Feral populations in Australia of the introduced cichlid, tilapia, were compared by using celluloseacetate electrophoresis to examine degrees of genetic differentiation among the disjunctive populations. Evidence was obtained to support the recognition of three morphs: two 'good' species (Oreochromis rnossambicus and Tilapia mariae) and a third morph that is a potential interspecies hybrid between 0 . mossambicus and one or more of the related Oreochromis species 0. honorum, 0 . niloticus and 0. aureus. Distributions of the three morphs are described, and their likely origins and potential impacts on native fauna are discussed.

Juvenile silver perch, Bidyanus bidyanus, were subjected to direct transfer from fresh water to various test salinities. No mortality was observed when the fish were transferred from fresh water to a salinity of 12, but 40% mortality was observed at a salinity of 15 after seven days. Pre-acclimation of silver perch to a salinity of 12 for seven days resulted in only marginally better survival at higher salinities. Plasma osmotic concentrations of silver perch rose slightly in salinities below 9 but rapidly at higher salinities, following the same track as the iso-osmotic line. Minimum body water content was observed in individuals subjected to a salinity of 15 for 24 h. As found in other freshwater teleosts, chloride cells were found in the branchial epithelium of silver perch. Accessory cells were observed beside the chloride cells in both freshwater and salt-water conditions. Fish subjected to a salinity of 12 for seven days showed chloride cells with a more developed tubular system than controls. The length of the junctions between chloride cells and accessory cells was significantly shorter in fish adapted to a salinity of 12 than in controls. The ultrastructural feature of 'interdigitations' of accessory cells was not observed during salt-water adaptation. These data indicate that silver perch is the least tolerant of high salinities and the most truly freshwater Australian teleost species examined to date.

In eastern Australia, two forms of the Australian magpie occur: a white-backed form and a black-backed form. These two forms hybridise across northern Victoria and into South Australia. In this study the response of territorial magpies to caged intruders was examined. Pairs of adult male magpies were introduced into territories. Both were adult black-backed birds, but in each case one of them had its back painted white. The pair was introduced to each territory twice, with the bird that was painted white differing between times. The experiment was run in a population of black-backed birds and a population in the hybrid zone containing white-backed, black-backed and hybrid birds. In both cases, the residents were more aggressive towards the intruder with the white-back than they were to the black-backed intruder. We suggest that this may be because a white-backed bird posed more of a threat to residents than a black-backed bird.

Isozyme electrophoresis and morphological comparisons were used to examine 40 populations of the skink Lampropholis delicata from eastern Australia. Four electrophoretically distinct forms were recognised amongst the sampled populations. Morphological comparisons were able to separate the four population groups only when meristic and colour characters were combined and compared by means of multivariate analysis. The taxonomic status of L. delicata was stabilised by nominating a neotype for the species, collected from the type locality.

Effects of feeding level and starvation on growth, water content and protein content were examined in juvenile Cherax quadricarinatus. Gain in body weight was positively related to feeding level. An increase in feeding level resulted in a decrease in water content and an increase in protein content. Although the majority of juveniles were able to tolerate starvation for at least 12 days, deprivation of feeding caused a loss of weight and a gradual decrease in protein content combined with a simultaneous increase in water content. Total protein content was reduced by 3.9% in juveniles starved for three days and by 8.3% in those starved for 12 days. Normal body protein content, however, was recovered within six days after subsequent feeding in juveniles that were deprived of food for 12 days.