Adequate levels of dietary sulphur amino acids impart improved liver and gut health in juvenile yellowtail kingfish (Seriola lalandi).

The sulphur amino acids methionine (Met) and cysteine (Cys) and their derivative taurine (Tau) are metabolically active molecules with interlinked roles in nutritional requirements. Deficiencies in these nutrients are linked to poor growth and health; however, the impacts of these deficiencies on organ structure and function are largely unknown. This study examined the effects of dietary Met, Cys and Tau fed at different levels on yellowtail kingfish (YTK) liver histology and surface colour, plasma biochemistry and posterior intestine histology. Samples were collected from two dose-response feeding trials that quantified (1) the Tau requirement and sparing effect of Met by feeding YTK diets containing one of seven levels of Tau at one of two levels of Met and (2) the Met requirement and sparing effect of Cys by feeding YTK diets containing one of five levels of Met at one of two levels of Cys. YTK fed inadequate levels of dietary Met, Cys and Tau exhibited thicker bile ducts, less red livers, more intestinal acidic goblet cell mucus and supranuclear vacuoles and less posterior intestinal absorptive surface area. Further, thicker bile ducts correlated with less red livers (a*, R), whereas increased hepatic fat correlated with a liver yellowing (b*). Our results indicate a shift towards histological properties and functions indicative of improved intrahepatic biliary condition, posterior intestinal nutrient absorption and homoeostasis of YTK fed adequate amounts of Met, Cys and Tau. These findings may assist in formulating aquafeed for optimised gastrointestinal and liver functions and maintaining good health in YTK.

Effects of dietary choline on liver lipid composition, liver histology and plasma biochemistry of juvenile yellowtail kingfish (Seriola lalandi).

Choline plays a crucial role in lipid metabolism for fish, and its deficiency in aquafeed has been linked to compromised health and growth performance. A 56-d experiment was conducted to examine the effects of dietary choline on lipid composition, histology and plasma biochemistry of yellowtail kingfish (Seriola lalandi; YTK; 156 g initial body weight). The dietary choline content ranged from 0·59 to 6·22 g/kg diet. 2-Amino-2-methyl-1-propanol (AMP) (3 g/kg) was added to diets, except for a control diet, to limit de novo choline synthesis. The results showed that the liver lipid content of YTK was similar among diets containing AMP and dominated by NEFA. In contrast, fish fed the control diet had significantly elevated liver TAG. Generally, the SFA, MUFA and PUFA content of liver lipid in fish fed diets containing AMP was not influenced by choline content. The SFA and MUFA content of liver lipid in fish fed the control diet was similar to other diets except for a decrease in PUFA. The linear relationship between lipid digestibility and plasma cholesterol was significant, otherwise most parameters were unaffected. When AMP is present, higher dietary choline reduced the severity of some hepatic lesions. The present study demonstrated that choline deficiency affects some plasma and liver histology parameters in juvenile YTK which might be useful fish health indicators. Importantly, the present study elucidated potential reasons for lower growth in choline-deficient YTK and increased the knowledge on choline metabolism in the fish.

Intestinal Transcriptome Analysis Highlights Key Differentially Expressed Genes Involved in Nutrient Metabolism and Digestion in Yellowtail Kingfish (Seriola lalandi) Fed Terrestrial Animal and Plant Proteins.

This study investigated the effects of dietary terrestrial animal and plant proteins on the intestinal transcriptomes of yellowtail kingfish (YTK), Seriola lalandi, an ecologically and economically important marine species in Australia. Five diets containing fish meal (FM), poultry by-product meal (PBM), blood meal (BLM), faba bean meal (FBM) and corn gluten meal (CGM) were formulated and fed over a period of 4 weeks. The Illumina RNA-sequencing (RNA-Seq) results identified a suite of differentially expressed genes involved in nutrient metabolism and protein digestion pathways, reinforced by quantitative polymerase chain reaction (qPCR) results. These findings provide molecular support to the notion that PBM and FBM are useful raw materials in commercial diets for YTK. Using the same evidence, we have demonstrated that BLM and CGM may be less useful and their incorporation into commercial aquafeeds for this species should be done cautiously. The differentially expressed genes showed a subtle difference and high correlation with apparent nutrient digestibility of raw materials. Further, our results indicate that transcriptome profiling provides a useful tool to evaluate alternative protein sources for use in aquaculture feeds.

Feeding preferences and the nutritional value of tropical algae for the abalone Haliotis asinina.

Understanding the feeding preferences of abalone (high-value marine herbivores) is integral to new species development in aquaculture because of the expected link between preference and performance. Performance relates directly to the nutritional value of algae--or any feedstock--which in turn is driven by the amino acid content and profile, and specifically the content of the limiting essential amino acids. However, the relationship between feeding preferences, consumption and amino acid content of algae have rarely been simultaneously investigated for abalone, and never for the emerging target species Haliotis asinina. Here we found that the tropical H. asinina had strong and consistent preferences for the red alga Hypnea pannosa and the green alga Ulva flexuosa, but no overarching relationship between protein content (sum of amino acids) and preference existed. For example, preferred Hypnea and Ulva had distinctly different protein contents (12.64 vs. 2.99 g 100 g(-1)) and the protein-rich Asparagopsis taxiformis (>15 g 100 g(-1) of dry weight) was one of the least preferred algae. The limiting amino acid in all algae was methionine, followed by histidine or lysine. Furthermore we demonstrated that preferences can largely be removed using carrageenan as a binder for dried alga, most likely acting as a feeding attractant or stimulant. The apparent decoupling between feeding preference and algal nutritive values may be due to a trade off between nutritive values and grazing deterrence associated with physical and chemical properties.

Protein and energy utilization and the requirements for maintenance in juvenile mulloway (Argyrosomus japonicus).

This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two temperatures (20 or 26 degrees C), on a commercial diet (21.4 g DP mJ DE(-1)) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency (ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26 degrees C respectively. ERE demonstrated a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26 degrees C respectively. Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and temperature. The partial utilization efficiencies of DE for protein (k (p)) and lipid (k (l)) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements estimated using linear regression were independent of temperature for DP (0.47 g DP kg(-0.7) day(-1)) while maintenance requirements for DE increased with increasing temperature (44.2-49.6 kJ DE kg(-0.8) day(-1)). Relative feed intake was greatest for small mulloway fed to satiation at 26 degrees C and this corresponded to a greater increase in growth. Large mulloway fed to satiation ate significantly more at 26 degrees C, but did not perform better than the corresponding satiated group held at 20 degrees C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE(-1).

The effect of temperature and body weight on the routine metabolic rate and postprandial metabolic response in mulloway, Argyrosomus japonicus.

Specific dynamic action (SDA) is the energy expended on the physiological processes associated with meal digestion and is strongly influenced by the characteristics of the meal and the body weight (BW) and temperature of the organism. This study assessed the effects of temperature and body weight on the routine metabolic rate (RMR) and postprandial metabolic response in mulloway, Argyrosomus japonicus. RMR and SDA were established at 3 temperatures (14, 20 and 26 degrees C). 5 size classes of mulloway ranging from 60 g to 1.14 kg were used to establish RMR with 3 of the 5 size classes (60, 120 and 240 g) used to establish SDA. The effect of body size on the mass-specific RMR (mg O(2) kg(-1) h(-1)) varied significantly depending on the temperature; there was a greater relative increase in the mass-specific RMR for smaller mulloway with increasing temperature. No statistical differences were found between the mass exponent (b) values at each temperature when tested against H(0): b=0.8. The gross RMR of mulloway (mg O(2) fish(-1) h(-1)) can be described as function of temperature (T; 14-26 degrees C) as: (0.0195T-0.0454)BW(g)(0.8) and the mass-specific RMR (mg O(2) kg(-1) h(-1)) can be described as: (21.042T-74.867)BW(g)(-0.2). Both SDA duration and time to peak SDA were influenced by temperature and body weight; SDA duration occurred within 41-89 h and peak time occurred within 17-38 h of feeding. The effect of body size on peak metabolic rate varied significantly depending on temperature, generally increasing with temperature and decreasing with increasing body size. Peak gross oxygen consumption (MO(2): mg O(2) fish(-1) h(-1)) scaled allometrically with BW. Temperature, but not body size, significantly affected SDA scope, although the difference was numerically small. There was a trend for MO(2) above RMR over the SDA period to increase with temperature; however, this was not statistically significant. The average proportion of energy expended over the SDA period (SDA coefficient) ranged from approximately 7-13% of the total DE intake while the proportion of total energy expended on SDA above RMR ranged from approximately 16-27%.

The routine metabolic rate of mulloway (Argyrosomus japonicus: Sciaenidae) and yellowtail kingfish (Seriola lalandi: Carangidae) acclimated to six different temperatures.

This study compared the mass-specific routine metabolic rate (RMR) of similar sized mulloway (Argyrosomus japonicus), a sedentary species, and yellowtail kingfish (Seriola lalandi), a highly active species, acclimated at one of several temperatures ranging from 10-35 degrees C. Respirometry was carried out in an open-top static system and RMR corrected for seawater-atmosphere O2 exchange using mass-balance equations. For both species RMR increased linearly with increasing temperature (T). RMR for mulloway was 5.78T-29.0 mg O2 kg(-0.8) h(-1) and for yellowtail kingfish was 12.11T-39.40 mg O2 kg(-0.8) h(-1). The factorial difference in RMR between mulloway and yellowtail kingfish ranged from 2.8 to 2.2 depending on temperature. The energetic cost of routine activity can be described as a function of temperature for mulloway as 1.93T-9.68 kJ kg(-0.8) day(-1) and for yellowtail kingfish as 4.04T-13.14 kJ kg(-0.8) day(-1). Over the full range of temperatures tested Q10 values were approximately 2 for both species while Q10 responses at each temperature increment varied considerably with mulloway and yellowtail kingfish displaying thermosensitivities indicative of each species respective niche habitat. RMR for mulloway was least thermally dependent at 28.5 degrees C and for yellowtail kingfish at 22.8 degrees C. Activation energies (Ea) calculated from Arrhenius plots were not significantly different between mulloway (47.6 kJ mol(-1) and yellowtail kingfish (44.1 kJ mol(-1).