Dietary supplementation of astaxanthin modulates skin color and liver antioxidant status of giant grouper (Epinephelus lanceolatus)

Giant grouper (Epinephelus lanceolatus) is an emerging aquaculture species in Southeast Asia and Australia with limited knowledge of its nutrient requirements and effects of supplements on its physiology. The present study investigated the effects of astaxanthin, vitamin E, and combinations on growth performance, body coloration, and the antioxidant status of juvenile giant grouper. Nine isonitrogenous (crude protein = 65 % ± 0.7 %) and isolipidic (crude lipid = 10 % ± 0.3 %) diets were formulated using a 3 × 3 factorial design, including three levels astaxanthin (0, 75, and 150 mg/kg) and vitamin E (0, 250, and 500 mg/kg), respectively. Each of the nine diets was fed to triplicate groups of 15 giant grouper (18.04 ± 0.92 g) for 30 days. Giant grouper fed the different diets exhibited no significant differences (p > 0.05) in specific growth rate (4.87 %/day - 5.21 %/day). However, dietary astaxanthin supplementation significantly enhanced the redness (a*), yellowness (b*b*), chroma, and hue values of the fin, regardless of the dose supplemented. Giant grouper fed astaxanthin at 75 and 150 mg/kg diet were more yellow and had three times higher b* values than fish fed non-supplemented diets. Further, total antioxidant capacity (TAC; mmol Trolox equivalent) in liver tissues was significantly increased in fish fed any of the astaxanthin-supplemented diets (p ≤ 0.05). In contrast, TAC levels were not affected by vitamin E supple-mentation. Malondialdehyde (MDA) levels were not significantly (p > 0.05) affected by astaxanthin or vitamin E. Findings from this study will contribute toward a better understanding of the dietary effects of antioxidant and pigment in juvenile giant grouper. We present that dietary treatment can modulate giant grouper pigmentation and may be used in the live fish trade. Further, this study contributes to narrowing the knowledge gap in formulating appropriate diets for giant grouper, which to date is fed diets formulated for other species

The sulfur amino acid requirements of juvenile Yellowtail Kingfish (Seriola lalandi)

The dietary methionine and cysteine requirements of Yellowtail Kingfish (YTK) are unknown. Methionine, an essential sulfur-containing amino acid, acts as a sulfur and methyl donor for key metabolites, such as cysteine and taurine. Cysteine, a conditionally essential sulfur-containing amino acid, can spare significant amounts of methionine in the total sulfur amino acid (TSAA) requirement. Both methionine and cysteine are an integral part of YTK aquafeeds, in which methionine supplementation levels are based on the requirements of the closely related Japanese Yellowtail (Seriola quinqueradiata) at approximately 11.1 g kg−1 diet. However, recent research has demonstrated better growth and feed efficiency in YTK fed diets containing more than 11 g methionine kg−1, although the precise methionine requirement and potential interactions with cysteine remain unknown. Therefore, the present study was designed to (1) elucidate the methionine requirement of YTK at low and high dietary cysteine contents and to (2) quantify cysteine’s sparing capacity for methionine in the TSAA requirement. These requirements and relationships were established by feeding ten isonitrogenous and isoenergetic diets, made from common feed ingredients, to triplicate groups of 12 fish (initial 52.6 ± 1.0 g fish−1) over 54 days. The orthogonal design consisted of two levels of dietary cysteine (5.6 & 13.9 g kg−1), crossed with five levels of dietary methionine, increasing from 7.9 to 25.2 g kg−1. Non-linear regression analysis indicated an average digestible TSAA requirement of 0.70 g kgBW−1 d−1 (0.56 g Met kgBW−1 d−1 & 0.14 g Cys kgBW−1 d−1) based on feed conversion ratio, specific growth rate, and protein retention efficiency. This approximates to an average dietary sulfur amino acid specification of 24.5 g kg−1 (18.9 g Met kg−1 & 5.6 g Cys kg−1). Cysteine spared 40.4–49.2% of methionine in the TSAA requirement on an equimolar sulfur basis. Sub- and supra-optimal levels of dietary methionine and cysteine induced inferior growth and feed efficiency. Additionally, fish fed the diet lowest in dietary methionine and cysteine indicated early stages of cataract. This study provides quantitative data on the sulfur amino acid requirements of juvenile YTK and will facilitate the formulation of better diets for this species

The sulfur amino acid requirements of juvenile Yellowtail Kingfish (Seriola lalandi)

The dietary methionine and cysteine requirements of Yellowtail Kingfish (YTK) are unknown. Methionine, an essential sulfur-containing amino acid, acts as a sulfur and methyl donor for key metabolites, such as cysteine and taurine. Cysteine, a conditionally essential sulfur-containing amino acid, can spare significant amounts of methionine in the total sulfur amino acid (TSAA) requirement. Both methionine and cysteine are an integral part of YTK aquafeeds, in which methionine supplementation levels are based on the requirements of the closely related Japanese Yellowtail (Seriola quinqueradiata) at approximately 11.1 g kg−1 diet. However, recent research has demonstrated better growth and feed efficiency in YTK fed diets containing more than 11 g methionine kg−1, although the precise methionine requirement and potential interactions with cysteine remain unknown. Therefore, the present study was designed to (1) elucidate the methionine requirement of YTK at low and high dietary cysteine contents and to (2) quantify cysteine’s sparing capacity for methionine in the TSAA requirement. These requirements and relationships were established by feeding ten isonitrogenous and isoenergetic diets, made from common feed ingredients, to triplicate groups of 12 fish (initial 52.6 ± 1.0 g fish−1) over 54 days. The orthogonal design consisted of two levels of dietary cysteine (5.6 & 13.9 g kg−1), crossed with five levels of dietary methionine, increasing from 7.9 to 25.2 g kg−1. Non-linear regression analysis indicated an average digestible TSAA requirement of 0.70 g kgBW−1 d−1 (0.56 g Met kgBW−1 d−1 & 0.14 g Cys kgBW−1 d−1) based on feed conversion ratio, specific growth rate, and protein retention efficiency. This approximates to an average dietary sulfur amino acid specification of 24.5 g kg−1 (18.9 g Met kg−1 & 5.6 g Cys kg−1). Cysteine spared 40.4–49.2% of methionine in the TSAA requirement on an equimolar sulfur basis. Sub- and supra-optimal levels of dietary methionine and cysteine induced inferior growth and feed efficiency. Additionally, fish fed the diet lowest in dietary methionine and cysteine indicated early stages of cataract. This study provides quantitative data on the sulfur amino acid requirements of juvenile YTK and will facilitate the formulation of better diets for this species

The critical oxygen threshold of Yellowtail Kingfish (Seriola lalandi)

Low concentrations of dissolved oxygen are one of the most limiting abiotic factors in land-based and marine aquaculture, impacting the welfare of target-species. Yellowtail Kingfish (Seriola lalandi) (YTK) is a high energy demanding species and its commercial aquaculture is rapidly expanding globally yet no information on its hypoxia tolerance is available. YTK is commonly cultured in sea pens, in which abiotic factors such as temperature and ambient oxygen can fluctuate substantially. The move away from marine fish oils to more sustainable terrestrial oil sources in aquafeeds implies a change in fatty acid intake. This shift in fatty acid concentrations and temperature fluctuations can impart physiological effects, impacting the animals stress tolerance. The critical oxygen threshold is a common method to quantify the lower, tolerated threshold of oxygen concentrations for an organism. This study assessed the critical oxygen threshold in fasted, juvenile YTK with respect to acclimation temperature (15 degrees C Sr 20 degrees C) and dietary lipid source (fish oil Sr poultry oil). Additionally, observations on the visual and behavioral hypoxia responses in YTK were made. This study demonstrated that YTK could regulate their oxygen consumption down to 2.92-1.84 mg dissolved oxygen L-1, but this strongly depends on the acclimation temperature, and to a lesser extent dietary oil source. At dissolved oxygen concentrations below this level, YTK became oxyconformers, unable to maintain an optimum rate of oxygen uptake. Warmer acclimation temperatures led to significantly less hypoxia tolerance compared to YTK held in cooler temperatures. Dietary oil source had no significant effect on the critical oxygen threshold; however, YTK fed a poultry-oil based diet displayed less hypoxia tolerance and greater deviation around the mean, attributing the non-significant difference to YTK fed a fish oil-based diet. Additionally, hypoxia triggered behavioral responses were initiated earlier in YTK fed the poultry oil diet. First behavioral responses, after passing the critical oxygen threshold, were attempted aquatic surface respiration, increased opercular frequency, and gulping, followed by darkening of skin coloration. We recommend rapid oxygenation of the rearing system if dissolved oxygen levels approach 2.92 mg L-1 at 20 degrees C or at first sign of these changes. Further onset, such as rush or rest behavior, may rapidly lead to the final stages of hypoxia. These results expand knowledge on YTK physiology and behavioral responses to low dissolved oxygen environments and provide information for farm managers to ensure adequate levels of dissolved oxygen throughout rearing, handling, bathing or transportation procedures

The critical oxygen threshold of Yellowtail Kingfish (Seriola lalandi)

Low concentrations of dissolved oxygen are one of the most limiting abiotic factors in land-based and marine aquaculture, impacting the welfare of target-species. Yellowtail Kingfish (Seriola lalandi) (YTK) is a high energy demanding species and its commercial aquaculture is rapidly expanding globally yet no information on its hypoxia tolerance is available. YTK is commonly cultured in sea pens, in which abiotic factors such as temperature and ambient oxygen can fluctuate substantially. The move away from marine fish oils to more sustainable terrestrial oil sources in aquafeeds implies a change in fatty acid intake. This shift in fatty acid concentrations and temperature fluctuations can impart physiological effects, impacting the animals stress tolerance. The critical oxygen threshold is a common method to quantify the lower, tolerated threshold of oxygen concentrations for an organism. This study assessed the critical oxygen threshold in fasted, juvenile YTK with respect to acclimation temperature (15 degrees C Sr 20 degrees C) and dietary lipid source (fish oil Sr poultry oil). Additionally, observations on the visual and behavioral hypoxia responses in YTK were made. This study demonstrated that YTK could regulate their oxygen consumption down to 2.92-1.84 mg dissolved oxygen L-1, but this strongly depends on the acclimation temperature, and to a lesser extent dietary oil source. At dissolved oxygen concentrations below this level, YTK became oxyconformers, unable to maintain an optimum rate of oxygen uptake. Warmer acclimation temperatures led to significantly less hypoxia tolerance compared to YTK held in cooler temperatures. Dietary oil source had no significant effect on the critical oxygen threshold; however, YTK fed a poultry-oil based diet displayed less hypoxia tolerance and greater deviation around the mean, attributing the non-significant difference to YTK fed a fish oil-based diet. Additionally, hypoxia triggered behavioral responses were initiated earlier in YTK fed the poultry oil diet. First behavioral responses, after passing the critical oxygen threshold, were attempted aquatic surface respiration, increased opercular frequency, and gulping, followed by darkening of skin coloration. We recommend rapid oxygenation of the rearing system if dissolved oxygen levels approach 2.92 mg L-1 at 20 degrees C or at first sign of these changes. Further onset, such as rush or rest behavior, may rapidly lead to the final stages of hypoxia. These results expand knowledge on YTK physiology and behavioral responses to low dissolved oxygen environments and provide information for farm managers to ensure adequate levels of dissolved oxygen throughout rearing, handling, bathing or transportation procedures