New B vitamin recommendations in fish when fed plant‐based diets

The present review presents data on fish requirement for B vitamins and describes their mechanism of action. Both general deficiency symptoms such as reduced growth and appetite, and more specific deficiency signs, for example abnormal swimming activity due to thiamine deficiency, are included. The rationale is to elucidate the need to establish B vitamin recommendations for fish fed practical diets where the major part consists of plant ingredients. Most requirement studies referred to were performed with semi-purified diets with relatively low growth rate compared to the growth potential of the fish obtained with practical diets. Further, when giving salmon a plant-based diet (70% plant ingredients), substantial lowered growth was obtained even when the diet was added vitamins according to the newest established requirements. New recommendations for B vitamin addition in plant-based diets are therefore urgent. Few requirement studies exist and often with lack of dose-response data. For riboflavin and biotin, this review includes a meta-analysis to support earlier requirement estimates. Too few data existed on the others to perform any meta-analyses that made sense. Based on literature data, meta-analyses, new experiments utilizing dose-response designs and identification of metabolic biomarkers, this review suggests new B vitamin recommendations for fish fed plant-based diets.