Training of Trainers - Library - Network of Aquaculture Centres in ...

This is a new approach used to build the organic matter content in the water by limited or no water exchange,thereby promote the growth of intensive microbial community (1 million to 1 billion cells ml). These bioflocs are usedby varieties of fish and shrimp as a high protein feed replacing some of the formulated feed and essentially recyclingprotein in different form. Main focus is on effective aeration to avoid any points within the pond to prevent anyanaerobic area. Provision for draining the excessive sludge is also essential and hence ponds have to be designedaccordingly. Water exchange for intensive fish ponds (10-50 kg fish /m 3 ) should be 5-10% per day whereas pondswith a biomass up to 2 kg /m 3 can be managed without any water exchange. Carbonaceous material are added toremove excess nitrogen and maintain a ratio of 15-20 : 1 carbon: nitrogen ratio. The technology has been widelyapplied both in the case of tilapia and shrimp. It appears that this would be a good technology in areas with limitedwater availability as well as in locations where environment concerns are major issues to promote aquaculturetechnology.(F) Low protein feeds in fish and shrimp farming:There is a tendency among the farmers to use high protein feeds than that are essentially required for field basedculture operations. Most nutritional requirement studies being conducted in closed door systems, particularly of earlysize and ages, feeding fish and shrimp in ponds of all sizes with same level of protein that too without taking in toconsideration of the natural food available in the system is viewed as a waste of nutrient input in to system anddamage to the environment. However, farmers without wanting to take any risk, always have a tendency to feed highprotein feeds. In the Vannamei it is well established that it grows well in feeds containing less than 30% (Fox andTreece, 2008). In the case of omnivorous tilapia, it is know that the fish can very efficiently exploit various nutrientsources from the natural food available in the water column. For such fishes, use of expensive feeds not only addscot to farmers, but also environmental qualities are affected because of the heavy discharge of nutrients.(G) Vitamins and minerals in outdoor systems:In outdoor pond systems, it is also shown that addition of vitamins and minerals may not be a necessity, particularlyin semi-intensive systems where there is abundance of natural food. These vitamins and minerals add significantfeed cost and farmers can well manage ponds without the addition of these nutrient elements Encouraging farmersto conduct on-farm trials on these types of findings would help them to decide for themselves and bring radicalchanges in the approaches. A number of experiments conducted in the case of shrimp and fish have clearly shownthat addition of these vitamins and minerals is not needed.(H) Growth based on sex:Research findings indicate that female shrimp eat less, but grow faster as compared to males. The findings of Mossand Moss (2006) on effects of gender and size on feed acquisition in the vannamei indicated that size and sexmatter in feed intake. Larger animals within the same gender ate more than the smaller animals. Females ate lessthan males even when the females were larger than males. When females and males were of similar size, males atemuch more feed than females. The results clearly indicate that females are growing larger is not because of eatingmore.(I) Pellet size and diameter:Shrimp are fed with different lengths and diameter based on the age factor. However, a research trial conducted byMishra (2006) in the Water Base Ltd company in India indicates that as the shrimp feed in the nature by holding anyfeed that attracts them by holding it with the second pair of chelated legs and cutting the feed using the mandibles, itmay not be necessary to give them feed of different dimensions at different ages. Limited trials indicate that there isno need to use such varied pellet size. As the decreasing pellet size would increase the cost of feed considerably,taking the natural feeding behavior of shrimp, it would be possible to reduce the feed cost significantly.104