Ontogenetic allometric coefficient changes: implications of diet shift and morphometric traits in <i>Hoplias malabaricus</i> (Bloch) (Characiforme, Erythrinidae)

Abstract

This study evaluated the relationship between body size and digestive tract characteristics of the important predatory freshwater fish Hoplias malabaricus , which is widely distributed in South America. The allometric coefficients were calculated for the mass and standard length ( L S ) relationships for two different L S groups: (1) between 20 and 100 mm (characterized as insectivores) and (2) &gt;100 mm (characterized as piscivores). Differential growth measured from the allometric coefficient, b , between the insectivore ( b &lt; 3) and the piscivore ( b &gt; 3) groups was detected. Anterior intestine length and pyloric caeca zone length showed significant differences between groups. Two complementary hypotheses were developed to explain the differential growth: (1) H. malabaricus has a digestive tract adapted to a piscivorous diet, which is independent of its ontogenetic stage of development, and (2) the negative allometry observed in group 1 individuals agrees with a general behavioural strategy, allowing individuals to grow in L S during a shorter period of time.