Effects of replacing fish meal with plant protein in diets for Atlantic cod (Gadus morhua L.)

Abstract

In Northern Europe, interest in farming Atlantic cod Gadus morhua L. has increased steadily over the past decade stimulated by the decline in landings from fisheries, and the more predictable supply by hatchery reared juveniles for on-growing. From 1999 to 2007 the sale volume of farmed cod has increased from 145 to 10000 tonnes, and in 2008 13500 tonnes were slaughtered. Until recently, the protein in cod diets has been based on expensive, highquality fish meal. Currently, most marine resources, which are used in production of fish meal, are exploited to the highest maximum level, simultaneously as the global production of farmed fish has increased. Pressure is laid on the farming industry to stop using unsustainable diets, and find solutions that are in agreement with sustainable management. It is therefore essential to evaluate the potential for using plant proteins in diets for Atlantic cod. Four feeding trials have been conducted to evaluate the use of plant proteins in diets for Atlantic cod. A mixture of soybean concentrate and wheat gluten can replace 58% protein from fish meal, and a mixture of soy protein concentrate, bioprosessed soybean and wheat gluten meal can replace at least 25% of the fish meal protein without reducing growth. Inclusion of plant protein reduces protein utilisation, but can to some extent be compensated for by increased feed intake. Corn gluten is not recommended used as it gave reduced nutrient digestibility and a yellow skin colour. Plant protein inclusion did not affect health negatively, except for severe gut damage when 100% of fish meal was replaced by plant protein (a mixture of protein concentrate, bioprosessed soybean and wheat gluten meal). Gut passage time was not affected by plant protein inclusion. Adding lysine above 1.9% of diet (corresponding to 4.0% of protein) did not improve total growth, but gave reduced lipid storage. Adding methionine above 0.9% of diet (corresponding to 1.8% of protein) did not improve total growth, and did not affect lipid storage. In conclusion there is a high potential for safe use of plant proteins in diets for Atlantic cod without challenging performance, provided that the plant ingredients are of high quality.