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 20·1142 (95 % CI 2 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 2·4373 (95 % CI 23·9004, 20·9742); n 10) did not have a substantial influence on the magnitude of cumulative effect sizes relative to no supplementation (mean 22·7306 (95 % CI 23·7991, 21·6620); 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.Fish meal: Soyabean products: Fish diets: Growth: Meta-analysis Reviews on the future of aquaculture production (1) and development of fish diets (2 -9) have centred around the replacement of fish meal, on which most fish diets are based, by economically viable and environmentally friendly plant protein alternatives. Defatted soyabean meal has received considerable attention due to a high protein content, reasonably balanced amino acid profile, consistent availability, cost effectiveness and palatability to most fish species (4,6) .Soyabeans, although evaluated after heat treatment in the whole form in fish diets, are predominantly processed into defatted soyabean meal with or without hulls, but also into soya flour, soya protein concentrate and soya protein isolate. However, costs hamper the use of the latter processed products for effective replacement of fish meal in fish diets (6) .As with all potential plant protein sources, the nutrient and antinutritional profiles of soyabean meal are currently not ideal for inclusion in fish diets (6,10) . Furthermore, as summarised by, among others, Chou et al. (11) and Lim et al. (12) , there generally appears to be large variability among fish species in the maximum dietary levels of soyabean meal tolerated, indicating different sensitivities to soyabean meal inclusion. Barrows et al. (13) concluded that the upper dietary inclusion levels of soyabean meal before fish performance or health will be deteriorated is 10 -15 % (25 % fish meal replacement) for carni...