ALBERT

Notes: The reproductive biology of three introduced Poeciliidae, Gambusia affinis holbrooki Baird and Girard, Xiphophorus helleri (Günther) and X. maculatus (Heckel) was studied over a 14-month period in Brisbane, Queensland. Photoperiod and water temperature determined the length of the breeding season in G. affinis, which produced up to nine broods between August and March, with the peak of reproductive activity in October. Fecundity was linearly related to body weight in G. affinis (mean fecundity = 22.78 ± 1.02, range = 3–108 offspring per brood). Xiphophorus helleri bred from August to May, producing eight to nine broods, with peak reproductive activity from October to December. Fecundity was curvilinearly related to body weight (mean fecundity = 60.15 ± 3.8, range = 7–183 offspring per brood. Xiphophorus maculatus bred between September and March, producing five to six broods during the study period. Fecundity was linearly related to standard length (s.l.) (mean fecundity = 27.27 ± 2.4, range = 3–92 offspring per brood). Although the reproductive strategy of the three species differs, all have the capacity to build up large populations in south-eastern Queensland. Their present distributions and relative abundance are discussed.

Notes: SUMMARY. 1. The reproductive cycle and growth of Craterocephalus marjoriae and Craterocephalus stercusmuscarum (Atherinidae) were studied in Brisbane, south-eastern Queensland, over a 17-month period (1981–82).2. Both species had a 5-month breeding season in spring and summer, with a breeding peak in spring (September-October). Multiple spawning occurred but life time fecundity was not determined.3. Gonosomatic index values and mean fecundity per female were higher in Craterocephalus marjoriae than in C. stercusmuscarum. Fecundity increased with body length in both species according to the relationship, F=aLb. Growth rates were similar and growth was adequately described by the von Bertalanffy equation. Both species grew rapidly during the first year and reached maturity the following season. Reproductive strategies are considered in relation to seasonal flooding in the streams inhabited.

Notes: 1. The ability of many introduced fish species to thrive in degraded aquatic habitats and their potential to impact on aquatic ecosystem structure and function suggest that introduced fish may represent both a symptom and a cause of decline in river health and the integrity of native aquatic communities.2. The varying sensitivities of many commonly introduced fish species to degraded stream conditions, the mechanism and reason for their introduction and the differential susceptibility of local stream habitats to invasion because of the environmental and biological characteristics of the receiving water body, are all confounding factors that may obscure the interpretation of patterns of introduced fish species distribution and abundance and therefore their reliability as indicators of river health.3. In the present study, we address the question of whether alien fish (i.e. those species introduced from other countries) are a reliable indicator of the health of streams and rivers in south-eastern Queensland, Australia. We examine the relationships of alien fish species distributions and indices of abundance and biomass with the natural environmental features, the biotic characteristics of the local native fish assemblages and indicators of anthropogenic disturbance at a large number of sites subject to varying sources and intensities of human impact.4. Alien fish species were found to be widespread and often abundant in south-eastern Queensland rivers and streams, and the five species collected were considered to be relatively tolerant to river degradation, making them good candidate indicators of river health. Variation in alien species indices was unrelated to the size of the study sites, the sampling effort expended or natural environmental gradients. The biological resistance of the native fish fauna was not concluded to be an important factor mediating invasion success by alien species. Variation in alien fish indices was, however, strongly related to indicators of disturbance intensity describing local in-stream habitat and riparian degradation, water quality and surrounding land use, particularly the amount of urban development in the catchment.5. Potential confounding factors that may influence the likelihood of introduction and successful establishment of an alien species and the implications of these factors for river bioassessment are discussed. We conclude that the potentially strong impact that many alien fish species can have on the biological integrity of natural aquatic ecosystems, together with their potential to be used as an initial basis to find out other forms of human disturbance impacts, suggest that some alien species (particularly species from the family Poeciliidae) can represent a reliable ‘first cut’ indicator of river health.

Notes: Descriptions and illustrations of stages in the larval development of two common sympatric freshwater fishes in streams of tropical north-east Queensland, the fly-specked hardyhead Craterocephalus stercusmuscarum stercusmuscarum and the purple-spotted gudgeon Mogurnda adspersa are presented. Larval development is described in terms of ontogenetic changes in gross morphology, notochord morphology, pigmentation, finfold morphology and fin structure. Developmental changes during the larval period of C. s. stercusmuscarum are similar to other atheriniformes, especially the genus Melanotaenia. The highly variable development and advanced state at hatching of M. adspersa in tropical streams contrasts with larval development of disjunct populations of the same species in southern Australia and also with other closely related species of the Eleotridae described elsewhere. Larvae of M. adspersa can be distinguished from C. s. stercusmuscarum on the basis of six key characters: pigmentation, presence of a pre-anal ventral finfold, general body form and shape, number of post-anal myomeres, notochord morphology at hatching and timing of swimbladder inflation. Characters that allow for the accurate discrimination between both of these species and other sympatric atheriniformes are identified.

Notes: Abstract – Fish assemblages in three rivers of eastern Cape York Peninsula, northern Australia, were sampled during the early part of the monsoonal dry season, and the diet of 23 species was quantified. Spatial variation (between-river) in diet was, in general, not pronounced. Sufficient specimens were collected to enable examination of ontogenetic changes in the diet of four species. Interspecific and ontogenetic variation in diet were most strongly related to differences in body size and mouth gape, with larger species or age classes feeding on fish and large aquatic invertebrates. Other gradients upon which dietary differences were arranged included gradients in detritivory and reliance on terrestrial invertebrates. Significant trophic separation was evident in the fauna despite aquatic invertebrates being the most important food item in most species. Seven, and possibly eight, trophic groups were recognized. Notable features of the trophic organization were the prevalence of omnivory and piscivory and relatively small representation by detritivores. Planktivores were essentially absent. Much of the observed trophic structure within the fishes of Cape York Peninsula could be ascribed to the effects of phylogenetic determinants of body size, morphology and foraging mode. The trophic structure within rivers of eastern Cape York Peninsula is compared to other aquatic systems in tropical northern Australia./〉

Notes: Abstract – We developed classification/multiple discriminant analysis models to predict fish assemblage structure and tested whether the predictive power of these models varied with discharge variability. Models developed for assemblages characterized by the density of component species for two rivers with low discharge variability had better predictive power than did models developed for two rivers of higher variability. Similar distinction between rivers of differing flow variability was not evident for models based on assemblages characterized by the presence or absence of component species. Factors such as the within-river level of beta diversity, location of study sites relative to the river mouth and the degree of covariation in species' occurrence appeared important determinants of predictive power in these models. Randomization tests (Mantel tests) were used to determine the degree of association between site by site association matrices generated for fish assemblage structure (both density and presence/absence) and habitat structure (catchment, physical, microhabitat or a combination). This approach revealed that in most cases, catchment-related variables explained almost as much of the variation in assemblage structure as variables related to in-stream habitat structure and that greater association was detected for comparisons based on presence/absence rather than density data. The addition of in-stream habitat variables to catchment-related variables usually resulted in explaining the greatest amount of variation. These data suggest that most of the structure observed in the fish assemblages of the study rivers was a result of the effect of regional or catchment factors in determining which species were present at an individual site and that local factors were then important in determining the abundance of the component species. It is at this level that the effects of regional differences in discharge variability were expressed. Although significantly different from random for all comparisons, Mantel's tests revealed that a substantial amount of variation in the fish assemblage data sets could not be explained by the abiotic (habitat) data sets. It is suggested that the assemblages in question did not represent unit discrete assemblages but were composed of species varying along individual environmental gradients. Predictive models may be better achieved by modelling the distribution and abundance of individual species rather than assemblages./〉

Notes: Abstract – The reproductive biology of three species of rainbowfish (Melanotaeniidae) in northeastern Australian rainforest streams was investigated. Two species, Melanotaenia eachamensis and Cairnsichthys rhombosomoides are endemic to the area, whereas the third, M. splendida splendida, is more widespread. The species were all highly fecund, producing many hundreds of eggs between 1.10 and 1.24 mm in diameter. Melanotaenia eachamensis was the most fecund, produced the largest eggs of the three species, and consequently exhibited the greatest maternal investment (as measured by gonadosomatic index). The majority of reproductive effort occurred during the dry season, although reproductively active fish were present year-round for each of the species, but particularly so for M. s. splendida and C. rhombosomoides. No evidence for a role by temperature or photoperiod as environmental cues for reproduction was found, and it was suggested that gonad development was strongly tied to somatic growth. The concentration of reproduction to the dry season ensures that larvae are produced during a period of relatively stable and benign physical conditions. Comparison of temporal changes in gonadosomatic index values suggest that the spawning season of M. eachamensis, which occurs in high-elevation streams, is more restricted and commences about 1 month earlier than either other species. A similar phenology was observed for the M. s. splendida population found at high elevation and highlights the potential for spatial differences in stream productivity to influence life history./〉