Larvae In Hatchery Research Articles

Exploring the nutritional potential of Monoraphidium littorale and enriched copepods as first feeds for rearing Nile tilapia (Oreochromis niloticus) larvae

One of the challenges in the aquaculture industry is providing nutritionally balanced and environmentally sustainable live food for fish larvae. Therefore, the rearing techniques of fish larvae with preferred starter food should be given importance for obtaining optimal hatchery production. Nile tilapia, Oreochromis niloticus larvae just after yolk absorption (body length 0.950 ± 0.004 mm; body weight 6.00 ± 0.02 mg) were reared in laboratory conditions for 16 days, feeding with 6 different diets to know their effect on survival and growth. The diets were live Monoraphidium littorale (T1), live enriched copepods with M. littorale (T2), powdered M. littorale (T3), powdered enriched copepods (T4), live M. littorale + live enriched copepods (T5), and powdered M. littorale + powdered enriched copepods (T6). The proximate composition, amino acid profile and fatty acid content of both M. littorale and copepods were analyzed. The biochemical analysis of the dried powder of enriched copepods and M. littorale revealed that both of them are excellent sources of protein, amino acids, and lipids, especially with monounsaturated and polyunsaturated fatty acids. The O. niloticus larvae fed the T2 diet exhibited the most favourable outcomes, with significantly higher larval gain in weight and percent weight gain, in comparison to the larvae fed other diets (p < 0.001 for all comparisons). The LG% and SGR of the larvae were also significantly higher in T2 in comparison to the T1, T3, T4, and T6 (p < 0.001 for all comparisons) except T5. In addition, the highest percent survival rate of the larvae was observed in T2 (95 %) followed by T4 (93 %), T6 (93 %), T3 (82 %), T5 (73 %) and then T1 (43 %). Based on the present findings, it is recommended that live copepods enriched with M. littorale can be utilized as a starter food for the rearing of Nile tilapia, O. niloticus larvae in hatcheries because of its enriched nutritional profile.

Using decapsulated local brine shrimp cysts on feeding common carp larvae in hatcheries.

The current study aims at using non-hatchable artemia eggs of local origin and making use of these eggs by decapsulating and presenting them as food for the larvae of the Cyprinus carpio as a source of animal protein with high nutritional value instead of throwing them away. The results showed that the second parameter (A2) was highly significant at the level (P≤0.05) in the growth rates of the larvae that were fed on decapsulated artemia eggs alone, and it was better than the two control parameters (A1), in which the larvae were fed with feed designated for Cyprinus carpio fish. It also outperformed the third parameter (A3), in which the feed was mixed with artemia eggs with 50% decapsulation, which also outperformed the control parameter with high significance at the same level (P≤0.05).

Bacterial community trends associated with sea scallop, Placopecten magellanicus, larvae in a hatchery system

Atlantic sea scallops, Placopecten magellanicus, are the most economically important marine bivalves along the northeastern coast of North America. Wild harvest landings generate hundreds of millions of dollars, and wild-caught adults and juvenile spat are increasingly being cultured in aquaculture facilities and coastal farms. However, the last two weeks of the larval maturation phase in hatcheries are often plagued by large mortality events. Research into other scallop- and aquacultured-species point to bacterial infections or altered functionality of microbial communities which associate with the host. Despite intense filtering and sterilization of seawater, and changing tank water every 48 h, harmful microbes can still persist in biofilms and mortality is still high. There are no previous studies of the bacterial communities associated with the biofilms growing in scallop hatchery tanks, nor studies with wild or hatchery sea scallops. We characterized the bacterial communities in veliger-stage wild or hatchery larvae, and tank biofilms using the 16 S rRNA gene V3-V4 region sequenced on the Illumina MiSeq platform. Hatchery larvae had lower bacterial richness (number of bacteria taxa present) than the wild larvae and tank biofilms, and hatchery larvae had a similar bacterial community (which taxa were present) to both wild larvae and tank biofilms. Bacterial richness and community similarity between tank samples fluctuated over the trial in repeated patterns of rise and fall, which showed some correlation to lunar cycle that may be a proxy for the effects of spring tides and trends in seawater bacteria and phages which are propagated into hatchery tanks. These results along with future work, will inform hatcheries on methods that will increase larval survival in these facilities, for example, implementing additional filtering or avoiding seawater collection during spring tides, to reduce bacterial taxa of concern or promote a more diverse microbial community which would compete against pathogens.

Identification and Characterization of Infectious Pathogens Associated with Mass Mortalities of Pacific Oyster (Crassostrea gigas) Cultured in Northern China.

The Pacific oyster (Crassostrea gigas) aquaculture industry increased rapidly in China with the introduction and promotion of triploid oysters in recent years. Mass mortalities affecting different life stages of Pacific oysters emerged periodically in several important production areas of Northern China. During 2020 and 2021, we conducted a passive two-year investigation of infectious pathogens linked to mass mortality. Ostreid herpesvirus-1 (OsHV-1) was detected to be associated with mass mortalities of hatchery larvae, but not juveniles and adults in the open sea. Protozoan parasites, such as Marteilia spp., Perkinsus spp. and Bonamia spp. were not detected. Bacterial isolation and identification revealed that Vibrio natriegens and Vibrio alginolyticus were the most frequently (9 out of 13) identified two dominant bacteria associated with mass mortalities. Pseudoalteromonas spp. was identified as the dominant bacteria in three mortality events that occurred during the cold season. Further bacteriological analysis was conducted on two representative isolates of V. natriegens and V. alginolyticus, designated as CgA1-1 and CgA1-2. Multisequence analysis (MLSA) showed that CgA1-1 and CgA1-2 were closely related to each other and nested within the Harveyi clade. Bacteriological investigation revealed faster growth, and more remarkable haemolytic activity and siderophore production capacity at 25 °C than at 15 °C for both CgA1-1 and CgA1-2. The accumulative mortalities of experimental immersion infections were also higher at 25 °C (90% and 63.33%) than at 15 °C (43.33% and 33.33%) using both CgA1-1 and CgA1-2, respectively. Similar clinical and pathological features were identified in samples collected during both naturally and experimentally occurring mortalities, such as thin visceral mass, discolouration, and connective tissue and digestive tube lesions. The results presented here highlight the potential risk of OsHV-1 to hatchery production of larvae, and the pathogenic role of V. natriegens and V. alginolyticus during mass mortalities of all life stages of Pacific oysters in Northern China.

Changes in Bacterial Communities of Kumamoto Oyster Larvae During Their Early Development and Following Vibrio Infection Resulting in a Mass Mortality Event.

Vibrio and Ostreid herpesvirus 1 are responsible for mass mortalities of oyster larvae in hatcheries. Relevant works have focused on their relationships with the disease when larval mortality occurs. On the contrary, little is known about how the resident microbiota in oyster larvae responds to Vibrio-infected disease causing mortality as the disease progressed, whereas this knowledge is fundamental to unveil the etiology of the disease. Here, we analyzed the temporal succession of the microbiome of Kumamoto oyster (Crassostrea sikamea) larvae during their early development, accompanied by a Vibrio-caused mortality event that occurred at the post D-stage of larval development in a shellfish hatchery in Ningbo, China, on June 2020. The main causative agent of larval mortality was attributable to Vibrio infection, which was confirmed by linearly increased Vibrio abundance over disease progression. Larval bacterial communities dramatically changed over host development and disease progression, as highlighted by reduced α-diversity and less diverse core taxa when the disease occurred. Null model and phylogenetic-based mean nearest taxon distance analyses showed that the relative importance of deterministic processes governing larval bacterial assembly initially increased over host development, whereas this dominance was depleted over disease progression. Furthermore, we screened the disease-discriminatory taxa with a significant change in their relative abundances, which could be indicative of disease progression. In addition, network analysis revealed that disease occurrence remodeled the co-occurrence patterns and niche characteristics of larval microbiota. Our findings demonstrate that the dysbiosis of resident bacterial communities and the shift of microecological mechanisms in the larval microbiome may contribute to mortality during oyster early development.

Genetic identification and comparative study on life history parameters of two strains belonging to Brachionus plicatilis species complex (Rotifera: Monogononta)

The rotifer Brachionus plicatilis is an important species for aquaculture, due to its use as food for bivalves, and fish and crustaceans larvae in hatcheries. However, being a species complex, it has become increasingly important to catalogue and describe the species and biotypes that constitute this complex. Therefore, the purpose of this study was to genetically identify two morphologically identical strains and evaluate their suitability to be used in aquaculture under the studied conditions. A correct identification and knowledge of life history characteristics of the biotypes and isolated strains is vital to avoid mass mortalities in aquaculture and to better interpret the responses of the organisms when these are used as a bioindicator and model for ecotoxicology. Strains MRS10 and IBA3 were identified as B. koreanus and, even though they have been maintained under the same laboratory conditions for several years, significant differences in several life history parameters were observed. A life table assay showed IBA3 rotifers to be larger at first reproduction, and to have longer post-reproductive period and mean lifespan. On the other hand, MRS10 rotifers produced less non-viable eggs and had higher population growth rate. Both strains showed to be a potential model for ecotoxicological and molecular studies, mainly due to the ease of maintenance, short generation time, and reproduction via parthenogenesis. However, MRS10 might present better characteristics than IBA3 to be reared in aquaculture as live food.

High-density production of Southern King Crab (Lithodes santolla) juveniles in the field for stock enhancement

The Southern King Crab -SKC- (Lithodes santolla) is a highly demanded gastronomic resource in South America, specially from tourism. As many others crab fisheries, the current state of L. santolla's population in the Beagle Channel is compromised, since the production of new recruits is below its potential. In this sense and in order to overcome this limitation, late efforts have been directed towards the development of efficient larvae and juvenile culture, either in hatcheries or in the field for future stock enhancement. With some progress in culturing larvae in hatcheries and some novel results on the feasibility of culturing juveniles in the field, the present study takes a step forward and addressed field culture at high density and for a mid-term period of 5 months. Field culture was performed in prefouled meshed-bags enclosures suspended in the water column. Thus, 2500 stage 1 SKC juveniles were massively cultured for 5 months and no external food provided. Over 62% of the juveniles survived and less than 10% were injured (i.e. lost appendages). The smallest and biggest crabs recovered were 2.20 and 7.05 mm of carapace length respectively. A total of 6 modal groups explained the size frequency distributions of the recovered crabs and over 70% of the survivors ranged between 3.75 and 4.75 mm of carapace length. In comparison with a previous work, our results also show that the longer the culture period, the grater the size disparity among crabs. The effectiveness of SKC juvenile massive culture in the field in terms of survival and growth is encouraging specially since the meshed-bags enclosure system stands as a low cost and low maintenance system to produce large numbers of bigger crabs. This knowledge is crucial in the context of the implementation of a stock enhancement program, which may help to L. santolla's population recovery in the Beagle Channel.

The role of zooplankton as live feeds on the thyroid hormone profile related to metamorphosis of marine fish larvae coral trout Plectropomus leopardus (Lacepède, 1802)

Coral trout Plectropomus leopardus is a high-economical value of marine fish commodity. So, the larviculture for this species should be performed in hatchery scale for their sustainability. One of the important thing in larval stage is hormonal mechanisms. Thyroid hormone is known plays an important role in the metamorphosis of marine fish larvae. The source of that hormone is assumed derived from zooplankton as their live feeds. The live feeds commonly used for marine fish larvae in hatchery are zooplankton copepods and rotifers. The purpose of this research to determine the influence of feeding copepods and rotifers on thyroid hormone profile activity, consisted of triiodothyronine (T3) and thyroxine (T4), related to the metamorphoses of coral trout larvae. The research was conducted using three feeding schemes: copepods (A), copepods-rotifers (B), and rotifers (C). It was done for 50 Days After Hatching (DAH). The results showed that larvae from treatment (A) and (B) achieved the highest level of T3 and T4 earlier at 30 DAH, which indicated that both of those larvae have entered the metamorphosis stage earlier. On the other hand, larvae from treatment (C) achieved it and entered the metamorphosis stage later at 40 DAH. In addition, iodine levels in the copepods were significantly higher than those of in rotifers (P < 0.05). Based on this research, live feeds copepods and rotifers have effect on thyroid hormone activity. Copepods have better potential in accelerating the metamorphosis achievement of coral trout larvae with the fact that they have higher iodine content.

Comparing the performance of four commercial microdiets in an early weaning protocol for European seabass larvae ( Dicentrarchus labrax )

The promise of an off-the-shelf, microparticulate diet for first feeding marine larval fish is still one of the ‘holy grails’ of the hatchery manager. Replacing the laborious live feed production facilities with high-quality microdiets will greatly increase marine larval production, improve hatchery consistency and will help in cost reduction in fry production. Over the last decades, many scientific and industrial efforts have focussed on developing microparticulate diets to reduce or replace the use of live feed for growing marine fish larvae in hatcheries. However, in most professional hatcheries, an extended live feed period is still the standard procedure. Thus, this study aimed to compare the performance of four state-of-the-art commercially available microdiets used in an early weaning protocol to the standard Artemia-based feeding. European seabass larvae were used as a model organism. The three most relevant parameters, survival, growth and deformities were used for the performance-rating of the four different microdiets. The results of the study depict that early weaning of European seabass between 15 and 20 days post-hatching (dph) onto the commercially available microdiets still result in lower survival, reduced growth and an increase in deformities in the early-weaned treatments. Nevertheless, one microdiet outperformed the others in this study, resulting in significantly fewer deformed larvae and improved growth. However, larvae fed with Artemia only still yielded the best results considering growth, survival and deformities.

Growth and survival of the hatchery larvae of pacific oyster &lt;i&gt;Crassostrea gigas&lt;/i&gt; under different concentrations of microalgae and salinity in conditions of southern Primorye

Growth and survival rates for larvae of pacific oyster Crassostrea gigas (Thunberg, 1793) hatched in artificial conditions are estimated for the stages of development from D-veliger to pediveliger. The experiment was conducted in the Mariculture Center located on Popov Island (Peter the Great Bay, Japan Sea) for 2 regimes of feeding and water salinity of 26 and 32 ppt. Microalgae Isochrysis galbana, Chaetoceros muelleri and Phaeodactylum tricornutum cultivated in the Mariculture Center were used as a feed in both regimes, in different concentrations. The maximum concentration was 4-fold higher than the minimum one: daily doses of food were 20 and 5 thousand cells/mL for veligers, 40 and 10 thousand cells/mL for early veliconkhes, and 80 and 20 thousand cells/mL for late veliconkhes, respectively, whereas 80 thousand cells/mL for all larvae in transition to pediveliger stage. Statistically significant difference of the growth rate was found for cases with different food concentration (p &lt; 0.05). The larvae with better feeding had higher growth rate under salinity of both 26 and 32 ppt. Besides, the lowered salinity (26 ppt) had some positive effect for growth in the regime of better feeding. Survival rate of the larvae from D-veliger to pediveliger was high under all regimes of the experiment and was estimated for the minimal diet as 77.4 and 64.7 % under salinity of 26 and 32 ppt, respectively, and for the maximum diet as 81.2 and 80.7 % under salinity of 26 and 32 ppt, respectively. According to the experiment results, deficit of food at early stages of the oyster larval development affects negatively on their growth but does not have significant impact on their survival.

Influence of rearing tank colour on Asian catfish, magur (Clarias magur) and pangas (Pangasius pangasius) larval growth and survival

Larval growth and survival are significantly influenced by the various biotic and abiotic factors. Rearing tank background colour is one such factor affecting the larval production in finfish hatcheries. The present study evaluated the effect of five tank background colours (black, white, blue, green and red) on growth and survival of larvae of two commercially important freshwater catfish species, Clarias magur (magur) and Pangasius pangasius (pangas) in a completely randomized experimental design in triplicate. The larvae of magur (9.33 ± 0.15 mm; 3.85 ± 0.05 mg) and pangas (10.07 ± 0.27 mm; 3.31 ± 0.08 mg) were stocked at a density of 45 and 30 larvae per tank, respectively in 15 L tanks. Experimental duration was 28 days for both the species. The results revealed that the final weight, weight gain, daily weight gain, and specific growth rate (SGR) of larvae of magur were significantly (P < 0.05) higher in white background coloured tank whereas, pangas shown the best performance (P < 0.05) in black tank. Thermal growth coefficient (TGC) of magur and pangas were recorded significantly higher in white and black coloured tank, respectively. Larval survival was significantly (P < 0.05) higher in black (97.04 ± 1.96%; F (4, 10) = 2.95, P = 0.002) tank for magur and green tank (87.78 ± 4.84%; F (4, 10) = 8.28, P = 0.003) for pangas. Whereas green and black tank colour were significantly reduced the larval survival of magur and pangas, respectively. This study clearly indicates that tank background colour had a significant impact on the larval growth and survival in both the species studied. It was also noticed that the tank colour effect is species specific. The study thus showed that black background tank colour for magur and green tank for pangas are more suitable for the higher production of catfish larvae in hatchery.

Phylogenetic Relationship Among Brackishwater Vibrio Species.

Vibriosis is regarded as an important disease of penaeid shrimps affecting larvae in hatcheries. Among the Vibrio species, Vibrio parahaemolyticus, Vibrio vulnificus, Vibrio furnissii, Vibrio campbellii, Vibrio harveyi, Vibrio alginolyticus, and Vibrio anguillarum are often associated with diseases in finfish and shellfish of brackishwater ecosystem. Accurate species differentiating methods for the organisms present in an ecosystem are required for precise classification of the species and to take steps for their management. Conventional methods like 16s rRNA phylogeny and multilocus sequence typing (MLST) have often failed to correctly identify Vibrio species. This has necessitated a comprehensive investigation on methodologies available to distinguish Vibrio species associated with brackishwater aquaculture system. To achieve this, 35 whole genomes belonging to 7 Vibrio species were subjected to phylogenetic analysis based on 16s rRNA gene, MLST genes, single-copy orthologous genes, and single-nucleotide polymorphisms. In addition, genome-based similarity indices like average nucleotide identity (ANI) and in silico DNA-DNA hybridization (DDH) were computed as confirmatory tests to verify the phylogenetic relations. There were some misclassifications occurred regarding phylogenetic relations based on 16s rRNA genes and MLST genes, while phylogeny with single-copy orthologous genes produced accurate species-level clustering. Study reveals that the species identification based on whole genome-based estimates or genome-wide variants are more precise than the ones done with single or subset of genes.

Total lipids content and fatty acids composition of the rotifer Brachionus plicatilis using artificial enrichments

Secondary feeding with commercial lipids enrichments such as the microencapsulated diets Diet A (33.42±3.00%) and Diet B (55.88±3.5%) compared with the marine yeast type product Diet C(8.59±1.0%) as a method of increasing the total lipids and ω-3 PUFA content of rotifers, hence enhancing their nutritional value as live feed prey for fish larvae in hatcheries. The total lipids the rotifers was affected analogous to the levels of these components in the feeds showing its maximum percentage uptake within 4 hours from the enrichment (20.27±3.52, 26.64±3.91, 11.31±2.30 respectively). There was not any significant toxicity to the animals due to the diets during the 16 hours experiment. The DHA/EPA for Diet A(1.31), Diet B(0.42) and Diet C(absent) as well as the DHA/EPA/ARA ratios for Diet A(10.70 ± 1.60 / 8.18 ± 1.10 / 2.08 ± 0.20), Diet B(6.20 ± 2.30 / 14.60 ±1.00 / 1.12 ± 0.40) and Diet C (0 / 5.14 ± 3.40 / 1.30 ± 1.10) indicates that Diet A is closer to the suggested DHA/EPA/ARA optimal value 10/5/1 for marine fish larval growth.

Bacterial Community Associated with Healthy and Diseased Pacific White Shrimp (Litopenaeus vannamei) Larvae and Rearing Water across Different Growth Stages.

Bacterial communities are called another “organ” for aquatic animals and their important influence on the health of host has drawn increasing attention. Thus, it is important to study the relationships between aquatic animals and bacterial communities. Here, bacterial communities associated with Litopenaeus vannamei larvae at different healthy statuses (diseased and healthy) and growth stages (i.e., zoea, mysis, and early postlarvae periods) were examined using 454-pyrosequencing of the 16S rRNA gene. Bacterial communities with significant difference were observed between healthy and diseased rearing water, and several bacterial groups, such as genera Nautella and Kordiimonas could also distinguish healthy and diseased shrimp. Rhodobacteraceae was widely distributed in rearing water at all growth stages but there were several stage-specific groups, indicating that bacterial members in rearing water assembled into distinct communities throughout the larval development. However, Gammaproteobacteria, mainly family Enterobacteriaceae, was the most abundant group (accounting for more than 85%) in shrimp larvae at all growth stages. This study compared bacterial communities associated with healthy and diseased L. vannamei larvae and rearing water, and identified several health- and growth stage-specific bacterial groups, which might be provided as indicators for monitoring the healthy status of shrimp larvae in hatchery.

A comparative histological study on early thyroid gland development in Acipenser stellatus and A. gueldenstaedtii larvae in hatchery

The thyroid is an endocrine gland, with an important role in fish growth, development and adaptation of larvae. The aim of this study was to describe the development of the thyroid gland and to determine the initial functional activity of thyroid gland and hormones in Acipenser gueldenstaedtii and A. stellatus larvae using immunohistochemistry. For this aim, fertilized eggs of two species were reared in a hatchery and larval samples were collected daily for 20 days post hatching (dph). For immunostaining, rabbit polyclonal primary antibodies for thyroglobulin and mouse monoclonal antibodies for thyroid transcription factor-1 (TTF-1) were used. In histological analyses, it was observed that the first development of the thyroid gland in stellate sturgeon larvae occurs on the 3–4 dph and on the 4–5 dph in Russian sturgeon larvae in the ventral pharyngeal region of the fish. In the immunostaining analyses of 12-day-old stellate larvae and 19-day-old Russian sturgeon larvae, the thyroid follicles showed dispersion in great numbers around the aorta, and also it was observed that they were stained positively with antithyroglobulin staining, but the same sections gave negative results with TTF-1 staining. Also melanomacrophage centres, which are generally found in the haemopoietic tissues in some cases, were first observed around the thyroid follicles of sturgeon larvae. The results of this study revealed a similarity in the early thyroid gland development between two sturgeon species but using immunostaining methods, it was described that A. stellatus shows a faster functional development and earlier hormone production than A. gueldenstaedtii.

Effects of different substrates on settlement and growth of pearl oyster (Pinctada maxima) larvae in hatcheries

Metamorphosis of pearl oyster Pinctada maxima pediveliger is affected by physical and chemical characteristics of the collectors. In the present study, we conducted four experiments to evaluate the effects of collector characteristics on the settlement and growth of hatchery-reared pearl oyster. In the first experiment, black, red, yellow, and white plastic sheets were used as collectors. Settlement of P. maxima larvae in black and red plastic sheets was significantly higher than that in yellow and white plastic sheets (P<0.05). Mean shell length was not significantly different among the four colored sheets (P>0.05). In the second experiment, pediveliger larvae were settled onto palm rope and polypropylene rope collectors. The number of spat in the palm rope collector was significantly higher than that of spat in the polypropylene rope collector (P<0.05). Mean shell length was not significantly different between palm rope and polypropylene rope collectors (P>0.05). In the third experiment, settlement and subsequent growth were compared between plastic sheets with and without biofilm. The number of spat in the plastic sheets with biofilm was significantly higher than that in the plastic sheets without biofilm (P<0.05). Mean shell length after settlement were not significantly affected (P>0.05). In the fourth experiment, pediveliger larvae were stored in tanks with (experimental group) and without collectors (control group). The settlement rate of larvae on the wall was not significantly different between the two groups(P>0.05). The settlement rates of the larvae on the wall and collectors in the experimental group were significantly larger than those on the wall in the control group(P<0.05). Mean shell length was not significantly different between the groups (P>0.05). Our results suggest that appropriate selection of collector types, color, and conditioning can improve the settlement of P. maxima larvae in hatcheries.

Reproductive and Larval Performance of the Pen ShellAtrina maurain Relation to the Origin and Condition of Broodstock

The pen shell Atrina maura has economic importance in northwestern Mexico, but limitations to rear larvae in hatcheries increased the interest of scientists and producers to study aspects of reproduction and larval cultivation. Reproductive and larval performances of the species were studied in relation to the origin (depth, phases of tidal cycle) and gross condition of broodstock. The results were correlated to variations in water temperature and concentration of chlorophyll a. Tide influenced spawning response, which was between 40% and 100% successful in broodstock collected during rising and falling tides and only 10% at high or low tides (this percentage corresponds tomales only). The number and size of released and fertilized eggs and the survival of larvae were higher in pen shells collected at 5–8 m depth, compared with those collected at less than 1m. The number and size of released and fertilized eggs, number of veliger larvae, and the survival and growth rate of larvae were significantly higher in January 2012 and correspond to low temperatures, high concentrations of food, high percent of ripe gonads, high-condition index (CI), and low-muscle index (MI). These indicators were significantly lower in March 2012, when broodstock had the lowest percent of ripe gonads, the lowest CI, and the highest MI of all samples. The number and size of released eggs was positively correlated with concentration of chlorophyll a and negatively correlated with temperature, indicating that both factors play a different role in regulating reproductive output.

Selection of Copepods as Live Food for Marine Fish Larvae Based on Their Size, Fecundity, and Nutritional Value

Copepods are a major food source for marine fish larvae in nature. Many studies on copepods culture have been conducted to develop a new live food for the seedling production of marine fish larvae. But fish farmers still depend on rotifer and Artemia nauplii. This study was carried out to find suitable copepods as live food for the larvae in hatchery. Eight species of copepods (1 calanoid, 2 cyclpoid, 5 harpacticoid) that were fed Isochrysis galbana were examined in terms of the size of nauplii, fecundity, amino acids, and fatty acids contents. These species were divided into small (nauplii length 46-86 <TEX>${\mu}m$</TEX>) and large (nauplii length 120-188 <TEX>${\mu}m$</TEX>) size group. Nitokra spinipes in the small group and Tigriopus japonicus in the large group showed the highest fecundity with 151.1 and 139.6 nauplii production per gravid female, respectively. With regard to nutrients, essential amino acids were the highest with 21.2% in cyclopoid Paracyclopina nana in the small group and n-3 HUFA were the highest in calanoid Pseudodiaptomus inopinus (8.5 <TEX>${\mu}g/mg$</TEX>) in the large group and P. nana (8.8 <TEX>${\mu}g/mg$</TEX>). In terms of the size, fecundity, and nutritional value of copepods examined in this study, N. spinipes and P. nana seem to be suitable copepod species to develop as a new live food for small mouth fish larvae.

Indigenous Lactobacillus plantarum as probiotic for larviculture of blue swimming crab, Portunus pelagicus (Linnaeus, 1758): Effects on survival, digestive enzyme activities and water quality

Portunus pelagicus larvae in hatcheries experience high mortality during the early stages of development, primarily due to bacterial infections. A study was performed to determine the effectiveness of the indigenous probiotic Lactobacillus plantarum as a water additive in P. pelagicus larviculture. Three treatments and the control were tested in triplicate. The treatments consisted of three levels of L. plantarum were added daily at designated concentrations 1.0×106 (T-1), 5.0×106 (T-2) and 1.0×107cfuml−1 (T-3) and control without any probiotic. The addition of the probiotic significantly enhanced (p<0.05) survival rate of crab larvae for all treatments over the control. L. plantarum population (cfu ml−1) progressively increased (p<0.05) in treated tanks over the time. Total bacteria and Vibrio counts found significantly lower (p<0.05) in treated tanks over the control. The addition of L. plantarum influenced the nitrogen content and pH of culture water. Supplementation of L. plantarum significantly increased (p<0.05) the protease and amylase activities in the treated groups over the control. The significantly highest protease activity was observed in T-2; while the amylase activity was higher in T-2 and T-3. The increased concentration of probiotic level (1×107) did not increase the enzyme activities and survival of larvae. These results signify that L. plantarum addition at 5.0×106cfuml−1 can effectively enhance the larval survival rate, enzyme activity and improve the water quality of P. pelagicus larviculture.

Use of the copepod Acartia tonsa as the first live food for larvae of the fat snook Centropomus parallelus

High-quality live food is essential for reducing the frequent high mortality of newly hatched fat snook (Centropomus parallelus) larvae in hatcheries. Copepods, a rich nutrition source, cultivated with the microalgae Chaetoceros muelleri and Isochrysis galbana, were evaluated as food for 0–14-day-old larvae. Two experiments were performed using nine 50-L tanks stocked with 2500 embryonated fat snook eggs. Three different dietary (treatments) were tested in triplicate: Experiment 1, Treatment 1 (Control), using rotifers Brachionus rotundiformis (20mL−1); Treatment 2 (Copepod), larvae were fed with Acartia tonsa (nauplii and copepodits, 0.1mL−1); and Treatment 3 (Mixed), larvae were fed with A. tonsa (0.05mL−1) and rotifers (10mL−1). In Experiment 2 to increase the density of live food, food organisms and the phytoplankton were introduced into the experimental tanks with the embryonated eggs and were stocked: Treatment 1, 20rotifersmL−1; Treatment 2, 0.5copepodsmL−1; and Treatment 3, 10rotifersmL−1 and 0.25copepodsmL−1. In Experiment 1, the Mixed Treatment increased significantly the survival rate (16.0%±7.5%) and mean larval weight (0.84±0.05mg) in relation to the other treatments. In Experiment 2, we observed significant improvements in larval notochord flexion in the Copepod and Mixed Treatment. The essential fatty acid profile of fat snook eggs had a DHA:EPA:ARA ratio of 11.4:2.4:1.0 while larvae in the Mixed and Copepods Treatments had ratios of 2.5:1.9:1.0 and 5.5:1.9:1.0, respectively. We conclude that the survival, development and the relationship between the major fatty acids were improved in treatments with copepods.