Effect of plant feedstuffs on nutritional physiology and intestinal health of Tilapia Oreochromis niloticus

Plant feedstuffs have been widely used as an alternative for fish meal due to reasonable price and acceptable protein concentration. However, plant feedstuffs are known to contain anti-nutritional factors that may affect fish performance, Some of these factors have also been implicated in intestinal disorders in several species such as Atlantic salmon, carp or trout. It is generally assumed that tilapia is tolerant to the use of plant feedstuffs, but effects on the intestinal level have not been documented. There is a general lack of knowledge on how to define intestinal ‘health’ in fish and how it is affected by sudden changes in diet composition. Histology was used to assess intestinal health, focussing on gut barrier function. In the current study, we assessed temporal effects of a sudden change in diet composition on the nutrient digestibility capacity and intestinal health of tilapia during a 6-week period. Tilapia fingerlings were reared on a fish meal based diet until they reached about 10 grams at the start of the experiment. Then, they were suddenly switched to one of seven experimental diets: 1) a basal diet based in fishmeal as protein source, 2) using feather meal, 3) using different plant proteins: soybean, canola, sunflower, rice bran and distillers dried grain with solubles (DDGS). The experimental diets 2-7 were based on basal diet 1 whereby part of the diet is replaced by one of the plant proteins or animal protein (70% basal diet plus 30% test ingredient). All diets contained yttriumoxide as a marker. All diets were tested in triplicate tanks, each with 35 fish per tank. Feeds were fed restricted twice daily to 3% body weight. Fish and feaces were sampled after 1, 3 and 6 weeks to study short term and longer term adaption to the diets. Faeces was collected by separate settling tanks. Overall growth and feed efficiency was calculated at the end-of-experiment. Water was recirculated over a large biofilter; oxygen, ammonia, nitrite and nitrate were regularly monitored and water temperature was kept at 280C. Fish (2 per tank per period) were sampled for stomach pH, histology of stomach and proximal, mid and distal parts of the intestine. A new method for quantitative scoring of the histology slides was developed. At the moment of submitting the abstract, the 6-week experiment with tilapia was finished, but most analyses including histological evaluation remained to be done. We will present and discuss our findings at the conference.