Feed is by far the single largest cost component of barramundi farming and accounts for about 35% of on-farm operating costs. Reducing feed costs by better tailoring dietary specifications to the nutrient requirements of the fish, by providing these nutrients at least cost and by adopting feeding practices that optimise productivity will greatly assist farm profitability. In Australia, barramundi are pond-reared over latitudes from 5°S to 22°S and this results in large seasonal variations in water temperature and consequently, in growth rate of the fish.

The research conducted in this project sought primarily to characterise the effect of water temperature on fish productivity and how modification of dietary nutrient specifications and/or feeding practices could assist in improving farming profitability. This entailed research to define the fish's response to changes in dietary supply of critical nutrients over a range of water temperatures. Research examining the efficacy of crystalline amino acids in diets for barramundi was carried out in a supplementary project (FRDC 95/69); research on the nutritive value of terrestrial feed ingredients and their suitability as replacements of fishmeal in diets for barramundi is reported in FRDC 93/120-04.

The fishery for king prawns which occurs between 18°S and 21°S has been investigated over a three year period. The fishery takes place predominantly during winter months. Availability of alternative target stocks as well as recruitment timing is responsible for the fishery's timing.

Annual catch has increased to about 2000 tonnes in 1987, from an annual catch of about 700 tonnes in 1984. This has been brought about by increased effort in the fishery, as the average annual catch rate has remained steady.

About 70% of the catch is red spot king prawn, Penaeus longistylus. The remainder is blueleg king, P. latisulcatus. Redspot kings recruit onto the main fishing grounds in the Great Barrier Reef lagoon over an extended period, whereas blueleg kings recruit over a comparatively short period.

Blueleg king prawns follow a conventional penaeid life cycle. Juveniles use coastal flats as nursery areas and move to deeper water as they mature. Red spot kings are unique in that they use coral reef lagoons as nursey areas. The species' biology is attuned to the coral reef environment.

Tagging studies conducted on red spot king prawns showed that adults were sedentary. Estimates of growth parameters and natural mortality obtained from tagging data are sufficient to use in a basic yield model.