Spawning of riverbream, Acanthopagrus berda, in Kosi estuary

ENGLISH ABSTRACT: The spawning habits of Acanthopagrus berda, an estuary-dependent seabream (Family Sparidae), are investigated. Spawning takes place in the Kosi estuary at night and eggs are transported out to sea during peak ebb tides. There is a preponderance of males in the spawning aggregation (sex ratio - 8,8 : 1 m/f) and indirect evidence suggests that males and females are continually recruiting to the aggregation, spawning, and moving back up into the lakes so that there are no more than 2000 individuals at the mouth at any one time. Sexed fish were tagged in an effort to produce evidence of protandrous sex change in this species. It is noted that the degradation of estuarine habitats could have serious effects on an estuarine-dependent species which has developed a spawning strategy of this nature. ********* AFRIKAANSE OPSOMMING: Die broeigewoontes van Acanthopagrus berda, 'n riviermond-afhanklike seebras (Familie Sparidae) is nagevors. In die Kosi tregtermonding vind kuitskiet in die nag plaas en die eiers word gedurende piek ebgetye na die see weggevoer. By die broeisameloop is daar oorwegend mannetjies (geslagsverhouding -8,8 : 1 m/f) en onregstreekse bewyse toon dat mannetjies en wyfies voortdurend by die sameloop aansluit, broei en dan na die mere terugbeweeg, sodat op 'n gegewe tyd daar nooit meer as 2000 individue by die tregtermond voorkom nie. Visse waarvan die geslag bepaal is, is gemerk in 'n poging om bewyse van protandriese geslagsverandering by die spesie te vind. Daar word kennis geneem dat die agteruitgang van die tregtermondhabitatte 'n ernstige uitwerking sal hê op riviermond-afhanklike spesies wat 'n broeistrategie van die aard ontwikkel het.