EFFECT OF PHYTASE SUPPLEMENTATION ON MINERALS AVAILABILITY, NUTRIENT DIGESTIBILITY AND GROWTH PERFORMANCE OF LABEO ROHITA FINGERLINGS FED ON PLANT BASED DIETS

Abstract

The Labeo rohita is one of the commercially important carp of the South Asia. It is being traditionally cultured extensively and semi-intensively since long in poly-culture and composite culture systems. Efforts are always required to introduce it in intensive culture systems to achieve highest productivity. The present research project was planned to determine the effect of phytase supplementation on mineral availability, nutrient digestibility and growth performance of Labeo rohita fingerlings fed on plant-based diets with the objective to increase the said freshwater cultured fish by formulating and feeding cost effective practical diet. Plant ingredients are usually rich in phytic acid, which reduces the bioavailability of proteins and mineral to fish. A diet containing 30.21% protein from fish meal and having caloric value of 4.26 Kcalg-1 was as reference diet. Four experimental diets were then prepared with the help of lab extruder by taking 70% reference diet and 30% sunflower meal, cottonseed meal, canola meal and corn gluten meal (30%) in diets 1,2,3 and 4 respectively. Each test diet was further splitted into seven components and treated with 0, 250, 500, 750, 1000, 1250 and 1500 FTU/kg-1 levels respectively. Chromic oxide was included at a concentration of 1.0 % as non-digestible marker in the feed. The fingerlings were stocked in V-shaped tanks specially designed for the collection of fecal material. Triplicate tanks were assigned to each treatment. Fish were fed @ 2 % of live wet weight of fish. Feces from each tank were collected twice a day. The collected material was dried at 60oC and pooled for each treatment. Water quality parameters viz., temperature, dissolved oxygen and pH in each tank, were monitored throughout the experimental period. Sufficient evidences were also available to conclude that 750 FTU kg-1 level in sunflower meal, cottonseed meal, canola meal and corn gluten meal (30%)-based test diets has increased the bioavailability of nutrients and mineral to Labeo rohita fingerlings which in turn resulted significant (P<0.05) increase in growth performance parameters also. Sunflower meal-based diet performed best with reference to all fish growth, nutrients digestibility and mineral availability indices followed by cottonseed meal, canola meal and corn gluten meal (30%) based diets. The most of the plant based diets supplemented with 750 FTU kg-1 level diet performed better than that of reference diet. Therefore, phytase application at 750 FTU kg-1 level in plant ingredients (sunflower meal, cottonseed meal, canola meal and corn gluten meal 30%) based diets was suggested to enhance the release of bound nutrients and mineral for optimal growth performance of Labeo rohita fingerlings.