Feeding aquaculture in an era of finite resources

Abstract

Aquaculture's pressure on forage fisheries remains hotly contested. This article reviews trends in fishmeal and fish oil use in industrial aquafeeds, showing reduced inclusion rates but greater total use associated with increased aquaculture production and demand for fish high in long-chain omega-3 oils. The ratio of wild fisheries inputs to farmed fish output has fallen to 0.63 for the aquaculture sector as a whole but remains as high as 5.0 for Atlantic salmon. Various plant- and animal-based alternatives are now used or available for industrial aquafeeds, depending on relative prices and consumer acceptance, and the outlook for single-cell organisms to replace fish oil is promising. With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it.

Fig. 1.

Sensitivity of FI/FO to changes in FCRs (A) and fishmeal and fish oil inclusion rates (B). Base assumptions for FCR and fishmeal and fish oil inclusion in diets (Incl_FM, Incl_FO) are taken from Table 1. FI/FO represents kg of reduction fish required to produce 1 kg of farmed fish, equal to the sum of the reduction fish equivalent for fishmeal (RFE_FM) and additional fish oil (RFE_AO). RFE_FM is calculated as: FCR × Incl_FM/0.225, assuming that the average yield of 1-kg reduction fish made into fishmeal is 22.5%. In calculating RFE_AO, residual fish oil and the amount of oil extractable from RFE_FM are both subtracted from the total fish oil inclusion. It is assumed that 8% residual fish oil on average is found in fishmeal. Hence RFE_AO is: [FCR × (Incl_FO − 0.08 × Incl_FM)/0.05] − (0.05 × RFE_FM), where the average yield of 1-kg reduction fish made into fish oil is assumed to be 5%. Original calculations by R.W.H. in 2008.

Fig. 2.

Comparison of macronutrient intakes required for producing 1 kg of biomass gain in different fish and livestock (pig, broiler chicken) species based on feed practices in 2007. These data are based on D.P.B. and K.H.'s original calculations from information obtained directly from industry sources and expert knowledge of feed practices (feed inputs, conversion ratios) during the entire life cycle of each species. The calculations represent commercial (not experimental) practices under normal operating conditions averaged across the industry. This average incorporates differences in regulatory environments, final market weights, ingredient prices, and production constraints such as disease. The calculations show g of macronutrient intake per kg of farmed weight gain. They include the whole animal and do not separate out the edible portions, the latter being too variable for this analysis.