Effects of genotype × environment interactions on the selection of broadly adapted Pacific oysters (Crassostrea gigas)

Broadly adapted genotypes are required if a single line of selection is to improve Pacific oyster (Crassostrea gigas) production throughout the heterogeneous growing environments found in the Pacific Northwest region of the United States. An experiment was conducted to determine if the relative rankings of average family performance (i.e. average individual weight, survival and yield) remain stable across a wide range of growing environments. Twenty-four full-sib oyster families were each planted both intertidally and subtidally in Yaquina Bay, Oregon, and Dabob Bay, Washington. Each family was represented by up to 12 replicate growout bags (stocked with 60 spat each) or 12 replicate lantern nets compartments (stocked with 40 spat each). Oysters were planted in Fall 2002 and yield (kg live weight replicate^− 1), average individual weight (g) and survival (%) were measured in Spring and Fall 2003 and at harvest in Summer 2004. Harvest average individual weight, survival, and yield were all significantly affected by family, environment, and family × environment interactions (P < 0.01). Family, environment, and family × environment interaction, accounted for 5%, 80%, and 2% of the total phenotypic variation in harvest average individual weight, respectively, 36%, 16%, and 7% of the total phenotypic variation in harvest survival, respectively, and 14%, 62%, and 5% of the total phenotypic variation in harvest yield, respectively. Although the effects of family × environment interactions were statistically significant, correlations among average family yields between all growout environments were significantly greater than 0 (r_P > 0.397; P < 0.04) indicating high-yielding families in one environment tended to be high-yielding in other environments. Results of this study suggest that the effect of G×E interactions on average individual weight, survival, and yield, while significant, are not large enough to prevent selection in a limited number of well chosen environments from resulting in favorable correlated gains in other environments in the Pacific Northwest.     

Quantitative genetics and heritability of growth-related traits in hybrid striped bass (Morone chrysops ♀ × Morone saxatilis ♂)

Commercially farmed, hybrid striped bass - female white bass (Morone chrysops) crossed with male striped bass (Morone saxatilis) - represent a rapidly growing industry in the United States. Expanded production of hybrid striped bass, however, is limited because of uncontrolled variation in performance of fish derived from undomesticated broodstock. A 10 × 10 factorial mating design was employed to examine genetic effects and heritability of growth-related traits based on dam half-sib and sire half-sib families. A total of 881 offspring were raised in a common environment and body weight and length were recorded at three different times post-fertilization; parentage of each fish was inferred from genotypes at 10 nuclear-encoded microsatellites. Dam and sire effects on juvenile growth (weight and length) and growth rate were significant, whereas dam by sire interaction effect was not. The dam and sire components of variance for weight and length (at age) and growth rate were estimated using a Restricted Maximum Likelihood algorithm. Estimates of broad-sense heritability of weight, using a family-mean basis, ranged from 0.67 ± 0.17 to 0.85 ± 0.07 for dams; estimates for sires ranged from 0.43 ± 0.20 to 0.77 ± 0.10. Estimates of broad-sense heritability of growth rate (based on weight), using a family-mean basis, ranged from 0.69 ± 0.12 to 0.82 ± 0.09 for dams and from 0.69 ± 0.13 to 0.81 ± 0.08 for sires. Similar results were obtained with length data. Both genetic and phenotypic correlations between weight and length were close to unity. High genetic (0.98-0.99) and phenotypic (0.79) correlations between growth rates measured at two time intervals suggested that selection for growth rate at an early life stage could affect growth rate at a later life stage. Estimates of general combining ability (GCA) for growth rates differed significantly among dams and among sires, whereas estimates of specific combining ability (SCA) for each dam × sire combination did not differ significantly from zero. These results suggest that additive-effect genes contributed to the differences in juvenile growth.     

Response to selection for harvest body weight of Oreochromis shiranus

Realised and predicted responses to selection were obtained for harvest body weight of Oreochromis shiranus from two generations of selection at the National Aquaculture Centre, Domasi, Malawi. The realised response was estimated from the difference in the least squares means of selected and unselected control populations, while the predicted response was obtained from the difference of the mean breeding values between generations. The realised (13.2%) and predicted (14.4%) responses for harvest body weight over the two generations of selection were not significantly different (P > 0.05). The intensity of selection from F₁ to F₂ (0.66) and from F₂ to F₃ (0.59) was low due to availability of few selection candidates per family at harvest caused by mortality, tag loss and the need to form broad heterogeneous multi-strain F₂ and F₃ populations. Within generation, the heritability estimates for the F₁ (0.31 ± 0.09), F₂ (0.31 ± 0.10) and F₃ (0.35 ± 0.11) generations were moderate. Across generation, the heritability estimate was low (0.14 ± 0.27). Within generation, the magnitude of the common full-sib effect was moderate (0.08-0.09) and not significantly different from zero (P > 0.05). However, across generations, the common full-sib effect was high (0.27 ±0.05) and significantly different from zero (P < 0.05). A substantial correlated selection response due to selection for increased harvest body weight was observed for both tagging body weight and for survival from tagging to harvest; for tagging body weight 22.8% from F₁ to F₂ and 15.9% from F₂ to F₃; for survival 7.2% from F₁ to F₂ and 13.8% from F₂ to F₃. The results are discussed in relation to the maximisation of the genetic gain in the future generations while constraining the rate of inbreeding.     

Setting of a procedure for experimental incubation of Pacific oyster (Crassostrea gigas) embryos

Standardized experimental protocols designed to study Pacific oyster (Crassostrea gigas) gamete quality have not been previously published. Gamete sampling variations and confounding effect of interacting factors result in large variations between replicates, decreasing the effects of the studied factors. This work aims at defining a standardized procedure for incubation of oyster embryos designed for experimental purposes.In a first phase, four experiments were developed to improve embryo sampling and handling. They showed that a minimum of 50 embryos must be counted to decrease the variation between counting replicates. For reliable results, sampling must be carried out from 0 to 7 min after a careful agitation of seawater containing embryos (salinity: 35.6‰). Compared to control and a 30 cm one, the D-larval yield of embryos submitted to a 1 m fall was significantly reduced, showing the limited effect of mechanical disturbance on Pacific oyster oocytes survival. Then, maintaining 2.2 million embryos in 250 ml seawater for a two hours period resulted in a decrease of D-larval yield which could not be explained by a decrease of O₂ content and pH of seawater.The second phase of this work included a set of five experiments, defining experimental incubation conditions. A higher larval yield was observed using 1.8 l beakers and 150 l tanks compared to 0.3 ml microtiter plates and 1 l fish egg incubators. Higher larval yields were recorded when embryo density ranged from 5 to 100 ml^− 1, compared to values between 500 and 2000 ml^− 1. Compared to controls (no antibiotic or no presence of light), no changes of D-larval yield were observed by adding 20 ppm chloramphenicol or by maintaining embryos in total darkness. Then, a significant decrease of pH and O₂ content was observed during the incubation period. However, these changes could not be considered as limiting for Pacific oyster embryo development.In conclusion, experimental incubation conditions have been defined in this study: 30 embryos ml^− 1 incubated in 1.8 l beakers without antibiotic and regardless of light intensity, when not higher than 500 lux. The mean coefficients of variation observed between tank replicates ranged from 13.1 to 16.5%. The standardized incubation procedure described in this work will help to study quality variations of Pacific oyster gametes.     

Selective particle feeding by the Chilean oyster, Ostrea chilensis; implications for nursery culture and broodstock conditioning

Hatchery broodstock conditioning and nursery culture of the Chilean flat oyster Ostrea chilensis have been hampered by the poor performance of oysters fed typical microalgal hatchery diets. To determine the feeding capabilities of this species the selective removal and consumption of natural planktonic assemblages and artificial inert particles (polystyrene beads) by juvenile and adult oysters were examined experimentally. The arrangement of the eulaterofrontal cirri of the ctenidia was also examined to infer their potential efficiency of particle selection for feeding. Polystyrene beads of 45 and 15 μm in diameter had high rates of removal from suspensions by both juvenile (45 μm = 70%, 15 μm = 73%) and adult (45 μm = 88%, 15 μm = 87%) oysters. In contrast, beads of 6 μm diameter had lower rates of removal (adults = 68%, juveniles = 53%), while 1 μm beads were not removed at all. Both adult and juvenile oysters feeding upon natural plankton assemblages removed only microphytoplankton (20-75 μm in size) despite the presence of nanophytoplankton (2-20 μm), picophytoplankton (< 2 μm), cyanobacterium Synechoccocus spp. (< 2 μm), and bacterial cells (< 75 μm) in the experimental suspensions. Eulaterofrontal cirri of both juvenile (15.2 μm ± 0.9 SE) and adult oysters (18.9 μm ± 0.3 SE) are the shortest that have been reported for any ostreid species which helps to explain the inability of this species to retain small food particles. The clearance rates for oysters feeding on microphytoplankton only were 1.49 (± 0.05 SE) and 7.1 (± 1.2 SE) l h^− 1g^− 1 for juveniles and adults respectively. These values are much higher than previously reported for this species being fed smaller sized cultured microalgae. Our results strongly suggest that the difficulties in the nursery and broodstock hatchery culture of this oyster may be due to inappropriate phytoplankton diets. We recommend the provision of cultured microalgae of 20-75 μm in diameter for improving the performance of hatchery maintained juvenile and adult O. chilensis.     

Successful culture of larvae of Litopenaeus vannamei fed a microbound formulated diet exclusively from either stage PZ2 or M1 to PL1

In three separate experiments, harpaticoid copepods Tisbe monozota (alive and dead) and a microparticulate microbound diet were evaluated as alternatives to live Artemia nauplii as food, beginning at either stage PZ2 or M1, in the larval culture of Litopenaeus vannamei. Larvae were cultured in 2 L round bottom flasks at a density of 150 L^− 1 (Experiment 1) and 100 L^− 1 ( 3.2 and 3.3) at 28 °C, 35‰ salinity and 12:12 LD photoperiod, and fed 4×/day^- 1. Larvae were initially fed a mixture of phytoplankton to stages PZ2 or M1 and then fed either live Artemia, live or dead copepods, or a microparticulate microbound diet. The experiments were terminated and all larvae were harvested when more than 80% of larvae had molted to postlarvae 1 (PL1) within any flask representing any of the treatments. The comparative value of the different diets and feeding regimes was determined by mean survival, mean dry weight and total length of individual larva, and percentage of surviving larvae that were PL1. Trypsin activity of samples of larvae from each treatment was also determined. The microparticulate microbound diet effectively served as a complete substitute for Artemia nauplii when fed beginning at stage M1. When fed at the beginning of the PZ2 stage, survival was comparable to that of larvae fed Artemia, but mean dry weight, mean total length, and percent of surviving larvae that were PL1 generally were significantly less. Responses to the feeding of copepods, whether fed dead or live, as a substitute were generally significantly less than those of larvae fed either the Artemia nauplii or the microparticulate diet. Values of trypsin activity (10^− 5 IU/μg^- 1 dry weight) corresponded to the relative proportions of the different larval stages within a treatment, with higher activity being characteristic of early stages. Previously demonstrated successful results with another species of crustacean suggest that the microparticulate microbound diet has characteristics that should be effective in the culture of the carnivorous stages of other crustacean and fish larvae that are currently fed live Artemia nauplii.     

Effect of dietary taurine and cystine on growth performance of juvenile red sea bream Pagrus major

Two experiments were conducted to investigate the effect of dietary taurine and cystine on growth and body composition of juvenile red sea bream Pagrus major. In Experiment I, a casein-based semi-purified diet included a small amount of fish meal were supplemented with taurine at the levels of 0 (control) and 1.0%. The experimental diets in Experiment II were without fishmeal and supplemented with taurine at 0 (control), 0.5, 1.0 and 2.0% or cystine at 1.0 and 2.0%. These diets were fed three times a day for 6 weeks to fish (average body weight: 2.3 g in Experiment I and 2.5 g in Experiment II). In Experiment I, fish fed the taurine-supplemented diet showed significantly (P < 0.05) improved growth, feed efficiency and feed consumption relative to fish fed the unsupplemental diet. The whole body taurine content increased, whereas the non-essential amino acid contents decreased, in fish fed the taurine-supplemental diet compared to fish fed the unsupplemented diet. In Experiment II, the growth, feed efficiency and feed consumption of fish fed the taurine-supplemented diets, irrespective of the dietary taurine levels, were significantly higher than those of fish fed the control diet and the cystine-supplemented diets. Taurine content in the whole body increased with the dietary taurine level, while the taurine contents did not increase by the supplemental cystine. Other free amino acid contents in the taurine-supplemented diet groups followed similar trends to those in Experiment I. These results indicate that supplemental taurine to a casein-based semi-purified diet at more than 0.5% improved the growth and feed performance of juvenile red sea bream. It is also suggested that juvenile red sea bream cannot metabolize cystine into taurine.     

Effect of different longline farming designs over the growth of Mytilus chilensis (Hupé, 1854) at Llico Bay, VIII Región of Bio-Bio, Chile

This study evaluates the effect of three culture design factors over the growth of the Mylitus chilensis, farmed through suspended systems known as longline with buoys, and longline with High Density Polyethylene (HDPE) tubes. The study was carried out at the Llico Bay, VIII Region of Bio-Bio, Chile. The three factors studied are: sleeve spacing, sleeve type and depth. The results show that in the longline with buoy system, the sleeve spacing presented a significant effect over the shell length and the wet meat weight (p < 0.001, for both growth variables). On the longline of HDPE tubes system, the sleeve spacing had a significant effect over the meat yield (p < 0.001). The depth factor had the most important effect over the growth on the longline with HDPE tubes system (p < 0.001). The sleeve type presented an effect on all growth variables (p < 0.001), but only in the longline of HDPE tubes. The conclusion is that on the longline with buoys, for M. chilensis farming, the best growth results and operational advantages are obtained under the following design configuration: continuous sleeve with spacing between sleeves of 40 cm, and a length/depth of 6 m. For the longline with HDPE tubes, the best configuration is a net sleeve, with gaps of 40 cm and a length of 6 m. When comparing results by both types of longline in a semi exposed zone, at the end of the study period, the longline of HDPE tubes shows superior results in shell length and meat yield over the longline of buoys with an 8.13% increase in the shell length and a 7.22% in meat yield.     

Phenotypic and genetic parameters for body measurements, reproductive traits and gut length of Nile tilapia (Oreochromis niloticus) selected for growth in low-input earthen ponds

In this study we present estimates of phenotypic and genetic parameters for body size measurements, reproductive traits, and gut length for Nile tilapia (Oreochromis niloticus) selected for growth in fertilized earthen ponds for two generations. Throughout the experiment, ponds were fertilized daily with 50 kg dry matter, (dm)/ha chicken manure. No supplementary feeds were added. For the analysis, 6429 fully pedigreed experimental fish from G0, G1 and G2 were used. Generations were discrete and therefore parameters were estimated separately for each year. Heritability estimates for body measurements ranged from 0.4-0.6 for standard length to 0.69-0.79 for head length. Phenotypic correlations between body weight and body measurements ranged from 0.64 to 0.89. Genetic correlations were close to unity. The heritability estimate for maturity at harvest (corrected for sex) was 0.13. Heritabilities for carcass traits were estimated from G₁ only and were 0.16 for gutted weight and 0.06 for dressing percentage. Phenotypic correlation between body weight and gutted weight was 0.84 and the genetic correlation was 0.20. Heritability estimate for gut length was 0.22. We also estimated a high genetic correlation between gut length index and standard length (0.78) but a low genetic correlation between gut length index and body weight (0.22 ± 0.28). These results suggest that selection for growth on an herbivorous diet could result in a correlated response in gut length.     

Growth and food sources of Pacific oyster Crassostrea gigas integrated culture with Sea bass Lateolabrax japonicus in Ailian Bay, China

Shell length and tissue growth of Pacific oyster Crassostrea gigas integrated culture with Sea bass Lateolabrax japonicus were monitored during April–October 2010 in Ailian Bay, China. And also, the food sources of the oyster were analyzed and quantified by stable carbon and nitrogen isotope methods. Results showed that the increment of shell length and flesh dry weight of oyster cultured at cage area were greater than that at control area significantly (P < 0.05). Enrichment of δ¹³C and δ¹⁵N in oyster tissue at the cage area relative to the control area was significant (P < 0.05). Based on the simple linear mixing model, the contribution rate of the fish feces and waste fish feed to oyster was 29.27 and 5.59 %, respectively. This work demonstrates that the differences in growth performance of oyster between cage area and control area were resulted from the utilization of organic matter derived from fish aquaculture. Integrated filter-feeding bivalves culture with marine fish can reduce the environmental impact of organic waste from fish-farming activities.     

Summer mortality of hatchery-produced Pacific oyster spat (Crassostrea gigas). I. Estimation of genetic parameters for survival and growth

The multidisciplinary project “MOREST” aims to improve our understanding of causes of summer mortality in Crassostrea gigas juveniles in France and to reduce its impact on oyster production. As part of the MOREST project, 43 full-sib families nested within 17 half-sib families were produced, planted out and tested in 3 sites during summer 2001 to assess to what extent genetic variability exists for this trait. A strong genetic basis was found for survival as narrow-sense heritability estimates ranged from 0.47 to 1.08, with higher values in sites where summer mortality was higher. Genetic correlations across sites were positive and very high for survival, indicating no genotype by environment interaction. In contrast, lower genetic variation was observed for growth in all sites. Finally, genetic correlations between growth and survival were low, in all sites. Selective breeding in a single site should therefore be an efficient means of improving survival in oysters less than one year old along the French Atlantic and Channel coastlines with only very limited effects on growth. As yield mostly depends on survival and growth, this approach should significantly improve harvestable yield. Possible reasons why a high genetic variance for survival appears to be maintained in wild populations are discussed.     

Development and evaluation of microsatellite markers for identification of individual Greenshell™ mussels (Perna canaliculus) in a selective breeding programme

A set of 49 microsatellite loci isolated from the endemic New Zealand Greenshell™ mussel, Perna canaliculus, were evaluated for inclusion in a parentage assignment marker suite by assessing their ease of PCR amplification, allele scoring and conformity to Mendelian inheritance in hatchery-produced families. Ten polymorphic loci (mean H_e = 0.78 and polymorphic information content (PIC) = 0.72) were identified as being suitable for parentage assignment. These 10 microsatellite loci gave a combined non-exclusion probability of < 0.001 (probability that an unrelated parent pair will not be excluded from parentage of an arbitrary offspring), based on allele frequencies from 16 broodstock mussels. Simulations predicted an assignment success rate of 99.9% with all 10 loci and > 95% with the best 5 or more loci (mean PIC = 0.84). In actual parentage assignments, 124 offspring from 8 full-sib families were assigned to the correct parent pair with 4 or more loci. We found evidence for null alleles and extensive size homoplasy in many loci, highlighting the importance of thoroughly characterizing and evaluating microsatellite markers prior to parentage assignment and other applications.     

Effects of the partial substitution of dietary fish meal by differently processed soybean meals on growth performance, nutrient digestibility and activity of intestinal brush border enzymes in the European sea bass (Dicentrarchus labrax)

This study evaluated the effects of replacing fish meal (FM) in the diet of European sea bass (Dicentrarchus labrax) with differently processed soybean meals on growth performance; apparent digestibility coefficients (ADCs); the activity of alkaline phosphatase and the brush border digestive enzymes: leucine amino peptidase, maltase and γ-glutamyl transpeptidase; and the fish morphometric and flesh quality. European sea bass with an initial average body weight of 187.8 ± 1.4 g, were fed either a FM based (control) diet or a soy replacement isoproteic, isolipidic and isocaloric diet. The treatments consisted replacing FM protein by: 25% toasted, dehulled and solvent-extracted soybean meal (SE25); 50% dehulled and toasted soy seeds subjected to dry extrusion and mechanical oil extraction (ME50); 50% enzyme-treated soybean meal (ET50) and an inclusion of 60% composed of 30% toasted, dehulled and solvent-extracted soybean meal and 30% enzyme-treated soybean meal (SE + ET/60). ADCs values of dry matter, crude protein, crude lipid and gross energy did not significantly differ between ME50 and SE + ET/60 but both of them were inferior to the other treatments (P < 0.05). Compared with the control FM-based diet, only the group that consumed the ME50 diet had lower specific growth rate, feed conversion ratio and gross protein retention efficiency values (P < 0.05). The protein efficiency ratio did not differ between the FM-based control group and all other soy derivate groups (P > 0.05). In order to gain more insight on the effects of the diet on fish growth, activity of the brush border enzymes was measured. No significant differences were found in leucine amino peptidase and maltase activities, between the control group and the other soy derivate groups. The activity of γ-glutamyl transpeptidase was significantly higher in the upper section in fish that consumed the control diet compared with fish that consumed the soy derivate diets. Yet, the main activity of this enzyme was found in the lower intestinal section. In all the soy derivate diets except for the SE25 diet, the activity of alkaline phosphatase was significantly lower than its activity in the control diet. Feeding diets that include various types and levels of soybean derivatives did not affect the whole body composition and slaughter yield but significantly reduced liver weight. The results show that in methionine supplemented diets, FM can be replaced in terms of protein by 25% SE, 50% ET or 60% soy composed of 30% SE and 30% ET without hampering fish performance. The inclusion of 50% protein from ME resulted in significantly lower growth performance and feed utilization.     

贝龄对马氏珠母贝植核贝生长、成活率和育珠性状的影响

以马氏珠母贝(Pinctada martensii)速长系F2为材料,分析了贝龄对植核贝生长、成活率和育珠性状影响。实验设2.0龄贝植核组(A)、2.0龄贝对照组(B),1.5龄贝植核组(C)和1.5龄贝对照组(D),按照常规技术进行插核手术与海区养殖,育珠期为450 d。在插核后第15、30、60、180、270和450天,比较各组的平均体质量和成活率差异;在插核后270 d和450 d,比较A和C组留核率、珍珠层厚度、优质珠率和珍珠产量的差异。结果表明,在插核后第15、30、60、180和270和450天,4个组的平均体质量和成活率均存在显著性差异(P<0.05),C和D组的成活率显著大于A和B组(P<0.05),C和D组的体质量日增长率显著大于A和B组(P<0.05)。在插核后第270天,A和C组的留核率、珍珠层厚度和珍珠产量均存在显著性差异(P<0.05),A和C组间优质珠率差异不显著(P>0.05);在插核后第450天,C组留核率、珍珠厚度、优质珠率和珍珠产量均显著大于A组(P<0.05)。结论认为,利用低龄贝进行插核育珠明显提高植核贝的留核率、成活率和珍珠层厚度,从而能够提高珍珠质量。本研究旨在为合理设计马氏珠母贝的养殖模式提供科学依据。     

Growth and gonadal development in diploid and triploid turbot (Scophthalmus maximus)

This study determined the effect of triploidy on the survival, growth and gonadal development of turbot from 6 to 48 months of age. From 6 to 24 months of age (first sexual maturity), survival was similar in both ploidies (P > 0.05). From 24 to 48 months of age, after the first sexual maturity, survival was 91.9% in diploids and 100% in triploids, which did not exhibit the post-spawning-associated mortality. Growth was similar for both ploidies during the first year of life. After that, triploids grew significantly (P < 0.05) more that diploids, with more marked differences after each spawning season. From 24 to 48 months, the average weight difference between both ploidies was 11.4 ± 1.9%, ranging from 4.3 to 23.0%. At 47 months of age, the biomass of triploids was 10.3% greater in total weight and 14.3% greater in eviscerated weight. Gonads of triploid males were similar to that of diploids, whereas in triploid females, they were significantly smaller and rudimentary. A histological analysis carried out at 47 months of age showed complete sterility of triploids in both sexes. Sex ratio was 1 male (M):0.6 female (F), for diploids, significantly (P < 0.05) different from 1:1, and 1 M:3.3 F for triploids, significantly (P < 0.05) different from 1:1 and from the diploids. Since females grow more than males, culture of triploids benefited from the high female ratio, which helped to reduce size dispersion. In addition, their sterility allowed better performance by avoiding the reduction in growth that takes place during the spawning periods. Together, these observations indicate that triploidy induction can be an interesting option for turbot aquaculture, especially for the production of large-size fish of more than 2 years of age.     

Suitability of the copepod, Acartia clausi as a live feed for Seabass larvae (Lates calcarifer Bloch): Compared to traditional live-food organisms with special emphasis on the nutritional value

Though artificial propagation of Asian seabass Lates calcarifer (Bloch) in captivity through induced breeding techniques is standardized under Indian conditions, larval and nursery rearing techniques including suitable nursery feeds have to be standardized to obtain better survival and growth. Feeding experiments in triplicate were conducted to evaluate the suitability of the marine copepod Acartia clausi as live prey for fourteen day-old seabass larvae (6.53 ± 0.06 mm; 8.58 ± 0.33 mg) and compared with the traditional live prey, rotifers and Artemia nauplii. While A. clausi and rotifers were mass produced using algae Isochrysis galbana, Chaetoceros affinis and Chlorella marina, Artemia nauplii were produced using cysts. Nutritional quality of cultured copepods was evaluated based on the proximate composition, amino acid and fatty acid composition, and compared with that of rotifers and Artemia nauplii. Proximate composition varied significantly (P < 0.05) among the different live feeds. A. clausi showed higher protein (63.12%) and lipid (16.65%) content than Artemia nauplii and rotifers. Total essential amino acids content was 2% lower in A. clausi compared to that in Artemia nauplii. Fatty acid profiles of the live feed organisms showed that A. clausi is a rich source of n − 3 fatty acids. The total n − 3 fatty acid content of A. clausi was 33.94%. Length, weight overall weight gain and survivorship were significantly (P < 0.05) different among the dietary treatments, and weight gain was comparatively higher in A. clausi fed larvae. Survival of seabass larvae fed A. clausi was obtained highest as 58.13% against the lower values of 39.93% and 41.62% in larvae fed rotifer and Artemia nauplii respectively. Final carcass composition of the larvae of L. calcarifer fed different live-food organisms showed significant differences (P < 0.05) among the dietary treatments. The fatty acid composition of the dietary treatments was reflected to a certain extent in the fatty acid composition of the seabass larvae. The present investigation revealed the nutritional value of calanoid copepod and thus underlining its usefulness as a suitable live-food organism for rearing larvae of the commercially valuable Asian seabass.     

A microsatellite marker tool for parentage analysis in Senegal sole (Solea senegalensis): Genotyping errors, null alleles and conformance to theoretical assumptions

A set of 50 potential microsatellite loci previously described in several flatfish species was evaluated for designing a suitable tool for parentage assessment in Senegal sole (Solea senegalensis). Low cross-amplification within Pleuronectiformes, even between congeneric species, was achieved. This suggests a low conservation of microsatellite flanking regions in this order regarding other fish orders of similar evolutionary age. Twelve loci showed appropriate amplification and polymorphism to acquire enough statistical power for parentage analysis. All forty-one individuals from one broodstock and 320 offspring were analyzed using this set of markers. The high potential of microsatellites for parentage exclusion (Excl1 = 0.9999; Excl2 = 1) permitted us to trace back all offspring to single pairs of parents. The families obtained were used to analyze the performances of the loci applied and to identify possible sources of error for parentage analysis in Senegal sole. The 2.5% of single mismatches in the families studied were attributed mostly to genotyping errors and to a lesser extent to null alleles. The average mutation rate estimated over 7680 gametes was in the range reported within fish (3.9 × 10^− 4) and did not compromise parentage analysis. All loci conformed to theoretical assumptions (Mendelian segregation, independent segregation), excluding the F13-II8/4/7 and Sol 9A loci, which showed strong genotypic association in the families analyzed. A set of 4 microsatellites (Sol CA13, F13-II8/4/7, Smax-02 and Sse GATA38) was finally selected for parentage evaluation in S. senegalensis combining both enough exclusion potential (> 0.970) and the lowest economic cost.     

Optimization of experimental infection protocols for the estimation of genetic parameters of resistance to White Spot Syndrome Virus (WSSV) in Penaeus (Litopenaeus) vannamei

Two infection protocols, individual oral (IO) and waterborne infection (WB), were evaluated to challenge Penaeus (Litopenaeus) vannamei with White Spot Syndrome Virus (WSSV). Five different batches of full and half-sib families were infected experimentally and tested for growth performance under commercial growth conditions. The genetic variance for WSSV resistance was estimated using a linear sire-dam repeatability model that considers test-day survival as the dependent variable. The heritability estimates using the IO protocol ranged from 0.01 ± 0.00 to 0.02 ± 0.01, whereas the heritability estimates using the WB infection protocol were not significantly different from zero. The genetic correlations measured as the product moment correlation between full-sib family breeding values for resistance to WSSV and harvest body weight in ponds were unfavourable in three of the five batches and favourable in one of them. The dosage of WSSV was better controlled with IO oral infection than with other methods, with all animals being exposed to approximately the same risk of infection at the same time. This should improve the accuracy of the genetic parameters and hence improve the accuracy of the breeding values. It should, however, be noted that once the outbreak was established and the mortalities began, the shape and the magnitude of the slope of the mortality curves showed little difference in the infection pattern between batches irrespective of the dosage and infection protocol, and in most of the cases the cumulative mortality was greater than 80%. The main reason for this is probably the high densities of animals in the tanks needed for the genetic evaluations.     

Performance of different types of diets on experimental larval rearing of endangered Chitala chitala (Hamilton) in recirculatory system

This is the first report on the successful larval rearing of captive bred population of Chitala chitala (Hamilton). C. chitala is one of the endangered fresh water fish species in India for which the development of controlled larval rearing procedures are needed for stock enhancement. Fifteen days old post-hatchlings were stocked for 28 d in a 30 L recirculatory tanks using eight different diets i.e. live feed (tubifex worms, chironomous larvae, zooplanktons,), dry feed (dry tubifex, spirulina, daphnia) and other non-conventional feed (fish eggs and boiled egg-yolk). Fishes accepted all types of diets. The study revealed that specific growth rate (SGR) was higher in post-hatchlings fed on live tubifex worms (2.40 ± 0.72) followed by fish eggs (2.15 ± 0.71), dry tubifex (2.12 ± 0.40), chironomous larvae (1.91 ± 0.44), spirulina (1.79 ± 0.38), daphnia (1.42 ± 0.79) and planktons (1.37 ± 0.77) whereas minimum SGR was recorded with boiled egg-yolk (0.63 ± 0.5). A highly significant difference (p < 0.01) in SGR was observed in fish fed on live feed (tubifex worms, chironomous larvae, planktons, spirulina), dry tubifex and fish eggs whereas for daphnia and boiled egg-yolk it was only significant (p < 0.05). The final mean weight and weight gain showed highly significant difference (p < 0.01) in live tubifex, zooplanktons, spirulina, chironomous larvae, dry tubifex and fish eggs, whereas daphnia and boiled egg-yolk fed larvae showed significant difference (p < 0.05). Highest mean survival rate on day 28 was observed in live tubifex worms (94%) and chironomous larvae (92%). The post-hatchlings reared with spirulina and daphnia showed same survival rate of 88% whereas the lowest mean survival of 66% was recorded in boiled egg-yolk. The experiments showed that captive bred post-hatchlings of C.chitala could be reared in experimental recirculatory system for attaining higher growth and survival during early life stages. However, methods to improve the larval rearing have to be improved further for commercial farming of the species.     

Growth, immune function, and disease and stress resistance of juvenile Nile tilapia (Oreochromis niloticus) fed graded levels of bovine lactoferrin

Juvenile Nile tilapia (Oreochromis niloticus) were fed nutritionally complete, practical basal diets supplemented with bovine lactoferrin (Lf) at 0, 200, 400, 800, or 1600 mg/kg diet to apparent satiation twice daily for 8 weeks. After the feeding trial, the effect of dietary Lf on growth performance, immune function, and resistance to Streptococcus iniae challenge and low-water stress was determined. Dietary Lf did not affect growth performance (weight gain, feed intake, feed efficiency ratio, or survival) or haematological parameters (haemoglobin, white and red blood cell counts, or haematocrit) (P > 0.05). Crowding stress produced significant increases in plasma cortisol, glucose, lactate, and osmolality from baseline values (P ≤ 0.001), but dietary Lf did not affect plasma glucose, osmolality, or cortisol concentrations (P > 0.05). The level of Lf in diet had a significant impact on survival following S. iniae challenge with fish fed the 800 mg/kg Lf diet having significantly higher survival than control fish (P ≤ 0.05). There was not a corresponding increase in activity of non-specific or specific immune parameters (plasma lysozyme and spontaneous haemolytic complement activities or agglutination antibody titer against S. iniae) with addition of Lf to diets (P > 0.05), but plasma iron decreased and total iron binding capacity (TIBC) increased significantly with increasing concentration of Lf in diet (P ≤ 0.05). The ability of Lf to sequester iron, an essential nutrient required for the growth of bacteria, is regarded as one of its key antibacterial properties. The increased survival with increasing dietary concentration of Lf seemed to correspond with a decrease in plasma iron concentration and not enhancement of non-specific or specific immune functions.