Utilization of Alternative Protein Constituents in Tilapia Feed
B.R. Stange, North American Fish Farmers Cooperative
Nutritional requirements of fish grown in closed recirculating systems must be entirely supplied through the feed. Although tilapia (Oreochromis spp.) are considered to be mainly herbivores by nature, most commercially available tilapia feeds contain significant levels of animal derived proteins (fish meal and blood meal primarily).
Feed is a costly expenditure for fish producers, accounting for as much as 50% of production costs. Fish meal is becoming more expensive due to a high demand and shrinking supply which has promoted investigation of more economical sources of protein. Vegetable-based proteins are usually less expensive than animal derived proteins. The latest trial conducted at the NDSU Carrington Research Extension Center tested eight rations which utilize one or more of the following in each: canola, soybeans, lupins, peas, wheat, barley, corn and flax (see table).
Trial system componentry consisted of 24 - 680 liter round plastic experimental tanks, each equipped with separate filtration systems (945 liter total system volume). Water recirculation was achieved through airlift pumping and oxygen was supplied using a regenerative blower. Temperature was regulated using aquarium heaters.
Eight feed rations were formulated at the Prairie Nutrition Center in Hebron, ND and were manufactured by Maertens Manufacturing in Center, ND. Plant based proteins which were utilized included barley, flax, soybean meal, lupine, field pea, corn, wheat and canola. Fish were fed using automatic belt feeders and amounts of feed were calculated based on a percentage of biomass in each tank. Feed amounts were periodically adjusted based on feed reaction and water quality. Most area fish producers currently utilize ration 6 which served as a control ration for this trial.
Within each of the experimental tanks, 100 sex reversed, all male fingerling tilapia were placed. Three random replicates were selected for each ration.
For the duration of the trial, temperature and dissolved oxygen (D.O.) levels were maintained at 27-29 C and 3.5-5.0 mg/l respectively. Levels of ammonia, nitrite and nitrate were monitored weekly. Water temperature and D.O. levels were monitored daily.
Ration 3 yielded the best feed conversion ratio while ration 4 was the poorest.
Despite the superiority of the conversion ratio of ration 3, growth rate was less than the top three performing rations. By week 18, no statistical differences (P) were detectable between rations 2, 3 and 8. At the end of the trial, the average weight of all fish fed ration 3 had surpassed the other rations, however, collectively among the tanks, significant mean weight differences did not exist between all of the rations except ration 4 which consistently yielded the lowest biomass values.
Fish fed ration 5 performed the best for most of the trial duration. Water quality
data in all ration 5 treatments exhibited the lowest levels of ammonia, nitrite and nitrate and rations which contained animal-based proteins tended to produce higher levels of nitrogenous compounds.
The results of this study indicate that the growth rate of fish fed rations containing plant-based proteins is equal to or greater than rations containing an animal-derived protein source. Additionally, it has been shown that rations containing a 26% crude protein content yielded results equal or better than rations containing 32%.