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This study investigated the effects of replacement of fishmeal (FM) with poultry by-product (PBM) protein, supplemented with black soldier fly, Hermetia illucens (HI) larvae on growth, histomormhology, immunity and resistance to Vibrio harveyi in juvenile barramundi. Two hundred and twenty five barramundi averaging 3.51 ± 0.03 g were randomly allocated into three groups and fed isonitrogenous and isocalorific diets containing different levels of PBM supplemented with HI as follows: Control (FM based diet), 45PBM + HI (45% PBM supplemented with 10% HI), and 90PBM + HI (90% PBM supplemented with 10% HI) for 6 weeks. Results showed that dietary inclusion of 45PBM + HI significantly improved the growth performance than control whereas growth inhibition occurred in the 90PBM + HI. The 45PBM + HI groups demonstrated significant increases in histometric measurements (villus and enterocyte width, and microvilli height) and acidic mucins. The impaired growth in 90PBM + HI groups was further associated with multifocal necrosis in the liver, an upregulation of the stress related genes (HSP70 and HSP90) and increase in the levels of liver enzymes. When 45PBM + HI was fed, survival against V. harveyi increased significantly and also an increase in serum immunity and immune-related genes in the head kidney was observed after infection.

An 8-week growth trial was conducted to evaluate the effects of dietary arginine (Arg) levels on growth, gut morphology, oxidation resistance and immunity of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) juveniles. Seven isoenergetic (1465 kJ (350 kcal)/100-g DM), isoproteic (53·5 % of DM) and isolipidic (7 % of DM) experimental diets were formulated to contain graded Arg levels ranging from 1·9 to 4·7 % (dry weight) at approximately 0·5 % increments. Each diet was randomly assigned to triplicate groups of 16 juvenile fish (average initial body weight: 11·7 (sd 0·1) g) and was administered twice daily (08.00 and 16.00 hours). After the growth trial, all remaining fish were fed their prescribed diets for 2 d and then exposed to 4·5 mg Cu2+/l water for 36 h. Results showed that growth performance and feed utilisation of experimental fish were significantly affected by different dietary Arg levels. Weight gain % (WG%) of fish was increased as dietary Arg increased, reaching a peak value at 3·8 % dietary Arg level, and when dietary Arg level increased to 4·7 % WG% was reduced. Fish fed 1·9 and 2·2 % dietary Arg levels had higher daily feed intake compared with fish fed other dietary Arg levels. Feed conversion ratios in fish fed 1·9, 2·2, 2·7 and 4·7 % dietary Arg levels were higher than those in fish fed 3·1, 3·8 and 4·1 % dietary Arg levels. Protein efficiency ratio and protein productive value (PPV) increased with an increase in dietary Arg, up to a peak value at 3·8 % dietary Arg level, above which these parameters declined. On the basis of quadratic regression analysis of weight gain % (WG%) or PPV against dietary Arg levels, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %. Fish fed 3·8 % dietary Arg had higher whole-body and muscle protein contents compared with fish fed other dietary Arg levels. Fish fed 3·8 and 4·1 % dietary Arg levels had higher levels of mRNA for insulin-like growth factor-I and target of rapamycin in the liver compared with fish fed other dietary Arg levels. Hepatic S6 kinase 1 mRNA expression in fish fed 3·8 % dietary Arg level was higher than that in fish fed any of the other dietary Arg levels. Gut morphology, hepatic antioxidant indices and immune indices in serum and head kidney were significantly influenced by dietary Arg levels. In conclusion, the optimal dietary Arg requirement for hybrid grouper was estimated to be 3·65 %, and suitable dietary Arg supplementations improved gut morphology and oxidation resistance of hybrid grouper.

The effect of a pollutant on the base of the food web can have knock-on effects for trophic structure and ecosystem functioning. In this study we assess the effect of microplastic exposure on juveniles of a planktivorous fish (Acanthochromis polyacanthus), a species that is widespread and abundant on Indo-Pacific coral reefs. Under five different plastic concentration treatments, with plastics the same size as the natural food particles (mean 2mm diameter), there was no significant effect of plastic exposure on fish growth, body condition or behaviour. The amount of plastics found in the gastro-intestinal (GI) tract was low, with a range of one to eight particles remaining in the gut of individual fish at the end of a 6-week plastic-exposure period, suggesting that these fish are able to detect and avoid ingesting microplastics in this size range. However, in a second experiment the number of plastics in the GI tract vastly increased when plastic particle size was reduced to approximately one quarter the size of the food particles, with a maximum of 2102 small (< 300μm diameter) particles present in the gut of individual fish after a 1-week plastic exposure period. Under conditions where food was replaced by plastic, there was a negative effect on the growth and body condition of the fish. These results suggest plastics could become more of a problem as they break up into smaller size classes, and that environmental changes that lead to a decrease in plankton concentrations combined with microplastic presence is likely have a greater influence on fish populations than microplastic presence alone.

Using fish meal (FM) as the predominant protein source in fish feeds for aquaculture operations poses considerable economic costs and ecological concerns. Therefore, feed nutritionists are looking for inexpensive and supply-stable alternatives to FM in fish feeds. This study aimed to assess the impacts of substituting FM with corn protein concentrate (CPC) in the diet of rockfish ( Sebastes schlegeli ) on the growth, feed availability, biochemical composition, and blood chemistry. Five hundred forty juvenile rockfish were uniformly dispersed into 18 tanks. Six isonitrogenous and isolipidic diets were prepared. The control (Con) diet contained 55% FM. The CPC 10 , CPC 20 , CPC 30 , CPC 40 , and CPC 50 diets were prepared to substitute 10%, 20%, 30%, 40%, and 50% FM with CPC in the Con diet, respectively. Triplicate groups of rockfish received the experimental diets twice daily for 56 days. The weight gain (WG) of rockfish fed the Con and CPC 10 diets was significantly ( P < 0.001) greater than that of rockfish fed all other diets. Rockfish fed the Con and CPC 10 diets exhibited a comparable specific growth rate (SGR) to that of fish fed the CPC 20 diet. Feed consumption (FC) of rockfish fed the Con diet was significantly ( P < 0.0001) higher than that of rockfish fed all other diets, with the exception of the CPC 10 diet. Rockfish fed the Con, CPC 10 , and CPC 20 diets exhibited significantly ( P < 0.0001) higher feed efficiency (FE) compared to rockfish fed all other diets. Protein efficiency ratio of rockfish fed the Con diet was significantly ( P < 0.001) higher than that of fish fed the CPC 40 and CPC 50 diets. Rockfish fed the Con diet exhibited significantly ( P < 0.01) greater protein retention than rockfish fed the CPC 50 diet. However, the biological indices except for hepatosomatic index, biochemical composition, and blood chemistry of rockfish were not significantly ( P > 0.05) influenced by FM substitution with CPC in diets. Conclusively, up to 10% and 20% of FM can be substituted with CPC in the rockfish diet without significantly lowering WG and FC, and SGR and FE, respectively.

The environmental DNA (eDNA) technique is expected to become a powerful, non-invasive tool for estimating the distribution and biomass of organisms. This technique was recently shown to be applicable to aquatic vertebrates by collecting extraorganismal DNA floating in the water or absorbed onto suspended particles. However, basic information on eDNA release rate is lacking, despite it being essential for practical applications. In this series of experiments with bluegill sunfish (Lepomis macrochirus), we examined the effect of fish developmental stage on eDNA release rate. eDNA concentration reached equilibrium 3 days after the individual fish were introduced into the separate containers, enabling calculation of the eDNA release rate (copies h-1) from individual fish on the assumption that the number of eDNA released from the fish per unit time equals total degradation in the container (copies h-1). The eDNA release rate was 3-4 times higher in the adult (body weight: 30-75 g) than in the juvenile group (0.5-2.0 g). Such positive relationship between fish size and eDNA release rate support the possibility of biomass rather than density estimation using eDNA techniques. However, the eDNA release rate per fish body weight (copies h-1 g-1) was slightly higher in the juvenile than the adult group, which is likely because of the ontogenetic reduction in metabolic activity. Therefore, quantitative eDNA data should be carefully interpreted to avoid overestimating biomass when the population is dominated by juveniles, because the age structure of the focal population is often variable and unseen in the field. eDNA degradation rates (copies l-1 h-1), calculated by curve fitting of time-dependent changes in eDNA concentrations after fish removal, were 5.1-15.9% per hour (half-life: 6.3 h). This suggests that quantitative eDNA data should be corrected using a degradation curve attained in the target field.

Mandarin fish (Siniperca chuatsi) is an important cultured fish in East Asia that shows sexual size dimorphism (SSD), with females growing faster than males when reaching marketable size. However, the regulatory mechanism of SSD is not clear. To characterize SSD of mandarin fish and its association with gh/igf1/igfbp-5 expression, gonadal developmental atlas of the females and the males were described, and growth parameters and serum levels of E2 and T, as well as the relative expression levels of gh, igf1, and igfbp-5a/b mRNAs, were determined. The results showed that the logistic growth equation of body mass and total length of female and male were W(♀) = 667.57/(1 + e^(4.19 − 1.24*t)), W(♂) = 582.71/(1 + e^(4.07 − 1.27*t)), L(♀) = 31.47/(1 + e^1.95 − 1.08*t)), L(♂) = 26.20/(1 + e^(2.56 − 1.5*t)). The month of inflection points for body mass for females and males were 3.37 mph and 3.20 mph, respectively, when the body mass were 333.79 g and 291.36 g. The month of inflection points for total length growth were 1.80 mph and 1.70 mph, respectively, when the total length were 18.52 cm and 16.28 cm. At 1.5–2.0 mph, SSD was not clearly demonstrated. At 3.0 mph, the body mass of the females was significantly higher than that of the males (P < 0.05), Serum E2, brain gh, and liver igf1 expression of the females was significantly higher than that of the males (P < 0.05); T content of the males was significantly higher than that of the females (P < 0.05). At 4.0 months of age, the body mass of the females was highly significantly higher than that of the males (P < 0.01), Serum E2, brain gh, and liver igf1 expression of the females was highly significantly higher than that of the males (P < 0.05); T content of the males was significantly higher than that of the females (P < 0.05). With the continuous development of gonads, muscle and liver igfbp-5a and -5b expression generally tend to increase in females and males, while igfbp-5a showed a gradual increasing trend, and igfbp-5b expression showed a trend of decreasing and then increasing. Male igfbp-5a/b expression was significantly higher than female at the age of 3.0–4.0 months (P < 0.05). This work verified that the females had faster growth rate since 3.0 mph compared to the males, which may be related to higher E2 levels in females leading to higher igf1 level, through inhibition of igfbp-5a/b expression.

Sterility in hybrid animals is widely known to be due to a cytological mechanism of aberrant homologous chromosome pairing during meiosis in hybrid germ cells. In this study, the gametes of four marine fish species belonging to the Sciaenid family were artificially fertilized, and germ cell development was examined at the cellular and molecular levels. One of the intergeneric hybrids had gonads that were testis-like in structure, small in size, and lacked germ cells. Specification of primordial germ cells (PGCs) and their migration toward genital ridges occurred normally in hybrid embryos, but these PGCs did not proliferate in the hybrid gonads. By germ cell transplantation assay, we showed that the gonadal microenvironment in hybrid recipients produced functional donor-derived gametes, suggesting that the germ cell-less phenotype was caused by cell autonomous proliferative defects of hybrid PGCs. This is the first evidence of mitotic arrest of germ cells causing hybrid sterility in animals.

A feeding trial of eight weeks was conducted to examine the influence of food supplementation with lauric acid (LA) on Acanthopagrus schlegelii (juvenile black sea bream). A 24 percent fish meal baseline diet was created, while the other two diets were generated with dietary supplementation of graded points of LA at 0.1 percent and 0.8 percent, respectively. Each diet was given a triplicate tank with 20 fish weighing 6.22 ± 0.19 g. In comparison with the control group, the weight gain rate, growth rate, as well as feed efficiency of fish fed of 0.1 percent diet of LA were considerably (P < 0.05) greater. The total body and dorsal muscle proximate compositions did not change significantly between groups (P > 0.05). Triglyceride (TG) content was considerably (P < 0.05) greater in the LA-supplemented meals eating group in comparison with the control group. In the group eating LA-supplemented meals, the height of villus and the number of goblet cells/villus were considerably (P < 0.05) larger. The microbial makeup of the gut was also studied. The differences in phyla, class, and family level were not statistically significant (P > 0.05). Firmicutes in the phylum, Betaproteobacteri, Gammaproteobacteria, and Clostridia in the class, and Clostridiaceae in the family were all substantially increased with higher levels of LA supplementation (P < 0.05). According to the findings of this study, an LA-supplemented diet improves fish development, antioxidative capability, gut microbiota and intestinal health.

The search for suitable fish meal replacements in aqua-diets is a salient agenda in the constant effort of making aquaculture practices more sustainable. In this study, we tested four customised diets composed by systematic inclusion of pre-selected fish meal substitutes, lupin kernel meal, BSF meal, TH and PBM on growth, metabolism, cytokine profile, gut morphology and microbiota of juvenile Lates calcarifer . Five isoproteic and isoenergetic diets were prepared viz. FM100 as a control (without fish meal substitute), while FM75, FM50, FM25 and FM0 indicates replacement of fish meal (FM) at 25%, 50%, 75%, and 100%, respectively by a mixture of four different pre-selected non-fish meal (NFM) ingredients. Fish fed FM100, FM75, FM50, FM25 exhibited consistent growth and haematological response, while the fish fed no fishmeal (FM0) showed significant decline in final body weight (FBW) and specific growth rate (SGR). The poor growth performance was correlated with a decrease in villous width, microvilli height and goblet cells density. A significant shift in abundance profile of Psychrobacter in the gut microbial profile of fish fed FM50 was noticed compared to fish fed FM100. The results of qRT-PCR showed up-regulated expression of innate immune responsive genes in the FM50 group. The adverse impacts on growth performance and gut health of fish fed FM0 suggest that the complete substitution of fishmeal is not advisable and the inclusion range of these alternatives should be decided for a species only after examining their effect on maximal physiological performance.

Yellowtail snapper Ocyurus chrysurus is commercially important throughout its distribution range. In southern Gulf of México, it is caught as part of a largely undocumented multispecific snapper fishery. Samplings were done at three fishing sites with the highest landings volume of Yucatán, México: Celestún, Dzilam de Bravo, and Río Lagartos. Age and growth parameters were generated with the von Bertalanffy growth model via annuli counts in otolith thin sections of 1,124 individuals. Marginal increment analysis confirmed that opaque zone formation is annual and occurs from July to September. Overall age range was 0  + to 12 years (17.7 to 38.9 cm fork length) but differed between Celestún (0  + to 9 years), Dzilam de Bravo (1 to 12 years), and Río Lagartos (2 to 12 years). Growth parameters and lifespan for combined sexes also varied between sites: Celestún (L  ∞ =  41.59 cm, K =  0.11 year -1 , t max =  22.41 years); Dzilam de Bravo (L  ∞ =  38.36 cm, K =  0.16 year -1 , t max = 15.5 years); and Río Lagartos (L  ∞ =  40.28 cm, K =  0.12 year -1 , t max =  20.01 years). Age at maturity was 1.3 years for females and < 1 year for males. Natural mortality based on t max was 0.28 year -1 overall. A principal coordinates analysis identified morphometric variables as explaining 92.2% of otolith differentiation by fishing site, with average centroid distances: Celestún, 1.98; Dzilam de Bravo, 2.22; and Río Lagartos, 2.75. Differences in growth rate, lifespan, natural mortality and otolith shape indicate that O. chrysurus in southern GoM exhibits structural complexities that suggest the occurrence of repercussions from fishing-induced demographic changes.