Body segments related to primary functions like feeding and predator avoidance show a higher relative growth rate and differentiation during larval development . This type of growth is called allometric growth and has been reported in many fish species during larval development and is considered as an adaptive response to increase survival. As a result, the early ontogeny of fishes is characterized by drastic changes in every stage of the larval period. The objective of the present study was to evaluate the allometric growth during the larval stages of the Pacific red snapper to test the hypothesis of a differential growth during early development which can be useful to evaluate growth under different experimental culture conditions.
Larvae were obtained by spontaneous spawning of Pacific red snapper broodstock held under controlled conditions. From hatching until day 30, random samples of 10 to15 larvae were s ampled and digitally photographed. On each digital photograph, the TL and several body proportions associated with feeding and locomotion were measured to the nearest 0.01 mm (Table1). Allometric growth patterns during the developmental stages were modeled by a power function of TL and the patterns in allometry were described by the growth coefficient (i.e. power function exponent, b) in the equation Y = aXb. Isometric growth occurred when b = 1. A positive allometric growth occurred when b >1 and a negative allometric growth when b <1.
The results showed that body segments have a different growth coefficient depending on the stage of the larval period (Table 1). Clear positive allometry was observed during the yolk-sac larvae in the TAL. During the preflexion stage, only the TRL showed a clear negative allometry. A tendency to isometry was observed in all the body segments during the p ostflexion stage. Our results showed that Pacific red snapper larvae have a differential growth suggesting priorities in development to increase survival during this critical period.