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Ornamental fishkeeping has increased in popularity over the past 50 years or so, with a resulting increase in demand for knowledge on the feeding and care of these animals. Even today, the dietary requirements of ornamental fish remain one of the least explored areas of pet nutrition. Most of the data currently available are based on research carried out by the aquaculture industry on a relatively small number of commercially farmed food-fish species. Understanding of fish nutrition has been greatly advanced by this work, but the results have limited relevance to ornamental fish species, which are often kept under totally different husbandry regimes. This was one of the key reasons for the establishment in the UK of the WALTHAM Aquacentre, to study the nutritional requirements of ornamental fish, their feeding behaviour and care, and to incorporate this knowledge into the AQUARIAN range of diets for fish. In the UK, the WALTHAM Aquacentre is situated in Birstall, near Leeds. The research facilities consist of over 150 tanks, including a marine recirculation system, and two freshwater recirculation systems of 6,000 litres. An in-house hatchery supplies fish for trials, as well as investigating the nutrition and husbandry of breeding fish. The tank facilities are backed up by a pilot plant fully equipped with flake, pellet and extruder manufacturing machines, and a state of the art laboratory where complete nutritional analysis of ingredients and trial diets are performed. The research facilities are staffed by fish nutritionists, behaviourists, veterinarians, and food technologists to ensure that all the latest advances in fish nutrition and care can be implemented in AQUARIAN products.
DIET TESTING AND DEVELOPMENTOne of the difficulties of feeding ornamental fish is that, with few exceptions such as the goldfish (Carassius auratus) and koi carp (cyprinus carpio), they are rarely kept in a single species environment. Differences in nutritional requirements and feeding habits complicate the formulation of a single diet, which will meet all the requirements of a mixed community, which may include representatives of herbivorous, omnivorous and carnivorous fish species. While an adequate supply of nutrients is essential for the optimum health of all the fish, the enclosed aquatic environment means that overfeeding and poor diet formulation will have a detrimental effect on aquarium water duality. Because of this, diets are subjected to a variety of different tests to ensure they perform to the highest standards. For example, digestion of major nutrients is not uniformly efficient for all species of fish, and there are a large number of factors that determine the digestibility of protein, fat and carbohydrate. The evaluation of digestibility for ornamental fish at the WALTHAM Aquacentre takes place using specially designed tanks that allow the continuous collection of faeces from even the smallest species. Test diets are routinely fortified with 0.5% indigestible chromic oxide as an inert digestibility marker to trace the fate of all protein, fat and carbohydrate consumed by the fish. These data, augmented by growth data and accurate assessment of water pollutants, indicate the efficiency of growth on various diet formulations. Studies have shown that four-fold differences exist between commercial diets in terms of growth per gram of food fed, indicating that some ornamental fish foods are largely indigestible and probably highly polluting.
VITAMIN BIOAVAILABILITY
Another important area of nutrient utilisation is vitamin bioavailability. As ornamental fish usually have limited access to natural food, vitamins must be supplemented through the diet. When food is distributed in the water, the rate of loss of water-soluble vitamins is very high. Studies at the WALTHAM Aquacentre have shown that, depending on solubility, up to 90% of some B vitamins, and 65% of vitamin C can be leached from foods within 30 seconds of contact with water. Using less soluble vitamin sources, and by careful control of vitamin levels in food, AQUARIAN diets have been formulated to overcome these problems of rapid vitamin loss.
PALATABILITY STUDIES
However digestible and complete the diet is on paper, it will do the fish no good at all unless it is eaten! Palatability in terms of food recognition and uptake is important to ensure that fish will be attracted to the food and consume all that is fed in a reasonable time, before it is degraded through exposure to the tank water. Like mammals, fish distinguish between taste and olfactory signals. The gustatory response varies for each species of fish, and can even be different for one species from different geographic locations. Work carried out at WALTHAM has shown that ornamental fish can exhibit very consistent preference for one diet over another when the two are fed simultaneously. This technique is used to determine species specific preference for experimental diets. The analyses described above are just some of the many tests that are performed to ensure that diets are continually improved and are of the best quality. Through many years of research and development the WALTHAM Aquacentre has defined the strict criteria which ornamental fish diets need to meet to be acceptable as ornamental fish foods and the AQUARIAN range of diets has been developed to meet these criteria.
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