In many parts of south-eastern Australia, native riparian vegetation has been cleared and exotic willows planted. In order to evaluate some of the possible effects of this practice, the decomposition and colonisation by invertebrates of the leaves of three native plant species along with those of willow were examined.Decomposition of leaves of the willow Salix babylonica L. and the indigenous macrophyte Myriophyllum propinquum A. Cunn. was much faster than for leaves of the indigenous trees Eucalyptus blakelyi Maiden and Casuarina cunninghamiana Miq. Both macroinvertebrates and current were found to have a significant influence upon decomposition. The pattern of preferential colonisation suggested that plant detritus represented a primary food source for invertebrates and not simply a refuge. Colonisation was found to be a function of the stage of decomposition, regardless of plant species. The lower temporal availability of willow leaves compared to the native evergreen tree leaves appears to be insufficient to enhance the production of the benthic macroinvertebrates.

Towards the end of the Wet season in the tropical coastlands of northem Australia, there are dramatic upstream movements of many fish species in some seasonally flowing streams. These movements are considered to be a part of refuge-seeking migrations. Aspects of the dynamics of the movements in Magela Creek (in the 'Top End' of the Northem Territory) downstream from the Ranger Uranium Mine have been examined with a range of techniques (mainly direct observation) to facilitate the development of a possible procedure for monitoring impacts of the mine on the fish community of the creek system. Data on diel pattems of movements validated that monitoring, for 1 h at midday at a single point adjacent to the mine, reflects day-to-day changes in total diel movements. To help identify the location of any impacts arising in the future, information on upstream progress rates, longitudinal changes in movements, and movements between the creek and lowland billabongs, were used to (i) demonstrate the creek-long continuity of movements and (ii) indicate the possible sources and destinations offish approaching the mine. Marked differences in sources were apparent for two groups of species: terapontids originating from the lowland creek channels, and chequered rainbowfish and ambassids originating from the floodplain and lowland billabongs. Identification of the relative contributions from these habitats will require additional monitoring effort.

The diets and growth rates of rainbow trout in the Wollomombi and Guy Fawkes Rivers in northern New South Wales were examined. The growth rate of trout in the Wollomombi River was much higher than that of fish in the Guy Fawkes River. Spearman rank correlation coefficients indicated that stream type was more important than fish size in determining the composition of the diet of the trout. Benthic invertebrates formed the largest component of the diet in both streams: 66.0 and 63.0% of ash-free dry weight (AFDW) in the Wollomombi River and the Guy Fawkes River, respectively. Trout in the Wollomombi River consumed more nektonic prey (33.3% of AFDW) than fish in the Guy Fawkes River (3.7% of AFDW). In contrast, surface food (aquatic imagines and terrestrial insects) made up a much higher proportion of the diet of trout in the Guy Fawkes River (33.9% of AFDW) than in the Wollomombi River (0.6% of AFDW). Crayfish were a major component of the diet (in terms of AFDW) in both streams, their proportions increasing with fish size. The significance of crayfish in relation to fish growth is discussed.

No abstract

The freshwater herring, Potamalosa richmondia Macleay, is a catadromous fish that inhabits coastal rivers of New South Wales. Estimates of the age and growth of this species in the Bellinger River were made from scales. Comparison of scale ages with those from whole otoliths and burnt otolith sections from a sample of 30 fish aged at 2 to 8 years resulted in a 73 and 79% exact agreement and a 97 and 100% agreement within one year, respectively. Marginal-increment analysis of the scales indicated that the annulus was formed during the winter, which is also the spawning season. The ageing method was validated for age classes of 2 to 8 years by these procedures. The age at the first annulus and at ages 9 to 11 years could not be validated. The oldest fish examined was estimated to be 11 years old. The growth rate was very slow in comparison with that of other clupeids. Parameters of the von Bertalanffy growth equation, based on lengths and ages at capture, were L∞ = 252.7 mm, K = 0.126, and t0 = -2.77 years. There was no difference between the sexes in their growth in length. However, the length-weight relationships of males and females were different, with females longer than 180 mm weighing more than males of the same length. The predicted weights at the asymptotic length were 213.2 g for males and 257.6 g for females.