Development of an enzyme-linked immunosorbent assay (ELISA) for vitellogenin measurement in greenback flounder Rhombosolea tapirina

Vitellogenin (Vtg) was purified from the plasma of 17-estradiol (E₂)-injected male greenback flounder,Rhombosolea tapirina. The molecular weight of the native Vtg was estimated by gel filtration as 540 kD. SDS-PAGE and Western blotting analyses indicated that this protein consisted of three bands with molecular weights of 155, 104, 79 kD, respectively. A polyclonal antibody against the highest molecular weight band of putative Vtg was generated in sheep and an indirect antibody-capture competitive enzyme-linked immunosorbent assay (ELISA) was developed. The assay was validatedfor plasma Vtg measurement in greenback flounder. Serial dilutions of plasma from vitellogenic females parallelled the standard Vtg curve, whereas no cross-reaction was observed with the plasma of males in the ELISA. The Vtg ELISA was used to assess the induction of Vtg by E₂ in vivo in males. The induction of Vtg in greenback flounder showed a time- and dose-dependent response as in other species. In E₂-treated fish, detectable levels of Vtg were first found at 48 h, and reached a peak at 96 h post-injection. Plasma levels of Vtg increased as the E2 dose increased with a threshold of 0.1 mg kg^–1.     

In vitro effect of pituitary,interrenal and gonadal hormones on vitellogenin synthesis in primary hepatocyte cultures of Chalcalburnus tarichi

Vitellogenin (Vtg) is an important precursor yolk protein in egg‐laying vertebrates, including fish. The 17β‐oestradiol (E2) plays a crucial role in the Vtg synthesis; moreover, certain hormones can stimulate Vtg synthesis. We investigated the possible role of E2, carp recombinant growth hormone (crGH), insulin (Ins), progesterone (P4) and 11‐deoxycortisol (11‐DOC) hormones in Vtg synthesis on primary juvenile Chalcalburnus tarichi hepatocyte culture. The amount of Vtg in the medium was measured at 2‐day intervals using enzyme‐linked immunosorbent assay (ELISA). The hepatocytes were maintained in culture for more than 2 weeks without the addition of serum components. Vitellogenin localization was visualized with the immunofluorescence method in E2‐supplemented hepatocytes. Among hormones applied to the culture, only E2 had an influence on Vtg synthesis in a time‐dependent manner, while crGH, Ins, P4 and 11‐DOC had no effect. However, in hepatocytes stimulated with E2 in combination with P4, a lower Vtg production was seen compared with Vtg produced when hepatocytes were stimulated with E2 alone. P4 proved to have potentiating effects on co‐treatment with E2‐induced Vtg production. As a result, E2 and P4 are the most important hormones for Vtg synthesis in juvenile C. tarichi hepatocyte culture.     

Production of recombinant capsid protein of Macrobrachium rosenbergii nodavirus (r‐MCP43) of giant freshwater prawn,M. rosenbergii (de Man) for immunological diagnostic methods

White tail disease (WTD) caused by Macrobrachium rosenbergii nodavirus (MrNV) and extra small virus (XSV) is a serious problem in prawn hatcheries. The gene for capsid protein of MrNV (MCP43) was cloned into pRSET B expression vector. The MCP43 protein was expressed as a protein with a 6‐histidine tag in Escherichia coli GJ1158 with NaCl induction. This recombinant protein, which was used to raise the antiserum in rabbits, recognized capsid protein in different WTD‐infected post‐larvae and adult prawn. Various immunological methods such as Western blot, dot blot and ELISA techniques were employed to detect MrNV in infected samples using the antiserum raised against recombinant MCP43 of MrNV. The dot blot assay using anti‐rMCP43 was found to be capable of detecting MrNV in WTD‐infected post‐larvae as early as at 24 h post‐infection. The antiserum raised against r‐MCP43 could detect the MrNV in the infected samples at the level of 100 pg of total protein. The capsid protein of MrNV estimated by ELISA using anti‐rMCP43 and pure r‐MCP43 as a standard was found to increase gradually during the course of infection from 24 h p.i. to moribund stage. The results of immunological diagnostic methods employed in this study were compared with that of RT‐PCR to test the efficiency of antiserum raised against r‐MCP43 for the detection of MrNV. The Western blot, dot blot and ELISA detected all MrNV‐positive coded samples as detected by RT‐PCR.     

A rapid latex agglutination test for gender identification in the Atlantic bluefin tuna,Thunnus thynnus (Linnaeus)

A rapid, one‐step agglutination assay has been developed, based on latex particles sensitized with antibodies against vitellogenin (Vtg), aimed at Atlantic bluefin tuna, Thunnus thynnus (Linnaeus) (ABFT), gender identification. The egg‐yolk precursor protein Vtg was used as a gender marker for the assay as it is a female‐specific protein synthesized during reproductive maturation. The presence of Vtg in the plasma was revealed in 60–120 s through an agglutination reaction by mixing small volumes of ABFT plasma and an anti‐Vtg antibody‐latex suspension on a microscope slide. The effectiveness of the present test was restricted to the months of May and June, concomitant with high circulating Vtg levels. Because of its rapidity and ease of performance in the field, the present gender identification assay could be useful for broodstock management in the aquaculture industry as well as in tagging studies on wild populations.     

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.     

Immunohistochemical characterization of polyclonal antibodies against Enteromyxum leei and Enteromyxum scophthalmi (Myxozoa: Myxosporea), intestinal parasites of fish

The enteric myxozoan parasites Enteromyxum leei (Diamant, Lom et Dyková) and Enteromyxum scophthalmi Palenzuela, Redondo et Álvarez‐Pellitero are responsible for high weight loss in infected fish, which leads to subchronic disease and low mortality rates in gilthead sea bream (GSB), Sparus aurata L., and to high mortality rates in turbot, Psetta maxima (L.). The detection of initial parasite stages in histological sections is particularly difficult, but can be simplified by means of specific antibodies. Rabbit polyclonal antibodies (pAbs) were raised against E. scophthalmi and E. leei, and direct enzyme‐linked immunosorbent assay (ELISA) and immunohistochemistry were used to characterize their sensitivity and specificity. Both pAbs were adsorbed (apAb) with non‐infected intestines to avoid non‐specific labelling of fish tissues and to improve their specificity. The highest titre obtained in ELISA was 1: 32 000 for apAb‐Eleei and 1:16 000 for apAb‐Escoph. Working dilutions in immunohistochemistry were 1:1000 for apAb‐Eleei and 1:8000 for apAb‐Escoph. Both apAbs labelled proliferative and sporogonic stages with high specificity. apAb‐Escoph was very specific, whereas apAb‐Eleei cross‐reacted with Sphaerospora dicentrarchi Sitjà‐Bobadilla et Álvarez‐Pellitero and Sphaerospora testicularis Sitjà‐Bobadilla et Álvarez‐Pellitero, suggesting the presence of shared antigens. These pAbs stand as new tools for antigenic characterization and the diagnosis of both Enteromyxum species.     

Comparative functional responses of native and high‐impacting invasive fishes: impact predictions for native prey populations

Comparative functional responses (FRs) can predict impacts of invasive species, including piscivorous fishes, via quantifying their depletion of native food resources as a function of prey density. The utility of FRs for predicting impacts on prey populations by invasive fishes of different trophic guilds was tested here by comparing the FRs of the invaders Cyprinus carpio and Carassius auratus, with three native, trophically analogous fishes, Barbus barbus, Squalius cephalus and Tinca tinca. Chironomid larvae and Gammarus pulex were used as prey items. Predictions, developed from studies on the foraging of C. carpio and C. auratus in the literature, were that the invaders would have significantly higher consumption rates for chironomids than the native fishes, but not for G. pulex. Mean consumption rates for chironomids were significantly lower for both invaders than B. barbus and S. cephalus, but were similar to T. tinca. Barbus barbus had a significantly lower consumption rate of G. pulex than both invaders, but there were no significant differences between S. cephalus, T. tinca and the invaders. All FRs were type II, with FR curves for the invaders preying upon chironomids never being significantly higher than the native fishes, contrary to predictions. For G. pulex, some significant differences were apparent between the invaders and native fishes, but again were contrary to predictions. These results indicated that when predation impacts of invasive fishes could also be a function of their population density and body sizes, these parameters should be incorporated into FR models to improve impact predictions.     

The effects of salinity on reproductive development and egg and larvae survival in the spotted scat Scatophagus argus under controlled conditions

In the present study, we report the first successful instance of controlled reproduction in Scatophagus argus, which has recently emerged as a new aquaculture resource. The controlled reproduction process for S. argus was optimized with regard to salinity acclimation. Gonadal maturation was affected by salinity in both sexes. Levels of plasma 17β‐estradiol (E₂) and 11‐ketotestosterone (11‐kT) were salinity dependent and increased significantly with the duration of acclimation. Plasma levels of gonadal steroids were higher in fish held at 25‰ salinity. The highest gonadosomatic indices (GSI), 15.1 ± 1.6 in the female and 6.4 ± 1.2 in the male, were also observed at 25‰ salinity. Nevertheless, the optimal salinity for S. argus embryonic development and larval culture was 15‰. Thus, the salinity requirement for gonadal maturation and early development are quite different. The use of advanced reproductive technologies combining salinity acclimation and stimulation of luteinizing hormone‐releasing hormone analog (LHRH‐A₂) resulted in a fertilization rate of 83.2%–91.3% and embryonic survival rates of over 90%. Embryos of S. argus at the 2‐cell, blastula, gastrula and pharyngula stages were observed. Most embryos hatched after 21.0 hr of incubation at 28.0 ± 1.0°C. The development of larvae into juveniles was completed at 40–45 days posthatch (dph). In this study, we provide information about the controlled reproduction of S. argus and identify the optimal environmental parameters for S. argus embryonic and larval culture, with the aim of developing reliable reproductive techniques for its mass production.     

Development of attenuated erythromycin‐resistant Streptococcus agalactiae vaccine for tilapia (Oreochromis niloticus) culture

Streptococcus agalactiae is an important pathogen in fish, causing great losses of intensive tilapia farming. To develop a potential live attenuated vaccine, a re‐attenuated S. agalactiae (named TFJ‐ery) was developed from a natural low‐virulence S. agalactiae strain TFJ0901 through selection of resistance to erythromycin. The biological characteristics, virulence, stability and the immunization protective efficacy to tilapia of TFJ‐ery were determined. The results indicated that TFJ‐ery grew at a slower rate than TFJ0901. The capsule thickness of TFJ‐ery was significantly less (p < 0.05) than TFJ0901. When Nile tilapia were intraperitoneally (IP) injected with TFJ‐ery, the mortality of fish was decreased than that injected with TFJ0901. The RPS of fish immunized with TFJ‐ery at a dose of 5.0 × 10⁷ CFU was 95.00%, 93.02% and 100.00% at 4, 8 and 16 weeks post‐vaccination, respectively. ELISA results showed that the vaccinated fish produced significantly higher (p < 0.05) antibody titres compared to those of control at 2 or 4 weeks post‐vaccination. Taken together, our results suggest that erythromycin could be used to attenuate S. agalactiae, and TFJ‐ery is a potent attenuated vaccine candidate to protect tilapia against S. agalactiae infections.     

Carp (Cyprinus carpio) lipovitellin is a highly stable phospholipoglycoprotein with the same immunogenicity as vitellogenin

Vitellogenin (Vtg) induction in carp (Cyprinus carpio) is a commonly used biomarker for oestrogenic contamination. However, the accurate quantification of Vtg was challenged because the easy degradation of Vtg standard would change the standard curves of the immunoassays. In this study, three yolk proteins were purified from carp ovarian extracts by a two‐step chromatographic method. The purified proteins were characterized as phospholipoglycoproteins with molecular weights of approximately 416, 398 and 383 kDa. In SDS‐PAGE, the purified proteins appeared as a major band of approximately 110 kDa and several faint bands. Based on these characteristics, purified proteins were identified as carp lipovitellin (Lv). Immunological analysis showed that anti‐Vtg antiserum reacted with the purified Lv. The results of stability analysis revealed that even heated at 60°C for 60 min, the electrophoretic patterns of carp Lv in native‐PAGE and SDS‐PAGE did not have a significant difference compared with the Lv solution stored at 4°C. Therefore, the purified carp Lv was confirmed to have similar immunogenicity with Vtg and possess exceptionally high stability, which would be helpful for the development of robust immunoassays for accurate quantification of carp Vtg.     

Comparative study on the kinetic behaviour of carnitine palmitoyltransferase I between Javelin goby Synechogobius hasta (carnivorous) and grass carp Ctenopharyngodon idella (herbirovous)

Up to date, the carnitine palmitoyltransferase (CPT) system in fish nutrition receives little attention. The present study compared CPT I kinetic behaviour of Synechogobius hasta (carnivorous) and Ctenopharyngodon idella (herbivorous). The optimal conditions (temperature, incubation time, mitochondrial protein concentration and pH) for maximum CPT I activity showed no significant difference between S. hasta and C. idella. CPT I activities in S. hasta were significantly higher than those in C. idella. Affinity constants (Km) for carnitine in liver, heart, white muscle and spleen of S. hasta were significantly higher than those in C. idella. K_m for palmitoyl‐CoA in liver and heart of S. hasta were significantly higher than those in C. idella. V_max for carnitine and palmitoyl‐CoA in S. hasta tended to be higher than those in C. idella. Catalytic efficiencies (V_max/K_m) for carnitine in liver, white muscle and spleen of C. idella were significantly higher than those in S. hasta. V_max/K_m values for palmitoyl‐CoA in liver and heart of C. idella were higher than those in S. hasta. Our study demonstrated that the lower catalytic efficiency for carnitine in liver of S. hasta indicated that the fish showed a low capacity for energy generation through β‐oxidation of long‐chain fatty acids, which easily caused fatty liver syndrome. This is the first study in which, by using carnitine and palmitoyl‐CoA as the substrates, the complete kinetic characterization of CPT I in fish has been described, which increases our knowledge about lipid metabolism and its critical role in lipid utilization in fish.     

Effects of taurine supplementation in live feeds on larval rearing performance of California yellowtail Seriola lalandi and white seabass Atractoscion nobilis

The larval rearing performance of California yellowtail (Seriola lalandi) and white seabass (Atractoscion nobilis) was compared between larvae fed taurine‐supplemented rotifers (Brachionus plicatilis) and Artemia (Artemia franciscana) and control groups fed live feeds with no taurine enhancement. Results from the S. lalandi trial demonstrated that when fed taurine‐supplemented rotifers, survival was significantly higher than the control group (20.1% vs. 9.1%, P < 0.01) as was notochord length (5.43 mm vs. 5.13 mm, P < 0.005). No larval performance differences were detected between experimental and control treatments of A. nobilis. Biochemical analyses demonstrated that taurine concentrations were significantly elevated in both S. lalandi (23.7 vs. 2.7 mg g^?1, P < 0.001) and A. nobilis (33.0 vs. 21.0 mg g^?1, P < 0.005) when live feeds were supplemented with taurine. Results suggest that taurine is a limiting nutrient in the larviculture of S. lalandi but may not be for A. nobilis.     

Effect of cyclical feeding on compensatory growth,nitrogen and phosphorus budgets in juvenile Litopenaeus vannamei

This study assessed the effect of cyclical feeding on compensatory growth, nitrogen (N) and phosphorus (P) budgets of juvenile Litopenaeus vannamei. A 36‐day growth trial was performed with four different feeding protocols. The control group (S0) was fed to satiation twice every day during the whole experimental period; treatment groups S1, S2 and S3 were fed by the 9, 5 and 3 cycles of 1:3, 2:5 and 3:9 (fasting days:feeding days) respectively. Fasting in S1, S2 and S3 groups did not change the specific growth rate in wet weight (SGR_w), but the feed conversion efficiency (FCE) and protein efficiency ratio (PER) were significantly increased (P < 0.05) in comparison with control. The N and P consumed per unit wet weight gain of shrimp in S1, S2, S3 groups were significantly lower (P < 0.05) than control group by 15.39%, 15.96%, 19.33% for N, and 15.16%, 15.98%, 19.26% for P respectively. The total discharge of N and P (including N and P discharged by faeces (F_N/P), non‐faecal excretions (U_N/P) and exuviations (E_N/P); ) was significantly lower (P < 0.05) in the experiment groups by 19.91–22.07% for N and 18.68–26.37% for P respectively. Overall, the results suggest that the L. vannamei can reach completely compensatory growth, and the total discharge of N and P per unit wet weight gain of L. vannamei significantly decreased by cyclical feeding, which could have a positive effect on the reduced of environmental N and P loading due to the cultured of L. vannamei.     

Evaluation of the immune response in rainbow trout fry,Oncorhynchus mykiss (Walbaum), after waterborne exposure to Flavobacterium psychrophilum and/or hydrogen peroxide

The immune response in rainbow trout fry against Flavobacterium psychrophilum was elucidated using an immersion‐based challenge with or without prior exposure to hydrogen peroxide (H₂O₂). Samples were taken from the head kidney 4, 48, 125 and 192 h after immersion, and the regulation of several genes was examined. Bacterial load was assessed based on the presence of 16S rRNA and correlated with gene expression, and the levels of specific antibodies in the blood were measured 50 days post‐infection. Separately, both H₂O₂ and F. psychrophilum influenced gene expression, and pre‐treatment with H₂O₂ influenced the response to infection with F. psychrophilum. Pre‐treatment with H₂O₂ also affected correlation between gene regulation and pathogen load for several genes. A delay in antibody production in H₂O₂‐treated fish in the early phase of infection was indicated, but H₂O₂ exposure did not affect antibody levels 50 days post‐infection. An increasing amount of F. psychrophilum 16S rRNA was found in the head kidneys of infected fish pre‐treated with H₂O₂ relative to the F. psychrophilum group. The results show that a single pre‐treatment with H₂O₂ impairs the response against F. psychrophilum and may intensify infection.     

Cloning,expression of Vibrio alginolyticus outer membrane protein‐OmpU gene and its potential application as vaccine in crimson snapper,Lutjanus erythropterus Bloch

The outer membrane proteins of the marine aquatic animal pathogen, Vibrio alginolyticus, play an important role in the virulence of the bacterium and are potential candidates for vaccine development. In this study, the gene encoding an outer membrane protein‐OmpU was cloned and expressed in Escherichia coli. Polyclonal antibodies were raised in rabbits against the purified recombinant OmpU, and the reaction of the antibody was confirmed by Western blotting using the isolated OmpU and the recombinant OmpU of V. alginolyticus. To analyze the immunogenicity of the recombinant OmpU, crimson snapper, Lutjanus erythropterus Bloch, were immunized by intraperitoneal injection, and antibody response was assessed by the enzyme‐linked immunosorbent assay (ELISA). The results demonstrated that the recombinant OmpU produced an observable antibody response in all sera of the vaccinated fish. The vaccinated fish were challenged by virulent V. alginolyticus and observed to have high resistance to infection. These results indicate that the recombinant OmpU is an effective vaccine candidate against V. alginolyticus in L. erythropterus.     

Dietary fish oil replacement by soybean oil: Effect on plasma vitellogenin,sex steroids and ovarian steroidogenesis in Chinese strip‐necked turtles (Mauremys sinensis)

In order to investigate the effects of dietary fish oil replacement, the turtles (Mauremys sinensis) were fed four experimental diets for 10 months: FO (100% fish oil), FSO (70% fish oil and 30% soybean oil), SFO (30% fish oil and 70% soybean oil) and SO (100% soybean oil), sampled at pre‐vitellogenesis, vitellogenesis and post‐vitellogenesis. The results showed that plasma gonadotropin‐releasing hormone (GnRH) levels were the highest at pre‐vitellogenesis, which promoted the secretion of gonadotropin and sex steroids. Therefore, plasma luteinizing hormone (LH) and estrogen (E₂) levels were significantly increased at post‐vitellogenesis (p < 0.05), while follicle‐stimulating hormone (FSH) levels increased at vitellogenesis (p < 0.05). The FO and FSO groups had significantly higher GnRH and E₂ levels than the other two groups (p < 0.05). In addition, plasma vitellogenin (Vtg) levels significantly increased at vitellogenesis and post‐vitellogenesis (p < 0.05), which were significantly higher in the groups of FO and FSO than SO (p < 0.05). Moreover, the expression levels of hepatic estrogen receptor α (Erα) mRNA were significantly increased at vitellogenesis and post‐vitellogenesis while ovarian Cyp19α1α mRNA were significantly increased at post‐vitellogenesis (p < 0.05), and both were the lowest in SO. Taken together, the replacement of fish oil with 66.7% soybean oil is feasible.     

Gender determination in the Paiche or Pirarucu (<Emphasis Type="Italic">Arapaima gigas</Emphasis>) using plasma vitellogenin, 17β-estradiol,and 11-ketotestosterone levels

Arapaima gigas is an air-breathing giant fish of Amazonian rivers. Given its great economic and cultural importance, the aquaculture development of this species represents an evident solution to face the decline of wild populations. In captivity, reproduction occurs generally in large earthen ponds where stocks of a few tens of brooders are maintained together at the beginning of the rainy season (December–March in the Peruvian Amazon). Fry production relies on the spontaneous formation of male and female pairs, which build a nest, delimit a territory and guard the offspring for at least 20 days from other congeners and predators. However, as sex determination of A. gigas is not possible by morphological criteria, it is very difficult to optimize reproduction conditions and fry production in each pond, which seriously hampers the culture of this species. This situation prompted us to develop sexing methodologies based on (1) the detection of female specific plasma Vitellogenin (Vtg) using an enzyme immuno assay (EIA), and (2) the determination of plasma 17β-estradiol and 11-ketotestosterone levels for immature specimens. The Vtg purification was performed by electro-elution after polyacrilamide gel electrophoresis (PAGE) from plasma of 17β-estradiol treated A. gigas juveniles. Two different Vtg molecules were isolated, (Vtg₁ and Vtg₂) with 184 and 112 kDa apparent molecular masses, respectively, and two antibodies were raised in rabbits for each Vtg molecule. Adult fish were 100% accurately sexed by Vtg EIA, while 100% of immature fish and 95% of adults were accurately sexed by 17β-Estradiol and 11-Ketestosterone ratios. We also observed different color pattern development in male and female adult fish (6-year-olds) around the reproductive period.     

Bench‐top validation testing of selected immunological and molecular Renibacterium salmoninarum diagnostic assays by comparison with quantitative bacteriological culture

No gold standard assay exhibiting error‐free classification of results has been identified for detection of Renibacterium salmoninarum, the causative agent of salmonid bacterial kidney disease. Validation of diagnostic assays for R. salmoninarum has been hindered by its unique characteristics and biology, and difficulties in locating suitable populations of reference test animals. Infection status of fish in test populations is often unknown, and it is commonly assumed that the assay yielding the most positive results has the highest diagnostic accuracy, without consideration of misclassification of results. In this research, quantification of R. salmoninarum in samples by bacteriological culture provided a standardized measure of viable bacteria to evaluate analytical performance characteristics (sensitivity, specificity and repeatability) of non‐culture assays in three matrices (phosphate‐buffered saline, ovarian fluid and kidney tissue). Non‐culture assays included polyclonal enzyme‐linked immunosorbent assay (ELISA), direct smear fluorescent antibody technique (FAT), membrane‐filtration FAT, nested polymerase chain reaction (nested PCR) and three real‐time quantitative PCR assays. Injection challenge of specific pathogen‐free Chinook salmon, Oncorhynchus tshawytscha (Walbaum), with R. salmoninarum was used to estimate diagnostic sensitivity and specificity. Results did not identify a single assay demonstrating the highest analytical and diagnostic performance characteristics, but revealed strengths and weaknesses of each test.     

Comparison of mudcrab‐based brackishwater polyculture systems with different finfish species combinations in Sundarban,India

To compare production and economic performance of polyculture systems with different species combinations, a 210‐day trial was carried out. In the first combination (T1), milkfish (Chanos chanos) and mudcrabs (Scylla serrata), and in the second (T2), mullets (Mugil cephalus, Liza tade and Liza parsia at 0.5:0.5:0.5 ratio) and mudcrabs were stocked keeping fish and mudcrabs at 15,000 numbers per ha, respectively, in both treatments. The finfish were fed floating pellet at 2%–3% and mudcrabs were fed fresh and farm made feed at 5%–8% body weight. Growth parameters of mudcrabs were similar in both T1 (407.64 ± 105.78 g) and T2 (418.89 ± 105.24 g), with no significant differences. Among finfish, M. cephalus attained highest final body weight, 241.55 ± 26.44 g followed by milkfish, 200.46 ± 11.82 g whereas lowest growth noticed in L. parsia (63.69 ± 6.62 g). Length–weight analysis of fish indicated negatively allometric growth (b < 3) for grey mullets, parsia and milkfish while L. tade recorded perfect cube low (b = 2.99). Male mudcrabs recorded positive allometric (b = 3.3) and female crab exhibited negative allometric growth (b = 2.68). The total productivity was 4,533 and 3,694 kg/ha with mudcrab contributes 53.69% and 60.56% to the total productivity in T1 and T2 respectively. The economic analysis indicated benefit–cost ratio (BCR) of 1.57 and 1.73 in T1 and T2 respectively with 10% and 35% insignificant increase (p > 0.05) in BCR and profit per kg, respectively, in T2 compared with T1. The study elucidates polyculture of mudcrabs with finfish can be a taken up as a profitable venture for sustainable diversification of brackishwater farming in Sundarbans.