THE LIFE-HISTORY OF THE TROPICAL SHAD TENUALOSA-TOLI FROM SARAWAK - FIRST EVIDENCE OF PROTANDRY IN THE CLUPEIFORMES

Sharp declines in catches prompted a detailed study of the commerciall y and culturally important 'terubok' Tenualosa toli, which lives in th e fast-flowing, turbid estuaries and adjacent shallow coastal waters o f Sarawak. Its reproduction, diet, age and growth were investigated. A n absence of small females and large males, together with histological data showing transitional gonads, suggest that T. toli is a protandro us hermaphrodite. Ageing based on otoliths indicates that individuals may not live more than about two years. Male fish spawn towards the en d of their first year, change sex (transitional gonads were recorded i n fish from 14 to 31 cm SL) and spawn as females in their second year. Spawning takes place in the middle reaches of estuaries and females d eposit all their eggs at once. Fecundity is linearly related to fish l ength but shows significant seasonal and site variations. Hermaphrodit ism is discussed in relation to possible environmental and isolating m echanisms. T. toli is a zooplanktivore eating mainly calanoid copepods . Laser-ablation inductively-coupled plasma mass spectroscopy of trace elements across otoliths revealed that the species does not move into full seawater or freshwater, but completes its life cycle in estuarin e and adjacent coastal waters. Therefore T. toli populations in each e stuary and adjacent coastal waters may be relatively isolated from one another, and hence particularly susceptible to overfishing.