The fishes occurring in the main tidal inlet to a typical saltmarsh situated in southern Moreton Bay were studied from January to December 1984. The aim of the study was to determine the type of fishes and their feeding habits within the inlet, particularly for species of economic importance. Sampling was conducted at night on the full and new moon phases, and during the day on the full moon phase. A total of 19 species were recorded from the inlet, of which 11 are of economic importance. Six species were considered common. Most fish which entered the inlet were juveniles. The diversity of the fish assemblage from the inlet was low when compared with findings of other studies conducted in Australian subtidal mangrove areas. Die! differences in the size offish entering the inlet were recorded for several species. Two mark-recapture programmes were conducted to investigate short-term utilization of the saltmarsh by fishes. Recapture rates indicated that individuals of some species regularly utilized the saltmarsh. The most abundant species from the inlet were predominantly benthic feeders although one species fed on plankton. Terrestrial foods formed an important part of the diet of some fishes. The inlet serves as a feeding area for certain species although it is unlikely that these species rely exclusively upon the area. Future management of saltmarsh areas should include protection and maintenance of tidal inlets wherever possible.

Yellowfin bream were tagged and released in three non-spawning areas and two spawning areas in Moreton Bay, a large estuarine system on the east coast of Australia. A total of 194 fish were recaptured. Juvenile fish made only small-scale movements (less than 6 km) from the release site. Small-scale movements were also recorded for adult fish, although largescale movements from 10 to 90 km were also recorded. The large-scale movements appear to be associated with the migration of adult fish to or from surf bar spawning areas. Some adult fish remained in feeding areas during the spawning season (May-August). There was no indication from tag recoveries of any movements of yellowfin bream outside Moreton Bay and the results indicate that adult yellowfin bream in Moreton Bay may be regarded as a unit stock for the purpose of fisheries management.

SynopsisThe fishes occurring in a subtropical Australian saltmarsh were studied from January to December 1984 to determine the seasonal abundance and feeding of the most common species. Wide variations in pool water levels and salinity were recorded. Eight species of fish were collected, four of which are of economic importance to fisheries. Three taxa, Gambusia affinis, Pseudomugil signifer, and gobiids predominated in terms of abundance and occurrence. The abundance of fishes fluctuated markedly on a seasonal basis with few fish being taken in winter and spring (June-November) when pool water levels were low. Diets of the most common species were similar with terrestrial foods forming an important component of all diets. Feeding activity was highest in summer (December to February) when mosquito larvae, copepods, and larval coleopterans formed a large proportion of the fishes' diets. Results from the present study indicate that fish important to commercial fisheries rarely utilise the upper littoral saltmarsh habitat and that resident fishes are unlikely to effectively control mosquito larvae in saltmarsh.

Monthly changes in the gonosomatic index indicate that yellowfin bream, Acanthopagrus ausfralis, in Moreton Bay have a short spawning season with a peak during the period July to August each year. The growth rate of A . australis was estimated from tag-recapture data and by length-frequency analysis. Modes representing age classes 0, I and 11 oRen appeared in length-frequency distributions, however modes for older age classes were difficult to identify. The von Bertalanffy growth curve parameters calculated from release-recapture data are: L , = 29.5 cm; K = 0.51; to = -0.32 years.

Yellowfin bream, Acanthopagrus australis, of all age classes were collected from Moreton Bay, Australia. The species possessed typical sparid ovotestes in which the testis and ovary occur in separate zones. During the spawning period (June‐August) juveniles, functional males and functional females could be distinguished by the macroscopic appearance of the gonad. The sex ratio of males to females decreases with age, indicating protandrous sex inversion. Histological and structural study of the ovotestis showed all fish have previtellogenic cells in the ovarian zone but only juvenile and male fish have developing spermatogenic cells in the testis. Most juveniles become functional males by the age of two years but a small proportion of juveniles develop directly into functional females (primary females). Protandrous sex inversion commences after the spawning period when male fish appear with spermatozoa and no other spermatogenic cells in the testis. During the period November‐January male fish with no spermatogenic cells are common and a reduction in size of the testis occurs so that by March‐April the ovotestis becomes structurally and histologically similar to the female ovotestis. Some fish remain functional males during their whole life‐history (primary males). In functional females vitellogenic cells are present in the ovary only during the spawning period and the testis remains very small in size.