Ectogenic Meromixis in a Brackish Water Pond in Tropical Northern Australian

Abstract

Heavy rainfall on a brackish water pond used to culture larval barramundi, Lates calcarifer, resulted in the stratification of the pond (average depth 1.5m) into freshwater and saline layers. The saline monimolimnion (ca.22 ppt salinity) accumulated heat from solar radiation, reachign a maximum water temperature of 38°C, while the fresher mixolimnion (ca.5ppt salinity) reached only 31°C during the same period. The probable causes of the total mortality of barramundi in this trial were water conditions resulting from ectogenic meromixis, i.e., the high temperature of the monimolimnion and the low salinity of the mixolimnion, which made both layers unsuitable for larval survival.