Establishing the principles by which the environment affects growth in fishes

David J. McKenzie and Peter V. Skov discuss the impact of J.R. Brett's chapter “Environmental Factors and Growth” in Fish Physiology, Volume 8, published in 1979.

This chapter reviews how abiotic and biotic environmental factors shape the growth of fishes, based upon how they influence “scope for growth”, the difference in growth rate between maintenance ration and maximum ration. Brett develops a framework to classify environmental factors based on the mechanisms by which they influence scope for growth, by direct analogy to the highly influential Fry Paradigm which focusses on how the abiotic environment affects metabolism and scope for activity. Brett was Fry's student and his highly inspired scope for growth paradigm considers the anabolic component of animal energetics, how food is used to grow body tissues, and how abiotic and biotic conditions affect feed intake and utilization. Brett adopts Fry's categorization of “Factors,” defined as being either Controlling, Limiting, Masking, or Directive, depending on whether they govern, restrict, modify, or cue a response, respectively. The main Controlling Factor is temperature whereas major Limiting Factors are food availability (ration) and oxygen availability (hypoxia). The chapter appeared just as the growth of fish farming began to take off and is still heavily cited in aquaculture journals because it covers issues that remain important in fish nutritional and bioenergetic research. Brett's paradigm has received some attention from fisheries biologists, but we believe that it deserves much greater attention from conservation physiologists and modelers that are interested in understanding and projecting how the multifaceted effects of global change will affect fish populations. In this context, Brett's careful consideration of how Factors can interact to influence growth is an exceptionally significant aspect of fish environmental physiology, since abiotic and biotic factors always occur in combinations. Overall, the chapter demonstrates the brilliance of Roly Brett as a scientist, his analysis of fish growth and bioenergetics was far ahead of his time and is still extremely relevant today.