loss of equilibrium and mortality were evident among the strains and crosses in the second experiment. This experiment demonstrated that DO concentrations must be below 2.0 mg/L before loss of equilibrium is observed. However, if fish are soon returned to well‐oxygenated water, losses can be minimized. Additionally, other hatchery practices that compromise hypoxia tolerance may increase mortality more quickly following low‐DO exposure, and care should be taken to correct low‐DO issues shortly after loss of equilibrium is observed.

Spawn date explains variation in growth rate among families of hatchery reared Hood River steelhead (Oncorhynchus mykiss)

Body size at release for hatchery-reared steelhead is positively correlated with probability of survival to return as an adult. Although the relationship between body size and survival is well documented, little is known about what factors influence growth in the hatchery at the family level. We test if parent length, parent type (hatchery or natural), parent run date, or date of spawning correlate with among-family variation in offspring growth in the hatchery. Using Hood River winter steelhead (Oncorhynchus mykiss), two experiments were performed over two brood years. No effect of father length, parental type, or parental run date was found on offspring length in either year. Mother length was positively correlated with offspring length during both brood years and egg size data suggest this result occurs because longer females have larger eggs (i.e., it is a maternal effect). Although run date of parents was not correlated with offspring size, the date of spawning was negatively correlated with offspring size in a year with a protracted spawning season. Families spawned later in the season were smaller than those spawned earlier even though all fish began feeding on the same date. The spawn date effect lasted surprisingly long, being correlated with offspring size one year after spawning. A possible explanation for the spawn date effect is that eggs from early-spawned families were reared in chilled water to slow development so all families would begin feeding on the same date (a common hatchery practice). Colder water could have reduced metabolic costs and provided a surplus of energy to be used for somatic growth. This study highlights a little-studied environmental effect that could have large effects on long-term growth rates for hatchery-reared O. mykiss.

Effect of dilution in sperm maturation media and time of storage on sperm motility and fertilizing capacity of cryopreserved semen of sex-reversed female rainbow trout

Masculinized females, also called neomales or sex-reversed females have a male phenotype but retain the female genotype (XX). Therefore, all spermatozoa produced in their functional testes carry an X chromosome, which is desired for the production of all-female rainbow trout populations. Semen of sex-reversed female rainbow trout is of low quality and in vitro maturation is required, which includes dilution of sperm suspensions with specially formulated maturation solutions. The aim of this study was to determine the effect of dilution in different maturation media on sperm quality (sperm motility characteristics and fertilizing capacity) of frozen/thawed sperm of sex-reversed female rainbow trout. The effect of time of post-thaw storage (0, 15, 60 and 120min) on semen quality was also tested. Sperm motility parameters and fertilization rate at the eyed and hatching stages were assessed for post-thaw semen diluted in different media. The cryopreservation procedure resulted in high post-thaw sperm motility of about 57% and did not differ from fresh semen. Unexpectedly, maturation media decreased sperm activation capacity immediately after dilution; however, sperm motility increased over time. Fertilization rates of frozen/thawed semen were high (71–87%) and did not differ significantly between experimental variants at any of tested periods of storage. Our results demonstrated that the effect of the maturation media on frozen/thawed sperm is different from that of fresh sperm. The progressive increase in post-thaw sperm motility in maturation media can potentially be applied to routine hatchery practice.