FISH FEED

As with all culture systems, there are many local variations in the feeds and feeding regimes utilized. There appears to be no universal system, and local availability seems to be the key criteria in developing a feeding schedule (Ottolenghi et al., 2004).

Fry and fingerlings are fed with mysids and small shrimp for a couple of days post-capture in tanks, to acclimatize them and check that all individuals are eating. Trash fish forms the main feed in nursery and production cages, which is minced or chopped to suit each size group; trash fish may be supplemented with vitamins and minerals. This kind of feed is gradually being replaced by moist pelleted feed.
Trash fish is commonly used for feeding in grouper cage culture, but its increasing cost, shortage of supply, variable quality and poor feed conversion ratios indicate that this form of feed may not be the best from either a nutritional or an economic point of view. However, groupers fed with bycatch (trash fish) in a study by Bombeo-Tuburan, Kanchanakhan and China (2001) fared significantly better in terms of final length and total production than when fed other diets (live tilapia, formulated diet).

A major problem is the limited supply of trash fish, so there is a need to develop a suitable diet for grow-out grouper production (Millamena, 2002). Fishery products, both in the form of low value trash fish or fishmeal, are presently the major sources of protein in the grow-out culture of most fish species and constitute up to 70 percent of their dietary composition. As the demand for fishmeal and fish oil for aquaculture increases, costs are expected to rise unless new sources (e.g. fish discards, krill, mesopelagics) can be economically exploited or substitutes for these marine products for inclusion in aquafeeds prove commercially applicable (New and Wijkstrom, 2002).
A dependable supply of cost-effective, non-marine, sources of alternative protein must be provided if fish farming is to remain profitable. Millamena (2002) conducted a feeding trial to evaluate the potential of replacing fishmeal with processed animal by-product meals, meat meal and blood meal, in practical diets for juvenile groupers (Epinephelus coioides). The study demonstrated that up to 80 percent of fishmeal protein can be replaced by processed meat and blood meal derived from terrestrial animals with no adverse effects on growth, survival, and food conversion ratio (FCR). From an economic standpoint, replacement of fishmeal with cheaper animal by-product meals in practical diets can alleviate the problem of low fishmeal availability and high costs. These processed by-products can be delivered in the Philippines, for example, at US$0.40/kg, less than half the price of most commercial fishmeals (US$1/kg). The effective use of meat meal-based diets for grouper grow-out also reduces the requirements for trash fish, another fishery resource that is extensively used (Millamena, 2002). Economic sensitivity analysis showed that a combination of improvements resulted in higher return-on-investment (ROI). However, these apparently favourable results must be balanced with the fact that some countries (e.g. in the EU) have banned the inclusion of all terrestrial meat-meal based products in fish feeds, due to fears concerning mad-cow disease (Ottolenghi et al., 2004).