Trophic Levels Predict the Nutritional Essentiality of Polyunsaturated Fatty Acids in Fish—Introduction to a Special Section and a Brief Synthesis

Abstract

AbstractDefining nutritional fatty acid essentiality in fish nutrition is complex given the wide range of taxonomic (e.g., divergence among species subjected to different selective pressures), biological (e.g., trophic levels and environmental tolerances), and external (e.g., experimental conditions and differences in feed formulation and manufacturing) factors involved, all of which can influence absolute requirements. Fishes vary in their ability to meet the physiological demand for long‐chain (LC) polyunsaturated fatty acids (PUFAs; i.e., 20:4[n‐6], 20:5[n‐3], and 22:6[n‐3]) via elongation and desaturation of C18 PUFA (i.e., 18:2[n‐6] and 18:3[n‐3]) precursors. Previous attempts to generalize dietary fatty acid requirements have been focused on thermal and salinity preferences, suggesting—in many cases inaccurately—that coldwater and/or marine fish exhibit dietary requirements for LC‐PUFAs but warmwater and/or freshwater species do not. Here, we provide a review of the current literature on the subject of dietary fatty acid essentiality in fish and introduce the experiments that form the basis of this special section. In these experiments, we tested the nutritional essentiality of C18 PUFAs versus LC‐PUFAs in feeds for five finfish relevant to intensive aquaculture: Rainbow Trout Oncorhynchus mykiss, Channel Catfish Ictalurus punctatus, Nile Tilapia Oreochromis niloticus, Florida Pompano Trachinotus carolinus, and hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), hypothesizing that the nutritional essentiality of C18 PUFAs versus LC‐PUFAs would be determined by trophic level. The findings collectively suggest that trophic level is the most reliable predictor of C18 PUFA versus LC‐PUFA nutritional essentiality in fish.