Study on the early larval development and growth of the red porgy, Pagrus pagrus with emphasis on the mass mortalities observed during this phase

Abstract

The purpose of this study was to determine the early growth scheme and development stages of the red porgy, Pagrus pagrus larvae through the transition from endogenous and exogenous food sources using as main criterion the body length gained at each development stage. The initial period of the species´ larval life can be divided into three phases: a) an initial phase characterised by no motility (0-24 h time after hatching; TAH); b) a phase characterised by active movement and exploitation of the endogenous food reserves (24 h to 96 TAH); and c) a phase characterised by the transition from endogenous to exogenous food (96 to 168 TAH). It was observed that there does not exist an overlapping period between phases b and c and therefore, there exists a gap of 24-36 hours during which the larvae have exhausted their internal food reserves (oil globule and yolk sac) while the digestive tract is not ready to digest external food items (rotifers). We observed a massive larval mortality reaching almost 85% between days 3 and 7 after hatching.