The migration of juvenile fishes (<5 cm) into the temporarily open Mhlanga estuary was monitored to determine the effects of different opening periods on immigration. The estuary opened at the end of January 1978 following a nine month closed phase. Only two marine species were recorded entering the estuary in February, compared to 11 species in November 1978. The estuary was closed between April and September. The large November recruitment may be attributed to the abundance of juvenile fishes in the sea adjacent to the estuary, whereas by February very few juveniles were present in Natal inshore waters. Estuarine and freshwater fish species were found to breed inside the estuary during the closed phase when environmental conditions were relatively stable. Mechanisms employed by these species to prevent eggs and larvae from being swept out to sea are discussed, as are strategies used by marine species to ensure recruitment during the very short open phase of the estuary. Die migrasie van jong vi sse (<5 cm) in die tydelike oop Mhlanga estuarium is gemonitor om die invloed van verskillende oop periodes op immigrasie te bepaal. Die estuarium het teen die einde van Januarie 1978 oopgegaan na 'n geslote tydperk van nege maande. Slegs twee mariene spesies is aangeteken wat die estuarium in Februarie binnegekom het, in vergelyking met 11 spesies in November 1978. Die estuarium was tussen April en September gesluit. Die groot Novemberaanwas mag te wyte wees aan die volopheid van jong visse in die aangrensende see terwyl daar in Februarie min in die Natalse waters was. Dit is gevind dat estuariese- en varswatervisspesies broei gedurende die geslote fase in die estuarium as omgewingstoestande relatief stabiel is. Meganismes wat aangewend word om te verhoed dat eiers en larwes meegevoer word na die see sowel as strategië wat deur mariene spesies gebruik word om hervestiging gedurende die baie kort oop-fase van die estuarium te verseker word bespreek.