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Liver histology and histomorphometry in hybrid sorubim (Pseudoplatystoma reticulatum × Pseudoplatystoma corruscans) reared on intensive fish farming

Published on 25/3/2017
This study aimed to characterize the liver histology and histomorphometry in sorubim hybrid of different categories (nursery, growth and grow-out) reared on fish farming. The categories were defined considering body weight (BW): nursery category (n = 5): BW = 37.06 ± 6.00 g (31.6–45.3 g); growth category (n = 5): BW = 310.40 ± 53.80 g (242.1–376.4 g) and grow-out category (n = 5): BW = 874.28 ± 27.59 g (846.2–913.1 g). Liver fragments were processed to paraffin inclusion, and sections were stained by haematoxylin and eosin (H&E), PAS (Periodic Acid Schiff) and Perl's staining to histology, histomorphometry and density volumetric of liver structures; glycogen analysis and to detect ferric irons (Fe3+) respectively. The hepatosomatic index decreased between the categories (P < 0.01). The percentage of PAS-positive hepatocytes in the nursery category was higher (P < 0.05) in relation to the growth and grow-out categories. The hepatocytes from all fish were positive to Perl's staining. The density volumetric of liver structures did not differ among categories except to blood vessels were higher (P < 0.01) in the nursery and growth. The area (μm2) and perimeter (μm) of hepatocytes, and the area (μm2), perimeter (μm) and volume (μm3) of the nuclei from grow-out fish were lower (P < 0.01) than those from the nursery and growth categories. Changes in morphometric characteristics of hepatocytes may result from metabolic changes associated with body growth surubins; therefore, these morphometric characteristics of liver tissue can be used as functional biomarkers for the assessment of fish health and nutrition status.

Effects of dietary mannan oligosaccharides in early weaning diets on growth, survival, fatty acid composition and gut morphology of gilthead sea bream (Sparus aurata, L.) larvae

Published on 25/3/2017
Early weaning of marine fish larvae with dry diets delays gut maturation and reduces growth rates. In juvenile and adult forms of several marine fish species, inclusion of dietary mannan oligosaccharides (MOS) improves gut integrity and functionality, but the effects of MOS inclusion in gilthead sea bream (Sparus aurata, L.) larval diets have not been addressed yet. Thus, this study assesses the effects of dietary MOS inclusion on survival, growth performance, gut morphology, feed acceptance and quality of gilthead sea bream larvae. For that purpose, 16 days post-hatched gilthead sea bream larvae were fed four graded levels of MOS (Biomos®, Alltech, Nicholasville, KY, USA) in weaning diets as follows: 0 g kg−1 MOS, 0.5 g kg−1 MOS, 1.5 g kg−1 MOS and 2 g kg−1MOS. Dietary MOS did not affect feed acceptance in gilthead sea bream larvae (P > 0.05). MOS supplementation was correlated in a dose-dependent way with higher larval survival (P = 0.026). After 15 days of feeding, dietary MOS increased whole larvae (P < 0.01) arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid. Gilthead sea bream larvae fed 2 g kg−1 MOS presented higher gut occupation with goblet cells after feeding compared with larvae fed the other dietary treatments. Overall, the results suggest that inclusion of MOS in early weaning diets for gilthead sea bream improves essential fatty acid utilization and may promote growth and final survival.

Influence of feeding regime and temperature on development and settlement of oyster Ostrea edulis (Linnaeus, 1758) larvae

Published on 25/3/2017
Under controlled conditions of food density and temperature, larval performances (ingestion, growth, survival and settlement success) of the flat oyster, Ostrea edulis, were investigated using a flow-through rearing system. In the first experiment, oyster larvae were reared at five different phytoplankton densities (70, 500, 1500, 2500 and 3500 μm3 μL−1: ≈1, 8, 25, 42 and 58 cells μL−1 equivalent TCg), and in the second, larvae were grown at four different temperatures (15, 20, 25 and 30°C). Overall, larvae survived a wide range of food density and temperature, with high survival recorded at the end of the experiments. Microalgae concentration and temperature both impacted significantly larval development and settlement success. A mixed diet of Chaetoceros neogracile and Tisochrysis lutea (1:1 cell volume) maintained throughout the whole larval life at a concentration of 1500 μm3 μL−1 allowed the best larval development of O. edulis at 25°C with high survival (98%), good growth (16 μm day−1) and high settlement success (68%). In addition, optimum larval development (survival ≥97%; growth ≥17 μm day−1) and settlement (≥78%) were achieved at 25 and 30°C, at microalgae concentrations of 1500 μm3 μL−1. In contrast, temperature of 20°C led to lower development (≤10 μm day−1) and weaker settlement (≤27%), whereas at 15°C, no settlement occurred. The design experiments allowed the estimation of the maximum surface-area-specific ingestion rate {J˙Xm} = 120 ± 4 μm3 day−1 μm−2, the half saturation coefficient {XK} = 537 ± 142 μm3 μL−1 and the Arrhenius temperature TA = 8355 K. This contribution put a tangible basis for a future O. edulis Dynamic Energy Budget (DEB) larval growth model.

Short-term starvation in silver pomfret (Pampus argenteus): molecular effects on lipid mobilization and utilization

Published on 25/3/2017
To investigate the effects of short-term starvation on lipid metabolism, juvenile silver pomfret (Pampus argenteus) with an initial weight of 18.1 ± 1.53 g were starved for 6 days. Fish were sampled on days 0, 2, 4 and 6 of starvation (S0, S2, S4 and S6, respectively) and then analysed. The results showed that short-term starvation induced a significant decrease in visceral index, hepatosomatic index. The crude lipid content was also significantly decreased by 42.22% and 82.96% on S2 and S6 respectively. In addition, short-term starvation significantly decreased the plasma triacylglycerol, non-esterified fatty acid and low-density lipoprotein cholesterol. Moreover, short-term starvation significantly increased the expressions of hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) at the mRNA and protein levels in the muscle and the ATGL expression at the protein level in the liver. The expressions of fatty acid translocase (CD36) and plasma membrane fatty acid-binding protein (FABPpm) at the protein level in the muscle were significantly increased by short-term starvation, while the expressions of fatty acid transport protein 1 (FATP1), FABPpm and lipoprotein lipase (LPL) at the protein level in the liver were significantly increased by short-term starvation. Furthermore, the expressions of peroxisome proliferator activated receptor (PPAR) α and PPARγ at the mRNA and protein levels in the muscle were significantly elevated by short-term starvation. These findings suggested that short-term starvation increased lipid mobilization and utilization possibly through activation of lipolysis-related genes (HSL and ATGL), lipid uptake-related genes (LPL, CD36, FATP1 and FABPpm) and PPARs.

Evaluation of dietary natural mineral materials as an antibiotic replacer on growth performance, non-specific immune responses and disease resistance in rainbow trout, Oncorhynchus mykiss

Published on 25/3/2017
We evaluated the effects of some dietary natural mineral materials as an antibiotic replacer based on growth performance, non-specific immune responses and disease resistance in juvenile and subadult rainbow trout, Oncorhynchus mykiss. First experiment, juvenile rainbow trout averaging 2.7 ± 0.02 g (mean ± SD) were fed one of the six experimental diets; a basal commercial diet as a control (CON), CON with oxytetracycline (OTC), with yellow loess (YL), with Macsumsuk® (MS), with Song-Gang® stone (SG) and with barley stone (BS) at 0.4% of each diet. At the end of 8-week feeding trial, weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) of fish fed YL diet were significantly higher than those of fish fed CON diet. Non-specific immune responses such as superoxide dismutase (SOD), myeloperoxidase (MPO), lysozyme (LYS) activity and oxidative radical production of fish fed YL diet were higher than those of fish fed CON diet. At the end of 15 days of challenge test with Aeromonas salmonicida, average cumulative survival rate of fish fed YL diet was significantly higher than that of fish fed BS and CON diets. However, there were no significant differences among fish fed YL, SG and OTC diets. Second experiment, subadult rainbow trout averaging 261.5 ± 3.5 g (mean ± SD) were fed one of the four experimental diets for 22 weeks: CON, and CON with OTC, YL or SG at 0.4% of each diet. At the end of feeding, growth performance of fish fed SG and YL diets was significantly higher than that of fish fed CON diet. Non-specific immune responses in terms of SOD, MPO, LYS and NBT of fish fed SG and YL diets were significantly higher than those of fish fed CON diet. However, there were no significant differences among the fish fed YL, SG and OTC diets. The results indicate that dietary yellow loess or Song-gang® stone at 0.4% of diet could replace oxytetracycline in juvenile and subadult rainbow trout.

Molecular cloning and functional characterization of the fatty acid delta 6 desaturase (FAD6) gene in the sea cucumber Apostichopus japonicus

Published on 25/3/2017
The sea cucumber (Apostichopus japonicus), an important echinodermata, had high value in nutrition and medicine for its rich collagen, sulphated polysaccharide, glycosides and polyunsaturated fatty acids (PUFA). The cDNA of the fatty acid desaturase gene in A. japonicus (AJFAD6) was cloned and was found to encode a desaturase with delta 6 FAD activity. Sequence analysis indicated that AJFAD6 included an open reading frame of 1392 bp, encoding 463 amino acids. AJFAD6 has all the conserved motifs found in other members of the FAD6 family, including an N-terminal cytochrome b5 domain and three histidine-rich regions. qRT-PCR showed that AJFAD6 was expressed in all tissues tested during juvenile development and was mainly expressed in the respiratory tree at 150 days after adherence (150 days) and in the intestine at 100 days. Furthermore, AJFAD6 mRNA was also detected in the analysed adult tissues, with higher expression in the intestine and testis. Functional characterization of AJFAD6 in a recombinant yeast, Pichia pastoris, showed that AJFAD6 could catalyse exogenous linoleic acid (LA) and α-linolenic acid (ALA) to produce γ-linoleic acid (GLA) and stearidonic acid (STA), respectively, at conversion rates of 11.1% for LA to GLA and 3.4% for ALA to STA. Our results suggested that the biosynthetic pathway of PUFA existed in the sea cucumber, but endogenous production of eicosapentaenoic acid, arachidonic acid and docosahexaenoic acid from either LA or ALA precursor appeared to be limited.

Effects of artificial selection practices on loss of genetic diversity in the Pacific abalone, Haliotis discus hannai

Published on 25/3/2017
The Pacific abalone, Haliotis discus hannai Ino, is one of most important aquaculture species in China. Artificial selection has been the common and inevitable approach in breeding. In present study, the effect of artificial selection on the genetic structure of two abalone lines (JJ selection strain, three successive selection lines based on the fast-growing trait, which was named JJF0, JJF1, JJF2, and JJF3; and R selection strain, the offspring of the red shell colored variants) were evaluated using 10 microsatellites. Loci showed from low to high polymorphism, with the number of alleles (A) ranging from 2 to 18 in each population. The mean observed (Ho) and expected heterozygosities (He) were 0.650 ± 0.022 and 0.711 ± 0.018, respectively. In selection strain JJ, the values for most diversity genetic indexes (Ae, the number of effective alleles, Ho and He) decreased from JJF0 to JJF3. Meanwhile, compared to JJ line, the genetic diversity estimates of R were close to those of JJF3. Nei's genetic distance ranged from 0.20357 to 0.51346. The unweighted pair group method with arithmetic mean tree based on Nei's genetic distance also showed that the control Japan population and JJF0 formed to a cluster firstly, which were subsequently grouped together with JJF1, JJF2, JJF3, whereas the R was isolated from the rest of the populations. Analysis of genetic information indicated that genetic diversity was lost with artificial selection practices. Mechanisms underlying the maintenance of an acceptable level of genetic diversity while pursuing economic interests should be conducted in future research studies.

A production season of turbot larvae Scophthalmus maximus (Linnaeus, 1758) reared on copepods in a Danish (56°N) semi-intensive outdoor system

Published on 25/3/2017
Turbot were reared from yolk sack larvae to juvenile in an outdoor semi-intensive system. Three production cycles were monitored from May to September. A pelagic food chain was established with phytoplankton, copepods and turbot larvae. Abiotic and biotic parameters of lower trophic levels together with turbot larval survival, development, prey electivity and growth were monitored. A decreasing larval survival from 18.4% in May to 13.6% in July and just 7.0% in September was observed. The overall phytoplankton and copepod abundance decreased during the productive season. The turbot larval growth showed significant differences between larvae below (isometric) and above (allometric) 7 mm. Larval fish gut content showed no differences with available prey between production cycles. Therefore, it appears that the available prey concentration is governing their growth in this outdoor system. First-feeding turbot larvae exhibited active selection for nauplii whereas developed larvae switched to copepodites and adult copepods. Although developing turbot larva exhibited active selection towards copepod size classes, there was no evidence of selective feeding on either of the two dominant copepod species. The turbot larvae's prey ingestion was modelled together with the standing stock of copepod biomass. The model results indicated that the estimated need for daily ingestion exceeded the standing stock of copepods. Hence, the initially established food web was unable to sustain the added turbot larvae with starvation as a consequence. We therefore suggest several solutions to circumvent starvation in the semi-intensive system.

Optimal egg viability storage conditions in two commercial fairy shrimps (Crustacea: Branchiopoda: Anostraca) from Thailand

Published on 25/3/2017
Optimal egg viability storage conditions for two commercial fairy shrimps, Branchinella thailandensis and Streptocephalus sirindhornae, were investigated. Eggs for each treatment were kept under eight different conditions at four different temperatures for 24 months. Every 2 months, representative eggs were hatched to evaluate hatching percentages. Low temperature and oxygen, darkness and dry conditions significantly influenced egg hatchability of both species. Undehydrated eggs hatchability in all conditions ranged from 0 to 10% in S. sirindhornae and 0 to 20% in B. thailandensis. Hatching percentages of B. thailandensis were higher than those of S. sirindhornae. Hatchability under all experimental regimes continuously decreased over time, except for dry eggs stored at −18°C in dark-anoxic conditions. Hatchability was markedly delayed in both species over time. We demonstrate that both species’ eggs can be stored at −18°C at least for 24 months with high hatchability in B. thailandensis (80%) and S. sirindhornae (60%) under dry, dark, anoxic conditions.

Effects of live and artificial feeds on the growth, digestion, immunity and intestinal microflora of mandarin fish hybrid (Siniperca chuatsi ♀ × Siniperca scherzeri ♂)

Published on 25/3/2017
How to acclimate mandarin fish to eat artificial feeds has been always a challenge for researchers. The mandarin fish after hybridization (Siniperca chuatsi ♀ × Siniperca scherzeri ♂) could be fed artificial feeds which solved the problem to some extent. However, the growth performance, digestibility, immunity and intestinal microflora of mandarin fish hybrid fed artificial feeds need further study. One hundred and twenty fish of similar size (average weight, 19.5 ± 0.9 g) were randomly stocked into six 250-L aquariums and separately fed live baits (the control) or artificial feeds in triplicate for 70 days. The weight gain and special growth rate of fish fed artificial feeds were significantly lower than those of fish fed live baits (P < 0.05). The protease activities of stomach, liver and intestine in fish fed live baits were all significantly higher than those in fish fed artificial feeds. The activities of catalase and lysozyme, the content of glutathione in serum of fish fed live baits were all significantly higher than those in fish fed artificial feeds. However, the content of malondialdehyde in liver of fish fed artificial feeds was significantly higher than that in fish fed live baits. The dominant bacteria in both groups were Proteobacteria, Bacteroidetes, Planctomycetes, Cyanobacteria, Verrucomicrobia. However, live baits greatly affected the amount of beneficial and harmful bacteria of intestine in mandarin fish hybrid and broke the balance of intestinal flora.

Changes in fatty acids profile, monosaccharide profile and protein content during batch growth of Isochrysis galbana (T.iso)

Published on 25/3/2017
To investigate the nutritional value of the marine micro-alga Isochrysis galbana Tahitian Isochrysis strain (T.iso) as an alternative feed for aquaculture during culture age, its biochemical composition was studied under autotrophic and controlled culture conditions at different growth stages: exponential phase, early and late stationary phases and decay phase. Analysis showed that C14:0, C16:0, C16:1, C18:4 (n-3) and C22:6 (n-3) were the most abundant fatty acids in this alga at different growth stages. The highest values of monounsaturated fatty acids were recorded at the late stationary and the decay phases. However, the highest levels of polyunsaturated fatty acids were observed at the early stationary phase. At all growth stages, I. galbana (T.iso) contained arabinose, xylose, mannose, galactose and glucose. Glucose represented the main sugar, and its content per dry alga biomass weight increased with increasing age of the culture and reached about fourfold in the decay phase. The maximum protein content was also observed during this last phase.

Ammonium bicarbonate supplementation as carbon source in alkaliphilic Spirulina mass culture

Published on 24/3/2017
Cyanobacterium Spirulina (Arthrospira) platensis is a commercial product with high content of protein and other nutritional elements, serving as a source of nutrients for food, feed and pharmaceutical industry. Generally, CO2 gas bubbling method is a common method to supply carbon source for algae culture. However, in commercial situation where the CO2 supply is limited, alternative bicarbonate could be utilized as a substitute carbon source in Spirulina cultivation. In this study, the optimum culture method of ammonium bicarbonate supplementation in open raceway pond as carbon source was firstly investigated to avoid the inhibition effect of ammonium bicarbonate. The optimal conditions estimated by experimental results for S. platensis cultivation were set as following: (1) the addition of ammonium bicarbonate at each time must be <2.0 mmol L−1; (2) the addition rate of ammonium bicarbonate is in the range of 10–20 g m−2 day−1. Then, S. platensis were cultured in eight 800 m2 raceway ponds with fed-batch addition of ammonium bicarbonate combined with sodium bicarbonate as carbon source. The results illustrated that ammonium bicarbonate addition not only did not show any adverse impact on productivity, chlorophyll and carotenoid content of S. platensis, but also significantly increased the protein content of S. platensis. With ammonium bicarbonate supplementation as carbon source in alkaliphilic Spirulina mass culture, the carbon utilization efficiency was dramatically increased to approximately 70% from 38.89%, and the carbon cost was reduced by approximately 57%. Therefore, ammonium bicarbonate can be applied as supplement of carbon source for alkaliphilic Spirulina culture.

In vitro assembly of Penaeus monodon densovirus (PmDNV)-like particles produced in a prokaryote expression system

Published on 24/3/2017
Viral diseases are a significant problem in the shrimp aquaculture industry as outbreaks can cause significant mortality and economic loss. While it has been shown that triggering the shrimp RNA interference pathway through dsRNA is a potentially viable treatment pathway, this approach is hampered by the lack of a suitable delivery mechanism. Virus-like particles (VLPs), which are structurally similar to native viruses but lack the genetic material, could possibly be developed as a delivery vehicle. To generate a candidate VLP, the Penaeus monodon densovirus (PmDNV) capsid protein was cloned with an added histidine tag and expressed in an E. coli expression system. While the protein was expressed in inclusion bodies, the recombinant PmDNV capsid protein could be dissolved and subsequently purified by nickel affinity column chromatography. The formation of VLP from this purified rPmDNV capsid protein was investigated by transmission electron microscopy, and PmDNV-VLPs were observed that looked similar to the native PmDNV virion. Our results suggest that the PmDNV-like particle could be promisingly applied towards vaccination and that this PmDNV-like particle can potentially serve as a system for delivery of nucleic acids to trigger innate immunity in shrimp.

Dietary thiamin and pyridoxine requirements of fingerling Indian major carp, Cirrhinus mrigala (Hamilton)

Published on 24/3/2017
Two experiments were conducted to quantify the dietary thiamin (experiment I) and pyridoxine (experiment II) requirements of fingerling Cirrhinus mrigala for 16 weeks. In experiment I, dietary thiamin requirement was determined by feeding seven casein–gelatin-based diets (400 g kg−1 CP; 18.69 kJ g−1 GE) with graded levels of thiamin (0, 0.5, 1, 2, 4, 8 and 16 mg kg−1 diet) to triplicate groups of fish (6.15 ± 0.37 cm; 1.89 ± 0.12 g). Fish fed diet with 2 mg kg−1 thiamin had highest specific growth rate (SGR), protein retention (PR), RNA/DNA ratio, haemoglobin (Hb), haematocrit (Hct), RBCs and best feed conversion ratio (FCR). However, highest liver thiamin concentration was recorded in fish fed 4 mg thiamin kg−1 diet. Broken-line analysis of SGR, PR and liver thiamin concentrations exhibited the thiamin requirement in the range of 1.79–3.34 mg kg−1 diet (0.096–0.179 μg thiamin kJ−1 gross energy). In experiment II, six casein–gelatin-based diets (400 g kg−1 CP; 18.69 kJ g−1 GE) containing graded levels of pyridoxine (0, 2, 4, 6, 8 and 10 mg kg−1 diet) were fed to triplicate groups of fish (6.35 ± 0.37 cm; 1.97 ± 0.12 g). Fish fed diet containing 6 mg kg−1 pyridoxine showed best SGR, FCR, PR, RNA/DNA ratio, Hb, Hct and RBCs, whereas maximum liver pyridoxine concentration was recorded in fish fed 8 mg kg−1 dietary pyridoxine. Broken-line analysis of SGR, PR and liver pyridoxine concentrations reflected the pyridoxine requirement from 5.63 to 8.61 mg kg−1 diet. Data generated during this study would be useful in formulating thiamin- and pyridoxine-balanced feeds for the intensive culture of this fish.

Reproductive performance of indoor-reared pikeperch (Sander lucioperca) females after wintering in outdoor earthen ponds

Published on 24/3/2017
Photo-thermal induction of gonadal maturation in completely controlled conditions is still not well explored in pikeperch. Thus, wintering intensively reared breeders in outdoor pond conditions might be rather suitable alternative to use these fish for larvae production. In this study, we compared the propagation success of indoor-reared [recirculating aquaculture systems (RAS)-reared fish, RRF] and wild (WCF) pikeperch females wintering them in outside earthen ponds. Each group was composed of six females and four males which were artificially propagated following hormonal induction with human chorionic gonadotropin. Beside the main parameters of reproductive success, fatty acid composition of dry eggs and mortality during early larviculture were assessed. The only statistically significant difference among reproductive parameters was found in latency time, which was significantly lower in RRF. Fatty acid profiles of dry eggs were rather similar between the groups; however, significant difference was noticed in phospholipid fraction in EPA/AA (eicosapentaenoic acid; C20:5n-3/arachidonic acid; C20:4n-6) ratio which was, on average, five times higher in the RRF (5.1 ± 3.8) than in WCF (0.9 ± 0.3). Significantly lower mortality was seen in the larvae originating from wild breeders (13.4 ± 1.7% and 27.0 ± 4.9% for WCF and RRF respectively). Wintering indoor-reared females in outdoor pond conditions led to appropriate gonadal maturation, and ovulation occurred in all examined females. The lower quality of larvae was likely caused by suboptimal broodstock nutrition, which should be studied further, with special consideration given to the EPA/AA ratio and the phospholipid content and composition of the diet.

Physiological and biochemical responses of Zhikong scallop, Chlamys farreri, to different thermal stressors

Published on 24/3/2017
Water temperature is a significant environmental stressor that affects physiology and biochemical activities of bivalves. Here, temporal variations in physiological and biochemical parameters of Zhikong scallop, Chlamys farreri, under three water temperature treatments were investigated. For the first treatment, scallops were transferred from rearing temperature (15°C, control temperature) to 5, 10, 20 and 25°C, respectively. The second group of scallops was gradually acclimated to above experimental temperatures at a rate of 1–2°C day−1. The third group was transferred directly between 15 and 7°C every 12 h and for six times. Results showed that significantly higher oxygen consumption and ammonia-N excretion together with a significant lower ingestion rate was observed for the acute temperature change treatment compared to those in the equivalent gradual temperature variation treatment (P < 0.05). In acute temperature change treatment, hepatopancreas antioxidant enzyme activities, that is, superoxide dismutase (SOD) and catalase (CAT), immune enzyme activities, that is, acid phosphatase (ACP) and lysozyme (LSZ), and heat-shock protein 70 gene (Hsp70) expression levels of scallops increased substantially within 48 h. Significant increases in SOD, CAT, ACP and LSZ activities, and malondialdehyde content occurred under exposure to fluctuating temperatures (P < 0.01). Gill and hepatopancreatic Hsp70 expression levels also increased significantly in response to water temperature fluctuations (P < 0.05). The study provides basic knowledge about thermal stress in Zhikong scallop and may contribute to the management of scallop mortalities.

Substituting fishmeal with mixtures of wheat, corn and soya bean meals in diets for the white leg shrimp, Litopenaeus vannamei (Boone): effect on production parameters and preliminary economic assessment

Published on 10/3/2017
We analysed the effect on production and economic performance of juvenile Litopenaeus vannamei of isoproteic diets substituting fishmeal by 25%, 50%, 75% and 100% with mixtures of wheat, soya bean and cornmeals. In a laboratory trial, 10 juveniles m−2 (1.1 ± 0.1 g) were reared in 60-L plastic containers using a recirculation system for 90 days. Three replicates were used to test each diet. A commercial diet serving as a reference and the diet with the highest content of essential amino acids (50% substitution, 6.46 ± 1.1 g) produced significantly higher shrimp final weight (7.12 ± 0.9 g, P < 0.05). There were not significant differences in specific growth rate and mean survival (85.9 ± 0.2%, P > 0.05). In a pond trial, 10 shrimp m−2 (1.08 ± 0.3 g) were cultivated in 1.5 m−3 cages for 35 days, testing the diets in triplicate. Final weight was significantly higher (P < 0.05) when 100% substitution was used (10.89 ± 0.24 g), while survival did not differ significantly among diets (P > 0.05). The optimal level of substitution was estimated at 86.0%. Apparently, nutrients contained in the diets combined well with natural feed available in the pond, up to a point where 7.3% of fishmeal inclusion is recommended. An economic analysis showed that 100% substitution produced the best results. We conclude that mixtures of wheat, corn and soya meals are potential alternatives to replace fishmeal effectively in diets for L. vannamei.

Qualitative analysis of cartilaginous jaw element malformation in cultured yellowtail kingfish (Seriola lalandi) larvae

Published on 10/3/2017
A central problem facing worldwide culture of yellowtail kingfish (Seriola lalandi) is the presence of skeletal malformations, including jaw deformities. This study presents a morphological characterization of normal and abnormal cartilage jaw structures during early larval development. Samples of 70–150 larvae were collected from three cohorts from 2 to 9 days post hatching, anaesthetized and fixed for cartilage staining. Cartilaginous components were defined clearly at four days post hatch (dph) (4.65 ± 0.05 mm total length), and abnormal jaw structures were detectable at this time. Jaw deformities observed included extension of Meckel's cartilage with or without ventral bending of the anterior tip, displacement of ceratohyal and hypohyal cartilage ventrally and below Meckel's cartilage, and shortening and dorsal flexion of the lower jaw. At 4 dph, between 44% and 47% of all larvae examined had jaw abnormalities. The contribution of each deformity to the total number of deformities was variable among the three cohorts examined. To compare shape difference accurately we performed an exploratory, landmark-based geometric morphometric analysis using seven homologous landmarks. Larvae were classified into three jaw morphology groups. The geometric morphometric approach provides a useful tool to standardize classification of cartilage jaw abnormalities at early developmental larval stages. Early recognition of developing abnormalities is of importance for fish farmers in both improving fish selection efficiency and for evaluating effects of rearing parameters.

Probiotic efficiency of Bacillus sp. in Labeo rohita challenged by Aeromonas hydrophila: assessment of stress profile, haemato-biochemical parameters and immune responses

Published on 10/3/2017
Fish are always susceptible to a wide variety of deadly pathogens which cause a huge loss in aquaculture industries. In this investigation, we have demonstrated the in vivo probiotic efficiency of Bacillus sp. MVF1 (GenBank Acc. No. KP256503) in Labeo rohita challenged with pathogenic strain of Aeromonas hydrophila (MTCC 1739). To check the probiotic potential of the selected bacterial strain, fish were divided into four groups: control, D1, D2 and D3. A total of 100 days (70 days probiotic feeding + 71th day sampling and 28 days challenged test + 29th day sampling) of feeding trial was conducted. To establish the probiotic potential of Bacillus sp. MVF1, certain haematological parameters (haemoglobin, total erythrocyte and leucocyte count), serum biochemical parameters (total protein, albumin and globulin), immune parameters (serum lysozyme and total IgM levels) and hepatic stress profile (malondialdehyde production, superoxide dismutase and catalase activity) have been measured. Our results demonstrated that red blood cell number, white blood cell number and haemoglobin content were much higher in D2 group fish compared to other groups and control fish. Similarly, total protein contents, albumin concentration, globulin concentration, lysozyme activity and IgM production were also recorded to be highest in D2 group fish. This finding clearly indicated the probiotic potential of Bacillus sp. MVF1 in L. rohita. Furthermore, our results also demonstrated that 1 × 107 CFU g−1 feed (D2) provides better immunity compared to 1 × 105 (D1) and 1 × 109 (D3). Due to beneficial effects, the bacterium Bacillus sp. MVF1 might be useful in aquaculture industries to reduce the disease susceptibility.

Rubrivivax gelatinosus biomass as an immunostimulant for pacu Piaractus mesopotamicus

Published on 10/3/2017
Rubrivivax gelatinosus is a bacterium present in the environment successfully used for treatment of fish industry effluent. Besides cleaning the effluent, this bacterium provides a biomass rich in proteins and carotenoid as a metabolic product. This study describes for the first time the use of this biomass as an immunostimulant feed. Haematological, immunological, biochemical and growth parameters in pacu Piaractus mesopotamicus fed control diet or diets supplemented with 0.5 or 1.5 g kg−1 of the R. gelatinosus biomass during 60 days were assessed. Fish were sampled at 0, 30 and 60 days. The inclusion of increasing levels of biomass in feed increased thrombocytes and neutrophils (P < 0.05) and decreased lymphocytes (P < 0.05) as well as activated the complement system (P < 0.05). Glucose levels, hepatosomatic index and weight were positively affected by the inclusion of R. gelatinosus biomass (P < 0.05). The use of R. gelatinosus biomass in feed improved the immune response of fish through the enhancement of some phagocytic cells, reduced time to activation of the complement system and increased growth parameters. This study reveals a promising use for a by-product resulted in the wastewater treating in aquaculture.

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