Alternating periods of food deprivation with those of unlimited provision of food depressed the growth of Arctic charr, Salvelinus alpinus, below that of controls. Fish that were deprived of food and then fed on alternate weeks (1:1) were larger than those that were exposed to periods of 1 5‐ or 3‐week deprivation and feeding (1·5:1·5 or 3:3). On receiving excess food supplies following 24 weeks on the restricted feeding regimes the previously‐restricted fish grew more rapidly than the controls. The greatest compensatory growth was displayed after the 3:3 regime, followed by the 1·5:1·5 and then the 1:1 feeding regime. At the termination of the experiment there were no significant differences in body weight between fish fed according to the different regimes during the period that food restriction was imposed. Growth patterns of the immature males and females were similar, but mature males were significantly lighter than the immature fish by the end of the experiment. Both immature and maturing fish displayed a compensatory growth response on return to adequate feeding. Beginning food restriction in May did not influence the proportions of male fish (c. 60%) which were mature in the autumn.
Better knowledge of food search behaviour in fish is essential for studies that aim to improve longline fishing, particularly through bait development. This review provides an overview of our understanding of how fish detect and locate sources of food odour, focusing on the stimuli and sensory modalities involved, and on factors that affect feeding activity. Studies that identify feeding attractants and efforts to develop alternative longline baits are presented. The review reveals that such studies are few in number, and that to date there are no alternatives to traditional baits in commercial longlining despite the growing demand for these resources, which are also used for human consumption. The chemical compounds that elicit food search behaviour differ from species to species, and species selectivity could be improved by incorporating specific feeding attractants in manufactured baits. The unique properties of chemical stimuli and odour dispersal form the basis for improving longline efficiency through the development of a long-lasting bait. Vision is important in prey capture, and manufactured baits can be made more visible than natural baits by increasing the contrast (e.g. via fluorescent or polarising coatings) and creating motion through buoyancy. Physical properties such as size, shape, texture and strength can also be manipulated in a manufactured bait to improve catch efficiency. Knowledge obtained from studies of various aspects of food search behaviour is of paramount importance for future research aimed at alternative bait development and improving longline fishing.
We compared the gonad-enhancing effects of two diets (NIWA and NIFA diets) in two size classes of sea urchins (Evechinus chloroticus): small and large urchins with a test diameter of 75.6 ± 1.2 mm and 93.8 ± 0.5 mm, weighing 174.8 ± 7.9 g and 315 ± 5.6 g, respectively. After eight weeks being fed prepared diets, urchin gonad index (GI) had significantly surpassed that of the initial and final samples of wild urchins. Urchins in the NIWA/small treatment had a larger GI than the NIFA/small and NIFA/large treatments. The NIWA/large treatment had a larger GI than the NIFA/large treatment. The overall percentage increase in GI for the NIWA/small, NIWA/large, NIFA/small and NIFA/large treatments were 183%, 135%, 132% and 85%, respectively. In terms of gonad colour (CIELAB), there were no significant differences in gonad redness (a*) or yellowness (b*) between experimental treatments, but there was a significant difference in gonad lightness (L*) with small urchins fed both diets having lighter-coloured gonads than the large urchins fed both diets. Sensory assessment of gonads revealed that gonads from small urchins fed both diets were rated as being of better colouration and more uniform in colour than gonads from large urchins. Gonads of urchins fed the NIFA diet were rated as being less bitter and of better overall taste than gonads from urchins fed the NIWA diet. This study shows that feeding prepared diets to E. chloroticus can significantly increase gonad yield but that different diets can affect the magnitude of GI increase and the taste of gonads, and that smaller urchins appear more suitable for gonad enhancement.
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