Direct and indirect responses to selection on individual body weight in the Pacific oyster (Crassostrea gigas)

Three experiments were performed to examine the heritability of body weight among adult Pacific oysters (Crassostrea gigas) evaluated in Yaquina Bay, Oregon, USA, and to determine if selection on individual body weight could result in changes in offspring survival and yield. The first two experiments utilized midparent-offspring regressions to estimate the heritability (h²) of adult oyster body weight and the coheritability (h_x,y) between adult midparent body weight and offspring performance, including juvenile average body weight, survival and yield as well as adult survival and yield. In Experiment 1 both parents and offspring were evaluated in an “upriver” environment in Yaquina Bay. In Experiment 2 parents were evaluated in a “downriver” environment, while offspring were evaluated in an “upriver” environment. Experiment 3 contrasted average body weight, survival, and yield of offspring (evaluated upriver) derived from three large sires and three small sires mated to the same five females that were chosen at random (all parents evaluated downriver). In Spring 2002, 12 full-sib families from Experiment 1, 19 families from Experiment 2, and 26 families from Experiment 3 were stocked into lantern nets and suspended in Yaquina Bay. Measurements of yield (kg tier^− 1), average body weight (g), and survival (%) were recorded after one and two growing seasons in the field. Heritability estimates for adult body weight at harvest ranged from 0.313 (± 0.083) in Experiment 1 to 0.003 (± 0.073) in Experiment 2. In Experiment 3, average body weight did not differ between offspring derived from large sires and offspring derived from small sires (P = 0.47). Significant negative coheritability estimates were observed between adult midparent body weight and offspring survival in both Experiment 1 and Experiment 2. Significant negative coheritability estimates between adult midparent body weight and offspring yield were observed in Experiment 2 but not in Experiment 1. In Experiment 3, offspring derived from large sires had significantly lower survival and yield than offspring derived from small sires. These results show adult oyster body weight to be heritable but also subject to site-specific adaptation such that selection in the downriver Yaquina Bay environment was ineffective at changing average body weight in the upriver environment. Negative coheritability estimates between performance traits indicate that adult oyster body weight may be a poor indirect measure of oyster yield potential, and that selection solely for increased body weight could lead to a decrease in offspring yield.     

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.     

Evaluation of β-(1 → 3, 1 → 6)-glucans and High-M alginate used as immunostimulatory dietary supplement during first feeding and weaning of Atlantic cod (Gadus morhua L.)

Stimulation of the non-specific defence enhances the disease resistance and growth, and has good potentials as a measure for increased microbial control in juvenile production of marine fish and shellfish. So far, the most commonly used immunostimulants are β-(1 → 3, 1 → 6)-glucans, and in this study the stimulatory potential of a β-(1 → 3, 1 → 6)-glucan of marine origin, the storage polysaccharide from the marine diatom Chaetoceros mülleri, was examined. The glucan (chrysolaminaran) was extracted from cultures of C. mülleri, and used as a dietary supplement in two first feeding experiments with larvae of Atlantic cod Gadus morhua L. In one experiment the microalgal glucan was compared to the commercial yeast-glucan product MacroGard®, and in the other to an alginate with a high content of mannuronic acid (High-M alginate) isolated from Durvillaea antarctica. The stimulants were given via rotifers, and weaning to formulated feed was initiated at day 17 or 18 after hatching. The survival ± SEM at day 27 after hatching was 24.5 ± 2.0%, 14.8 ± 4.5% and 13.1 ± 1.4% for the groups fed C. mülleri-glucan, yeast glucan and for the control, respectively, in the first experiment. The group fed C. mülleri-glucan group had higher survival compared to the control (P < 0.05) group, whereas the yeast glucan had no positive effect on the survival (p > 0.05). The dry weights of the groups at day 27 were low, with 203.2 ± 52.2, 165.2 ± 43.4 and 198.5 ± 58.1 μg per larva for the C. mülleri-glucan, yeast glucan and control groups, respectively. In the second experiment the survival in the period of feeding formulated feed (days 18-30) were 44.6 ± 4.3%, 44.7 ± 1.3%, and 33.8 ± 4.1% survival for the C. mülleri-glucan, High-M alginate and control group, respectively. The cod larvae fed C. mülleri-glucan reached an average weight of 531.6 ± 17.2 μg at day 30, which was significantly higher (p < 0.05) than the control group that had an average of 473.6 ± 3.5 μg. The larvae fed High-M alginate had an average weight of 470.3 ± 31.6 μg per larva at day 30, and not significantly different from the control (p > 0.05). The early weaning to formulated diet had detrimental effect on the growth of the larvae. In both experiments the C. mülleri-glucan group was the only group showing a positive growth rate in the period of weaning to dry feed. The microbial conditions in larval gut and water were monitored with respect to total colony forming units on Marine agar, and Vibrio- and Pseudomonas-like species on selective agars (TCBS and marine Pseudomonas Agar with CFC-supplement). The larvae were rapidly colonised after hatching, but no or weak effects of the stimulants were observed on the colonisation rates or the composition. The total CFU varied from 10¹ to 10² CFU per μg larva after initiation of the first feeding. The percentages of Pseudomonas-like bacteria increased throughout the period, whereas the levels of Vibrio-like bacteria were low and stable. The chrysolaminaran from the diatom C. mülleri was shown to be a promising candidate for use as an immunostimulatory feed additive, and which should be further explored.     

Developing bioelectrical impedance analysis methods for age‐0 brook trout

Year class strength of many fishes often is determined by survival through the first winter. Increased fat reserves improve survival and overall cohort success. Bioelectrical impedance analysis (BIA) methods are established for estimating proximate composition of adult brook trout, Salvelinus fontinalis (Mitchill), but none have been developed for early life stages. Small‐fish BIA would provide information about age‐0 percent dry weight, a proxy for fat reserves, allowing for better prediction of cohort success. The objective of this study was to develop BIA methods that provide reliable estimates of percent dry weight for age‐0 brook trout. BIA measurements were taken at seven anatomical locations from 48 to 115 mm fish. A model developed using BIA measures taken by subdermal needle electrodes precisely predicted percent dry weight (best model, RMSE = 1.03, R² = 0.86). Although lacking support, as determined by information theoretical analysis, BIA measured with non‐invasive external rod electrodes also precisely predicted percent dry weight (RMSE = 1.09, R² = 0.85). Models developed using two electrode locations performed better than models developed with only one location. For small brook trout, a dorsal to ventral pre‐dorsal fin electrode location should be used in conjunction with a dorsal total length location when measuring BIA to predict percent dry weight.     

Heritability for body weight at harvest size in the Pacific white shrimp, Penaeus (Litopenaeus) vannamei, from a multi-environment experiment using univariate and multivariate animal models

To estimate family BLUP breeding values and the heritability of body weight at harvest size (BW) in the Pacific white shrimp, Penaeus (Litopenaeus) vannamei, an experiment was conduced using information from two farm units of a Mexican hatchery and two shrimp population densities at each location. Data consisted of 12,658 shrimps that were siblings from 48 sires and 77 dams with a nested dam-sire structure. Shrimps were individually weighed at an average age of 130 days post-hatching. BW phenotypic mean (S.D.) was 18.2 (2.4) g, with values ranging from 8.4 to 30.0 g. Data were analyzed using univariate and multivariate models that considered BW within location by density pond environment as a different trait and included or not a common full-sib effect (c). The multivariate animal model included fixed effects of days from hatching and sex. For univariate models that included c effects, BW heritability (S.E.) estimates ranged from 0.24 (0.14) to 0.35 (0.18) across environments (heritability was zero in one environment). For multivariate models (excluding the environment with zero heritability) the heritabilities increased and ranged from 0.37 (0.06) to 0.45 (0.09). Standard errors of heritabilities and c effects were both drastically reduced in the multivariate analysis. Pairwise genetic correlations between environments were from 0.80 (0.08) to 0.86 (0.04). These differences may be indicative of genotype-environment interaction for BW at 130 days post-hatching. Statistical problems found to separate c from additive genetic effects both in univariate models were reduced using multivariate models. Correlation between family raw phenotypic means and family BV means from the multivariate analysis was 0.93 indicating a rather low risk of miss selecting superior families if BLUP solutions were neglected using replicated environment data. It is also concluded that use of incorrect statistical models or unreplicated data may lead to biased or inaccurate estimates of genetic parameters in shrimp breeding programs.     

Genetic improvement of farmed tilapias: Composition and genetic parameters of a synthetic base population of Oreochromis niloticus for selective breeding

The present study is based on data recorded from fish of the third generation of the GIFT project (Genetic Improvement of Farmed Tilapias). The objective of the study was to compose a synthetic base population of Nile tilapia for further selective breeding, and to estimate phenotypic and genetic parameters in that population. The base population was formed by choosing parent stock among the best performing animals within the best strain combinations resulting from a full diallel cross design (8 × 8) involving four African wild strains and four Asian farmed strains (64 strain combination cells altogether). The grandparent ancestors of the base population were mainly representing the three strains originating from Egypt, Kenya and Thailand (20.2, 27.3 and 19.6%, respectively). The proportion of ancestors from the Senegal strain was medium (12.2%) whereas the proportion of ancestors from Ghana, Israel, Singapore and Taiwan strains was low (3 to 8%) and mainly due to a restriction that all parent strains should be represented in the synthetic base. Statistical analyses using a mixed animal model were carried out on records from 13,570 individually tagged and surviving progeny of 50 sires and 123 dams. The growth performance of the fish was tested in seven diverse environments. The test environments covered a wide range of tilapia farming systems, namely, earthen ponds fertilized with inorganic fertilizer and organic manure or on-farm agricultural residues, cage culture, and test stations located in different agro-climatic regions. The model fitted included the fixed effect of test environment and sex and the linear and quadratic covariate of age at stocking. The random terms were the additive genetic effect of individual fish and the additional effects common to full-sib groups. The estimates of heritability for body weight at harvest in different test environments ranged from moderate to high (0.12 to 0.56) and the estimate across test environments was 0.15. The variances due to other effects common to full-sib families were significant, accounting for 8 to 16% of total variation in body weight. The genetic correlations among body weights recorded in similar environments were high (mostly > 0.80, i.e. among the earthen ponds in experimental locations). By contrast, the genetic correlations between harvest weight in earthen pond and in cage environments were more variable (0.36-0.82). Overall, the results suggested that the genotype by environment interactions were of limited importance, at least for the target pond farming systems in the Philippines. It was concluded that as the additive genetic variation in the base population was large, the harvest weight of the GIFT fish could be effectively improved by selective breeding, and that there was no immediate need to develop separate strains for different environments.     

Experimental integrated aquaculture of fish and red seaweeds in Northern Portugal

Three potentially valuable red seaweeds, Chondrus crispus Stackhouse, Gracilaria bursa pastoris (S.G. Gmelin) P.C. Silva and Palmaria palmata (L.) O. Kuntze, collected in northern Portugal, were cultivated using the nutrient-rich effluents from a local turbot (Scophthalmus maximus Linnaeus) and sea bass (Dicentrarchus labrax Linnaeus) farm. The algae were cultivated in a two level cascade system. Several arrangements of the cascade system, stocking densities (3, 5, 7 and 8 kg m^− 2) and water fluxes (140 and 325 l h^− 1) were tested to optimize biomass yield and nitrogen uptake rate and efficiency. The yield and the total ammonium nitrogen (TAN) uptake of the three species were highly seasonal. Palmaria could not survive culture conditions during the summer when water temperature was above 21 °C. In the spring, Palmaria had an average yield of 40.2 (± 12.80) g DW m^− 2 day^− 1 and a nitrogen uptake efficiency (NUE) of 41.0% (± 17.26%). NUE expresses, in percentage, the average reduction in TAN concentration between the inflows and the outflows of the tanks. Chondrus performed better in summer with an average yield of 37.0 (± 11.10) g DW m^− 2 day^− 1 and removing 41.3% (± 17.32%) of nitrogen. Gracilaria grew year round, but also performed better during spring/summer, producing an average of 29.1 (± 2.90) g DW m^− 2 day^− 1, and only 7.3 (± 5.08) g DW m^− 2 day^− 1 during autumn. Yield of C. crispus did not differ significantly when grown at two different stocking densities (5 kg m^− 2 and 8 kg m^− 2). On the other hand, Gracilaria had significantly higher yields at 5 than at 7 kg m^− 2. Better NUE, on average 76.7% (± 22.13%), was also obtained with 5 kg m^− 2 stocking density and only 63.8% (± 24.62%) with 7 kg m^− 2. The yield of Gracilaria increased significantly with the increase of water flux from 140 to 325 l h^− 1 and more nitrogen was removed from the water. However, NUE decreased from 48.4% to 33.4% at 140 and 325 l h^− 1, respectively. Biofiltration was highly improved by a cascade system with a NUE as high as 83.5%.     

Effects of temperature on the induced spawning of channel catfish and the production of channel × blue catfish hybrid fry

Hybrid catfish (channel catfish, Ictalurus punctatus, female × blue catfish, I. furcatus, male) can be obtained by induced spawning and artificial fertilization but with variable results. Temperature of the surrounding environment affects the rates of physiological processes in fish including time to ovulation following hormone injection and time post-ovulation when quality eggs can be obtained. Brood females were held at 24, 26, and 28 °C in 100 L aquaria and injected with LH-RHa at 20 μg/kg followed 12 h later with 100 μg/kg. Fish were monitored hourly recording the time of the first egg deposit. Some females were manually stripped soon after the first eggs were observed, and the remaining females were stripped 4-6 h after the first eggs were observed. Eggs were artificially fertilized with blue catfish sperm and incubated. The percent of females that ovulated were 52.9%, 82.4% and 95.5% at 24, 26, and 28 °C (P = 0.001) respectively. The majority of females that ovulated did so between 58 to 64 h at 24 °C, 48 to 52 h at 26 °C and 24 to 40 h at 28 °C for a degree hour response time of 1405 ± 117, 1141 ± 238 and 951 ± 261 respectively (P < 0.001). Differences in eggs/kg female, eggs/g of eggs, percent viable eggs, percent hatch and survival of sac fry to swimup resulted in an average of 384.4 ± 316.97 fry/kg female at 24 °C, 370 ± 219.2/kg at 26 °C and 1284 ± 1394.1/kg at 28 °C (P = 0.136). Egg quality varied with how soon eggs were stripped after the first egg was observed. For fish held at 26 and 28 °C. the combined effects of egg quality and fry survival resulted in an average 1081 ± 1483.9 fry/kg female for fish stripped within 2 h after the first eggs were released and 500 fry/kg female when stripped after 4 or more hours once the first eggs were released.     

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.     

Family growth response to different laboratory culture environments shows genotype–environment interaction in the sea urchin Strongylocentrotus intermedius

This study investigated the genetic variation and genotype–environment interaction (GEI) in the early growth stage among seven full‐sib families of the sea urchin Strongylocentrotus intermedius. From each of the seven families, 180 or 270 sea urchins of the same size were exposed to three laboratory environments (E₁, E₂ and E₃). These environments were commonly used in breeding programs for S. intermedius. After a 102 days trial, test height, test diameter, body weight and the coefficient of variation of body weight were determined. The results revealed significant family effects on most growth traits in all the three environments (except for test diameter in environment E₂), and significant environmental effects on growth in several families (family 1, 5, 6, 7). The study also revealed that the coefficient of variation in body weight varied significantly among the families (P < 0.01) but not among the environments. Highly significant GEI effects were also recorded for all growth traits (P ≤ 0.001), except for the coefficient of variation in body weight (P > 0.05). Variances of GEI accounted for about 0–2.742% of phenotypic variances for the investigated traits. Significant GEI caused a certain degree family ranking inversions for the growth traits. The present study provides evidence for the existence of GEI in the family selection of sea urchin S. intermedius. More attention should be paid to the GEI to obtain satisfactory genetic gain in S. intermedius.     

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.     

Histopathology and a real-time PCR assay for detection of Bonamia ostreae in Ostrea edulis cultured in western Canada

Bonamia ostreae is an intracellular haplosporidian parasite in European flat oysters Ostrea edulis that occurs on both coasts of the United States and causes significant mortality in Europe. Canada was considered free of B. ostreae until 2004, when it was first detected in O. edulis obtained for laboratory study from a western Canadian oyster farm. Bonamia ostreae was confirmed in O. edulis at the index farm in November 2004 using histopathology, conventional polymerase chain reaction (PCR) assays, restriction fragment length polymorphism (RFLP) analysis, and sequencing of the PCR product. Archived samples of European flat oysters obtained from the index farm between 1999 and 2004 (n = 343) were re-examined and all samples collected before 2003 (n = 306) were confirmed negative for B. ostreae by histopathology (n = 306) and PCR (n = 62). In archived samples from 2003, B. ostreae was detected in 3 of 37 O. edulis by histopathology (n = 2) and/or PCR (n = 2). Also, records indicate that B. ostreae was not detected in O. edulis (n = 348) from five other locations in western Canada between 1986 and 2000. To better understand the distribution and prevalence of B. ostreae in western Canada, 607 oysters from the index farm and 2 additional farms were sampled in the summer of 2005. All 3 farms had been stocked with O. edulis spat from the State of Washington, USA, where B. ostreae is endemic. Samples were analyzed by histopathology and a new real-time PCR that amplifies a 68-bp target DNA fragment. B. ostreae was detected in all three locations, with prevalence ranging from 0.5 to 11.1%. Diagnostic sensitivity of the real-time PCR method was consistently greater than histopathology. Also, preliminary evidence supports the conclusion that real-time PCR on paraffin sections is more sensitive than histopathology; B. ostreae DNA was confirmed in 4 oysters by real-time PCR on paraffin-embedded tissues (and independently confirmed on unfixed tissues) that was not detected by histopathology. As a result of these findings, O. edulis spat are no longer allowed to be imported from endemic areas into Canada.     

Genetic parameters of growth and survival in the Pacific oyster Crassostrea gigas

The Pacific oyster Crassostrea gigas is a representative bivalve mollusc that is widely cultured in the world and is the largest molluscan group cultured in China. In order to assess the feasibility of improving survival of C. gigas through genetic selection, the heritability and genetic correlations for growth and survival traits between different life stages were examined. Genetic parameters were estimated based on intraclass correlations of 49 full‐sib families (29 half‐sib families) in larvae (4 and 20 days after fertilization) and spat (140 days after fertilization) stages. The heritability for growth traits in larvae and spat was 0.30–0.86 and 0.53–0.59, respectively, and varied with ages. The heritability of survival was low in larvae (0.13 ± 0.05 and 0.17 ± 0.04, respectively for 4 and 20 days after fertilization) but medium (0.39 ± 0.07) in spat, suggesting that selection for increasing spat survival was feasible. The genetic correlation between growth traits within age was medium to high and positive (ranging from 0.47 to 0.96, respectively, between shell length (SL) and shell height (SH) at 20 days and between SL and SH at 140 days after fertilization), suggesting that selection to improve single growth trait will cause positive response in another growth traits in C. gigas. The genetic correlations between survival and growth traits at 140 days were low but positive (ranging from 0.23 to 0.27, respectively, between survival and SH and between survival and SL at 140 days after fertilization), suggesting that selection for survival may not have a negative response in growth. Overall, this study suggests that survival traits should be taken as improving target of next selection breeding programme in C. gigas.     

The effects of supplemental dietary cholesterol on growth, development and survival of mud crab, Scylla serrata, megalopa fed semi-purified diets

The effects of varying levels of dietary cholesterol on growth, development time and survival of mud crab, Scylla serrata megalopa were investigated using semi-purified microbound diets (MBD). Five iso-energetic diets containing different level of cholesterol ranging from 0.14% to 1% of dry weight of the diet were tested. Fifteen megalopa were reared individually for each dietary treatment, and development time and survival were recorded on a daily basis. More than 25% of megalopa from all treatments were able to metamorphose into the first crab stage, suggesting that the endogenous level of cholesterol in the basal diet (0.14%) was sufficient to support development of the megalopa stage of this species. Widest mean carapace width (3.53 ± 0.08 mm) and highest mean dry weight (2.11 ± 0.22 mg) were recorded for juveniles that molted from megalopa fed live Artemia, whereas no megalopa in the unfed control treatment metamorphosed into crabs. The average development time from megalopa to the juvenile crab stage varied between the treatments, where megalopa fed live Artemia or MBD containing 0.2%, 0.4% or 0.8% total cholesterol showed the most synchronized molting (between 8.0 and 9.9 days). Longest development time was recorded for the megalopa fed diets containing 0.14% or 1% total cholesterol (both 11 days). Highest survival (74.3%) was recorded for the megalopa fed a diet containing 0.8% cholesterol. The results of this study are valuable in research to develop formulated diets for mud crab larvae as a replacement for live food in hatchery culture.     

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.     

The tetrasporophyte of Asparagopsis armata as a novel seaweed biofilter

The red seaweed Asparagopsis armata (Harvey; Rhodophytae, Bonnemaisoniaceae) produces biologically active secondary metabolites that are valuable natural ingredients for cosmetics and medicine and its cultivation may therefore be a profitable venture. The tetrasporophyte of this species (“Falkenbergia rufolanosa”) was successfully tank-cultivated as a continuous biofilter for the effluent of a commercial fish farm in southern Portugal. Optimal stocking density for highest biomass yield and a low level of other algal species in winter and late spring was 5×g centrifuged fresh weight l^− 1. The effect of total ammonia nitrogen supply (TAN flux) on biofiltration and biomass yield was investigated in winter and spring. Results revealed that A. armata is currently the seaweed-biofilter with the highest TAN removal of up to 90 μmol l^− 1 h^− 1 at a TAN flux of about 500 μmol l^− 1 h^− 1. In the tanks used, this is equivalent to a removal of up to 14.5 g TAN m^− 2 day^− 1. At a lower TAN flux of about 40 μmol l^− 1 h^− 1, TAN removal by A. armata is more than double to what is reported at this flux for another successful seaweed biofilter, the genus Ulva. Monthly variation of A. armata biomass yield peaked in May and was lowest in January. At TAN fluxes between 300 and 400 μmol l^− 1 h^− 1, an average water temperature of 21.7 °C and a total daily photon flux density of 47 Mol m^− 2, seaweed yield was over 100 g DW m^− 2 day^− 1 with a recorded maximum of 119 g. During spring, autumn and early summer, the biomass of A. armata within the experimental tanks doubled every week. A model for the up scaling of this finfish integrated aquaculture of A. armata varies the investment in biofilter surface area and estimates the return in biofiltration and biomass yield. Highest TAN removal efficiencies will only be possible at low TAN fluxes and a very large biofilter area, resulting in a low production of biomass per unit area. To remove 50% of TAN from the effluent (1 mt Sparus aurata; 21 °C), 28 m² of biofilter, designed to support a water turnover rate of 0.8 Vol h^− 1 would be necessary. This system produces 6.1 kg FW (1.5 kg DW) of A. armata per day and has the potential to turn biofiltration into an economically sustained, beneficial side effect.     

Effects of varied levels of incorporation of Labeo gonius in carp polyculture system in India

Growth performance of kuria labeo, Labeo gonius as a component species in the major carp polyculture system was evaluated at two incorporation levels against a control without the species through a year‐round grow‐out study in nine earthen ponds (0.08 ha). Three species ratio of catla, silver carp, rohu, mrigal and kuria labeo at 15:15:40:30:0 (T‐1: control), 15:15:40:20:10 (T‐2) and 15:15:40:10:20 (T‐3) were evaluated as three treatments. The carps were stocked at a combined density of 7500 fingerlings ha^?1. Silver carp demonstrated the highest survival (75–81%) followed by rohu (70–76%), catla (69–76%), kuria labeo (69–71%) and mrigal (67–69%). Species‐wise yield attributes such as survival, harvest weight, SGR and biomass yield of silver carp, catla and rohu were similar in their respective treatments. Kuria labeo at 10% inclusion demonstrated 12% higher harvest weight than its 20% inclusion. However, such higher weight gain could not affect the total biomass yields of carps which remained similar among the treatments. Furthermore, harvest weight of kuria labeo at 10% inclusion was comparable to that of mrigal when the latter incorporated at 20–30% level. Therefore, the study suggested 10% to be a suitable incorporation level for kuria labeo in the commercial grow‐out carp polyculture system.     

Heritability estimates and response to selection for growth of Nile tilapia (Oreochromis niloticus) in low-input earthen ponds

This study presents results of two generations of selection (G₁ and G₂) for growth of Nile tilapia. The selection environment consisted of earthen ponds which were fertilized daily with 50 kg dry matter (dm)/ha chicken manure. No supplementary feeds were provided. In total, 6429 fully pedigreed experimental fish were included in the analysis. Survival till harvest was highly variable ranging from 35% to 77% and was affected by initial weight, pond, and age effects. Body weight at harvest (BW) increased from a mean of 67.4 g in the grandparental (unselected) population (G₀) to 129.5 g in G₂ was affected by initial weight, pond, sex and age effects. Generations were discrete and therefore genetic parameters were estimated separately for each year. Heritability estimates for BW ranged from 0.38 to 0.60, and the heritability for survival ranged from 0.03 to 0.14. The estimated selection response was 23.4 g (34.7%) between G₀ and G₁ and 13.0 g (14.9%) between G₁ and G₂. These results demonstrate the feasibility of selection for growth of Nile tilapia in low-input environments.     

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.     

Intensive production of juvenile tiger shrimp Penaeus monodon: An evaluation of stocking density and artificial substrates

Tiger shrimp Penaeus monodon were intensively grown from PL₁₅ for 56 d in tank systems at stocking densities of 1000 and 2000 shrimp m^− 3, with and without the addition of artificial substrates (AquaMat® (buoyant and non-buoyant) and polyethylene mesh) at each density. Shrimp growth was significantly greater at the lower density and when substrates were added. Mean shrimp weight at harvest ranged from 0.64 ± 0.06 g (2000 shrimp m^− 3, no added substrate) to 1.17 ± 0.01 g (1000 shrimp m^− 3, added substrate). Survival was high and averaged 79.5 ± 2.7% across all treatments. The addition of substrates significantly increased survival at both stocking densities; however, survival was not significantly affected by stocking density. A maximum harvest density of 1645 shrimp m^− 3 and biomass of 1.27 kg m^− 3 were produced at a stocking density of 2000 m^− 3 with added substrates. Both harvest density and biomass significantly increased with stocking density and addition of substrates. The feed conversion ratio (FCR) of formulated feed was significantly lower when substrates were added. The results show that growth of P. monodon juveniles was inversely related to stocking density during intensive production. However, production output was significantly increased by addition of artificial substrates, which enhanced both growth and survival.