Sea Bass Fingerlings Research Articles

Effects of skin abrasion in immersion challenge with Vibrio harveyi in Asian seabass Lates calcarifer fingerlings.

Skin abrasions often occur in farmed fish following handling by labourers, injury by farm facilities, cannibalism and ectoparasites. Vibrio spp. are opportunistic pathogens that can invade host fish through damaged tissues and cause outbreaks of vibriosis. This study describes the effect of skin abrasions on the infectivity of V. harveyi using Asian seabass Lates calcarifer (Bloch, 1790) fingerlings as a case example and compares bacterial load and fish survival following immersion challenge with different doses. In total, 315 fish (6.67 ± 1.8 g) were divided into 3 treatments: skin abrasion followed by immersion infection, immersion infection only and an uninfected, uninjured control. Fish in the infection treatments were divided into 3 subgroups and exposed in triplicate to a 7 d immersion challenge with 106, 107 and 108 CFU ml-1 of live V. harveyi. No mortalities were observed in the control and immersion infection groups. However, fish in the skin abrasion treatment group that were infected with 108 CFU ml-1 of live V. harveyi showed signs of progressing disease throughout the experiment, which resulted in mortalities. Significantly higher bacterial loads (p < 0.05) were recorded in the intestine, liver and gills of the fish in this group. Fish in the skin abrasion treatment that were exposed to 107 and 108 CFU ml-1 of V. harveyi showed 100% mortality by Days 5 and 4, respectively. These findings confirm that skin injuries increase the susceptibility of seabass fingerlings to V. harveyi infection.

The effect of Yucca schidigera extract dietary supplementation on growth performance, feed and protein utilization of European seabass, Dicentrarchus labrax, fingerlings

A total of 180 apparent healthy European seabass, Dicentrarchus labrax, fingerlings (5.0±0.5 g fish-1) were used to investigate the effect of different levels of Yucca, Yucca schidigera, extract (YE) on growth performance, feed utilization and survival rate. Yucca extractwere used at level of 0, 0.25, 0.50 and 1 g YE kg-1 diet for 45 days. The fish were reared in twelve glass aquaria (three replicates per treatment), measuring (70x40x30 cm; approximately 70 liters each) at an initial stocking density of 15 fish aquarium-1. The aquaria were supported with artificial aeration and the water exchange rate was 15% with saline ground water (32‰). The results indicated that YE dietary supplementation significantly improved final weight, weight gain and specific growth rate in groups fed on 0.50 and 1 g YE kg-1 diet compared to the control. Feed intake tended to increase with all groups fed on YE supplemented diet. The feed conversion ratio and protein efficiency ratio improved significantly with the highest two level of YE compared to the control. From the above mentioned, it can be concluded that YE can be used at level of 1 g YE kg-1 diet as feed additive in sea bass fingerlings diet for improving growth performance and FCR and protein metabolism and maintaining survival rate.

Use of high protein distiller’s dried grains (HPDDG) with enzyme phytase as a cost effective ingredient in the diet of fingerlings European sea bass, Dicentrarchus labrax

The present study was conducted to evaluate the effect of various dietary levels of high protein distiller’s dried grains (HPDDG) supplemented with enzyme phytase on growth performance, feed utilization and haematological indices of European sea bass Dicentrarchus labrax fingerlings. A total of 150 D. labrax fingerlings with an average body weight of 7.5 ± 0.5g were divided in the five experimental treatments (in triplicates each). The experiment was conducted for 56 days. Fish were fed to apparent the satiation six days a week. Five isonitrogenous 45% CP experimental diets were formulated. The control (C) diet had no high protein distiller’s dried grains (HPDDG) and phytase enzyme added. Diet 2 (C+) was formulated as control diet and supplemented with phytase at a level of 0.5 g/kg. Diets 3-5 each contained HPDDG at levels of 20, 30, and 40 %, respectively with soybean meal and supplemented each with phytase at a level of 0.5 g/kg. Over the 56 days feeding period, all fish fed HPDDG-supplemented with phytase diets resulted in higher growth than the control diet, suggesting that the using of HPDDG-supplemented with phytase enhanced the growth performance of sea bass fingerlings. The same trend was recorded for the best FCR and PER. The hematology and serum biochemistry (hemoglobin (Hb), red blood cells (RBCs) count, white blood cells (WBCs) and hematocrit (Hct %) and immune parameters (total protein, albumin, globulin, cholestorl, lysozyme activity and total antioxidant capacity) of D. labrax fingerlings significantly (P ≥ 0.05) increased with increasing dietary HPDDG with phytase. Result indicates that HPDDG with phytase is a good alternative protein source for compromising growth performance and physiological parameters of European sea bass, Dicentrarchus labrax Fingerlings

Effect of the pesticide deltamethrin as a treatment of Ceratothoa oestroides infestations of farmed sea bass Dicentrarchus labrax

The haematophagic isopod parasite Ceratothoa oestroides (Risso, 1816) causes significant production losses in the commercial aquaculture of sea bass (Dicentrarchus labrax L. 1758). These are often expressed as reduced fish growth and lower survival rates of sea bass fingerlings <20 g mass. Deltamethrin is a synthetic pyrethrin with demonstrable positive results in the control of C. oestroides. The aim of this study was to determine its efficacy in the control of C. oestroides in commercial production conditions. The experiment was carried out at a commercial sea bass farm and in two net cages of 16 m diameter stocked with 200,000 sea bass fingerlings of the same origin and weight. After 5 months culture, a deltamethrin treatment was performed in one cage, while the other cage served as a non-treated control. The average sea bass mass during the antiparasitic bath was 19.70 ± 0.47 g and 18.48 ± 0.50 g (mean ± SEM) for the treated and the control cages, respectively. Two months after the treatment, visual examination of the entire population was carried out. The results revealed that the number of C. oestroides in the treated cage was significantly lower (P < .01) compared to those in the control cage. Also, the C. oestroides were smaller in length in the treated group compared to the control cage. No sexually mature females were found in the treated group whereas in the control cage 21.3% of the C. oestroides were sexually mature, containing average 39.7 pulli larvae. The monthly mortality rate during this study was <0.5%, but mortality in the treated cage, after treatment in June, was lower than in the control cage. The results indicate that the deltamethrin treatment was successful in sea bass infected with C. oestroides. After two months, however, a new generation of immature C. oestroides appeared. These results show that sea bass weighing over 20 g can be reinfected, but the absence of sexually mature females points to the importance of this treatment to reduce the dynamics of C. oestroides population on a farm site. Despite good antiparasitic results, there is a further need to improve fish farming in the Mediterranean through the introduction of changes in husbandry practices with a purpose of prevention of parasitic horizontal transmission.

Effect of dietary prebiotic inulin on histology, immuno-haematological and biochemical parameters of Asian seabass (Lates calcarifer)

The present study was carried out to investigate the effect of supplementation of inulin on histology, immuno-haematological and biochemical parameters of Asian seabass (Lates calcarifer) fingerlings with an initial average body weight of 7.14 ± 0.05 g. Inulin was supplemented at four different concentrations (control) 0, 5, 10, 15, and 20 g/kg in the L. calcarifer diet containing 400 g/kg protein and 90 g/kg lipid. At the end of the 60 days feeding trial, the absorptive surface area of the intestine and glycogen deposition in liver were increased in fish fed inulin supplemented diets. The immune parameters lysozyme, alternative complement pathway, superoxide dismutase and nitroblue tetrazolium assay showed significant (p < 0.05) difference between control and treatment groups. Haematological parameters showed that red blood cells, white blood cells, haemoglobin, packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration levels increased significantly (p < 0.05) in the fish fed with inulin supplemented diets. The analysis of biochemical parameters revealed that glucose, urea, cholesterol, triglyceride, aspartate aminotransferase, alkaline phosphatase, alanine aminotransferase, and lactate dehydrogenase showed significant differences (p < 0.05) between control and treatments groups. No significant difference (p > 0.05) was observed for total protein among different treatments. The results of the study revealed that 15–20 g/kg inulin supplementation has a beneficial effect in the histology, immuno-haematological, and biochemical parameters in L. calcarifer juveniles.

Jerusalem artichoke enriched diet on growth performance, immuno-hematological changes and disease resistance against Aeromonas hydrophila in Asian seabass (Lates calcarifer)

A 45 days feeding trial was conducted to study the effect of Jerusalem artichoke (JA) on growth performance, body composition, biochemical, immuno-hematological parameters and disease resistance in Asian seabass (Lates calcarifer) fingerlings against Aeromonas hydrophila. JA was supplemented at three different levels viz., control 0, 5, 10, and 20 g kg−1 in the commercial diet (403 g kg−1protein and 89 g kg −1lipid) in L. calcarifer. The results showed that there were no significant (P > 0.05) differences in various growth parameters, while the whole body composition showed significant differences (P < 0.05) between control and treatment groups. Hematological parameters showed that red blood cells (RBC), white blood cells (WBC), hemoglobin (Hb), pack cell volume (PCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were not significantly (P > 0.05) affected by dietary supplementation of JA at different concentration. However, the mean corpuscular volume (MCV) was significantly (P < 0.05) higher in the fish fed with 20 g kg−1 JA supplemented diet. Biochemical parameters revealed that glucose, urea, cholesterol, and triglyceride showed significant (P < 0.05) differences between control and treatments groups. Interestingly, 20 g kg−1 JA supplemented diet significantly modulates the innate immune response and disease resistance against Aeromonas hydrophila compared with control and other treatment groups. The results of the study revealed that 20 g kg−1 JA supplementation has a beneficial effect in the biochemical, immunological and disease resistance in L. calcarifer juveniles.

Replacement of fish meal with corn gluten meal in feeds for Asian seabass (Lates calcarifer)

A 45-day feeding trial was conducted to study the effect of replacing dietary fish meal (FM) with corn gluten meal (CGM) on diet digestibility and growth and proximate body composition of Asian seabass (Lates calcarifer) fingerlings (21.1 ± 0.95 g). Five isonitrogenous and isocaloric diets, formulated to contain 40% protein and 10% lipid, were prepared with fish meal replacement at 0 (control), 5, 10, 15, and 20% (w/w basis) using CGM. The trial was carried out in 1000-L fiber-reinforced polymer (FRP) tanks with three replicates (each containing 20 fish) for each treatment, and fish were hand fed in excess twice daily at 10.00 and 16.00 h. There was no significant difference in final body weight, average daily gain, and survival for fish fed the CGM0, CGM5, and CGM10 diets, with fish in these treatments performing better than the others. Feed conversion ratios for fish fed CGM0 (1.73 ± 0.05 g feed /g gain), CGM5 (1.65 ± 0.06 g feed g−1 gain), and CGM10 (1.84 ± 0.07 g feed g−1 gain) were better than for the other treatments. Protein retention (28.85 ± 0.65%) and energy retention (20.60 ± 0.39%) were better in the group fed with CGM5 than the other treatments. Apparent digestibility coefficients of dry matter (65.1 ± 0.3, 64.7 ± 0.2%), protein (91.6 ± 0.5, 91.7 ± 0.3%), and energy (79.0 ± 0.27, 8.4 ± 0.1%) were highest for the CGM5 and CGM10 diets. Highest crude lipid (7.29 ± 0.09%) and gross energy (7.19 ± 0.05 kJ g−1) were observed in fish fed the CGM 20 diet. The results indicate that CGM is a potential feed ingredient for seabass and can be included at 10% of the diet without compromising digestibility and growth.

Effect of Dietary Addition of Green Tea Camellia sinensis, on Growth, Body Composition and Hematic Biochemistry of the Asian Seabass Lates calcarifer Fingerlings

The current study aimed to evaluate the effect of dietary supplementation of different levels of green tea (Camellia sinensis) on growth performance, body composition and serum biochemistry of Asian Sea bass, Lates Calcarifer. Therefore, Asian sea bass fingerlings with an initial body weight of 43.20 ± 0.11 grams were randomly assigned into 3 groups as triplicates. Fish were tested with three experimental diets of similar protein content (514.8 ± 0.06 g/kg-1) and energy (48.4 ± 0.02 kcal/g) for 90 days. The first diet was treated as control without any inclusion of additives. The other two diets were mixed with green tea of 10 g/kg-1 and 20 g/kg-1 respectively. The results clearly shown a significant (P<0.05) improvement of growth performance in all fish fed with green tea as dietary additive when compared with control, whereas the maximum performance is attained from the first treatment with lower dose (10 g/kg-1) of green tea additive. the current study can concluded that, the dietary inclusion of low levels of green tea as feed additives has relatively improved the growth performance, feed utilization and general health without any adverse effects on biochemical profile of Asian sea bass (Lates calcarifer).

Growth performance of Asian seabass Lates calcarifer (Bloch, 1790) stocked at varying densities in floating cages in Godavari Estuary, Andhra Pradesh, India

Present study was undertaken in Godavary Estuary, Andhra Pradesh for evaluation of the effect of three stocking densities on growth performance, survival and production of Lates calcarifer (Bloch, 1790) in floating cages and for optimisation of stocking density in cage farming. Seabass fingerlings having length and weight of 8.36±0.32 cm and 8.10±0.61 g respectively, were stocked in six cages (6 m dia; 3 m net depth) at three different stocking densities of 15, 30 and 45 nos. m-3 and their growth performance was monitored every fortnight for five months. All fishes were fed with chopped trash fish @ 8 - 12% of body weight. After 150 days of grow-out culture, seabass fingerlings reached 36.0±6.0 cm in length and 690.7±41.3 g in weight at density of 15 nos. m-3, 33.9±0.4 cm and 633.2±17.9 g at density of 30 m-3 and 30.2±0.4 cm and 465.0±21.2 g at density of 45 nos. m-3. Growth was allometric and did not differ with stocking density. Survival percentage was comparatively higher at lower (87.3%) and moderate (83.9%) stocking densities, while production was higher at moderate (1363.2 kg) and higher (1258.4 kg) stocking densities (p&lt;0.5). Gain in weight as well as specific growth rate (SGR) were higher at lower and moderate stocking densities (p&lt;0.5). The results of the study indicated that among the three stocking densities tested, 30 nos. m-3 is superior to 15 and 45 nos. m-3, with higher yield.

Pathogenesis of Photobacterium damselae subspecies infections in sea bass and sea bream

Photobacterium damselae is a Gram negative bacterium causes photobacteriosis, a worldwide septicemic disease in aquaculture including sea bass (Dicentrarchus labrax) and sea bream (Sparus aurata). The pathogenicity of bacterial subspecies and the disease pathological changes in natural and experimental infections have thus far yielded inconsistency of effective preventive measures. This study aimed to represent a comprehensive analysis of the potential pathogenic capacities of the two subspecies of P. damselae in cultured sea bass and sea bream in the Northwestern region of Egypt. Diseased 321 sea bass and 257 sea bream, in addition to 99 healthy sea bass fingerlings were sampled from three farms located along the Mediterranean Sea. P. damselae subspecies were isolated from diseased fish and characterized using bacteriological, molecular, and antimicrobial susceptibility methods. Healthy fish were challenged by a virulent P. damselae subsp. piscicida, monitored for disease signs and mortality, and the histopathological abnormalities and hematological disorders were carried out. Clinical signs and gross lesions in naturally infected sea bass and sea bream showed great similarities with absence of a subspecies-specific characteristic sign or lesion. The two subspecies were recovered through the entire year from individual fish sample, suggests a coexistence of two subspecies endemic infection. In diseased sea bass, 38.32% and 16.20% were positive for P. damselae subsp. piscicida and subsp. damselae, respectively. However in diseased sea bream, 44.47% and 26.46% were positive for P. damselae subsp. piscicida and subsp. damselae, respectively. High mortalities and devastating clinicopathologic abnormalities represented by sever clinical signs, hematological disorders and histological abnormalities strengthen the pathogenicity of P. damselae subspecies in the two fish species and therefore, a vaccination strategy against both subspecies should be taken into account.

Effects of dietary protein-to-lipid ratio on digestive and absorptive processes in sea bass fingerlings

Two 8-week trials, one in spring and the other in autumn-winter, were performed with sea bass fingerlings. After each growth period, pancreatic digestive enzyme synthesis in the pyloric caeca (PC), food anticipatory activity adaptation in the proximal intestine (PI) and nutrient absorption capacities in the distal intestine were measured at 24h post-feeding.In spring, five isoenergetic diets with different protein levels (40, 45, 50, 55 and 59%) were formulated by simultaneously changing lipid and starch content. Animals fed the low-protein diets showed reduced accumulation of alkaline protease (40 to 50% diet), lipase (40 to 45% diet) and α-amylase (40 to 55% diet) in the PC; however, the activities of digestive enzymes in the PI were high in fish fed both low and high dietary protein diets, being significant for alkaline protease (40 and 59% diet) and α-amylase (40 and 45% diet). Zymography of the PC identified four proteases with trypsin-like activity (23, 22, 20 and 17kDa) and an 18kDa chymotrypsin activity that were modulated differentially according to diet. The PC/PI ratios were highest for alkaline protease and lowest for α-amylase, showing different patterns of response to changes in dietary composition: higher for protease on 45, 50 and 55% animals and α-amylase on 59% sea bass. l-Lys and d-Glc uptake capacities were down-regulated as dietary protein content declined, while no changes were found in l-Met and l-Trp. Based on the above-mentioned data and the optimum growth of animals fed with 50% protein, a protein-to-energy ratio study was performed.Sea bass were fed with five isoproteic (52%) diets that differed in dietary lipid content (12, 14, 16, 18 and 20%). Alkaline protease and lipase synthesis in the PC was up-regulated in low energy diets (12, 14 and 16% and 12 and 14%, respectively) and no changes were found in α-amylase. PC zymography was consistent with protease measurements. Only food anticipatory activity of lipase was up-regulated in animals fed 12% of lipid. l-Met and d-Glc were up-regulated by increasing dietary lipid and l-Lys and l-Trp were not modified. Dietary lipid content had no effect on final body weight.Finally, seasonal effects on alkaline protease synthesis in the PC were significantly higher in spring and animals showed higher growth in this season than in the autumn-winter. However, adaptation of food anticipatory activity in the PI was higher in autumn-winter. No differences were found in nutrient absorption capacities between seasons.

Growth performance for European sea bass fingerlings, Dicentrarchus labrax, reared at different salinities

Growth performance for European sea bass fingerlings, Dicentrarchus labrax, reared at different salinities

Effect of dietary mannan oligosaccharide on growth, body composition, haematology and biochemical parameters of Asian seabass (Lates calcarifer)

A feeding trial was conducted to study the effect of mannan oligosaccharide (MOS) supplementation on growth, body composition, haematology, biochemical parameters and histology of Asian seabass (Lates calcarifer) fingerlings (8.13 ± 0.06 g average weight). Mannan oligosaccharide was supplemented at five different concentrations viz., 0%, 0.5%, 1%, 1.5% and 2% levels in the diet (40% protein and 9% lipid) of L. calcarifer. The results of the 60 days feeding trial showed that there was a significant (P < 0.05) increase in the final body weight, weight gain (WG), WG%, average daily gain, survival, specific growth rate, daily growth coefficient, hepatosomatic index and viscerosomatic index in the fish fed diet containing 1% MOS. Whole body composition of post-fed animals showed non-significant differences (P > 0.05) among the various treatment groups. The analysis of haematological parameters showed that there was no significant (P > 0.05) differences among different treatments but for the haemoglobin content which was significantly (P < 0.05) higher in the fish fed 1% MOS. Biochemical parameters revealed that glucose, urea, cholesterol and triglyceride content showed significant (P < 0.05) difference between control and MOS-supplemented group. Histological observations of post-fed animals revealed that MOS supplementation resulted in increased absorptive surface area of the intestine and increased glycogen deposition in liver. The result of this experiment infers that MOS supplementation has got a beneficial effect in the diet of seabass and supplementation at 1% level is optimal for improving the growth.

Effect of xylan oligosaccharides generated from corncobs on food acceptability, growth performance, haematology and immunological parameters of Dicentrarchus labrax fingerlings.

The objective of this study was to determine the effect of two levels of inclusion of xylan oligosaccharides (XOS) extracted from corncob on growth, feed utilization, immune status and disease resistance of Mediterranean sea bass (Dicentrarchus labrax) fingerlings. Specimens of 4.75 ± 0.69 g at initial density of 2.7 ± 0.13 kg/m(3) were fed during 12 weeks at 0 g kg(-1) diet, 5 g kg(-1) diet and 10 g kg(-1) diet, dietary XOS level of inclusion in a commercial sea bass diet. Feeding the fish at both XOS dietary inclusion levels significantly increased weight gain, protein efficiency ratio and feed conversion ratio. Feeding of supplemented diets to fish led to reducing mortalities after challenging with A. hydrophila. The haematological and immunological parameters were assayed in both pre-challenged and post-challenged groups. There was an increased trend in red blood corpuscles, white blood corpuscles, pack cell volume, haemoglobin (Hb %) and serum protein content in treated groups over the control as time elapsed with the feeding trials. The serum immunoglobulin level and lysozyme activity showed an increased trend in the fed groups. Histological features of the liver showed lower lipid vacuolization and regular-shaped morphology of hepatocytes around the sinusoidal spaces denoting a better utilization of dietary nutrients supported with the morphometric data. In conclusion, XOS added at a designated dose (5 g kg(-1) diet) in the diet improves growth and stimulates the immunity and makes D. labrax fingerlings more resistant to infection by A. hydrophila.

Production Economic Analysis of Black Sea Bass Juveniles to Support Finfish Mariculture Growout Industry Development in the Southeastern United States

A pilot-scale finfish mariculture hatchery was established at the University of North Carolina Wilmington. In 2011, research-based hatchery protocols were scaled up to produce 37,000 advanced (1–5 g) black sea bass fingerlings. Based on engineering, biological, and cost data from operating the pilot hatchery, an economic analysis of a hypothetical commercial scale black sea bass hatchery operation was conducted. The financial performance of two alternative facilities that produce 97,200 5-g and 388,800 1-g fingerlings per year over a 30-year project life showed cumulative net present value (NPV) of $445,000, and $3,168,000, modified internal rates of return (MIRR) of 6.52% and 10.52%, and per unit breakeven prices of $1.67 and $0.47, respectively. Sensitivity analyses showed that final stocking density was critical to financial performance. Fingerlings were supplied to startup growers in NC and in VA, and market-size fish from these growout facilities were distributed (live or whole on ice) to premium-value markets on the eastern seaboard. This pilot hatchery is enabling new farmers to access fingerlings, establish growout technology and understand market value and demand.

Some Studies on the Effect of Protexin on Immune Status of Cultured Seabass Fingerlings

The present study aimed to investigate the effect of different concentrations of protexin probiotic (Enterococcus faecium) on growth performance, differential leucocytes count, phagocytic activity, phagocytic index, serum total protein, albumin, globulin, Total bacterial count, Total enterobacteriaceae count and Total coliform count of intestinal microbial flora of seabass and disease resistance against challenge with Vibrio alginolyticus. Fish were separated in to four experimental groups of 0.0 g/kg feed (control), 0.1 g/kg feed, 0.2 g/kg feed, 0.3 g/kg feed of commercial probiotic protexin concentrate. Fish fed at 3% body weight per day. Results showed that protexin supplementation have significant improvement in growth performance, significantly increasing in lymphocytes, monocytes, phagocytic activity, phagocytic index, Serum total protein and globulin in all treated groups compared to control Contrary neutrophils and albumin/globulin ratio significantly decreased in all treated groups comparing to the control as well as decreasing in Total bacterial count, Total enterobacteriaceae count and Total coliform count of all treated groups comparing to the control. The mortality rates after challenging with Vibrio alginolyticus were significantly lower in all treated groups than the control. Results indicated that by increasing the concentration of the protexin probiotic results getting better in all examined parameters comparing to control. The present study clearly indicated that inclusion of 0.3gm / kg feed of protexin probiotic in fish diet for not less than 6th weeks can improve the immune status of seabass fingerlings to the favor of resistance to diseases.

Isolation and characterization of Indian betanodavirus strain from infected farm-reared Asian seabassLates calcarifer(Bloch, 1790) juveniles

We isolated the infectious viral agent from infected Asian seabass, Lates calcarifer (Bloch, 1790) using SSN-1 cells. The isolated virus was cultivated in indigenous marine fish cell lines developed from ornamental sea anemone fish Amphiprion sebae and from Asian seabass. Reverse transcriptase PCR using betanodavirus-specific primers gave positive results for the RNA from virus-infected cells (hereinafter referred to as L. calcarifer nervous necrosis virus Indian strain – LCNNV-In01). Serum neutralization test indicated partial homogeneity between Atlantic halibut nervous necrosis virus (AHNNV 692/9/98) and LCNNV-In01. Transmission electron micrographs of the virus-infected cell culture showed large numbers of 25–30-nm particles in cellular vacuoles with features similar to betanodaviruses. Pathogenicity study in seabass fingerlings using cell culture grown virus revealed nervous necrosis in retinal cells following a 21-day challenge trial. The nodavirus was reisolated from the infected fish using clownfish and seabass cell lines. Sequence analysis of the coat protein gene showed that the virus belonged to RGNNV group (GenBank Acc. No. FR669249). The isolation of the nodavirus from seabass in India and its potential to grow in non-homologous cell lines indicate the serious threat of the Indian strain of betanodavirus (LCNNV-In01) to cultured and ornamental marine fish that have their hatchery production successfully standardized in India.

Life cycle of the marine leech ( Zeylanicobdella arugamensis) isolated from sea bass ( Lates calcarifer) under laboratory conditions

Infestation of unidentified marine leeches in Malaysia was first reported in 1988 in grouper ( Epinephelus coioides) cultured in floating cages with a prevalence of 0.4%. Recently (2004–2006), the marine leech Zeylanicobdella arugamensis was regularly isolated from marine fish cultured in cages. In May 2006, approximately 60% of moribund sea bass fingerlings reared in cages were infected with Zeylanicobdella arugamensis, which may also serve as a vector for the bacteria, Vibrio alginolyticus. The aim of the present study was to determine the life cycle of Z. arugamensis under laboratory conditions. A total of 105 adult leeches, 4.5–14.0 mm in length, from five trial experiments were sampled and brought to the laboratory. Leeches with average size exceeding 10.00 mm could deposit cocoons after 5–8 h of isolation. Seven days were needed for the new egg inside the cocoon to develop into juvenile under 27 °C at 28 ppt. It took another 9 to 10 days for the juvenile leeches to grow to mature adults. Overall, the Z. arugamensis took 16 to 17 days to mature. In the present study, we observed that a single leech can reproduce and this self-fertilization or direct fertilization has never been reported in a piscicolid leech.

Immunization of European Sea Bass, Dicentrarchus labrax L. 1758, Fingerlings with a Commercial Vaccine Against Vibriosis

In order to study the effects of bath vaccination against vibriosis in European sea bass fingerlings, Dicentrarchus labrax L. 1758, reared in Sardinia in land-based concrete tanks and sea cages, a commercial preparation was used. The achievement of the immune response, the presence of the disease and the growth performances were determined monthly in a one year study. The results showed an increase of antibody titers in immunized fish when compared to the controls. Moreover, although vibriosis spreads every year in the farms, and also during the trials year, no disease outbreaks were observed in the immunized fish. Regarding growth performances, a significant difference on body weight's increase was recorded only in off-shore cultured immunized fish when compared to the controls. Furthermore, a better “general condition” of immunized fish was recorded; therefore, a higher production, at least 10%, was estimated.

Replacement of a large portion of fish oil by vegetable oils does not affect lipogenesis, lipid transport and tissue lipid uptake in European seabass ( Dicentrarchus labrax L.)

In order to investigate the impact of dietary lipid sources on mechanisms involved in lipid deposition, three groups of European seabass fingerlings with average initial body weight of 5.2 ± 1.0 g were fed three diets differing only by lipid source. These diets were: 100% anchovy oil (diet A), 40% anchovy oil–60% mix of vegetable oils (35% linseed, 15% palm, 10% rapeseed) (diet B) and 40% anchovy oil–60% mix of vegetable oils (24% linseed, 12% palm, 24% rapeseed) (diet C). After 64 weeks of rearing, when seabass reached the size of 160 g, the activity of lipogenic enzymes (fatty acid synthetase, glucose-6-phosphate dehydrogenase and malic enzyme) in liver and of lipoprotein lipase (LPL) in perivisceral adipose tissue, liver and white muscle were measured. Transport of lipid by lipoproteins was examined by determining plasma lipid composition and lipoprotein classes. Dietary oil source did not modify growth performance or lipid content of flesh and liver of seabass. Replacement of 60% of fish oil by the two mixtures of vegetable oils had no significant effect on hepatic lipogenesis and activity of LPL in liver and adipose tissue. Activity of LPL in white muscle was decreased in fish fed diet C compared to those fed diets A and B. Diets containing the mixture of vegetable oils led to lowered plasma, VLDL and LDL cholesterol levels compared to diet A. It is concluded that replacing 60% of fish oil by the two mixtures of vegetable oils in the feeds of European seabass fingerlings until they reach the size of 160 g has no marked effect on growth performance, lipogenesis and tissue lipid uptake but has a hypocholesterolemic effect.