Comparison of growth and survival of white shrimp postlarvae (Litopenaeus vannamei) fed dried Artemia biomass versus four commercial feeds and three crustacean meals

The use of dried Artemia biomass meal as an exclusive feed for postlarval white shrimp (Litopenaeus vannamei) was compared with four commercial feeds and three crustacean meals in a series of trials. Postlarvae (PL1–PL6) were stocked at a density of 1.5–2.5/litres in 16 tanks (100 litres volume) and fed, ad libidum, five times a day, over 23–29 days. Feeding postlarval shrimp with dried Artemia biomass resulted in a significantly larger size than feeding with three of the commercial feeds, and the crustacean meals. There was no significant size difference observed in animals fed with Artemia biomass and the commercial 'Golden Pearls' feed for postlarvae, however the coefficient of variation among the size of the 'Golden Pearls' fed animals was significantly higher. The weight increase of animals fed with Artemia biomass was higher than in animals fed with all the tested feeds. The survival rate was not significantly different in animals fed with Artemia flakes from 'Salt Creek', 'Bio-Marine', 'Golden Pearls' and Artemia biomass, however the survival rate was significantly larger in animals fed with Artemia biomass than in animals fed with the crustacean meals and 'Artemac.' Results suggest that dried Artemia biomass is a well-suited feed for postlarval L. vannamei.     

Chilled storage of white shrimp (Litopenaeus vannamei) spermatophores

Chilled storage of spermatophores from white shrimp (Litopenaeus vannamei) is needed to generate a consistent and reliable supply of spermatozoa for domestication purposes. The objective of this study was to develop a protocol for the chilled storage of white shrimp spermatophores and to evaluate bacterial propagation during such storage. In the first experiment, spermatophores were immersed in four extenders, mineral oil, Ringer's solution, phosphate buffer and 0.85% NaCl, and stored at low temperature (2-4 °C) for 35 days. Characteristics of preserved spermatophores changed the least and viable sperm was highest when spermatophores were stored in mineral oil. Spermatophores preserved with mineral oil appeared morphologically normal. Bacillus circulans, Staphylococcus hominis and S. lugdunensis, S. sciuri, S. xylosus and Micrococcus spp. were identified as the predominant bacteria during chilled storage, and total bacterial counts gradually increased during the experiment. A second experiment investigated the effect of antibiotic on chilled storage. Spermatophores were preserved in only mineral oil or mineral oil with 0.1% penicillin-streptomycin. These were evaluated for changes in external morphology of spermatophores, sperm viability and total bacteria count every week during a 35-day experimental period. Percentages of viable sperm (69.5 ± 3.9%) were significantly higher (P < 0.05) among spermatophores preserved in mineral oil with 0.1% antibiotic compared with those preserved only in mineral oil (57.7 ± 3.4%) over 35 days. The number of total bacteria in the treatment with mineral oil ranged between 28.3 ± 4.8 and 2416.7 ± 299.4 CFU/g, but in mineral oil containing antibiotic bacteria were undetectable. This study suggests that chilled storage of spermatophores is a feasible approach for the management and spawning of white shrimp broodstock.     

A stochastic approach for analysis of the influence of white spot disease, zootechnical parameters, water quality, and management factors on the variability of production of shrimp Litopenaeus vannamei cultivated under intensive commercial conditions

We investigated the variability of shrimp Litopenaeus vannamei production by incorporating stochastic elements into deterministic stock models and determined the contribution that white spot disease, zootechnical parameters, water quality, and alternative management strategies have on variability. The model was calibrated for intensive shrimp cultivation in the State of Nayarit, Mexico. Mean annual production increased as a consequence of improved management from 8000 kg ha⁻¹ to 22,000 kg ha⁻¹ when cultivation was not affected by the disease and from 3200 kg ha⁻¹ to 10,400 kg ha⁻¹ when the disease affected production. When simultaneously considering both cases, mean annual production increased from 6300 kg ha⁻¹ to 16,800 kg ha⁻¹. White spot disease was a major factor determining variability of production. Shrimp production was particularly sensitive to levels of dissolved oxygen when management was inadequate, while final weight and mortality rate of shrimp were more sensitive when management improved. Water temperature and salinity had intermediate importance, and mortality caused by the disease and the time when mortality occurred had intermediate or low relevance. Improving management increased shrimp production and diminished variability. The duration of cultivation and stocking density were the most important management variables controlling variability of production when cultivation was affected by the white spot disease. When the disease was not present, pond size and duration of cultivation were the main factors affecting production. Starting time of aeration had relatively lower importance in determining variability, while the stochastic values of dissolved oxygen, in contrast, became most important. These results call for studies on improving aeration management to reduce variability of dissolved oxygen in ponds.     

饲料锌添加水平对凡纳滨对虾免疫抗菌机能和溶菌酶mRNA及Toll受体mRNA表达的影响

在基础饲料中添加不同水平蛋氨酸锌(添加水平分别为0、50、150 mg Zn/kg)并饲喂凡纳滨对虾,养殖14 d后,取样测定对虾鳃组织中Toll受体mRNA和溶菌酶mRNA的表达水平以及肝胰腺、肌肉和血淋巴中超氧化物歧化酶(SOD)和溶菌酶(LSZ)活性,并进行溶藻弧菌人工急性感染试验。结果表明,凡纳滨对虾肝胰腺及肌肉中锌蓄积水平随饲料锌添加量的增加而显著增加(P<0.05),肝胰腺中锌蓄积更明显。添加50 mg Zn/kg组(锌含量为73.25 mg Zn/kg饲料)对虾鳃组织中的Toll受体mRNA和溶菌酶mRNA表达量均显著高于未添加锌组和添加150 mg Zn/kg组(P<0.05)。添加50 mg Zn/kg组对虾肌肉、肝胰腺和血淋巴中溶菌酶活性显著高于未添加锌组(P<0.05)。添加50 mg Zn/kg组对虾肝胰腺和血淋巴中的SOD活性也显著高于未添加锌组,但与添加150 mg Zn/kg组无显著差异。而肌肉中SOD活性在添加150 mg Zn/kg组中最高。经溶藻弧菌人工急性感染后,添加50 mg Zn/kg组对虾半致死时间和全致死时间大于未添加锌组和添加150 mg Zn/kg组。本研究表明,相比摄食未添加锌组饲料和添加150 mg Zn/kg组饲料,凡纳滨对虾的免疫抗菌机能在摄取添加50 mg Zn/kg(锌含量为73.25 mg Zn/kg饲料)饲料时得到改善。     

凡纳滨对虾标准化生态养殖全程管理系统

阐述了基于Web的凡纳滨对虾标准化生态养殖全程管理系统的研发过程。该系统立足数字农业发展与新农村建设的基本国情,采用B/S系统结构、Windows 2000/2003 Server平台、SQL Server 2000数据库、ASP技术和Dreamwaver MX 2004开发环境;依据凡纳滨对虾标准化生态养殖生产工艺过程,采用面向对象的分析和设计方法,最终实现水产养殖环境、苗种放养、渔药使用、饲料投放和产品销售等环节全过程标准化管理。系统包括日常管理、基础信息、系统管理、个人工具、信息查询和报表打印等6大功能模块。广大养殖用户可借助覆盖全球的无线广域通信网络,使用架设在Internet上的管理系统,进行所辖池塘的日常生产信息维护。     

Brachionus vs Artemia duel: Optimizing first feeding of Upogebia pusilla (Decapoda: Thalassinidea) larvae

Larval rearing of many marine organisms is dependent on the availability of live food. The aim of this study was to optimize larval first feeding for the mud shrimp Upogebia pusilla, by comparing the effectiveness of the two most commonly used live feeds: Brachionus plicatilis and Artemia sp. nauplii. Survival, larval duration, molt synchronism and megalop size were compared using five feeding treatments: Artemia from zoea I to IV (B0), Brachionus during zoea I and Artemia from zoea II to IV (B1), Brachionus during zoea I and II and Artemia during zoea III and IV (B2), Brachionus from zoea I to III and Artemia during zoea IV (B3) and Brachionus from zoea I to IV (B4). The proportion of larvae that reached the megalop stage was 0.00% in treatment B0, 3.33% in treatment B1, 33.33% in treatment B2, 66.67% in treatment B3 and 76.67% in treatment B4. Larvae fed on rotifers until zoea III or zoea IV stages had a higher survival but no differences were found either in time to reach megalop or in megalop size. This study demonstrates that rotifers are essential for the survival and development of U. pusilla early larval stages but that rotifers can be successfully replaced by Artemia nauplii in the zoea IV stage.     

Effects of salinity and pH on ion-transport enzyme activities, survival and growth of Litopenaeus vannamei postlarvae

Effects of the salinity and pH on ion-transport enzyme activities, survival and growth of Litopenaeus vannamei postlarvae were investigated. Shrimp were transferred from salinity 31‰ and pH 8.1 to different salinity levels of 22, 25, 28, 31 (control), and to different pH levels of 7.1, 7.6, 8.1 (control), 8.6 and 9.1. The results showed ion-transport enzyme activities and weight gains of postlarvae were significantly affected by salinity and pH variation, which had no obvious effect on survival rate. The changing salinity affected the activities of total ATPase and Na⁺-K⁺-ATPase notably (F > F_0.05), meanwhile, non-significantly to the activities of V-ATPase, HCO₃⁻-ATPase. Within 48 h of salinity changing, the activities of ATPase, Na⁺-K⁺-ATPase in each treatment group gradually increased with the sampling time and reached their climax at 48 h, and then stabilized, showing negative correlation with salinity. The changing of pH affected greatly the activities of ATPase, Na⁺-K⁺-ATPase, V-ATPase and HCO₃⁻-ATPase (F > F_0.05), the activities of ATPase, Na⁺-K⁺-ATPase in each treatment group (pH = 7.1, 7.6, 8.6, 9.1) showed peak change within 72 h and stabilized afterwards, and the Na⁺-K⁺-ATPase activities came back to the level of the control group; Meanwhile the changing extent of V-ATPase and HCO₃⁻-ATPase activity corresponded with the grads of pH, and these ATPase activities showed negative correlation with pH changing, the activities of V-ATPase, HCO₃⁻-ATPase in postlarvae of each treatment group came to stable level after 24 h. The experiment also indicated the strength order of these ion-transport enzyme activities were as follows: Na⁺-K⁺-ATPase > V-ATPase > HCO₃⁻-ATPase. Na⁺-K⁺-ATPase was the chief undertaker of osmoregulation under the salinity effects, while V-ATPase and HCO₃⁻-ATPase were the chief osmoregulation undertakers under pH changing. In different salinity environment, the contributions of Na⁺-K⁺-ATPase, V-ATPase and HCO₃⁻-ATPase of L. vannamei postlarvae approximately accounted for 62.0-78.0%, 15.9-29.0% and 2.03-4.12% of ATPase activities in total, respectively. Meanwhile, in different pH medium, the contributions of these ATPases approximately accounted for 50.7-67.4%, 21.3-31.8% and 2.15-7.90% of total ATPase activities, respectively. Weight gain of shrimp transferred to salinity 31 (control) and 28‰ was significantly higher than that of shrimp reared at 25 and 22‰, and weight gain of shrimp transferred to pH 8.1 (control) and 8.6 was significantly higher that that of shrimp transferred to pH 7.1, 7.6 and 9.1. It was suggested that during the process of desalting and culturing of postlarvae, the salinity changing should not exceed 3 and pH variety not more than 0.5.     

Genetic differentiation in hatchery strains and wild white shrimp Penaeus (Litopenaeus) vannamei (Boone, 1931) from northwest Mexico

Ten enzymatic systems were analyzed to determine allozyme genetic differentiation among three hatchery strains (A, B and C) of white shrimp, Penaeus (Litopenaeus) vannamei, commonly used in shrimp farming in northwest Mexico. A wild population from northern Sinaloa was used as a reference. Fifteen loci were detected, nine of which were polymorphic (ACP-1*, ACP-2*, AKP-2*, EST-2*, EST-3*, EST-4*, EST-5*, LAP*, and LDH*). Polymorphism of A, B and C were 53, 53, and 40%. The mean observed heterozygosity per locus was 0.071, 0.093, and 0.050 without any significant difference among them or with respect to the wild population (0.056). In all samples observed heteroxygosity was smaller than expected. The mean number of alleles per locus was 1.8 in A and 1.87 in both B and C. Strain A was the only sample without rare alleles. Only EST-3* and LAP* of strain A were in Hardy-Weinberg equilibrium; the other loci were in disequilibrium in all samples. High inbreeding values and heterozygote deficiencies were detected in all samples. Distribution of allelic frequencies was heterogeneous among the samples (G-test), involving all polymorphic loci and suggesting a genetic differentiation. According to Fst, a moderate genetic differentiation (7.4%) was detected among the samples. Greater differences were between strains A and C. Based on genetic distance, the samples were grouped into two pairs, B-C and A-wild. Strain A is a young strain related to the wild sample, whereas strains B and C have a different geographic origin than the wild sample.     

Oxytetracycline (OTC) accumulation and elimination in hemolymph, muscle and hepatopancreas of white shrimp Litopenaeus vannamei following an OTC-feed therapeutic treatment

The white shrimp, Litopenaeus vannamei, has become a very important species for the development of shrimp aquaculture in Northwest Mexico. However, viral and bacterial diseases are considered a major threat to the development of this industry. In the present study a trial was conducted to evaluate the tissue distribution, maximum concentration, and elimination of the widely used antibiotic oxytetracycline (OTC) in L. vannamei using indoor tanks under laboratory-controlled conditions. OTC was given to shrimp simulating a therapeutic treatment through medicated feed for 14 days followed by a period of feeding without antibiotic for another 14 days to evaluate the elimination pattern. Samples of hemolymph, muscle, and hepatopancreas were taken from medicated animals every two days for 28 days. All tissues were removed and frozen immediately in liquid nitrogen. OTC levels were analyzed by High Performance Liquid Chromatography (HPLC). Results showed an important OTC increase during consumption of medicated feed in all examined tissues. OTC maximum concentrations were 33.54 ± 11.19, 194.37 ± 16.11, and 18.79 ± 5.87 µg g^− 1 for muscle, hepatopancreas and hemolymph, respectively. Although the highest OTC level was found in the hepatopancreas, it required only two days after the start of dosing to reach this value, whereas the maximum OTC for muscle and hemolymph was detected after eight days of dosing. Ten days after the cessation of medicated feeding, the drug content in the shrimp tail muscle was under the detectable limit for the method (0.01 µg g^− 1 of OTC).     

Effects of dietary medicinal herbs and Bacillus on survival, growth, body composition, and digestive enzyme activity of the white shrimp Litopenaeus vannamei

The basal diet (C), with 0.20% medicinal herbs (M) and 0.30% Bacillus (BM1), with 0.10% medicinal herbs and 0.15% Bacillus (BM2), and with 0.30% Bacillus (B), was used to feed white shrimps (Litopenaeus vannamei) (1.91 ± 0.03 g) in order to assess survival, growth, body composition, and digestive enzyme activity. At the end of the feeding trial, survival ranged from 95.83 to 98.33% with no significant difference (P > 0.05) among all groups. Growth measured as weight gain was significantly (P < 0.05) higher in shrimp fed with BM2, BM1, and M compared to that of C. However, no significant differences were found among B, BM1, and M. In the case of specific growth rate, the shrimp fed with BM1 and BM2 exhibited significantly (P < 0.05) higher values than that of C. The contents of body moisture, crude protein, and ash seemed to be unaffected by the feed supplements, though lipid content was found to be significantly (P < 0.05) different among the treatments. The shrimp fed with BM1 and BM2 had the lowest and highest lipid contents, respectively. The digestive enzyme activity assessed using shrimp hepatopancreas revealed that the activities of amylase and protease in shrimp fed with BM2 were significantly (P < 0.05) higher than those of C at the end of the 2nd and 6th weeks. However, better performance of the specific amylase activity was shown by the shrimp fed with B at the end of the 8th week.     

Relationship of precipitation, freshwater input, and sea level height with the abundance of the white shrimp (Litopenaeus occidentalis; Street, 1871) off Buenaventura, eastern tropical Pacific

Penaeid shrimp fisheries are an important source of income for the fishing communities that live in estuarine zones around the world. Off Buenaventura, the habitat of the western white shrimp (Litopenaeus occidentalis) is subject to high precipitation associated with the intertropical convergence zone, contributions from numerous short rivers descending from the Andes Mountains, and seasonal alternations in Trade Winds directions responsible for the upwelling in the Panama Bight. This work analyzes the relationship of precipitation, the San Juan River runoff, and sea level height with Litopenaeus occidentalis abundance in fishing areas between 1968 and 1989. The results indicate that precipitation is significantly correlated (p < 0.01) with the catch per unit effort on a monthly scale with a lag of approximately 1 calendar year but the inclusion of the data in a transfer function model does not improve considerably the forecasting power of a simpler autoregressive moving average model of the catch per unit effort. On an annual scale, the catch per unit effort for white shrimp depends significantly [r² = 0.36, p (corrected for autocorrelation)  0.01] on the precipitation that fell the previous December, whereas the residuals of this regression are significantly associated with variations of mean sea level between January and March (the upwelling season in the Panama Bight) of the current year at Buenaventura (r² = 0.61, p (corrected for autocorrelation)  0.01). The inclusion of these two variables in a multiple linear regression model accounted for a substantial proportion of the total annual variance of the mean CPUE (r² = 0.54), suggesting that freshwater contributions (lower salinities) and offshore transport during the main settlement period of postlarvae in the estuaries play a significant role in determining the strength of the cohorts recruited in the fishing areas. The industrial fishing yield decreased sharply after the 1982–1983 El Niño event. However, a high percentage of this change can be explained not by invoking El Niño effects but by a decreasing tendency of precipitation and offshore advection of early life stages between December and March, which took place on a multi-annual scale since the mid 1980s     

Prediction of apparent protein digestibility of ingredients and diets by in vitro pH-stat degree of protein hydrolysis with species-specific enzymes for juvenile Pacific white shrimp Litopenaeus vannamei

Aquafeed production faces global issues related to availability of feed ingredients. Feed manufacturers require greater flexibility in order to develop nutritional and cost-effective formulations that take into account nutrient content and availability of ingredients. The search for appropriate ingredients requires detailed screening of their potential nutritional value and variability at the industrial level. In vitro digestion of feedstuffs by enzymes extracted from the target species has been correlated with apparent protein digestibility (APD) in fish and shrimp species. The present study verified the relationship between APD and in vitro degree of protein hydrolysis (DH) with Litopenaeus vannamei hepatopancreas enzymes in several different ingredients (n = 26): blood meals, casein, corn gluten meal, crab meal, distiller's dried grains with solubles, feather meal, fish meals, gelatin, krill meals, poultry by-product meal, soybean meals, squid meals and wheat gluten. The relationship between APD and DH was further verified in diets formulated with these ingredients at 30% inclusion into a reference diet. APD was determined in vivo (30.1 ± 0.5 °C, 32.2 ± 0.4‰) with juvenile L. vannamei (9 to 12 g) after placement of test ingredients into a reference diet (35 g kg^− 1 CP; 8.03 g kg^− 1 lipid; 2.01 kcal g^− 1) with chromic oxide as the inert marker. In vitro DH was assessed in ingredients and diets with standardized hepatopancreas enzymes extracted from pond-reared shrimp. The DH of ingredients was determined under different assay conditions to check for the most suitable in vitro protocol for APD prediction: different batches of enzyme extracts (HPf5 or HPf6), temperatures (25 or 30 °C) and enzyme activity (azocasein): crude protein ratios (4 U: 80 mg CP or 4 U: 40 mg CP). DH was not affected by ingredient proximate composition. APD was significantly correlated to DH in regressions considering either ingredients or diets. The relationships between APD and DH of the ingredients could be suitably adjusted to a Rational Function (y = (a + bx)/(1 + cx + dx²), n = 26. Best in vitro APD predictions were obtained at 25 °C, 4 U: 80 mg CP both for ingredients (R² = 0.86; P = 0.001) and test diets (R² = 0.96; P = 0.007). The regression model including all 26 ingredients generated higher prediction residuals (i.e., predicted APD − determined APD) for corn gluten meal, feather meal, poultry by-product meal and krill flour. The remaining test ingredients presented mean prediction residuals of 3.5 points. A model including only ingredients with APD > 80% showed higher prediction precision (R² = 0.98; P = 0.000004; n = 20) with average residual of 1.8 points. Predictive models including only ingredients from the same origin (e.g., marine-based, R² = 0.98; P = 0.033) also displayed low residuals. Since in vitro techniques have been usually validated through regressions against in vivo APD, the DH predictive capacity may depend on the consistency of the in vivo methodology. Regressions between APD and DH suggested a close relationship between peptide bond breakage by hepatopancreas digestive proteases and the apparent nitrogen assimilation in shrimp, and this may be a useful tool to provide rapid nutritional information.     

Detailed monitoring of white spot syndrome virus (WSSV) in shrimp commercial ponds in Sinaloa, Mexico by nested PCR

WSSV has caused great losses to the global shrimp industry in recent years. This virus can infect shrimps asymptomatically. However, once the clinical signs are developed, mortalities can reach 100% in 3-10 days. PCR has been extensively used to detect WSSV in a specific and sensitive manner. Nested PCR is even more sensitive than single-step PCR and had been used for the detection of WSSV in asymptomatic populations. In this work, a detailed monitoring of WSSV by nested PCR in shrimp commercial ponds in Guasave County, State of Sinaloa, Mexico, is presented. Five ponds from two different farms were monitored for growth and presence of WSSV. At the beginning of the culture, ponds from both farms showed no or very slight WSSV presence. A 3-day period of rain occurred at both farms 10 and 14 weeks of culture for farms 1 and 2, respectively. At this time, WSSV was widely distributed in the shrimp populations of farm 1 according to nested-PCR data, although no visual symptoms were observed. In ponds of farm 2, WSSV was present at low level. However, the number of PCR-positive groups was drastically increased in both farms by nested and single-step PCR. Abrupt fluctuations in temperature and salinity were documented in farm 2 after the rain, which may have contributed to the increasing of viral load in the pond's shrimp populations. Twelve days after the rain period, estimated mortalities of 80% occurred in farm 1. Nevertheless, the study ponds at farm 2 culture continued normally for three more weeks and were harvested successfully (52% and 67% of survival for ponds 1 and 2, respectively). The removal of 40% and 50% of shrimp population 2-4 days after the raining period may have contributed to the thriving of the cultures. Analyses of the presence of WSSV in individuals of both sexes indicated that there is no preference for this virus to infect male or female shrimp. Also, no differences in weight were found between WSSV infected and non-infected individual shrimps, as well as nested-PCR positive against single-step PCR positive organisms. Nested PCR is more useful to monitor shrimp cultures than single-step PCR since it allows knowing how widely distributed the virus is in asymptomatically populations.     

Decapsulated Artemia cysts as dietary supplement for juvenile crayfish (Pacifastacus leniusculus, Astacidae) at different food supply frequencies from the onset of exogenous feeding under controlled conditions

Considering that the use of decapsulated Artemia cysts as direct food for juvenile crayfish could be an alternative to live nauplii, a 100-day experiment was carried out under controlled conditions to evaluate the effects of cysts, comparing with nauplii, as supplement to a dry diet for salmonids on the survival and growth of juvenile signal crayfish (Pacifastacus leniusculus) from the onset of exogenous feeding (stage 2). The reduction of feeding frequency was also tested. According to a bifactorial design, six treatments, differing in the supplement and feeding frequency, were tested: the dry diet supplemented with Artemia nauplii or decapsulated cysts was supplied once a day, once every two days and once every three days. Survival rates ranged from 56.7% to 81.7%, rising significantly with increasing the feeding frequency. The highest growth (12.94 mm carapace length and 593.08 mg weight) was reached by the crayfish that received the dry diet supplemented with cysts once a day, with significant differences from the rest of the treatments. Considering the supplement, the cysts supported significantly higher growth than the nauplii. Regarding the feeding frequency, growth was higher when the food was supplied once a day, showing significant differences from the other two frequencies (once every two days and once every three days). This study shows that decapsulated cysts are better dietary supplement than live nauplii. In crustacean culture, this is the first report of successful use of Artemia cysts from the onset of exogenous feeding.     

Antioxidant effect of dietary tocopherol and ascorbic acid on growth and survival of Litopenaeus vannamei postlarvae

The nutritional effect of vitamin E in dietsfor Litopenaeus vannamei postlarve (PL19)was investigated. Four formulated diets withdifferent combinations of -tocopherylacetate (-TA), ascorbic acid (AA) andhighly unsaturated fatty acids (HUFA) weretested, using four replicates.No significant differences in survival wereobserved among treatments after 34 days offeeding. However, shrimp fed with a dietcontaining 2% fish oil (low n-3 HUFA content),200 mg.kg^–1 -TA and100 mg.kg^–1 AA (diet H/E/C) showedsignificantly better growth than those fed adiet supplemented with 5% fish oil (high n-3HUFA content), 200 mg.kg^–1 -TA and100 mg.kg^–1 AA (diet H+/E/C). Shrimp fedwith a diet containing 5% fish oil,900 mg.kg^–1 -TA and100 mg.kg^–1 AA (diet H+/E+/C) showed a significantly higher tissue level of n-6 PUFAthan postlarvae fed diet H+/E/C. No definiteconclusion could be drawn about a possibleinteraction between -TA and AA, since acomparison of the diet containing 5% fish oil,200 mg.kg^–1 -TA and700 mg.kg^–1 AA (H+/E+/C+) and the dietH+/E/C did not show any significant differencesin any of the measured parameters. Theantioxidative status of the shrimp tissue(measured by means of the thiobarbituric acid(TBA) assay and expressed as nM malonaldehyde(MA) per gramme dry weight) was equal for alltreatments. Nevertheless, there was a slightlylower MA value with the diet H+/E/C+,indicating that AA may be an effectiveantioxidant in the aqueous phase and at thewater/lipid interface of the tissue. The tissuelevels of -T and AA were highlydependent on the amounts in diets and nocorrelation between -T and AAincorporation could be observed.     

Effect of high water temperature (33 °C) on the clinical and virological outcome of experimental infections with white spot syndrome virus (WSSV) in specific pathogen-free (SPF) Litopenaeus vannamei

White spot syndrome virus (WSSV) is the most lethal pathogen of cultured shrimp. Previous studies done with undefined WSSV titers showed that high water temperature (32-33 °C) reduced/delayed mortality of WSSV-infected shrimp. This study evaluated the effect of high water temperature on the clinical and virological outcome of a WSSV infection under standardized conditions. Groups of specific pathogen-free Litopenaeus vannamei were challenged either by intramuscular or oral routes with a low (30 SID₅₀) or a high (10,000 SID₅₀) virus titer. Shrimp were kept (i) continuously at 27 °C, (ii) 30 °C or (iii) 33 °C; (iv) maintained at 33 °C before challenge and 27 °C afterwards, or (v) kept at 27 °C before challenge and 33 °C afterwards. Shrimp were maintained at the respective temperatures for 120 h before challenge and 120-144 h post challenge (hpc). Gross signs and mortality were monitored every 12 h until the end of the experiment. Dead and surviving shrimp were screened for WSSV infection (VP28-positive cells) by indirect immunofluorescence (IIF). Shrimp kept continuously at 27 °C or 30 °C, or switched to 27 °C post challenge developed gross signs within 24 hpc, first mortalities at 36-60 hpc and 100% cumulative mortality between 60 and 144 hpc depending on the virus titer. All dead shrimp were WSSV-positive. In contrast, shrimp kept at 33 °C continuously or after WSSV challenge showed no signs of disease and low mortalities (0-30%) regardless of the virus titer. Dead and surviving shrimp were WSSV-negative. Further, early virus replication was studied in two groups of shrimp: one maintained at 27 °C before and after challenge and one switched from 27 °C to 33 °C after challenge with 10,000 SID₅₀. Immunohistochemistry (IHC) analysis showed that WSSV-positive cells were first displayed at 12 hpc in shrimp kept at 27 °C and by 24 hpc the infection became systemic. In contrast, shrimp kept at 33 °C did not display WSSV-positive cells at 12 or 24 hpc. This work confirms previous reports that high water temperature prevents the onset of disease and significantly reduces mortality of WSSV-inoculated shrimp regardless of the route of inoculation or virus titer used. This strategy may have practical applications to control WSSV in tropical shrimp farming countries.     

Comparison of age estimates from scale, opercular bone, otolith, vertebrae and dorsal fin ray in Labeo rohita (Hamilton), Catla catla (Hamilton) and Channa marulius (Hamilton)

The present study was undertaken with a view to compare the precision and reliability of the age readings obtained from different bony structures of some important freshwater teleosts viz., Labeo rohita (Hamilton), Catla catla (Hamilton) and Channa marulius (Hamilton). Standard procedures were followed to prepare and study the age structures. In L. rohita and C. marulius percent agreement between reader's age estimates was highest for scales, i.e. 96.3% and 90.5%, respectively and in C. catla percent agreement was highest (93.3%) for opercular bone. When scale ages were compared with other alternative structures viz., otoliths, opercular bone, vertebral centra and dorsal fin rays, percent agreement was found highest between scale and opercular bone age estimates (77.8%) in L. rohita and between scale and otoliths (94.8%) in C. marulius. In case of C. catla highest percent agreement was found between opercular bone and scale age estimates. In L. rohita each of the ageing structure showed significant (P < 0.05) underestimation of age in comparison to scales. In C. catla mean age estimates from opercular bone were comparable (P > 0.05) to the values obtained from all other structures except dorsal fin rays. In C. marulius mean age estimates from scales were comparable (P > 0.05) to those from all other structures except from dorsal fin rays. Results indicated scales to be the most suitable structure for ageing L. rohita and C. marulius and opercular bone for C. catla. However, in C. catla also scales may be used as a non-destructive method of age estimation with satisfactory results.