Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 159

The feeding behavior of fish is complex. Fish possess several chemosensory systems which include gustation (taste), olfaction (smell), and chemical sensory and chemoreceptor cells, with the acceptance or rejection of food being primarily attributed to inputs from chemoreception (Lall and Tibbetts 2009). Hunger is the cue for feeding behavior in fish, with the primary stimulus being gut fullness and/or metabolite levels in the circulatory system (Jobling and Wandsvik 1983). Numerous abiotic and biotic factors affect food intake in fish including how the diet is presented, diet composition, hormonal and biological state, environmental conditions, fish health and developmental state, and system design (Lall and Tibbetts 2009).

It is generally accepted that fish feed to satisfy their energy requirements. Fish fed a diet low in energy content are forced to increase their consumption rate and gastric evacuation rate to compensate for a low‐calorie diet. Correct food size is also important. Food items should be sufficiently small to be physically ingested, while large enough to be consumed without expending too much energy in the process (Lall and Tibbetts 2009). In European eels (Anguilla anguilla), optimal particle size was ~40–60% of mouth width (Knights 1983). Trout showed a similar optimal particle size, although particles up to 100% of mouth width could be consumed, particularly when the particle was smooth (Knights 1983).

Determining the optimal feed amount is important to maintain health and minimize nitrogenous waste, but it can be difficult. Feed requirements vary with diet, species, life history stage (e.g. juveniles require more energy per unit weight than adult fish); water quality (e.g. temperature, salinity); exercise level and habitat size; and social interactions (e.g. dominance hierarchy). In aquaculture, feed amount is calculated as a percentage of the total biomass of fish, with the percentage decreasing as the individuals grow. Rates for juvenile cultured species range from 4–11% BW, decreasing in adults to 0.5–2% BW, but this is highly species‐ and temperature‐dependent (New 1987). In aquarium‐maintained species, feed amounts can be more difficult to assess since the goal is longevity rather than production, and animals are often maintained in complex, multispecies systems. Generally, fish species in aquariums are fed at lower rates than those in aquaculture. In adult bony fish, 0.5–1% BW/day is a good starting point, as this is the average stomach volume of many bony fish. This should be reduced if the entire ration is not consumed within five minutes for individuals, or within 15 minutes for animals maintained in large groups. Food around the edges of the tank or settling on the bottom, or increases in ammonia, are signs of overfeeding and should be avoided. For adult elasmobranchs, starting food amounts have been outlined by Janse et al. (2004), with bottom‐dwelling sharks (e.g. Hemiscylliidae and Stegostomatidae), bottom‐dwelling rays (e.g. Dasyatidae), and ram‐ventilating rays (e.g. Myliobatidae) at 4–6% BW/week; slow‐swimming ram‐ventilating sharks (e.g. Odontaspididae) at 1.0–2.5% BW/week; and fast‐swimming ram‐ventilating sharks (e.g., Carcharhinidae) at 3–4% BW/week. Elasmobranchs with higher metabolic rates (e.g. Mobula spp.) or those that are more endothermic may require much higher rations than described above. Rations for juveniles should be multiplied by a factor of 1.5–3.0. Feeding amounts should be adjusted based on growth data, body weight and body condition comparisons with wild counterparts, and blood analyses where available (Janse et al. 2004).