The effects of dietary lipid sources and lecithin on the production of giant freshwater prawn <Emphasis Type="Italic">Macrobrachium rosenbergii</Emphasis> larvae in the Mekong Delta region of Vietnam

The giant freshwater prawn, Macrobrachium rosenbergii, is cultured widely in the Mekong Delta region of Vietnam but it is often difficult or expensive for hatchery operators to purchase commercial diets used as a feeding supplement to Artemia nauplii. Therefore, in the present study, the effects of lipid sources and lecithin on the growth and survival rate of M. rosenbergii larvae were examined in order to develop suitable hand-prepared larval diets for seed production of M. rosenbergii in this area. Six egg custard diets consisting of various ratios of lipid (originating from soybean oil and squid oil) and lecithin were used for rearing Macrobrachium rosenbergii larvae. Treatments in which larvae were fed diets containing squid oil exhibited the highest body length and survival rates (7.14–7.43 mm and 51.1–68.1%, respectively), and differed significantly from other treatments (P<0.05). Use of dietary soybean oil yielded the lowest body length and survival rates (6.29–6.75 mm and 22.0–48.7%), respectively). The supplementation of dietary lecithin did not increase final body weight but did improve larval survival rates. The n-3 HUFA content of prawns fed dietary squid oil was higher than those of animals provided with other diets. These results indicated that the most appropriate diet for rearing M. rosenbergii larvae is the diet containing 3% squid oil and 1.5% lecithin.     

Egg quality criteria in common dentex (Dentex dentex)

The spawning quality, in terms of hatching rate, larval mortality at 3 and 5 days post-hatching (dph) and day of total mortality of two broodstock groups of common dentex was evaluated for 1 month in 2005. Several biochemical parameters including total lipid content, lipid class and fatty acid composition, carbohydrate content and metabolic enzyme activities were analysed in all the egg batches collected. Comparison was carried out between low- (mortality at 3 dph higher than 35%) and high-quality (mortality at 3 dph lower than 10%) batches. No differences were observed in lipid content and/or lipid class and fatty acid composition although a slightly higher content of neutral lipids was detected in high-quality batches. However, significant differences were obtained regarding carbohydrate composition and the activity of enzymes such as alkaline phosphatase and pyruvate kinase being higher in low-quality egg batches.     

Effects of dietary arachidonic and eicosapentaenoic acids on common dentex (Dentex dentex Linnaeus 1758) larval performance

Oily emulsions containing constant levels of total fatty acids (FAs) and varying eicosapentaenoic acid (EPA) and arachidonic acid (ARA) levels were used to enrich rotifers. Common dentex larval survival and growth were compared between groups fed different enriched live prey. Growth, survival rate, and lipid composition of larvae suggest that feeding common dentex in the first 15 days posthatching with 2.5–3% EPA, 6–8% docosahexaenoic acid (DHA), and DHA/EPA ratio of 2.0–2.5 is sufficient to fulfill their EPA requirements. Higher amounts of dietary EPA did not result in any significant improvement in growth or survival. EPA requirement during this period of larval development does not seem to be as critical as other FAs during the first 15 days of common dentex larval development, but it does not exclude its essentiality later in development. In the case of ARA, nutritional requirements are low compared to other marine finfish species, with the upper limit of this essential FA being around 2% of total FAs provided in the live prey composition.     

Breeding and larval rearing of the camouflage grouper Epinephelus polyphekadion (Bleeker) in the hypersaline waters of the Red Sea coast of Saudi Arabia

This is the first report on the successful year-round natural spawning and larval rearing of Epinephelus polyphekadion (Bleeker) in captivity and under hypersaline water conditions of 42-43%₀ salinity in the Red Sea coast of Saudi Arabia. Although the fish spawned naturally once or twice a year during 1992-94 culture period, incorporation of cod-liver oil in the broodstock diet during the 1995 culture period enabled the fish to spawn continuously for 2-3 days in each month during March, April, May and August. The egg fertilization and hatching rates also increased during the 1995 spawning period. The egg fertilization rate varied from 90 to 100% with a mean of 96.5 ± 3.38%. The egg hatching rate varied from 70 to 95% with a mean of 83.1 ± 10.12%. The fertilized egg diameter averaged 757.3 ± 37.36 μm. There was a linear relation between the fertilized egg size and the egg hatching rate. The increase in the hatching rate relevant to the egg size was statistically significant (P < 0.01). The egg development time until hatching lasted for 19 h at 29°C. The newly hatched larval size ranged from 1.55-1.71 mm with a mean of 1.65 ± 0.052 mm in total length. The larval growth was slow in the early stages and the growth curve until metamorphosis showed a curvilinear pattern. Wide variations in larval size, range 22-47 mm with a mean of 33.40 ± 7.01 mm, were observed during the metamorphosis stage at day 50. No significant difference (P > 0.05) in growth and survival was observed between the larvae reared using white and grey coloured tanks. The larval survival up to metamorphosis was 1.6-4.7% with a mean of 2.98 ± 1.56% in the grey coloured tanks and 1.6-1.9% with a mean of 1.73 ± 0.16% in the white tanks. The results demonstrated the possibility of breeding E. polyphekadion under captive culture conditions. However, methods to improve the larval survival have to be pursued further for commercial farming of this species.     

The effect of vitamin A supplementation in broodstock feed on reproductive performance and larval quality in Penaeus chinensis

The effect of feeding four semi‐purified diets A1, A2, A3, A4, containing different vitamin A acetate levels 0, 20, 40, 60 mg kg^?1 diet, respectively, on fecundity, egg hatching rate, larval survival rate and vitamin A content in eggs of Chinese shrimp (Penaeus chinensis) broodstock was compared with a fresh clam diet (control) in a 60‐day feeding trial. The broodstock shrimp fed the diet with 60 mg kg^?1 vitamin A acetate added exhibited significantly higher fecundity (P < 0.01). Hatching rate was highest with diet A4 (P < 0.05), whereas hatching rates were similar fed diets A1, A2, A3. Increasing levels of vitamin A in broodstock diet resulted in improvement in larval quality. The vitamin A levels in shrimp eggs from broodstock fed with diet A4 were higher compared with those from broodstock fed with diet A1, A2 (P < 0.01). The fecundity and hatching percentages were positively correlated with the vitamin A content in eggs in the present study. The results of this study showed that higher level of vitamin A in broodstock diet may have positive effects on fecundity and larval quality in P. chinensis.     

Characterizing egg quality and larval performance from captive mahi‐mahi Coryphaena hippurus (Linnaeus, 1758) spawns over time

Mahi‐mahi Coryphaena hippurus is a promising species for aquaculture development and has been used as a model species for oil toxicology and physiology studies. This species has one of the fastest growth rates of any marine teleost and a unique reproductive biology due to its high spawning frequency and reproductive energy allocation. These characteristics lend the species to being an excellent model for understanding broodstock nutrition for other high energetic pelagic species. In this study, egg morphometrics and larval survival were tracked over a 10‐week period from the initial capture of wild mahi‐mahi broodstock. Larval quality from subsequent spawns collected over time was quantified using larval survival activity indices (SAIs) as a metric to assess egg quality. Larval SAIs were maintained and did not significantly decrease (p < .05) over the time course of this study. A multiple linear regression based on the elapsed time in captivity of the broodstock, egg diameter and larval SAI at 1 dph provided the most accurate prediction of larval SAI at 3 dph (R² = 0.996 p < .05). There were strong positive correlations with larval SAIs at 1 and 3 dph and the key nutrients: eicosapentaenoic acid (C20: 5n‐3, EPA) and related fatty acid ratios, vitamin E and nearly all amino acids under investigation. This study demonstrated that larval survival was maintained over time due to the supply of these key nutrients in the broodstock diet.     

The effects of dietary HUFA level on flame angelfish (Centropyge loriculus) spawning,egg quality and early larval characteristics

This study was conducted to determine the effects of dietary highly unsaturated fatty acids (HUFA) on flame angelfish (Centropyge loriculus) reproduction, and egg and larval quality. In the experiment, formulated diets containing 1.8, 2.9 or 3.6% n‐3 HUFA were fed to flame angelfish broodstock (n = 4) for 5 months. Mean fecundity (daily egg production), egg fertilization rates and embryo viability were used as indicators of egg quality. In addition, mean egg diameter, oil globule diameter, per cent hatch, larval size at hatch, per cent survival to yolk exhaustion and larval size at yolk exhaustion were recorded for each treatment. Flame angelfish fed the diet containing 3.6% n‐3 HUFA exhibited significantly increased fecundity, fertilization rates and embryo viability than fish that were fed the other two formulated diets. Egg diameter, egg oil globule diameter, larval size at hatch, larval survival to yolk exhaustion and larval size at yolk exhaustion from the 3.6% n‐3 HUFA broodstock treatment group were not significantly different from those derived from the Control broodstock treatment. These data revealed that flame angelfish egg quality could respond rapidly (within weeks) to maternal dietary changes. Results from this study further support that dietary HUFA composition can significantly affect broodstock reproductive performance as well as subsequent performance of eggs and larvae.     

Induced Spawning and Egg Quality Evaluation of Red Snapper, Lutjanus campechanus

Brood red snapper, Lutjanus campechanus, were captured from the wild and induced to ovulate by human chorionic gonadotropin (hCG) injection; eggs and sperm were manually stripped; and the eggs were artificially fertilized. Eggs were evaluated by the following egg quality parameters: buoyancy, fertilization, egg size, and oil globule size and number. The relationship of these egg quality parameters and brood characteristics (female size, fecundity, time of year, and response time to ovulation) to 36 h posthatch larval survival was considered. Injection of wild‐caught red snapper females with 1100 IU/kg of hCG resulted in 75% of the females ovulating. The average fecundity was 343,377 ± 30,805 eggs/kg, with a mean percent fertilization of 79.0 ± 1.74%. The mean percentage of floating eggs per spawn was 91.8 ± 1.75%. Mean egg diameter for floating eggs was 778.3 ± 2.09 μm, with a mean oil globule diameter of 117.5 ± 1.53 μm. Brood‐related characteristics were a better predictor of larval survival than postovulation egg characteristics. The percentage of floating eggs in a spawn was not correlated to larval survival. Spawns with eggs having a single oil globule had a similar larval survival as those eggs where multiple globules were common. No clear relationships were found for any one factor and larval survival, but rather a combination of factors was more predictive of survival, most notably spawn date, fecundity, and response time following hCG injection.     

Effects of egg stocking density on egg hatchability,larval quality and water quality for pinfish,Lagodon rhomboides,and pigfish,Orthopristis chrysoptera

Pinfish (Lagodon rhomboides Linnaeus) and pigfish (Orthopristis chrysoptera L.) are relatively new, cultured species commonly used as marine baitfish in the south‐eastern United States and currently have no defined protocols for egg incubation. Thus, experiments were conducted to determine efficient egg stocking densities during static and flow‐through incubation that yielded higher quality larvae. Eggs of each species were incubated statically at 250, 500, 1000 and 2000 eggs L^?1, and after incubation, egg hatching success, larval survival to first feeding, larval morphometrics and water quality were assessed. Stocking densities above 250 eggs L^?1 led to significant reductions in pinfish hatching success and water quality degradation, evident from decreased dissolved oxygen and pH levels and increased nitrogenous wastes. Increased stocking densities for pigfish also resulted in significant water quality degradation, although hatching success was unaffected up to a density of 1000 eggs L^?1. A high flow‐through water exchange rate of 2000% daily resulted in significant reductions in nitrogenous wastes and greater stability in dissolved oxygen and pH levels during incubation when compared to static treatments of the same egg density. Additionally, the high exchange rate of 2000% was critical in maintaining high hatching success and larval survival to first feeding at stocking densities of 1000 eggs L^?1 for pinfish and up to 4000 eggs L^?1 for pigfish. No clear patterns in larval morphometrics were observed among stocking densities. Static incubation densities of 250 and 1000 eggs L^?1 are recommended for pinfish and pigfish, respectively.     

Egg quality determinants in cod (Gadus morhua L.): egg performance and lipids in eggs from farmed and wild broodstock

Lipids and essential fatty acids, particularly the highly unsaturated fatty acids, 20:5n‐3 (eicosapentaenoic acid; EPA), 22:6n‐3 (docosahexaenoic acid; DHA) and 20:4n‐6 (arachidonic acid, AA) have been shown to be crucial determinants of marine fish reproduction directly affecting fecundity, egg quality, hatching success, larval malformation and pigmentation. In Atlantic cod (Gadus morhua L.) culture, eggs from farmed broodstock can have much lower fertilization and hatching rates than eggs from wild broodstock. The present study aimed to test the hypothesis that potential quality and performance differences between eggs from different cod broodstock would be reflected in differences in lipid and fatty acid composition. Thus eggs were obtained from three broodstock, farmed, wild/fed and wild/unfed, and lipid content, lipid class composition, fatty acid composition and pigment content were determined and related to performance parameters including fertilization rate, symmetry of cell division and survival to hatching. Eggs from farmed broodstock showed significantly lower fertilization rates, cell symmetry and survival to hatching rates than eggs from wild broodstock. There were no differences in total lipid content or the proportions of the major lipid classes between eggs from the different broodstock. However, eggs from farmed broodstock were characterized by having significantly lower levels of some quantitatively minor phospholipid classes, particularly phosphatidylinositol. There were no differences between eggs from farmed and wild broodstock in the proportions of saturated, monounsaturated and total polyunsaturated fatty acids. The DHA content was also similar. However, eggs from farmed broodstock had significantly lower levels of AA, and consequently significantly higher EPA/AA ratios than eggs from wild broodstock. Total pigment and astaxanthin levels were significantly higher in eggs from wild broodstock. Therefore, the levels of AA and phosphatidylinositol, the predominant AA‐containing lipid class, and egg pigment content were positively related to egg quality or performance parameters such as fertilization and hatching success rates, and cell symmetry.     

Influence of food quality and quantity on the growth and development of Crassostrea gigas larvae: a modeling approach

A biochemically based model was developed to simulate the growth, development and metamorphosis of larvae of the Pacific oyster, Crassostrea gigas. The model is unique in that it (1) defines larvae in terms of their protein, neutral lipid, polar lipid, carbohydrate and ash content; (2) tracks weight separately from length to follow larval condition index and (3) includes genetic variation in growth efficiency and egg quality to better simulate cohort population dynamics. The model includes parameterizations for larval filtration, ingestion and respiration that determine growth rate and processes controlling larval mortality and metamorphosis. Changes in tissue composition occur as the larva grows and in response to the biochemical composition of the food.

The simulations show that genetically determined variations in growth efficiency produce significant changes in larval survival and success at metamorphosis. Larvae with low growth efficiency are successful under a much narrower range of culture conditions than larvae with high growth efficiency. The impact of low growth efficiency is primarily controlled by the ability of larvae to store lipid for metamorphosis. Culture conditions that provide increased dietary lipid counterweigh low growth efficiency. Changes in food quantity and quality had little effect on size at metamorphosis. On the other hand, larval life span and success rate at metamorphosis varied over a wide range depending upon the conditions of the simulation. Food quality and food availability both influence larval life span and, hence, larval survival. As ingestion rate decreases, larval life span increases and cohort survival declines. Increased lipid or decreased protein in the diet improves cohort survival. Changes in carbohydrate content are less influential. If cohort success is significantly affected by mortality during larval life rather than success at metamorphosis, the influence of food quality becomes more complex. The range of food compositions yielding high survival is restricted by a balance between improved success at metamorphosis obtained by increased lipid storage and the shortening of larval life span as a result of more rapid growth, a function of protein availability. These simulations illustrate the strength and utility of numerical models for evaluating and designing hatchery protocols for optimizing yield of C. gigas larvae.     

Evaluation of egg quality in broodstock cobia Rachycentron canadum L.

Twenty egg batches spawned naturally from 17 different females over two spawning seasons were used to evaluate the egg quality of cobia Rachycentron canadum. A reduction in egg size was observed towards the end of the spawning season for both years. The proportion of floating eggs demonstrated a positive linear relationship with both yolk‐sac larval survival (r²=0.91, P<0.05) and batch larval production (r²=0.80, P<0.01). Viable egg batches (i.e. fertilization success >50%) were of higher batch fecundity, had larger eggs and a higher proportion of floating eggs than non‐viable batches (i.e. 0% fertilization success). Also, biochemical analyses revealed that these viable eggs had significantly higher protein and amino acid contents. A multiple regression model based on the proportion of floating eggs, batch fecundity and fertilization success provided the most accurate predictions of batch larval production (r²=0.95, P<0.001). Similarly, using the egg content of arginine/glycine and methionine significantly increased the correlation coefficient in the multiple regression model predicting larval deformity (r²=0.92, P=0.002). This study reveals that accurate determination of egg quality in cobia can be improved using a combination of several variables rather than a single variable.     

Measures of egg quality in induced spawns of the Asian sea bass, Lates calcarifer Bloch

The egg morphometry and lipid and protein components were determined in induced spawns (n=14) of the sea bass, Lates calcarifer, to identify measures of egg quality. Based on fertilization and hatching rates, the spawns were classified either in Group I, (zero fertilization) or Group II (where fertilization and hatching occurred). The egg morphometry did not differ between the two groups (p > 0.05). The total lipid was higher in Group II than in Group I, although the difference was not significant (p > 0.05). The EPA and linoleic acid were significantly higher in Group II (p < 0.05). There were positive correlations between the total saturated fatty acids and fertilization rate (p < 0.05; r=0.58), the total saturated fatty acids and percentage of normal zygotes (p < 0.02; r=0.62), and DHA and the percentage of normal zygotes (p < 0.04; r=0.56). The total protein and FAAs were higher in Group I than in Group II, but the differences were not significant (p > 0.05). Proline, glycine, p-ethanolamine, and aspartic acid were significantly higher in Group II (p < 0.05), while tyrosine and glutamic acid were significantly higher in Group I (p < 0.05). Phosphoserine and fertilization rate were positively correlated (p < 0.03; r=0.60), as well as aspartic acid and hatching rate (p < 0.05; r=0.54). Arginine was negatively correlated with fertilization rate (p < 0.03; r=–0.61) and the percentage of normal zygotes (p < 0.03; r=–0.63). Serine was inversely correlated with yolk volume of the newly-hatched larvae (p < 0.03; r=–0.77). The moisture content of the eggs, which was significantly higher in Group II than in Group I (p < 0.03), was directly correlated with the FAAs:protein ratio (p < 0.03; r=0.76). The present results reveal egg components that may be used as quality measures in induced spawns of sea bass, a euryhaline teleost that spawn pelagic eggs containing an oil globule.     

The effects of sperm–egg ratios on polyspermy in the blood clam,Tegillarca granosa

Polyspermy in Tegillarca granosa, which leads to failure or abnormal development of early embryos, appears to be directly related to varying sperm–egg ratios. We investigated the correlation between sperm–egg ratios and conditions of embryonic development by setting six strict sperm–egg ratios and subsequently scoring fertilization rate, abnormal rate, rates of trochophore and D‐shaped larvae. When sperm–egg ratios rose from 2 × 10²:1 to 1 × 10³:1, D‐shaped larvae rate dropped significantly from 78.8 ± 13.3% to 47.8 ± 14.9% (analysis of variance, P< 0.05), and to 3.6 ± 2.8% in the 2 × 10⁴:1 group. Using fluorescence microscope observation, polyspermy rates rose from 2.6 ± 0.8% to 72.9 ± 4.8% with increases in sperm–egg ratios. Sperm–egg ratios were therefore correlated with polyspermy rate, which seriously affected larval survival. Under the premise of higher fertilization rate, the sperm–egg ratios of ≤2 × 10²:1 appeared to be more beneficial for embryonic development of T. granosa.     

Advance in the Culture Research of Small-Eye Flounder,Paralichthys microps,and Chilean Flounder,P. adspersus,in Chile

ABSTRACT

Over 71% of the aquaculture production of Chile is based on salmonids, and given the recents problems in the world salmon industry, it is necessary to investigate the culture of new species as a vital priority to maintain an industry of great social and economic impact for Chile. Small-eye flounder, Paralichthys microps, and chilean flounder P. adspersus, are native, high-value flatfish present off the coasts of Perú and Chile, that are commonly exploted by artisanal fishermen. Since 1986 both species have been objects of research studies for culture based on techniques developed for Japanese flounder. This paper is a review of current knowledge of this species and to identify research needs for the near future. Natural spawning of small-eye flounder and chilean flounder broodstock in captivity is already possible, but the manipulation of spawning using photoperiod and hormonal inducement, as well as the role of broodstock nutrition in egg and larval quality, needs to be explored. Successful incubation and larval culture protocol for both species have been developed, with larval survival over 24% from certain egg batches. Nutritional characterization and requirements for chilean flounder eggs and larvae during the culture period, optimal temperature, density, light intensity and green-water culture, are all subjects of ongoing research. Efforts to improve early culture protocol continues with emphasis on causes of larval mortality, early use of dry feed, microbial ecology of culture tanks and water quality. Weaning from live to formulated diets has been investigated, demonstrating survival of 30-50%. Presently only about 1-5% of hatchery raised flounder show a pigment disorder. Research on formulated diets and the weaning process are under way to ameliorate these results. Juveniles are being grown experimental in tanks and net pens systems and their performance (growth, survival, health) in both systems is being evaluated. Chilean flounder require approximately 2.8 years to reach 1 kg. Effort is also focusing on improving juvenile growing protocol, including recirculation systems, culture environment and diet formulation. Much future research will be required to attain optimal production of the species, such as species-specific nutritional requirements, optimum stocking density, disease and health management and growing protocols with new systems (shallow raceway). At present there is enough known about chilean flounder to begin a pilot-stage that will be the key for future development of its culture.     

Fluctuations of abundance and survival rate during the egg and larval stages of Japanese anchovy Engraulis japonicus in the Seto Inland Sea (1980–2007)

In order to understand the processes affecting early survival of the Japanese anchovy Engraulis japonicus population in the Seto Inland Sea, we examined the monthly fluctuations in the abundance and survival rates from eggs to recruits (15-day-old larvae, 13?mm in standard length fish, defined as 1-month-old fish) during their main spawning season from 1980 to 2007. The abundance of the yolksac larvae positively correlated with the abundance of eggs, but the abundance of recruits did not significantly correlate with the abundance of yolksac larvae. These results imply that the survival rate during the egg stage is relatively stable, but that the rate during the larval stage is variable. Of the three most recent decades (1980s, 1990s and 2000s), the abundance of recruits was highest in the 1980s. The decrease in the abundance of recruits after the 1990s can be considered to have occurred through a decline in survival rate during the larval stage because there were no significant differences in egg abundance, yolksac larval abundance, and survival rates during the egg stage in the three decades of the study period.     

Biochemical composition and quality of turbot (Scophthalmus maximus) eggs throughout the reproductive season

The present study investigated the biochemical composition and quality of turbot (Scophthalmus maximus) eggs throughout the reproductive season. Results showed that the fertilization, hatching and egg floating rates were variable throughout the reproductive season, with the highest values recorded during the mid-season. Meanwhile, positive correlations were found between fertilization, hatching rate and floating rate. The composition of turbot eggs, including total lipid, protein, carbohydrate, moisture and dry weight showed no significant differences during the reproductive season. Furthermore, no correlations were found between egg compositions and viability parameters (VPs), including fertilization and hatching rates as well as larval deformity rate. However, egg diameter varied and correlated with fertilization, hatching and egg floating rates. The fatty acid in eggs at mid-season had significantly higher levels of C14:0, C16:0, C16:1n-7, C18:0, C18:1, C20:4n-6, C20:5n-3 and C22:6n-3. Moreover, significant relationships were found between fatty acids and VPs. Eggs of the middle season had significantly higher concentration of isoleucine, leucine, lysine, methionine, valine, alanine, aspartate, glutamate and serine, whereas no significant relationships were found between amino acids and VPs. These observations suggest that the biochemical profile of eggs may be useful in evaluating egg quality and improving broodstock management for turbot.     

Effect of the lipid droplet adherence on growth and survival of the European hake (Merluccius merluccius) larvae

The effect of the adherence of the lipid droplet in the yolk‐sac on the growth and survival of the European hake (Merluccius merluccius) larvae was studied under starved and feeding conditions. Recently hatched hake larvae with adhered and non‐adhered lipid droplet (ALD and non‐ALD) were maintained during 8 days under starvation conditions. The adherence of the lipid droplet positively affected larval survival during starvation. At the end of the yolk consumption period (7–8 days after hatching), 90% of the surviving larvae had an ALD, while 10% of the survivors had a non‐ALD and showed a higher mortality rate. In a month feeding experiment, results show that the presence of non‐ALD in newly hatched hake larvae negatively affected their growth and survival. Dry weight and length (TL) of 20‐days‐old larvae with ALD were significantly higher than those with non‐ALD. Furthermore, lifespan of those larvae with non‐adhered lipid droplet was shorter, with most of them dying during the first 15–20 days of culture. As conclusion, the percentage of the lipid droplet adherence at hatching could be used as an indicator of ‘quality’ for European hake larvae: the greater the number of larvae with adhered lipid droplet, the better larval growth and survival.     

Antarctic krill (Euphausia superba) meal in the diets improved the reproductive performance of tongue sole (Cynoglossus semilaevis) broodstock

A three‐month feeding trial was conducted to investigate the effects of dietary krill meal on the reproductive performance of tongue sole broodstock. Three diets were formulated to contain different levels of krill meal, 0 (Diet K‐0), 10 (K‐100) and 200 (K‐200) g kg^–1 dry matter, replacing the corresponding contents of protein and lipid from fishmeal and fish oil. Each diet was assigned to triplicate tanks. Compared with K‐0, both K‐100 and K‐200 increased the egg properties such as buoyant eggs rate, egg diameter, oil droplet diameter and SOD activity of the fertilized egg. However, the maturation rate, serum estradiol content, the relative fecundity and hatching rate were improved only by K‐100. The krill meal supplementation increased the concentrations of astaxanthin and n‐3 fatty acids in eggs, but decreased the n‐6 fatty acid concentrations. Both K‐100 and K‐200 increased the survival activity index, but the larval deformity rate was decreased only by K‐100. At 15 DPH, the larval length and the digestive enzyme activities were significantly higher in group K‐200 compared with groups K‐0 and K‐100. In conclusion, dietary supplementation of krill meal, at the level of 100 or 200 g kg^–1 dry matter in exchange of fishmeal and fish oil had the considerable positive effects on C. semilaevis reproduction.