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Utilising novel ingredients in aquafeeds is necessary for the continued expansion and intensification of aquaculture production. Microalgae are utilised widely in aquaculture for a variety of purposes; as live feed for fish and shellfish larvae and juveniles, for the production of algae‐based meals and oils to replace marine derived raw materials in aquafeeds, and for the production of astaxanthin, the carotenoid that gives salmon flesh its characteristic reddish colour. Notably, long‐chain polyunsaturated fatty acids, amino acids, proteins, fibres, antioxidant pigments, vitamins and minerals are among the compounds in microalgae with great biological value. A growing collection of experimental data has demonstrated that these substances are crucial for increasing larval survival and enhancing the growth and well‐being of fish and shellfish. In this review, the processing of microalgae utilised as aquafeed ingredient, the health promoting compounds in microalgae and their role in growth, immunity and disease resistance of fish and shellfish are described and discussed. Simultaneously, major hurdles in the commercial use of microalgae in aquafeed, and future research and development perspectives are all critically discussed. [ABSTRACT FROM AUTHOR]

The gut transit rate of ingested feed in fish affects the utilization of dietary nutrients; however, the influence of water temperature, remains underexplored in Atlantic salmon (Salmo salar). The present study quantified the gut transit rate of four distinct regions of the gastrointestinal tract (stomach, pyloric caeca, small and large intestine) of post‐smolt Atlantic salmon at two temperatures; 11 and 20°C, by feeding fish a diet incorporated with Ballotini beads. A determination of relative and total bead density in each region was assessed for 48 h, post‐feeding. A clear inverse relationship in bead density between the stomach and large intestine was recorded at both temperatures. However, fish subjected to 20°C recorded a faster gut transit rate compared to fish at 11°C in both the stomach and large intestine. The pyloric caeca and small intestine transit rate appeared unaffected by temperature. The present study re‐iterates the positive relationship between temperature and gut transit rate and also the critical function of the stomach in controlling gut transit rate in gastric fish. This information may be used to improve dietary strategies aimed at enhancing nutrient utilization through increased understanding of the gut transit rate in commercially important fish species. [ABSTRACT FROM AUTHOR]

Driven by consumer demand and government policies, synthetic additives in aquafeed require substitution with sustainable and natural alternatives. Seaweeds have been shown to be a sustainable marine source of novel bioactive phenolic compounds that can be used in food, animal and aqua feeds, or microencapsulation applications. For example, phlorotannins are a structurally unique polymeric phenolic group exclusively found in brown seaweed that act through multiple antioxidant mechanisms. Seaweed phenolics show high affinities for binding proteins via covalent and non-covalent bonds and can have specific bioactivities due to their structures and associated physicochemical properties. Their ability to act as protein cross-linkers means they can be used to enhance the rheological and mechanical properties of food-grade delivery systems, such as microencapsulation, which is a new area of investigation illustrating the versatility of seaweed phenolics. Here we review how seaweed phenolics can be used in a range of applications, with reference to their bioactivity and structural properties. [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]

Abstract A common strategy for aquafeed manufacturers has been the utilisation of relatively large amounts of terrestrial, both animal and plant, oil sources to produce diets with a high energy content. The provision of high fat diets is aimed at promoting the utilisation of energy from lipid, thus increasing the amount of dietary protein used for tissue synthesis. However, in recent years the cost of marine sourced dietary lipids has risen, at the same time, farming operations are under increasing pressure to limit environmental degradation associated with nitrogenous waste effluent. Currently there is limited information available regarding the environmental and economic impacts of an altered dietary protein: lipid ratio in diets for large Atlantic salmon (Salmo salar) reared in seawater, presenting a potential impediment for nutritional based solutions. Accordingly the present study compared two isoenergetic diets with varied protein: lipid ratios via an assessment of growth, fatty acid utilisation, human nutritional quality, nitrogenous waste output and economic considerations. The trial diets were fed to the fish for the final 150 days of an on-farm grow-out period and resulted in minimal differences in fish growth, fatty acid utilisation and fillet quality. A decreased dietary protein: lipid ratio resulted in a more efficient protein utilisation both in terms of digestibility and assimilation into fish and, therefore, nitrogenous waste output was reduced. However, due to small differences in feed utilisation, the cost of fish production was numerically higher. Highlights • An altered dietary protein: lipid ratio had virtually no effect on fillet fatty acid composition and fatty acid metabolism. • A reduction in the dietary protein:lipid ratio resulted in lower nitrogenous waste output emanating from undigested protein. • Differences in growth were shown to equate to considerable differences in terms of the cost of fish production. [ABSTRACT FROM AUTHOR]

The mucosal surfaces of fish, including their intestines, gills, and skin, are constantly exposed to various environmental threats, such as water quality fluctuations, pollutants, and pathogens. However, various cells and microbiota closely associated with these surfaces work in tandem to create a functional protective barrier against these conditions. Recent research has shown that incorporating specific feed ingredients into fish diets can significantly boost their mucosal and general immune response. Among the various ingredients being investigated, insect meal has emerged as one of the most promising options, owing to its high protein content and immunomodulatory properties. By positively influencing the structure and function of mucosal surfaces, insect meal (IM) has the potential to enhance the overall immune status of fish. This review provides a comprehensive overview of the potential benefits of incorporating IM into aquafeed as a feed ingredient for augmenting the mucosal immune response of fish. [ABSTRACT FROM AUTHOR]

Aquafeed manufacturers are increasingly interested in ensuring consistently high-quality products, while relying heavily on poultry offal meal (POM), which is inevitably variable. This study examined the chemical composition of 22 different commercially and experimentally produced POM to determine which chemical variables best predict in vivo protein digestibility in Atlantic salmon (Salmo salar) and to evaluate which production variable, rendering temperature or raw material freshness, has a greater impact on digestibility. The chemical composition of commercially and experimentally produced POM was extremely variable. Significant relationships were found between in vivo dietary protein digestibility and D-glutamic acid (R2 = 0.64) and D-aspartic acid (R2 = 0.62). Rendering temperature and raw material freshness had significant effects on D-amino acids and biogenic amines. D-glutamic and D-aspartic acids may provide rapid-assessment indication of POM quality, as these D-amino acids were linked to protein digestibility and affected by the production variables. This study supports the well-held notion that POM is subject to significant variability and addresses the specific chemical characterisation of POM and the production conditions which impact nutrient digestibility in Atlantic salmon. These results prove beneficial to aquafeed manufactures aiming to ensure consistency and high nutritional quality in protein sources for aquafeed. • The chemical composition of poultry offal meals was extremely variable. • Digestibility correlated with D-glutamic acid and D-aspartic acid. • Rendering temperature and freshness affected D-amino acids and biogenic amines. • D-glu and D-asp may be rapid-assessment quality indicators of poultry meal. [ABSTRACT FROM AUTHOR]