Genetic parameters for survival during the grow‐out period in the GIFT strain of Nile tilapia (Oreochromis niloticus) and correlated response to selection for harvest weight

The aims of this study were the estimation of genetic parameters for survival rate from tagging until harvest and the evaluation of the correlated response in survival rate to selection for harvest weight in the genetically improved farmed tilapia (GIFT) strain. The heritability for survival rate was low (0.038), and so was its genetic correlation with harvest weight (0.065), suggesting that selecting for the latter trait would have had no effect on survival. The calculation of the probability of survival by spawning season and line, fitting a model that included the random effects of individual animal and common environment, confirmed this prediction. There were very small and variable between line differences in the probability of survival, which generally favoured the selection line. We conclude that the focus of the GIFT programme on improving harvest weight was not detrimental to the survival of the fish during the grow‐out phase.     

Hatchery production of blue tilapia, Oreochromis aureus (Steindachner), in small suspended hapa nets

Abstract Two-year-old blue tilapia, Oreochromis aureus (Steindachner), were stocked into five replicate breeding hapas (1·2 m × 1·2 m × 2·7 m) at a density of six males and six females per hapa. At stocking, males and females averaged 415 and 225g respectively. During the 50-day trial (July-August), 62900 seed (eggs and sac-fry) representing 78 spawns, were collected from 30 females. In comparative treatments, prestocking surgical removal of the male's maxillary bone did not influence hatchery productivity. However, removal of the female's maxillary bone significantly reduced frequency of repeat spawning and clutch size (P < 0·05). Removal of the maxillary bone also influenced weight gain of broodstock. It is hypothesized that these significant responses were due to the surgical removal of the maxillary bone and the subsequent breakdown in dominance hierarchies.     

Genetic differences between sexes for morphometric traits of GIFT tilapia

The study was carried out to verify the genetic differences in the morphometric traits between male and female tilapia GIFT under the selection for weight gain. The data set used contained information of 6650 animals of the third (2198), fourth (1720) and fifth (2732) generations of GIFT in Brazil, in addition to the 8590 animals, of the first five generations, included in the relationship matrix. The morphometric traits used were standard length (SL: 19.8 ± 1.7), body depth (BD: 7.6 ± 0.76), body width (BW: 3.5 ± 0.54), body area (BA: 151.3 ± 27.6) and body volume (BV: 536.7 ± 143.5). Bicharacter analyses were performed considering the same morphometric measure evaluated for each sex as different traits to estimate the (co)variance components. The heritability and environmental common effects of the larval and fry phases for each trait of each sex were estimated. Genetic correlations between males and females for the same body trait were estimated. The larval effect was higher for females (SL = 0.1; BD = 0.07; BW = 0.05; BA = 0.09; BV = 0.09) than for males (SL = 0.04; BD = 0.03, BW = 0.01, BA = 0.04; BV = 0.03), while the fry effect was similar between the sexes. The heritability of males (SL = 0.25; BD = 0.3; BW = 0.33; BA = 0.31; BV = 0.35) was, in general, higher than those present in females (SL = 0.19; BD = 0.2, BW = 0.18, BA = 0.2; BV = 0.2), and the genetic correlations between males and females were below 0.5 (SL = 0.5; BD = 0.39, BW = 0.42, BA = 0.45; BV = 0.43). Thus, it can be seen that the males respond differently to the females in terms of body shape, of the selection for weight gain.     

Soldier fly, Hermetia illucens L., larvae as feed for channel catfish, Ictalurus punctatus (Rafinesque), and blue tilapia, Oreochromis aureus (Steindachner)

Abstract. Three feeding trials, involving pre-pupal larvae of soldier fly, Hermetia illucens L., grown on poultry manure, were conducted to assess: (1) channel catfish, Ictalurus punctatus (Rafinesque), response to substitution of dried meal larvae for the fish meal component of the catfish diet and (2) if feeding 100% whole or chopped larvae to channel catfish or blue tilapia, Oreochromis aureus (Steindachner), will support normal growth comparable to those fed a commercial diet. Effects on fish quality were also evaluated. Replacement of 10% fish meal with 10% soldier fly larvae resulted in slower growth over a 15-week period for subadult channel catfish grown in cages (trial 1). However, the replacement did not reduce growth rate significantly when channel catfish were grown in culture tanks at a slower growth rate (trial 2). Feeding 100% larvae did not provide sufficient dry matter or protein intake for good growth for either species grown in tanks (trials 2 and 3). Chopping of the larvae improved weight gain and efficiency of the utilization.     

Lack of association between Flavobacterium columnare genomovar and virulence in hybrid tilapia Oreochromis niloticus (L.) × Oreochromis aureus (Steindachner)

Columnaris disease can be problematic in tilapia (Oreochromis spp.) production. An understanding of the pathogenesis and virulence of Flavobacterium columnare is needed to develop prevention strategies. The objective of this study was to determine the virulence of genetically defined isolates of F. columnare in sex‐reversed hybrid tilapia, Oreochromis niloticus (L.) × O. aureus (Steindachner). A series of immersion challenge trials were performed using isolates of the five established genomovars of F. columnare: I, II, II‐B, III and I/II. The mean per cent mortality of fish challenged with genomovar I, II and III isolates ranged from 0 to 100, 3.3–78 and 3.3–75%, respectively. The mean per cent mortality of fish challenged with genomovar II‐B ranged from 35 to 96.7%, and the only genomovar I/II isolate tested caused no mortality. Contrary to previous work in other fish species, there did not appear to be an association between F. columnare genomovar and virulence in tilapia. The challenge model used resulted in acute mortality. An alternative challenge model was tested by cohabitating healthy fish with dead fish infected with F. columnare. This method resulted in rapid appearance of clinical signs and mortality, suggesting the potential for F. columnare to increase in virulence upon growth on/in a fish host.     

Genetic analysis of the Pacific white shrimp (Litopenaeus vannamei): heterosis and heritability for harvest body weight

The aim of this study was to estimate heterosis and heritability for harvest body weight of the Pacific white shrimp (Litopenaeus vannamei) measured at commercial farm conditions. Heterosis and heritability were estimated using a base population from diallel crosses of eight introduced strains. The base population included 9936 shrimp from 207 families that were produced with 188 sires and 172 dams using a nested mating design by artificial insemination. Heterosis was calculated basing on the least squares means (LSM) of harvest body weight. The results showed that most of the hybrids (75%) have positive heterosis for harvest body weight, which ranged from ?13.36% (UA2 × UA5) to 13.80% (UA6 × UA5) with a mean of 2.41%. The high amount of heterosis manifested in the hybrids indicated the usefulness of these hybrids for improving the growth. Variance components and heritability for harvest body weight were estimated using an animal model. The heritability estimate for harvest body weight was 0.092 ± 0.082 (h²) when genetic groups were excluded from the pedigree, but it was decreased when genetic groups were included in the pedigree ( = 0.066 ± 0.050), implying that there are strain additive genetic effect and heterosis in the base population. However, the heritability estimates for harvest body weight were significantly different from zero (P < 0.05) and there was no significant difference between h² and (P > 0.05). The results from this study indicated that significant improvement for growth is possible through cross‐breeding and selective breeding in L. vannamei.     

Structure and function of the small intestine of the tilapia Oreochromis niloticus×Oreochromis aureus (Teleostei, Cichlidae)

This study examined the microscopic structure of the small intestine and digestion and absorption in the hybrid tilapia, Oreochromis niloticus×Oreochromis aureus. The small intestine was lined on the luminal face with villi, which were narrower and more dense in the proximal small intestine and became wider and sparser distally. The columnar epithelial cells lining the villi were predominantly enterocytes containing a brush border, interspersed with mucus containing goblet cells approximately every 4–6 cells. These mucus‐secreting cells contained both acid and basic mucins and increased in density in the distal and the terminal sections of the intestine. Proliferation of enterocytes was observed in the intervillus areas and lower third of the villus. Fish were fed diets of either fish meal or fish meal–wheat to which chromic oxide had been added as a non‐absorbed reference standard. Activity of the pancreatic enzymes, lipase, trypsin and amylase were determined along the small intestine relative to the non‐absorbed marker. Activity of these pancreatic enzymes was maximal in the proximal segments and decreased distally. Changes in the activity patterns of trypsin and amylase were observed with the different diets in the proximal small intestine. Net secretion of both N and fatty acids was found in the hepatic loop and absorption commenced distally decreasing in rate with distance from the pylorus. The pattern of N absorption in the proximal small intestine changed with the different diets. The structure and function of the small intestine of the tilapian omnivore thus are generally similar to mammals and digestion and absorption adapt with diet.     

Genetic changes during mass selection for growth in Nile tilapia, Oreochromis niloticus (L.), assessed by microsatellites

Two control (C1 or first control generation, and C4 or fourth control generation) and three selected (S1 or first selected generation, S2 or second selected generation, S4 or fourth selected generation) stocks of Chitralada Nile tilapia were analysed for microsatellite variation to determine the effect of size‐specific mass selection on genetic variability. Genetic variation based on five microsatellite loci (UNH123, UNH147, UNH172, UNH222 and UNH216) showed a slightly higher allelic diversity in the selected stocks (7.4–10 alleles) than in the control stocks (6.8–8.8 alleles). Apparent reductions in the mean number of alleles and H_e values were noted in successive generations of both control and selected lines. Significant deviations from Hardy–Weinberg equilibrium because of an excess of homozygotes indicated inbreeding in all control and selected stocks. Although estimated inbreeding levels were not significantly different among selected and control lines based on Welch's t‐tests, the increase in the degree of inbreeding within the selected line was higher (107.9%) than the control line (64.2%) after four generations. The implications of these results on the management and conservation of genetic diversity in improved breeds are discussed, while the importance of monitoring and minimizing inbreeding are likewise emphasized.     

Genetic parameters for resistance against Flavobacterium columnare in Nile tilapia Oreochromis niloticus (Linnaeus, 1758)

Columnaris disease is a major cause of mortality in tilapia hatcheries and commonly occurs during the summer season in Thailand. One way of reducing the problem is by selective breeding for increased disease resistance. The objective of this study was to estimate quantitative genetic parameters for resistance against columnaris in the Chitralada 4 strain of Nile tilapia. Data from 43 full‐sib families (2,580 records) of fry (age = 32 ± 4 days post‐hatch) were used in the analyses. Initially, fry were subjected to bath challenge with Flavobacterium columnare (LD₅₀ concentration = 1.2 × 10⁶ CFU/ml) for 14 days. Disease resistance was defined as the number of days from challenge until death (DD) or as a binary trait (dead/alive) on day 14. Linear animal and sire‐dam models were used for DD, while threshold animal, threshold sire‐dam, binary linear animal and binary linear sire‐dam models were used for binary outcomes. Covariate effect of age, fixed effect of challenge day and random effects of the individual animals or sires and dams were included in the models. Mean survival was 32.4 ± 11.6%, and survival rates of the best and poorest families were 70% and 8%, respectively. The highest estimate of heritability (0.30 ± 0.025) was obtained under the threshold sire‐dam model. Heritability estimates for DD (0.16 ± 0.034 and 0.17 ± 0.046) were comparable to those obtained from the threshold animal (0.15 ± 0.031) and the binary linear (0.14 ± 0.045 and 0.15 ± 0.044) models. The linear animal and sire‐dam models for DD and the threshold sire‐dam models performed equally with similar values of r_EBV (0.629, 0.628 and 0.627) and accuracy of selection (0.793, 0.793 and 0.791). This study reveals the potential of selective breeding to increase disease resistance to F. columnare in the studied population of Nile tilapia.     

Relative performance of two Nile tilapia ( Oreochromis niloticus Linnaeus) strains in Egypt: The Abbassa selection line and the Kafr El Sheikh commercial strain

The Abbassa selection line (developed by selective breeding) and the Kafr El Sheikh commercial strain (widely used in Egypt), both Oreochromis niloticus, were compared at two stocking densities (two and four fish m^?2). Harvest weight, length, depth, width and head length were recorded. The Abbassa line showed a superior harvest weight (28 per cent) over the Kafr El Sheikh strain. Males were heavier than females, but the between‐sex difference was greater in the commercial than in the Abbassa line (39 and 31 per cent respectively). Females in the Abbassa line grew almost as fast as males in the commercial line. Both strains grew faster at the lower density, and the percentage reduction in harvest weight at the higher density was about the same for both strains (27 per cent). The advantage of the Abbassa line was 28 per cent at both densities. Both strains had a similar survival rate (approximately 80 per cent) during the grow‐out period. We conclude that the Abbassa line is ready for release to the tilapia industry in Egypt. Further evidence is being sought in currently underway on‐farm evaluations. Measures should be taken to ensure the long‐term viability of the Abbassa line.     

Effects of non-starch polysaccharides enzyme, phytase and citric acid on activities of endogenous digestive enzymes of tilapia (Oreochromis niloticus × Oreochromis aureus)

Non-starch polysaccharides (NSPs) enzyme, phytase and citric acid have been shown to increase digestibility in pigs, poultry and some fish. To examine their roles in digestion in tilapia ( Oreochromis niloticus  ×  Oreochromis aureus ), the present study was designed to evaluate their effects on activities of a number of endogenous digestive enzymes in tilapia. Neither NSPs enzyme (1 g kg⁻¹) nor phytase (1 g kg⁻¹) affected the activities of protease in digestive organs. In contrast, NSPs enzyme increased the activities of amylase in the hepatopancreas and intestine by 11.4% and 49.5%, respectively, while phytase (1 g kg⁻¹) increased the activities of amylase in the hepatopancreas and intestine by 14.0% and 24.1%, respectively. Citric acid (10 g kg⁻¹) increased the activities of protease in stomach by 29.6%, but reduced the activities of protease in the intestine by 35.1%. Citric acid increased the activities of amylase in the hepatopancreas and intestine by 30.7% and 29.4%. Lipase activities were not affected by NSPs enzyme, phytase or citric acid. Above results suggest that NSPs enzyme, phytase and citric acid primarily influence the activities of amylase in digestive tract of tilapia.     

Comparison of the pathogenicity of Francisella orientalis in Nile tilapia (Oreochromis niloticus), Asian seabass (Lates calcarifer) and largemouth bass (Micropterus salmoides) through experimental intraperitoneal infection

Francisella orientalis is a highly virulent, emerging bacterium that causes mass mortalities in tilapia. This pathogen also affects numerous other warm-water fish species, including three-line grunt, hybrid striped bass and various ornamental fish. This study sheds light on two new species of fish that are susceptible to F. orientalis. Asian seabass and largemouth bass showed variable levels of susceptibility in a bacterial challenge experiment. After intraperitoneally injected with a dose of 10⁶ CFU/fish, a total of 64.28% and 21.42% mortalities were obtained in Asian seabass and largemouth bass, respectively. Meanwhile, Nile tilapia showed acute mortality of 100%. All fish showed typical lesions of francisellosis, including multifocal granulomas in the spleen and head kidney. Immunohistochemical analysis revealed strong positive signals inside the granulomas of all fish. The bacterial recovery in solid media from infected fish was highest in Nile tilapia (85.71%), followed by Asian seabass (35.71%) and largemouth bass (21.42%). PCR results tested 100% positive for Nile tilapia, and 78.57% and 21.42% for Asian seabass and largemouth bass, respectively. In conclusion, Asian seabass and largemouth bass are susceptible to this pathogen, which warrants new management strategies when employing predation polyculture systems of these species with tilapia.     

In vivo and in vitro assessment of Lactobacillus acidophilus as probiotic for tilapia (Oreochromis niloticus,Perciformes:Cichlidae) culture improvement

In this study, the use of Lactobacillus acidophilus as a probiotic for Nile tilapia (Oreochromis niloticus) culture was studied. Fish survival and the expression of some genes involved in the immune response were assessed. Diet supplementation with L. acidophilus for 15 days caused a significant increase in fish survival during a challenge with Aeromonas hydrophila and variations in immune response related to IL‐1β and transferrin expression in Nile tilapia spleen and kidney. Moreover, extracellular products (ECPs) of L. acidophilus showed high antibacterial activity against fish pathogens such as A. hydrophila and Streptococcus agalactiae in vitro. It was also observed that viable L. acidophilus was able to disrupt quorum sensing activity in Chromobacterium violaceum.     

Genetic parameters and response to selection for harvest body weight of pacific white shrimp,Litopenaeus vannamei

Genetic parameters and response to selection were estimated for the harvest body weight of Litopenaeus vannamei. The data consisted of 24 072 progeny from 178 sires and 171 dams in two generations (G₀ and G₁) with a nested mating structure. All families were randomly divided into two groups and then cultured in two farms at different locations (Huanghua and Qingdao). The heritability estimates from G₀ and G₁ were 0.278 ± 0.136 and 0.423 ± 0.065 respectively. Over two generations, the heritability estimate was 0.335 ± 0.087, and the common environmental effect was 0.084 ± 0.031. A bivariate animal model was used to estimate variance and covariance components, whereby the body weight in the two farms was treated as a genetically distinct trait. Genetic correlation was close to unity (0.943 ± 0.066), indicating that a genotype by environmental interaction for harvest body weight was small. The response to selection in harvest body weight was estimated using two methods (the realized and predicted responses). The realized response was estimated from the difference in the least squares means of body weight for the selection and control populations. The predicted response was obtained from the difference in the mean estimated breeding values between generations. The realized response was 2.30%, while the predicted responses were 2.00% and 1.37% for within‐ and across‐generation datasets using two sets of genetic parameters respectively. The results would provide crucial information in pacific white shrimp breeding programs in China.     

Genetic parameters for loin eye area and other body traits of an important Neotropical aquaculture species,Colossoma macropomum (Cuvier, 1818)

Estimating components of variance and genetic parameters of economically relevant traits is the first step towards planning a breeding program for aquaculture species. This study estimated the (co)variance components for growth rate and other body traits and then determined a multiple regression equation to assess the loin eye area (LEA) from morphometric traits of the Neotropical aquaculture species Colossoma macropomum. Estimation of variance components was performed using derivative‐free restricted maximum likelihood estimation using the MTDFREML package. Six predictive variables were tested to estimate the coefficient of regression equation and to select the most suitable model for predicting LEA. The estimated genetic parameter for body weight showed moderate‐to‐high heritability estimates of 0.26 (0.01) and 0.49 (0.01) at 221 and 623 days respectively. The genetic correlation (r_g) estimates between body size measurements were positive and ranged from low to high at both ages. The heritability for LEA in this assessment was 0.39 (0.03). The genetic and phenotypic correlations between LEA and the other body measurements ranged from 0.16 to 0.94 and 0.75 and 0.90 respectively. The outcomes of this study can contribute to the development of a genetics‐based breeding program that will improve (tambaqui) productivity and carcass quality.     

盐度对奥尼罗非鱼仔稚鱼生长、存活及其消化酶活力的影响

研究了不同盐度对奥尼罗非鱼仔、稚鱼生长、存活和消化酶活力的影响。试验设计2、4、6、8、10和纯净淡水0（对照组）共6个盐度梯度组,仔鱼的初始体重0.0080.001 g。结果表明,不同盐度对奥尼罗非鱼仔、稚鱼生长有显著差异（P0.05）,盐度4和6时,仔、稚鱼的生长速度和绝对增重率最高,分别为0.08 cmd-1和0.033 gd-1;盐度10时较低,只有0.06 cmd-1和0.023 gd-1;仔、稚鱼的肥满度介于3.43~3.81,各组之间差异不显著（P0.05）;盐度0~10时,各组存活率介于92.3%~94.7%,幼鱼所占比例介于66.0%~67.3%,各组之间差异不显著（P0.05）;胃蛋白酶和胰蛋白酶活力随盐度升高而降低,均在盐度0时活力最高,10时最低;脂肪酶和淀粉酶活力在盐度4时达到最高,10时活力最低。根据试验结果,奥尼罗非鱼仔、稚鱼培育的盐度最好控制在4.6左右。     

Antimicrobial susceptibility and enrofloxacin resistance of streptococcal bacteria from farmed Nile tilapia,Oreochromis niloticus (Linnaeus 1758) in Thailand

This study examined the antimicrobial susceptibility and mutation(s) in quinolone resistance‐determining regions (QRDRs) in streptococcal pathogens isolated from farmed Nile tilapia Oreochromis niloticus in Thailand. Surveillance of antimicrobial susceptibility in tilapia streptococcal pathogens reveals that Streptococcus agalactiae (n = 97) and Streptococcus iniae (n = 3) from diseased tilapia were susceptible to amoxicillin, florfenicol, sulfamethoxazole/trimethoprim and sulfadimethoxine/ormetoprim, however, only 78 isolates were susceptible to enrofloxacin. Twenty‐two enrofloxacin‐resistant S. agalactiae isolates were further examined for mutations in the QRDRs of gyrA, gyrB, parC and parE genes. Twenty isolates had single base pair changed in the gyrA sequence, C‐242‐T. Point mutations in gyrB, GC‐1135, 1136‐AA and T‐1466‐G, were identified in one isolate. All resistant isolates harboured a mutation in the parC gene, C‐236‐A, while no mutations were observed in the parE gene. The study represented mutations of gyrA and parC genes as marked modification of the enrofloxacin‐resistant S. agalactiae from farmed tilapia. This study is a primary report of the QRDRs mutations associated with fluoroquinolone resistance from streptococcal pathogen in the cultured fish. The phenotypic and genotypic characterization of enrofloxacin resistance S. agalactiae evident in this study has led to an improved regulation of antimicrobial use in Thai aquaculture.     

Effects of replacing soybean meal with rubber seed meal on digestive enzyme activity,nutrient digestibility and retention in tilapia (Oreochromis niloticus × Oreochromis aureus)

A feeding trial was conducted to evaluate the effects of replacing soybean meal (SBM) with rubber seed meal (RSM) on digestive enzyme activity, nutrient digestibility and retention in juvenile tilapia (Oreochromis niloticus × Oreochromis aureus). Five isonitrogenous and isoenergetic diets were formulated with 0 (control), 100, 200, 300 and 400 g kg⁻¹ RSM replacing graded levels of SBM respectively. Each diet was randomly assigned to triplicate groups of 30 fish (initial average weight 5.2 g) per aquarium in a rearing system maintained at 29 ± 1°C for 8 weeks. The hepatic protease and lipase activities gradually decreased with increasing dietary RSM level, but no significant differences were observed among the low inclusion level (0–200 g kg⁻¹) groups. The apparent digestibility coefficients of dry matter, crude protein, crude lipid and ash showed a similar trend as the hepatic protease and lipase activities. The retentions of protein and individual essential amino acid (except lysine, threonine and leucine) in fish fed diet with 200 g kg⁻¹ RSM were similar to those in fish fed the control diet. These results indicate that dietary RSM inclusion level up to 200 g kg⁻¹ did not markedly affect the digestive enzyme activity, nutrient digestibility and retention in tilapia, whereas these were depressed by the inclusion of 400 g kg⁻¹ RSM.