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Using stable isotope analysis, we assessed the relative contributions of the main protein contributors fishmeal, soya and sunflower meal to mature abalone muscle and gonad tissue over 1 year. Prerequisites for the use of stable isotope mixing models were established in this species. The δ13C and δ15N discrimination factors and turnover rates were influenced by diet composition, and there were tissue‐specific and sex‐specific differences. Abalone were fed the two combination diets (fishmeal–soya and fishmeal–sunflower meal) grew at similar rates. However, feed was most efficiently utilised in abalone fed a combination of fishmeal and soya. The relative contribution of fishmeal, soya and sunflower meal to female and male abalone tissue growth fluctuated throughout the 1‐year study. Overall, fishmeal contributed over 50% of the gonad (54%–82%) and muscle (54%–84%) tissue growth in females. Similarly, fishmeal contributed over 50% of gonad tissue growth of male abalone, ranging from 59% to 87%, while the contribution to meat tissue growth in males ranged from 44% to 94%. These findings support the importance of laboratory studies when using stable isotope analysis and mixing models for nutrient allocation in aquaculture. [ABSTRACT FROM AUTHOR]

The effects of adding a probiotic mixture of Bacillus subtilis and B. licheniformis to an aquaponics system on water quality, fish growth and digestive enzyme activity in Mozambique tilapia, Oreochromis mossambicus, were tested. The fish (36.4 g fish−1 ± 0.10; 3.64 kg m−3 tank volume, 10 fish per tank) were kept in 386-L systems and fed 2% of body mass day−1 for ten weeks. The Bacillus product (Sanolife®PRO-W; 5.0 × 1010 CFU g−1) was added twice weekly. Each treatment was duplicated. The product reduced total dissolved solids and electrical conductivity levels and increased weight gain of Mozambique tilapia. There was no difference between treatment and control in the proximate analysis of the fish. In the Bacillus treatment the activity of the digestive enzymes α-amylase, alkaline protease and alkaline phosphatase was higher than in the control. The probiotic used in this study improved water quality and increased fish growth. [ABSTRACT FROM AUTHOR]

Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra- and interspecific variation in predator-prey body size ratios are lacking.We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra- and interspecific predator-prey body mass ratios on the scaling of attack rates and handling times.Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium-large prey types. Attack rates for both predators peaked unimodally at intermediate predator-prey body mass ratios, while handling times generally shortened across increasing body mass ratios.We thus demonstrate effects of body size ratios on predator-prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator-prey participants.Considerations for intra- and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift., Competing Interests: The authors declare no conflicts of interest., (© 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)