Potential use of poultry meal in diets for gilthead seabream (Sparus aurata): effect on growth performance, feed utilization and digestibility

One of the biggest challenge in aquaculture is the formulation of nutritionally balanced diets, at a reduced coast but still maintain fish as valuable food for human consumption. Fishmeal has been an essential ingredient used in aquaculture feeds, due to its nutritional profile, being the primary choice as protein source in diets for carnivorous fish species. However, the price of fishmeal is expected to increase dramatically over the next few years as aquaculture production and livestock increase, which will certainly affect the profitability and economic sustainability of the aquaculture industry. Sustainable aquaculture industry will necessarily involve the dietary fishmeal replacement by alternative ingredients, ideally with an equivalent nutritional value to fishmeal. Poultry by-product meal (PBM) is a rendering animal by-product that has a relatively high protein content and a balanced amino acid profile. It was banned to be included in aquafeed in the European Community since the bovine spongiform encephalopathy (BSE) crises. Recently, with the re-authorization of non-ruminant processed animal proteins in European aquafeeds, it is expected that research insights will greatly contribute for its use and so for the sustainable development of European aquaculture. Gilthead seabream (Sparus aurata) is a highly important commercial value specie in Europe, particularly in Mediterranean Sea, but to maintain its production it will be needed to consider new strategies, as the development of environmental sound diets at reduced cost. Therefore, present study aims to evaluate the effect of gradual replacement of fishmeal by a local animal by-product, poultry by-product meal (PBM), in growth, feed efficiency, digestibility and economic efficiency of gilthead seabream juveniles. Six isoproteic and isolipidic diets were formulated (45% CP; 18%CL): a control diet (PBM0), with fishmeal as the main protein source, and PBM7.5; PBM15; PBM22.5; PBM30; PBM37.5 where fishmeal was replaced by PBM at 7.5%, 15%, 22.5%, 30%, 37.5%, respectively. Triplicate groups of juvenile gilthead seabream, with an average body weight of 63g, were fed for 70 days with each experimental diets. At the end of the feeding trial, growth rate, weight gain, voluntary feed intake, feed and protein utilization, were not affected by the dietary treatment. Similarly, whole-body composition was unaffected by the experimental diets. Apparent digestibility coefficients of dry matter, protein, energy and phosphorus were also not affected by the dietary replacement of fishmeal by PBM. Additionally, no effect of diets on the digestive protease, trypsin, chymotrypsin, lipase and amylase activities were observed, in both the anterior and posterior intestine. However, posterior intestine showed higher enzyme activity than that of posterior intestine. Economic efficiency ratio decreased with the increase of fishmeal replacement by PBM. Overall, results shown that for gilthead seabream, up to 37.5% of PBM can be incorporated in practical diets, reducing the dietary fishmeal level to 7.5%, without affecting growth performance, digestibility, feed and protein utilization. Economic analysis revealed that PBM diets were less expensive and have the same economic profit index than fishmeal basis diets. Further investigations are required to determine the modulation effect of the dietary inclusion of PBM on other important aspects, such as the immunity and health status of the animal as well as on the fish/fillet quality traits.