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Determining the macronutrient requirements for commercially valuable aquaculture species remains crucial for maximising production efficiency. Yet, such information is lacking for Australian hybrid abalone (Haliotis rubra × Haliotis laevigata), particularly with respect to life stage and water temperatures. The present study aimed to evaluate the effect of dietary protein inclusion level on the growth performance, nutrient utilisation and nutritional quality of juvenile (3·3 g) Australian hybrid abalone reared at three different temperatures representative of winter (12°C), average annual (17°C) and summer (22°C) grow-out periods and fed five diets containing graded dietary protein levels of 35, 38, 41, 44 and 47 %. Abalone growth increased with increasing water temperature with weight gains of approximately 100, 280 and 380 % of their initial weight at 12, 17 and 22°C, respectively. Furthermore, the present study clearly demonstrated that higher dietary protein inclusion levels (41 %) than those currently used commercially (35 %) would significantly improve the growth performance when water temperatures are ≥17°C without any adverse impacts on nutrient utilisation, nutrient deposition or nutritional quality of the abalone soft tissue. For example, at 22°C abalone fed a diet containing 41 % protein obtained a significantly higher weight gain percentage (421 %) compared with those fed a diet containing 35 % protein (356 %). Lastly, it is suggested that maintaining a dietary protein inclusion level of 35 % or implementing a 'least cost' feeding approach during cooler seasons, or where water temperatures are ∼12°C, may be beneficial, considering only marginal growth improvements were observed during these periods of slow growth. [ABSTRACT FROM AUTHOR]

Seasonal changes in water temperature affect the utilization of dietary fatty acids in Atlantic salmon (Salmo salar L.). Furthermore, fatty acid profiles of terrestrial oils dictate their suitability in terms of provision of metabolic energy and final product quality. An on‐farm, growth trial of Atlantic salmon was conducted in Tasmania, Australia over the final year of grow‐out (323 days), consisting of a 'summer phase' and a 'winter phase'. Poultry by‐product oil, canola oil and tallow were fed at high dietary lipid inclusion level (80%) to assess growth, fillet fatty acid composition and sensorial attributes. In the summer phase, the tallow diet appeared to provide added substrate for metabolic energy, potentially enhancing the deposition of n‐3 LC PUFA into the fillet, despite lower final weight and a reduced apparent lipid digestibility. Subsequent winter phase results suggested all diets adequately provided metabolic energy and fillet n‐3 LC PUFA concentrations were comparable. Additionally, this study highlights the importance of a well‐considered experimental design and subsequent statistical interpretation, for commercial scale, on‐farm feeding trials. Ultimately, this study demonstrates the importance of seasonally tailored diets for Atlantic salmon, using high terrestrial oil inclusion, under challenging Australian farming conditions. [ABSTRACT FROM AUTHOR]

The Murray cod (Maccullochella peelii peelii), an iconic Australian freshwater fish, is subject to a small but growing aquaculture sector in Australia. Optimal larviculture techniques for this species have yet to be established, particularly with regard to the nutritional quality of starter diets. As such, optimisation of current Murray cod hatchery practices and feeding regimes is essential to maximize the production of high quality larvae and expand commercial aquaculture prospects. The aim of this investigation was to assess the effects of Artemia nauplii enriched with high levels of long-chain polyunsaturated fatty acids (LC-PUFA; ENR treatment), on the growth and fatty acid composition of larval Murray cod. Using untreated Artemia nauplii as a control treatment (CTL), larvae were fed either treatment to apparent satiation twice daily in triplicate groups of 700 fish with initial mean weights of 0.012 ± 0.06 g for 21 days at 19.85 °C. Survival was not significantly different between treatments (P >.05). Final mean weight and length, as well as specific growth rate, were significantly higher for ENR compared to CTL. Enriched larvae also contained significantly higher total lipid contents and across all three of the major fatty acid groups. Of the individual fatty acids, increases in ARA (20:4n-6) and DHA (22:6n-3) were recorded in the ENR fish, while CTL fish contained high concentrations of 18:4n-3, 20:4n-3 and 22:5n-3, which are intermediate fatty acids along the n-3 conversion pathway, suggesting desaturation and elongation toward EPA (20:5n-3) and DHA. Results demonstrate that enriched Artemia nauplii are vastly superior to untreated Artemia as a starter diet for optimal growth and fatty acid composition of Murray cod larvae. Thus, despite the clear ability of Murray cod larvae to undergo elongation and desaturation of ALA (18:3n-3), the present study demonstrates that this is not sufficient to sustain growth or LC-PUFA tissue levels akin to those possible through high dietary LC-PUFA intake. • Optimal larviculture techniques for Murray cod larvae should include live feed enrichment. • Enrichment of Artemia with long-chain polyunsaturated fatty acids improves the performance of Murray cod larvae • Murray cod larvae showed active elongation and desaturation of 18:3n-3 (α-linolenic acid). • In vivo long chain omega-3 biosynthesis in Murray cod larvae is not sufficient to compensate for limited dietary supply. • DHA content in Murray cod larvae is tightly regulated, and is limiting nutrient. [ABSTRACT FROM AUTHOR]