Size-independent growth in fishes: patterns, models and metrics

A combination of a dynamic energy budget (DEB) model, field data on Atlantic salmon Salmo salar and brown trout Salmo trutta and laboratory data off Atlantic salmon was used to assess the underlying assumptions Of three different metrics of growth including specific growth rate (G), standardized mass-specific growth rate (G(S)) and absolute growth rate in length (G(L)) in salmonids. Close agreement was found between predictions of the DEB model and the assumption of linear growth in length and parabolic growth in mass. Field data comparing spring growth rates of age 1+ year and 2+ year Atlantic salmon demonstrated that fit all years the larger age 2+ year fish exhibited it significantly lower G, but differences in growth in terms of G(S) and G(L) depended on the year examined. For brown trout, larger age 2+ year fish also consistently exhibited slower growth rates in terms of G but grew at similar rates as age 1+ year fish in terms of G(S) and G(L). Laboratory results revealed that during the age 0+ Year (autumn) the divergence in growth between future Atlantic salmon smolts and non-smolts was similar in terms of all three metrics with smolts displaying higher growth than non-smolts, however, both G(S) and G(L) indicated that smolts maintain relatively fast growth into the late autumn where G suggested that both smolts and non-smolts exhibit a sharp decrease in growth from October to November, During the spring, patterns of growth in length were significantly decoupled from patterns in growth in mass. Smolts maintained relatively fast growth though April in length but not in mass. These results suggest G(S) can be a useful alternative to G as a size-independent measure of growth rate in miniature salmonids. In addition, during certain growth stanzas G(S) may be highly correlated with G(L). The decoupling of growth in mass from growth fit length over ontogeny, however, may necessitate a combination of metrics to adequately describe variation in growth depending on ontogenetic stage particularly if life histories differ. Journal compilation (C) 2008 The Fisheries Society of the British Isles.