Detection and pathogenicity of Vibrio parahaemolyticus strains in Penaeus vannamei

Background and purpose: The Vibrio spp. are indigenous bacteria in the marine environment and usually constitute the majority in normal microflora of farmed and wild penaeid shrimp; and are one of the most diverse and vital shrimp pathogens that cause heavy mortalities in aquaculture facilities worldwide. The present study aimed to isolate and characterize the causative agent concerned with mass mortality in Peneaus vannamei collected from the shrimp farms of Kakinada, Andhra Pradesh, India.Materials and methods: To isolate and characterize the pathogenic bacteria from the hepatic pancreatic tissue of moribund, P. vannamei performed conventional culture tests, physical and biochemical tests, and molecular analysis. In addition to that virulence gene study, bacterial pathogenicity with different salinity and antibacterial activity of the stem extract of Tinospora cordifolia against Vibrio parahaemolyticus were tested.Results: The phenotypic traits, 16s rRNA gene, and phylogenetic tree analysis showed that the isolated pathogen was V. parahaemolyticus strain KKD 02. A study on bacterial pathogenicity with different salinity 0, 5, 10, 15, 20, and 25 ppt showed that 5 ppt to 10 ppt was connected to the maximum resistance against bacterial infection in P. vannamei with higher CFU/shrimp value. Two genes encoding thermostable direct hemolysin (tdh) and the thermostable direct hemolysin-related hemolysin (trh) were present in the isolate. The antibacterial activity of the stem extract of T. cordifolia, tested against V. parahaemolyticus, revealed that both the ethanol extracts and the crude stem juice exhibited antibacterial activity against V. parahaemolyticus.Conclusion: The cause for the mass mortality of juvenile shrimp P. vannamei in Kakinada, Andhra Pradesh, India, was V. parahaemolyticus strain KKD 02. Further work is necessary to isolate and purify the active constituents in T. cordifolia stem extracts and examine the absorption pattern of the active ingredients of these plants, which will allow the scientific community to recommend their utilization as an accessible alternative to synthetic antibiotics

Genetic variation among full-sib families and the effect of non-genetic factors on growth traits at harvest in Clarias magur (Hamilton, 1822)

Magur (Clarias magur) is an Indian catfish species with a good potential for aquaculture. The expansion of magur aquaculture is hindered because of low reproductive and survival rates. Furthermore, males need to be sacrificed to collect milt for artificial fertilization. At present, magur seed production mainly depends on the wild-caught juveniles and to a smaller extent, from broodfish whose genetic potential is unknown. The availability of high-quality seeds in a sustainable way can be ensured through the selective breeding program for magur. The knowledge of factors influencing growth traits and their genetic parameters is a pre-requisite for implementing a genetic selection program. The present study aimed to quantify the performance of C.magur reared in a two-year class and estimate their heritabilities at stocking and harvest and also to estimate the genetic and phenotypic correlations among them. The growth traits such as Body Weight (BW), Total Length (TL), Body Depth (BD), Head Width (HW), and Average Daily Gain (ADG) were recorded from 1413 animals belonging to 78 fullsib families produced by adopting single pair mating design, after one year of pond culture (traits at harvest). Genetic parameters were also estimated for body weight (BW0) and total length (TL0) measured from 2328 fish from 78 fullsib families at the time of stocking. Magur attained an average BW of 135 g and 24.5 cm TL after one year culture period. The heritabilities of BW, TL, and ADG were 0.44 ± 0.07, 0.32 ± 0.06, and 0.42 ± 0.07, respectively and may be biased upwardly due to the single pair mating design. Genetic correlations between harvest traits were all positive and varied in magnitude between traits (0.74 to 0.99). The results obtained from the current study indicate the presence of genetic variation in magur population for growth traits and selection based on genetic merit can produce improvement in these traits

Dietary Iron Requirement of Goldfish (Carassius auratus) Fry

To estimate the dietary iron requirement of common goldfish, Carassius auratus (Linnaeus, 1758), eight isoproteinous diets containing graded levels of dietary iron (FeSO4.7H2O) ranging 34.27-537.14 mg/kg were fed to triplicate groups of C. auratus fry in glass tanks. The rearing medium was groundwater passed through a reverse osmosis water treatment unit. Fish were fed 3% of their body weight per day. After 75 days, the fish were randomly sampled and anesthetized, blood was withdrawn from the caudal vein, and red blood cell count, hemoglobin content, and hematocrit value were evaluated. Tissue samples were randomly collected for muscle, liver, and whole-body iron analysis. The iron concentrations in the diets and fish tissues were measured by atomic absorption spectrophotometer. Broken-line regression analysis and analysis of variance (ANOVA) with multiple mean comparisons of the data indicate that the dietary iron requirement for optimal hematological values and tissue iron levels of C. auratus fry should be at least 139.06 mg/kg dry diet

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Evaluation of alternative methods for estimating the precision of REML-based estimates of variance components and heritability

Residual Maximum Likelihood (REML) analysis is the most widely used method to estimate variance components and heritability. This method is based on large sample theory under the assumption that the parameter estimates are asymptotically multivariate normally distributed with covariance matrix given by the inverse of the information matrix. Hence, these sampling variances could be biased if the assumption of asymptotic approximation is incorrect, especially when the sample size is small. Though it is difficult to assess the impact of sample size, an alternative option is to generate a full distribution of the parameters to determine the uncertainty of estimates. In this study, we compared the REML estimates of variance components, heritability and sampling variances of body-weight (BW), body-depth (BD), and condition-factor (K) with those obtained from four sampling-based methods viz., parametric and nonparametric bootstrap, asymptotic sampling and Bayesian estimation. The aim was to understand if a sample size of order 1413 was sufficient to contain adequate information for a reliable asymptotic approximation. The REML solution was close to values obtained from different sampling-based methods indicating that the present sample size was sufficient to estimate reliable genetic variation in different traits with varying heritability. The variance and heritability estimated by a nonparametric bootstrap estimate based on randomization of family effects gave comparable results as evaluated by REML for different traits. Hence, the nonparametric bootstrap estimate can be effectively used to understand whether the sample size is large enough to contain sufficient information under likelihood estimation assumptions

Effect of Bacillus circulans and fructooligosaccharide supplementation on growth and haemato-immunological function of Labeo rohita (Hamilton, 1822) fingerlings exposed to sub-lethal nitrite stress

The present study was undertaken to evaluate the effect of a probiotic strain, Bacillus circulans (BC) and prebiotics fructooligosaccharide (FOS) supplementation in Labeo rohita fingerlings subjected to sub-lethal nitrite stress. Earlier a sixty days feeding trial was conducted using eight experimental diets viz. T1 (106 cfu/g BC+0%FOS), T2 (108 cfu/g BC+0% FOS), T3 (0BC+1%FOS), T4 (0BC+2%FOS), , T5 (106 cfu/g BC + 1% FOS), T6 (106 cfu/g BC+2% FOS), T7 (108 cfu/g BC+1%FOS), T8 (108 cfu/g BC+2%FOS) & control (0BC+0%FOS) assigned to triplicate groups. After the initial experiment, fishes were subjected to sub-lethal nitrite (1/5 96 h LC50 = 2.08 mg/L) for another 30 days. At the end of the experiment growth and feed utilization parameters viz. weight gain, specific growth rate (SGR), feed conversion ratio (FCR) & survival percentage were calculated. Haemato-immunological parameters viz. total leukocyte count (TLC), total erythrocyte count (TEC), hemoglobin (Hb), hematocrit (Hct) values, lysozyme and respiratory burst activity were assayed after exposure to stress. Growth and feed utilization was significantly (p < 0.05) better in probiotic fed groups at all level of supplementation whereas prebiotics supplementation at 2% level had negative impact. Percentage survival was also better in the supplemented groups with highest survival observed in T4 group. Similarly, post challenge haemato-immunological parameters were better in supplemented group compared to control and higher levels were observed in combination groups (T4 and T5). From the present investigation, it can be concluded that probiotic B. circulans and prebiotics FOS supplementation improves immune status and thereby conferring better protection of L. rohita under sub-lethal nitrite stress