The effect of fish meal replacement by soyabean products on fish growth: a meta-analysis

Meta-analysis was applied to quantify the effect of replacement of fish meal by soyabean products in diets on fish growth. Measurement of growth in different units among studies required the use of a standardised effect size (Hedges' d). From a total of ninety-nine studies concentrating on fish meal replacement by defatted soyabean meal, 53% were eliminated due to, among others, absence of a fish meal control diet (n 18), or no statistical differences or measurement of dispersion (n 6) indicated. Replacement of 4 to 40% fish meal by soyabean meal (inclusion levels of 71-366 g/kg) resulted in a mean effect size of -0.1142 (95% CI - 0.4665, 0.2382) obtained in forty-eight comparisons evaluated with seventeen different fish species. However, at higher fish meal replacement levels the 95% CI calculated for combined effect sizes did not overlap with zero. With soya protein concentrate replacing 25 to 100% of fish meal in diets for seven fish species, methionine supplementation (mean -2.4373 (95% CI -3.9004, -0.9742); n 10)did not have a substantial influence on the magnitude of cumulative effect sizes relative to no supplementation (mean -2.7306 (95% CI -3.7991, -1.6620); n 16). Information on other soyabean products (full-fat soyabeans, soya flour) used as protein sources in fish diets was found as too limited for analysis and definite conclusions. The present study contributes by putting a numerical value to the magnitude of growth differences in fish when replacing dietary fish meal by soyabean products.