Comparative studies on survival and growth performance among diploid,triploid and tetraploid dojo loach <Emphasis Type="Italic">Misgurnus anguillicaudatus</Emphasis>

To determine the cytotype with better traits for the aquaculture practices of the dojo loach Misgurnus anguillicaudatus from the viewpoint of fish farming improvement, factorial crosses (2n♀ × 2n♂, 2n♀ × 4n♂, 4n♀ × 2n♂, 4n♀ × 4n♂) were conducted between natural diploids (D) and tetraploids (T), producing DD, DT, TD, and TT groups (female listed first). The potential benefits of the different cytotypes in culture were evaluated by comparing growth performance and survival rate for a 15-month rearing trial under the same production conditions. The average fertilization rate in DT and TT was significantly lower than in the DD and TD groups, possibly indicating the poor fertilizing capacity of the tetraploid sires. Survival rate in DT and TD was slightly lower than in DD but significantly higher than in the TT groups. Tetraploid females produced obviously larger eggs than diploids and, subsequently, significantly longer initial body length of TT and TD than DD and DT fry. However, from the second month of the growth trial, TT suffered higher mortality than other cytotypes, which significantly influenced morphometric growth parameters. The TD group exhibited superior growth performance throughout the experiment. The mean body length of DT was comparable with that of DD fish during the first 7 months but began to outgrow DD from the 9th month. This study suggests that the relatively better growth of tetraploid and higher survival rate of diploid can be integrated via inter-ploidy hybridization to get TD triploids with better culture traits.     

Triploidization in rohu × mrigal hybrid and comparison of growth performance of triploid hybrid

The present study was aimed at the identification of treatment optima to induce triploidy in ‘Labeo rohita (rohu) × Cirrhinus cirrhosus (mrigal)’ hybrid using heat shock treatment. The eggs were exposed at four different temperature regimes viz., 38, 39, 40 and 41°C for 1–3 min, applied 3–5 min after fertilization. After 4 min of fertilization, heat shock treatments for 1 and 1.5 min durations were found the best inducing triploidy up to 100% and 96% respectively. Survival rates upto yolk sac absorption were found to be 73% and 71% in rohu and mrigal, 68% and 67% in the reciprocal diploid hybrids and 61% and 60% in the reciprocal triploid hybrids (RTH). Triploidy was confirmed by chromosome counting that revealed the diploid chromosome number of rohu and mrigal at 2n = 50 and in their triploid hybrid chromosome number was found to be 3n = 75. Growth rate of the RTH showed a significant difference (P < 0.05) from the single species and the diploid hybrids. Triploids also showed higher survival rate over the diploids.     

Identification of growth‐related nucleotide polymorphism in cultured Pacific bluefin tuna,Thunnus orientalis

Pacific bluefin tuna (PBF), Thunnus orientalis, is commercially one of the most important species of tuna. In this study, amplified fragment length polymorphism (AFLP) screening was conducted to find the growth‐related polymorphic DNA in cultured PBF. Fish hatched in 2007 were harvested at an age of 818–1994 days. They were categorized into superior, average and inferior growth groups, depending on their growth score at the time of harvest. On AFLP screening of 24 fish, with eight fish from each group, 215 polymorphic DNA fragments were observed. A second amplification, with EcoRI + ACC and MseI + CCC primers, generated a polymorphic fragment of 630 bp at a rate of 80.0% (n = 15) in the superior, 56.3% (n = 16) in the average and 20.0% (n = 15) in the inferior growth groups. Polymerase chain reaction (PCR) primers, which could amplify both AFLP‐positive and AFLP‐negative loci, were developed using the consensus sequence outside the AFLP target fragment. Eleven haplotypes were obtained by sequence analysis of the PCR product at the AFLP target loci. Among those, haplotype 1 was statistically significant in the superior and average growth groups and could be used as a molecular marker for distinguishing the individuals with superior and average growth from those with inferior growth.     

Riverine and fjord migration of wild and hatchery‐reared Atlantic salmon smolts

Migration timing, speed, survival and effects of environmental parameters on migration, between wild and hatchery produced Atlantic salmon, Salmo salar L., smolts in the River Lærdalselva were studied. Hatchery‐reared (n = 40) and wild pre‐smolts (n = 40) were tagged with acoustic tags, and an array of receivers along the migration route was deployed. In all, 77 and 85% of the fish from the two groups, respectively, were recorded as migrating smolts, that is, predation rate and/or numbers of fish opting to remain in the river were low. Hatchery‐reared smolts showed a migration pattern, speed and migration route similar to wild smolts, even though the time period between river release and onset of migration was relatively short. Both groups of smolt showed high migration speed through both the river and the fjord compared with other studies.     

Effects of dietary astaxanthin on the growth,innate immunity and antioxidant defence system of Paramisgurnus dabryanus

The effects of astaxanthin supplementationon the growth, innate immunity and antioxidant defence system of loach (Paramisgurnus dabryanus) were investigated in this study. A total of 450 fish (initial average weights of 3.00 ± 0.10 g) were fed five diets with graded levels of astaxanthin (0.00, 50.00, 100.00, 150.00 and 200.00 mg/kg) for 56 days. The results showed that astaxanthin supplementation significantly stimulated the growth (FBW, WG, FER, HSI), innate immunity (AKP activity in the hepatopancreas, intestinal tract, muscle and skin and LZM activity in the hepatopancreas, intestinal tract and skin), antioxidant ability (T‐SOD, GSH‐PX and CAT activities and T‐AOC, GSH and MDA contents in the hepatopancreas, intestinal tract, muscle and skin) of loach. Moreover, dietary astaxanthin supplementation significantly up‐regulated the relative mRNA levels of Nrf2 and Maf, and down‐regulated the relative mRNA level of Keap1 in the hepatopancreas when the supplementation levels of astaxanthin were 50–200 mg/kg. In conclusion, the diets with 100–151.06 mg/kg astaxanthin supplementation were optimal for loach, which based on the growth, immunity and antioxidant‐related indicators, and the astaxanthin supplementation regulated the antioxidant ability partially referring to Keap1‐Nrf2 signallings.     

Improvement of reproductive indices,lysozyme activity,and disease resistance in live‐bearing ornamental fish,Poecilia latipinna using Artemia supplementation with treated yeast cell,Saccharomyces cerevisiae

In the present study, the effects of Artemia supplemented with 2‐β‐mercapto‐ethanol (β‐ME) treated yeast cell, Saccharomyces cerevisiae, on growth and reproductive performance, lysozyme activity, and disease resistance to Aeromonas hydrophila of freshwater ornamental species, Poecilia latipinna, were investigated. Within 60 days, molly fish were fed with three treatments including commercial food (T1), un‐supplemented Artemia (T2), and Artemia supplemented with β‐ME‐treated yeast cell (at concentration of 4 × 10⁷ CFU/L of water) (T3). After the feeding period, the fish were exposed to 100 μl of a suspension (1.1 × 10⁷ cells/ml) of A. hydrophila (BCCM5/LMG3279) and the cumulative mortality rates were recorded for 12 days. No significant difference was found between survival rate and growth performance of P. latipinna except for weight gain that was higher in fish fed through Artemia supplemented with β‐ME‐treated yeast cell compared to control group. Fecundity rate was significantly improved in fish fed using T3 with the maximum amount of 49.5 ± 2.29 per female (p < 0.05). Besides, lysozyme activity was significantly increased in group 3 (p < 0.05). Moreover, lowest fish mortality was significantly observed in this treatment (p < 0.05). In addition, the number of colonies formed by yeast cell in T3 (634 × 10³ CFU/g intestine) showed significant difference with other treatments (p < 0.05). In sum, Artemia enriched with β‐ME‐treated yeast improved reproductive indices, immune responses, and resistance against A. hydrophila of P. latipinna.     

Heterosis analysis at early generations for complete diallel crosses in three different geographical culture populations of Sinonovacula constricta (Lamarck 1818) in Zhejiang,China

The paper reports a study focused on breeding new rapidly growing and heat‐tolerant strains in a commercially important Asian bivalve, Sinonovacula constricta. To breed a new strain of S. constricta with fast growth and high temperature tolerance, complete diallel crosses were carried out using three different geographical culture populations from Zhejiang (Z), Fujian (F) and Guangdong (G) provinces, China. Larval and spat growth and the survival and heat tolerance of spats were compared in detail. The experimental serial growth traits extracted from larval and spat measurements (shell length and shell height) indicated that there was no difference between six hybrid crosses and parental crosses at the larval stage; while at the spat stage, some differences were observed. The hybrid crosses ZF (Z♀ × F♂), ZG (Z♀ × G♂) and FG (F♀ × G♂) outperformed the parental groups in shell length at the end of intermediate culture, with lengths of 21.77 ± 0.28 mm, 21.55 ± 0.29 mm and 21.44 ± 0.20 mm respectively. For spat survival rate, the hybrid cross ZF (Z♀ × F♂) had a significantly larger value (88.89 ± 4.16%) than all the other groups, and the hybrid cross ZG (Z♀ × G♂) had a significantly larger rate than the cross GZ (G♀ × Z♂) and parental crosses ZZ (Z♀ × Z♂) and GG (G♀ × G♂). The hybrid crosses ZF (Z♀ × F♂), ZG (Z♀ × G♂) and FG (F♀ × G♂) exceeded the parental groups in heat tolerance, but there was no significant difference. The growth, survival and heat tolerance results showed that the crosses ZF, ZG and FG in this study were the best hybridization combinations for genetic improvement, which could have significant implications for the development of razor clam aquaculture. This work provides a theoretical basis for breeding new varieties (strains) that grow rapidly and are heat tolerant.     

The obvious heterosis and genetic characters of intergeneric cross and backcross juveniles between blunt snout bream (Megalobrama amblycephala) and topmouth culter (Culter alburnus)

In this study, we used artificial insemination to generate hybrid groups of fish [MC‐F₁(MA♀×CA♂) and MC‐F₂(MC‐F₁♀×♂)] by intergeneric crosses of Megalobrama amblycephala (MA) and Culter alburnus (CA); sequential backcrosses [CAM‐B₁ (CA♀×MC‐F₁♂) and MCC‐B₁ (MC‐F₁♀×CA♂)] were also performed. All these hybrids showed high rates of fertilization, hatching and survival (p > 0.05). For genetic traits, compared with those of the M. amblycephala and C. alburnus parental lines (Table 1), the fertilization rate, hatching rate and 7‐day survival rate of MC‐F1(MA♀×CA♂), MC‐F2(MC‐F1♀×♂), CAM‐B1 (CA♀×MC‐F1♂) and MCC‐B1 (MC‐F1♀×CA♂) by artificial insemination exhibited similar high rates (p > 0.05). The morphology of the four hybrids MC‐F₁/F_2, CAM‐B₁ and MCC‐B₁ were intermediate between those of their parents. Compared with their parents of MA and CA, weight gain rate (WG), specific growth rate (SGR) and protein efficiency ratio (PER) of hybrids MC‐F₁/F₂, CAM‐B₁ and MCC‐B₁ were significantly (p < 0.05) increased and feed conversion ratio (FCR) was significantly (p < 0.05) decreased after 3 months feeding. Moreover, protein content of muscle for MC‐F₁/F₂, CAM‐B₁ and MCC‐B₁ was significantly (p < 0.05) higher and carbohydrate content of muscle was significantly (p < 0.05) lower than their parents. The females and males of the four hybrids had normal gonadal development. In this study, we successfully generated intergeneric and backcross hybridization lines with fertile potential among fish of the Cultrinae subfamily and these hybrids had obvious heterosis in terms of growth performance, feed utilization and muscle quality.     

Survival,male morphotypes,female and male proportion,female reproductive status and tag loss in crosses among three populations of freshwater prawn Macrobrachium rosenbergii (de Man) in India

The present study examined the variation in survival, proportion of male morphotypes, female and male proportion, female reproductive status and tag losses in nine crosses from a complete (3 × 3) diallel mating of three populations of Macrobrachium rosenbergii in India. The populations originated from Gujarat (north‐west), Kerala (south‐west) and Odisha (east), representing different agro‐ecological regions in India. Progeny from 60 families (4773 juveniles) were individually tagged and reared for 16–17 weeks in earthen ponds. Binary logistic regression was used to analyse the data. Survival rate was greatest (0.88) for Kerala × Odisha (KO; the first letter represents the sire), whereas it was lowest (0.75) for both Kerala × Kerala (KK) and Gujarat × Kerala (GK). Significantly greater proportions of large male morphotypes were observed in KK cross and in combinations involving Kerala population. The highest proportion of immature females, as well as of non‐berried females, was observed in the Odisha × Odisha (OO) cross. Tag loss was greatest for KK (0.35) and lowest for GG (0.19). We found significant variations among crosses for all studied traits suggesting the possibility of including them in genetic improvement programmes of this species.     

Effect of farming patterns on growth,antioxidant activity and nonspecific immunity of loach,Paramisgurnus dabryanus

This study was carried out to compare growth, intestinal enzymes activity, antioxidation and nonspecific immunity of loach between farmed and imitative ecological farming loach, Misgurnus anguillicaudatus. Loach from farmed (average body weight 15.03 ± 0.36 g) and imitative ecological farming (average body weight 12.44 ± 0.62 g) population were used to analyse growth, whole-body composition, intestinal enzymes, antioxidant enzymes activity and resistance to bacteria. The results showed specific growth rate, average daily gain and protease, lipase, amylase and γ-GT activities in intestine and hepatopancreas of farmed loach were significantly higher (p < 0.05) than of imitative ecological farming loach. However, total protein, lysozyme and albumin contents and superoxide dismutase, catalase and glutathione peroxidase activities of imitative ecological farming loach were significantly higher (p < 0.05) than of farmed loach. Moreover, resistance to Aeromonas hydrophila of imitative ecological farming loach was higher than of farmed loach (p < 0.05). Taken together, ecological farming loach possesses higher antioxidant capacity and resistance to bacteria than farmed loach.     

Effects of vitamin E supplementation on growth,lipid peroxidation and fatty acid composition of Dojo loach (Misgurnus anguillicaudatus Cantor) fingerlings

A high mortality of cultured loach during their early development has constrained loach aquaculture industry in China. The objective of this study was to evaluate the effects of dietary vitamin E (VE) supplementation on growth performance, lipid peroxidation and fatty acid composition of loach Misgurnus anguillicaudatus fingerlings. Six test diets supplemented with 0 (0E), 50 (50E), 100 (100E), 150 (150E), 200 (200E) and 500 mg kg^?1 (500E) of dl‐α‐tocopheryl acetate were fed loach fingerlings (mean initial weight 24.0 ± 0.2 mg) in triplicate for 40 days. Results showed that the fish fed diet 100E and 200E had significantly higher body weight gains and specific growth ratios and significantly lower feed conversion ratios compared with fish fed diet 0E. With the increase in dietary VE level, whole‐body VE content was significantly increased (except 500E) and thiobarbituric acid reactive substances value was significantly reduced. Increasing dietary VE level increased the percentages of 20:4n‐6 and 20:5n‐3 in neutral lipid fraction, but decreased the percentages of 20:4n‐6 and 20:5n‐3 in polar lipid fraction. In conclusion, VE requirement of loach fingerlings for optimum growth and functionally preventing lipid peroxidation was 136.1 mg kg^?1 of dry diet under the present experimental conditions.     

Effects of dietary n‐3 to n‐6 fatty acid ratios on spawning performance and larval quality in tongue sole Cynoglossus semilaevis

This study investigated the effect of n‐3 to n‐6 fatty acid ratios in broodstock diets on reproduction performance, fatty acid composition of eggs and gonads of tongue sole Cynoglossus semilaevis. Broodstock were fed five isonitrogenous and isoenergetic diets for 60 days. The supplemented lipids were prepared by a combination of fish oil and soybean oil inclusion FO (fish oil); FSO1 (fish oil: soybean oil = 7:1); FSO2 (fish oil: soybean oil = 2.2:1); FSO3 (fish oil: soybean oil = 1:1); FSO4 (fish oil: soybean oil = 1:4.3) as lipid sources with different n‐3 to n‐6 fatty acid ratios 10.40, 5.21, 2.81, 1.71 and 0.87. Results showed that relative fecundity, fertilization rate and survival rate of larvae at 7 days posthatching were all higher in broodstock fed FSO1 and FSO2 diet and significantly (P < 0.05) decreased in groups fed FSO3 and FSO4 diets. The best result in starvation tolerance test was obtained in FSO2 diet. The present study suggests that n‐3 and n‐6 PUFA ratio in broodstock diet has a considerable effect on spawning performance, egg and larval quality for C. semilaevis.     

Reciprocal Hybrids among Diploid,Tetraploid Dojo Loach,Misgurnus anguillicaudatus,and Large‐scale Loach,Paramisgurnus dabryanus: Fertilization,Survival and Growth Performance

To determine the genotype with better traits for aquaculture practices of the loach, factorial crosses were made among diploid (D), tetraploid (T) dojo loach, Misgurnus anguillicaudatus, and large‐scale loach, Paramisgurnus dabryanus (P), producing DD, DT, DP, TD, TT, TP, PD, PT, and PP genotypes (female listed first). The growth performance and survival of different genotypes in culture were evaluated through a 48‐wk rearing trail. The average fertilization rate in genotypes with P. dabryanus as female parental was significantly higher than those of M. anguillicaudatus as female parental. The average fertilization level of sperm from P. dabryanus was about the same as diploid M. anguillicaudatus but significantly higher than tetraploid M. anguillicaudatus. The highest survival rate was found in DD group (52.77%) and PP group (50.31%) (P > 0.05). The intergenetic crosses between P. dabryanus and M. anguillicaudatus, especially for PD (19.05%), DP (17.89%), and PT (15.44%) groups, exhibited poor survival rates. Under the similar rearing conditions, PP group showed significant growth advantage. Growth rates of the interspecific hybrid progenies were found to be intermediate in comparison with the parental species. According to these results, the PP genotype is more suitable for aquaculture practice .     

A novel 79‐bp insertion/deletion polymorphism in 3′‐flanking region of IGF‐I gene is associated with growth‐related traits in common carp (Cyprinus carpio L.)

Insulin‐like growth factor‐I (IGF‐I) participates in the modulation of the cellular development, differentiation and proliferation in various vertebrate tissues. Therefore, variations in IGF‐I gene are good candidates as growth regulators. In this study, a novel 79‐bp insertion/deletion (I/D) polymorphism was identified in 3′‐flanking region of IGF‐I gene by polymerase chain reaction (PCR) and sequencing approaches in common carp Cyprinus carpio. To gain insight into the association of the 79‐bp I/D polymorphism with growth‐related traits, a total of 747 individuals from Heilongjiang carp Cyprinus cario haematopterus (YL) (n = 263), selective line of German mirror carp Cyprinus carpio L. mirror (JL) (n = 229), and cold‐resistance line of Hebao red carp Cyprinus carpio var. wuyuanensis (HL) (n = 255) were genotyped. The DD genotype of the polymorphism was significantly associated with higher body length (135), body weight (325, 385, and 445 days), net weight (445 days) and lower overwintering body loss rate in JL. In addition, in pooled population (YL+JL+HL), fish with DD genotype also showed significantly higher body weight (445 days) and net weight (445 days) than those with II genotype. Taken together, these results suggest that the novel polymorphism in IGF‐I gene could be considered as a potential genetic marker for selection of growth performance in common carp.     

Androgenetic haploid Japanese pufferfish (Takifugu rubripes) induced by cold shock

Here, we explored cold‐shock‐induced haploid androgenesis in Japanese pufferfish (Takifugu rubripes) and analysed chromosomes by fluorescence in situ hybridization (FISH), single nucleotide polymorphism (SNP) in sex determination locus and microsatellite genotypes to verify all‐male inheritance. We also observed early embryonic development to have an insight into the cytological mechanism of cold‐shock‐induced gynogenesis. The chromosome number of control group was diploid (2n = 44), while in cold‐shock group haploid (1n = 22) and triploid (3n = 66) embryos were detected. Cellular DNA content flow cytometry showed that the rate of haploid induction was 90%. One signal of nucleolar organizing region (NOR) was detected by silver nitrate staining and FISH using rDNA probe in androgenetic haploids from cold‐shock group. SNP analysis revealed that about half of haploid embryos examined had the G genotype indicating male‐specific Y chromosome. Microsatellite genotyping showed that 26 out of 29 haploid embryos from cold‐shock group exclusively inherited paternally derived genotypes. Cytological observation revealed that both second polar body and egg nucleus were located on the blastodisc surface at 60 min post fertilization in cold‐shock group, suggesting simultaneous extrusion of both nuclei.     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.     

Long‐chain polyunsaturated fatty acid metabolism in carnivorous marine teleosts: Insight into the profile of endogenous biosynthesis in golden pompano Trachinotus ovatus

Golden pompano Trachinotus ovatus is an important farmed carnivorous marine teleost. Although some enzymes for long‐chain polyunsaturated fatty acid (LC‐PUFA) biosynthesis have been identified, the ability of T. ovatus for endogenous biosynthesis is unknown. Here, we evaluated in vivo LC‐PUFA synthesis in a 56‐day culture experiment using six diets (D1–D6) formulated with linseed and soybean oils to produce dietary linolenic/linoleic acid (ALA/LA) ratios ranging from 0.14 to 2.20. The control diet (D0) used fish oil as lipid source. The results showed that, compared with the corresponding indices of fish fed D0, the weight gain rate and specific growth rate as well as the contents of eicosapentaenoic (EPA) and docosahexaenoic acids in tissues (liver, muscle, brain and eye) of D1–D6 groups were significantly lower (p < .05). These data suggested that T. ovatus could not synthesize LC‐PUFA from C₁₈ PUFA or such ability was very low. However, tissue levels of 20:4n‐3 in fish fed diets D1–D6 were higher than that of D0 fish (p < .05), and positively correlated with dietary ALA/LA ratio, while levels of EPA showed no difference among the D1–D6 groups. These results indicated that Δ5 desaturation, required for the conversion of 20:4n‐3 to EPA, may be lacking or very low, suggesting incomplete LC‐PUFA biosynthesis ability in T. ovatus.     

Effects of dietary probiotic Lactobacillus plantarum and whey protein concentrate on the productive parameters,immunity response and susceptibility of Nile tilapia,Oreochromis niloticus (L.), to Aeromonas sobria infection

Immunostimulatory feed supplements have an increasingly interest in aquaculture management. Generally, an individual supplement was used in fish diets but it is expected that the use of multi‐supplements may show synergistic enhancements in fish performance, health, and immunity. Therefore, the present investigation was carried out to evaluate the use of dietary probiotic Lactobacillus plantarum and whey protein concentrate (WPC) in practical diets for Nile tilapia, Oreochromis niloticus. Hence, probiotic L. plantarum, WPC and their mixture were incorporated into a basal fish diet (300 g/kg crude protein) as follows: T1 = a basal control diet, T2 = a basal diet containing L. plantarum, T3 = a basal diet containing 1.0 g WCP/kg diet and T4, T5 or T6 = basal diets containing probiotic L. plantarum + 1.0, 2.0 or 3.0 g WCP/kg diet, respectively. Fish (15.2 ± 0.6 g) were fed on one of the tested diets up to apparent satiation twice a day for 60 days. After that, fish were intraperitoneally injected with pathogenic bacteria Aeromonas sobria and fish mortality was observed for 10 days postchallenge. Fish growth and feed intake were significantly improved by dietary probiotic L. plantarum (T2) and/or WPC (T3) over the control group (T1), and highest fish performance was observed in T5–T6 fish groups. Similarly, highest values of haematocrit, glucose, total proteins, albumin, and globulin were significantly observed in T5–T6 fish groups. Likewise, fish fed dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) showed antioxidants and immune‐stimulating activities better than the control group. Fish fed the control diet were more susceptible to A. sobria infection showing highest fish mortality (75.0%). Meanwhile, dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) enhanced significantly the fish resistance to A. sobria infection resulting in maximum values of relative percent of fish survival (73.3%–80.0%) in T5–T6 groups. The present investigation recommended the use of probiotic L. plantarum with 2.0 g WPC/kg diet to improve the growth, antioxidant, immunity responses and tolerance of Nile tilapia to A. sobria infection.     

The effects of temperature and photoperiod on egg hatching success,egg production and population growth of the calanoid copepod,Acartia grani (Calanoida: Acartiidae)

Calanoid copepods, including species of the genus Acartia, are commonly used as larval diets for marine finfish. This study aimed to determine the separate effects of water temperature (18, 22, 24, 28° ± 0.5°C) and photoperiod (24L:0D; 18L:6D; 12L:12D; 8L:18D; 0L:24D) on Acartia grani egg production (EP), hatching rate (EHR) and population growth. Egg production rate was not affected by the two abiotic parameters. A. grani eggs incubated at T24°C and T28°C were the first to achieve 50% hatching rate (23–25 hr), with significant differences at the end of the experiment (48 hr) between T28°C treatment (EHR 88 ± 5%) and T18°C treatment (EHR 65 ± 2%). However, different temperature regimes did not affect final number of individuals in population growth experiment. Still, when eggs were excluded from data, population at lower temperatures (18°C) was mainly composed by the nauplii stage (72%), while at higher temperatures (24°C and 28°C) more than 60% of the population was composed by copepodites and adults. A. grani subjected to long‐day photoperiods had significantly lower EHR (16.7% at 24L:0D; 20.8% at 18L:6D) than at short‐day photoperiods (52.6% at 6L:18D; 50.0% at 0L:24D). In population growth experiment, eggs were the most common life stage after 12‐day culture. Lowest population number was found at constant light conditions (665.0 ± 197.1), suggesting higher metabolic rates and depletion of energy reserves in long‐day conditions. This study expanded knowledge on the biological response of A. grani to separate temperature and photoperiod regimes, and provided ground to improve the culture of this potential life feed species for hatcheries.     

Replacement of fish oil with a DHA‐rich Schizochytrium meal on growth performance,activities of digestive enzyme and fatty acid profile of Pacific white shrimp (Litopenaeus vannamei) larvae

This trial was conducted to evaluate the effects of replacing dietary fish oil with Schizochytrium meal for Pacific white shrimp (Litopenaeus vannamei) larvae (initial body weight 4.21 ± 0.10 mg). Six test microdiets were formulated using Schizochytrium meal to replace 0 g/kg, 250 g/kg, 500 g/kg, 750 g/kg, 1000 g/kg or 1500 g/kg fish oil DHA. No significant differences were observed in survival, growth, final body length and activities of digestive enzyme among shrimp fed different diets (p > .05). No significant differences were observed in C20:5n‐3 (EPA) in muscle samples (p > .05). C18:3n‐3 and C20:4n‐6 in muscle increased as Schizochytrium meal replacement level increased (p < .05). No significant differences were observed in C22:6n‐3 (DHA) and n‐3 fatty acids among shrimp fed diets that algae meal replaced 0 g/kg ‐ 1000 g/kg of fish oil. Shrimp fed diet R150 had higher DHA content than other groups and had higher n‐3 fatty acids than that of shrimp fed diets R50, R75 and R100 (p < .05). C18:2n‐6, PUFA and n‐6 fatty acids in muscle increased, while n‐3/n‐6 ratio decreased with increasing algae meal replacement level from 0 g/kg to 1000 g/kg (p < .05). In conclusion, Schizochytrium meal could replace 1500 g/kg fish oil DHA in the microdiets without negatively affecting shrimp larvae survival, growth and activities of digestive enzyme.