Nile Tilapia Oreo chromis niloticus has become one of the most preferred and consumed farmed fish species globally . There are commercial diets without fish meal available for Nile tilapia , and many of these contain high inclusion levels of plant ingredients. Some of these, such as soybean meal, have favorable amino acid profiles. However, plants also contain anti-nutritional factors that can limit their use in fish diets. In addition, s oy (and some other plant ingredients) are scarce in many developing countries where tilapia species are cultured, and are valued more for human food. T he availability of alternative high-quality feedstuffs with a consistent nutrient profile is often limited in these regions. The addition of commercial concentrates containing high levels of digestible protein and essential micronutrients to diets could make up for the inferior quality of cheaper ingredients and improve production profitability of tilapia .
We conducted a digestibility trial and a feeding trial with the commercial products Omni 55, Elite 60, Elite 65, and Elite 70 , which are proprietary blends provided by H J Baker & Bros, Tuscola. Test diets for the digestibility trial were formulated from a 35% protein commercial-type reference diet and were composed of a 70:30 mix of reference diet to the following test ingredients: Aqua-PakTM , Aqua-Pak® 60, Aqua-Pak® 65, and Aqua-Pak® 70.
Ingredient ADCs of dry matter and lipid were different for all ingredients - the Aqua-Pak® 70 had higher dry matter and lipid ADCs than other ingredients. The ADCs for protein were similar and uniformly high among all Aqua-Pak ingredients. The apparent digestibility coefficients (ADC) of dry matter and crude protein were similar for Aqua-Pak™ , Aqua-Pak® 60 , Aqua-Pak® 65 , and Aqua-Pak® 70 diets. A higher lipid ADC was observed for Aqua-Pak® 70 than other diets .
For the feeding trial, 5 diets (one per concentrate and a control) were formulated using the nutrient digestibility data and fed to 5 groups of 20 fish (weighing 047 g initially) per diet twice daily to satiation for 12 weeks. Mean increase in weight gain (%) was highest in the fish fed the control diet (with chicken by-product meal) , but similar to the Elite 70. The fish fed the Elite 60, Elite 65, or Omni 55 had the lowest increase in weight gain. The FCR (range: 1.03-1.32) was lowest in fish fed the control diet and highest for those fed Omni 55, with others intermediate . Survival ranged from 82-91% and did not differ among diets. Alternative complement and lysozyme activity did not differ among diets. Overall, fish performance was similar on the concentrates and the control diet with no adverse effects of any of the diets. Therefore, economic analysis needs to be conducted to determine the commercial potential for inclusion of the concentrates in tilapia diets.