Evaluation trials were undertaken in two evaporation basins filled with saline groundwater to identify finfish and shellfish that have the potential to survive and grow in these conditions. Test animals were reared in replicate culture units in each of two basins filled with saline groundwater located in the Goulburn±Murray Irrigation District (GMID), southeastern Australia. Salinity in basin 2 (9.5±24.6 p.p.t., mean 16.8 p.p.t.) was significantly higher than in basin 1 (8.8±15.2 p.p.t., mean 11.6 p.p.t.). Some differences were observed between the ionic concentrations in the groundwater and sea water (at 10 p.p.t.) and may have affected growth and survival of some species. Survival and growth for oysters (Crassostrea gigas and Saccostrea glomerata) in the basins were low. Shrimps (Penaeus monodon and Marsupenaeus japonicus) did not survive beyond 3 weeks. Of the eight species of fish stocked into the basins, Salmo salar, Macquaria novemaculeata and Acanthopagrus butcheri survived and grew in both basins. Oncorhynchus mykiss did not survive in the low-salinity basin, whereas Bidyanus bidyanus did not survive in the high-salinity basin. These results indicate that some species of fish in particular can be cultured in saline groundwaters within the GMID.

The gonadal development of Murray cod, Maccullochella peelii peelii, in Lake Charlegrark, Victoria, and adjacent farm ponds was evaluated. Gonadosomatic index, macroscopic classification and histological analysis were used to determine the age at first maturity and the gonadal development in this introduced population. There is a marked difference between the sexes in the size at first maturity, with females maturing at approximately 6 years of age and 2000 g in weight and males maturing at 3-4 years and 700 g. Gonadosomatic index data indicate that spawning occurs around November. Ovarian development in this species follows a pattern similar to that in a number of other teleosts. Testes have a lobular structure. Macroscopic evaluation of ovaries provided a good indication of the stage of the development of the gonad. However, the presence of spermatozoa throughout the year in the gonads of mature male fish makes the macroscopic evaluation of testicular development less reliable. Three cod, approximately 1% of the population, contained gonads with both ovarian and testicular tissue.

Hybridization is confirmed between two wild, naturally sympatric populations of Murray cod, Maccullochella peelii peelii, and trout cod, M. macquariensis, from the Murray River, Australia. Electrophoretic comparisons of proteins in muscle and liver tissues from trout cod, Murray cod, an artificially produced hybrid of Murray cod and trout cod, and putative wild hybrids from the Murray River indicated that the last group were first-generation interspecific hybrids. This is the first record of hybridization between naturally occumng populations of these two species. Naturally occurring wild populations of both trout cod and Murray cod are nonetheless genetically distinct and there is no evidence of introgression between the species. These findings have some implications for management policies and practices in relation to both species, and these are discussed.

The concept of integrating aquaculture with irrigated farming systems was evaluated in three projects in the Goulburn–Murray Irrigation District (GMID) in south‐eastern Australia. (1) Semi‐intensive cage culture trials using silver perch, Bidyanus bidyanus (Mitchell), were undertaken in a range of irrigated farming systems: irrigation supply channels; groundwater supplies; and on‐farm storage dams. Survival and growth of fish under these conditions were comparable to fish reared in conventional aquaculture ponds. However, poor water quality at some sites reduced survival and growth. (2) A study was undertaken to assess the feasibility of the cage culture of silver perch and rainbow trout, Oncorhynchus mykiss (Walbaum), in three irrigation water storage reservoirs. Conditions within each reservoir, particularly water quality, wind and wave action, and cage fouling, varied considerably, and influenced fish growth and survival. (3) Mariculture trials were undertaken in two saline groundwater evaporation basins, which were part of an integrated agriforestry and salt reclamation system. The species tested included two oyster, two prawn and nine fish species. Some species exhibited exceptional survival and growth rates under trial conditions. These projects indicate that the concept of integrating aquaculture with existing irrigated farming systems has the potential to enhance productivity, water use efficiency and overall environmental sustainability in the GMID.

The age and growth of Murray cod, Maccullochella peelii, in Lake Charlegrark, western Victoria, were determined by using otoliths from fish sampled by beach-seine and gill-net, or caught by anglers, between August 1978 and August 1982. Annulus formation was validated up to 11 + years by several methods. Otoliths were examined from hatchery-bred fish of known age (up to 4+ years) that had been stocked into local farm ponds. Analysis of incremental growth for all fish sampled from the lake indicated that the mean edge-growth ratio was lowest, and the percentage of otoliths with an annulus at the edge was highest, in October. A nominal birth date of 1 October was designated for the population to enable calculation of the absolute age for each fish. Age-composition data for those fish taken by gill-net and by anglers (up to 21 + years) revealed modal progression of strong year classes (1970 to 1973 inclusive) during the sampling period. Length-frequency data for those fish taken by beach-seine (up to 3 + years) revealed modal progression, on a seasonal basis, of two relatively strong year classes (1978 and 1979) during the sampling period. A von Bertalanffy growth curve was fitted to length and age data for all fish collected in the lake (no sex difference, P>O.05), and growth parameters were estimated for the population (L∞ = 695 mm). This curve did not adequately describe the growth of fish older than 11 + years because the majority of sampled fish (98.3%) were aged 11 + years or younger. The length-weight relationship for the population was determined by using data from all fish collected in the lake (no sex difference, P>0.05).