Scope for growth versus actual growth in the juvenile predatory gastropod Chorus giganteus

Abstract

The scope for growth (SFG) calculated on measurements of physiological variables in juvenile of the predatory gastropod Chorus giganteus was compared with the actual growth under an energetic point of view. The continuous increase in the amount of food ingested and absorbed by C. giganteus was clearly related to the body size of the snails. The pronounced increase in the metabolic processes of respiration and excretion at the end of the study was related with the high rates of growth experienced by the snails under the experimental conditions. These results were supported by the correlation analysis where ingestion rate (r=0.99), oxygen consumption (r=0.88) and excretion rate (r=0.89) were significantly correlated with the actual growth (P≤0.05). Comparing the estimated growth curve (SFG) with that directly measured on juvenile individuals of C. giganteus, a high similarity in results was observed. The high sensitivity of the scope for growth argues for the use of this index as an adequate tool for estimating the growth of juvenile gastropod molluscs without interference from reproductive processes such as gametogenesis and spawning which may produce corresponding rises and falls in the biomass of individuals. Scope for growth is thus validated as a reliable measurement of the physiological/energetic condition of the organism, representing an effective index for indirect estimation of the growth of a species.