Australian Bass Research Articles

Initial swim bladder inflation in intensively reared Australian bass larvae, Macquaria novemaculeata (Steindachner) (Perciformes: Percichthyidae)

Laboratory experiments conducted on newly hatched Australian bass ( Macquaria novemaculeata) larvae in 60-l aquaria demonstrated that initial swim bladder inflation took place 6–11 days after hatch at a temparature of 19±1°C. While inflation occurred at the time when exogenous feeding normally started, feeding was not a requirement for inflation. Larvae were small (4.4–4.6 mm), negatively phototactic and lightly pigmented at the time of inflation. The mean number of larvae with dilated (liquid filled) swim bladders increased from 0.3% on day 7 to 23.0% on day 10. Survival was not significantly affected by continuous light (100–200 lux), salinity (10 and 30‰) or aeration (0–3000 ml/min). Under conditions of darkness, salinities above 25‰ and low to zero aeration, 66.8–72.0% of larvae inflated their swim bladders by day 11. Continuous exposure to fluorescent light (100–200 lux) almost totally inhibited inflation with only 0.1±0.4% (mean±SD) of larvae inflating their swim bladders. Exposure to light on a 12:12 light:dark photoperiod at intensities of 0.3–50 lux reduced inflation to 18.3–11.0%. Inflation was also reduced at a salinity of 10‰ (32.3±23.0%) and under high aeration, 1000–3000 ml/min (18.4±9.2%).

Demography of Australian bass, Macquaria novemaculeata (Perciformes, Percichthyidae), in the Sydney Basin

A mark-recapture experiment showed Australian bass to be sparsely distributed through sheltered parts of their habitat, but no significant differences in population density among major habitat categories were detected by catch-per-effort analyses. Total mortality, estimated from the catch curve, was low (Z = 0.28). Tabular and graphical calculations of annual production in a lagoon resulted in similar low estimates (0.84 g m-2 year-1), and a strikingly low P/B (annual production/biomass) ratio (0.19) results from the bass' catadromous life history. Populations of bass in the Sydney Basin showed declining recruitment, distribution restricted by impoundments, and increasing mortality attributable to exploitation and habitat damage during the period 1977-82. Estimates of initial cohort abundance indicated that recruitment and subsequent year-class strength are positively related to the level of flooding in the spawning months, but flooding is suppressed by dams. Population declines and continuing environmental degradation give cause for concern over the status of bass populations.

Active osmoregulation in the Australian Bass, Macquaria novemaculeata (Steindachner), and the golden perch, Macquaria ambigua (Richardson) (Percichthyidae)

The Australian bass, M. novemaculeata, and the golden perch, M. ambigua, differed in the osmoregulatory response of the gills to salinity change. Bass displayed lower gill Na+/K+-transporting ATPase and succinate dehydrogenase activities in salt water than in fresh water, whereas golden perch displayed the opposite pattern. This difference may indicate that the golden perch has evolved further toward a fresh- water life cycle than the bass, with reduced osmoregulatory effort, particularly in the critical juvenile phase, in fresh water. The spawning and initial juvenile residence of bass in hypertonic conditions may similarly represent preference for, or adaptation to, a habitat that requires reduced osmoregulatory effort by the juveniles. It is suggested that artificial rearing conditions known to compromise the development of Na+/K+-transporting ATPase-dependent osmoregulation in other species should be avoided, particularly in bass reared in high salinities for stocking into fresh water.

Growth of Australian bass Maquaria novemaculeata (Perciformes : Percichthyidae) in the Sydney Basin

Habitat type and sex are the principal determinants of the variable length-at-age of M. novemaculeata. Growth was studied in three main habitat types: lagoons, gorge streams, and freshwater estuarine habitats, and a total of 1071 adult bass and 644 young fish were examined. Observations were made on the growth of young wild bass, and their rapid growth after stocking in isolated lentic waters was measured. The three von Bertalanffy growth parameters were estimated for populations from the main habitat types. A growth curve generated from tag-return data provided comparable values. Variation in length was tested by three-way ANOVA using age, habitat type and sex as independent variables. Female bass grew faster than males towards a larger asymptotic size (L∞ = 396 mm). Lagoon populations grew the most rapidly, and those in freshwater tidal sites grew slowest. T'he proportion of variarion in bass length that was due to habitat type, sex, and age was 15, 10, and 56% respectively. Marked flexibility of the growth, diet and reproduction of M. novemaculeata is seen as an adaptive response to variable environmental conditions.

Effect of Food Concentration on the Survival and Growth of Australian Bass (Macquaria novemaculeata) Larvae

Abstract Larvae of Australian bass (Macquaria novemaculeata) were offered various concentrations of rotifers (Brachionus plicatilis) at 0-24 organisms/mL for 2 weeks starting at completion of yolk absorption. In another experiment, larvae initially fed rotifers for 2 weeks were offered brine shrimp (Artemia salina) at concentrations of 0-15 nauplii/mL. In each experiment the concentration of zooplankton had a significant (P < 0.01) effect on larval survival. The minimum concentrations that resulted in high survival and growth rates of larvae were 9 rotifers/mL for the first 2 weeks after yolk absorption and 6 brine shrimp nauplii/mL for the next 2 weeks.

Reproduction of the Australian bass, Macquaria novemaculeata (Perciformes : Percichthyidae) in the Sydney Basin

The reproduction of Australian bass from the Sydney Basin was studied between 1977 and 1982. The gonadal cycle was investigated using a four-stage gonad maturity classification, the gonado-somatic index, oocyte measurements, and histological examination of representative gonads. An ichthyoplankton survey was conducted, fecundity was estimated, and sperm viability in different salinities was also measured. Spermatogenesis and vitellogenesis commenced between February and April each year. Bass spawned between late June and early September in 1978 and 1981. Final ovarian maturation, and the catadromous migration of females from freshwater to the brackish spawning zone were dependent on flooding. Ovarian involution ensued if river levels did not rise before September. Reproductive success was high after floods in1978. Bass did not reproduce during the drought in 1979 and 1980, and reproductive success was low in the low river flows of the 1981 winter. The results suggest that bass are cyclical spawners, shedding eggs that are demersal in the spawning salinity. Fecundity is high (mean = 440 000). The location of spawning and recently spent bass, the distribution of larvae in the estuary, and results of the sperm viability experiments indicated that bass spawn in the estuary in salinities between 8 and 14 g kg-1. Most males were sexually mature by age 3 + years, and females by 5 + or 6 + years.

Effects of temperature and salinity on the hatch rate and survival of Australian bass ( Macquaria novemaculeata) eggs and yolk-sac larvae

Eggs of Australian bass, Macquaria novemaculeata, were incubated at temperatures of 12, 16, 20 and 24°C and a salinity of 35‰. Other batches were incubated at salinities of 5, 10, 15, 20, 30 and 35‰ and a temperature of 15°C. Hatching occurred at all temperatures but hatch and survival rates of larvae were significantly lower at 12°C than at 16 or 20°C. The optimum temperature for survival was 20°C. Many of the larvae incubated at 24°C were abnormal. All eggs incubated in fresh water died. At a salinity of 5‰, 21% of eggs hatched but no larvae survived. At 10‰ only 3% survived. There were high hatch rates (89–97%) and survival at 25, 30 and 35‰.

Age of Australian bass, Macquaria novemaculeata (Perciformes : Percichthyidae), in the Sydney Basin

The age of M. novemaculeata from the Hawkesbury River and other streams in the Sydney Basin, New South Wales, was determined by using otoliths. Annuli were counted after simple sectioning of otoliths and intensification of the growth-check pattern by a two-stage burning technique. Age determinations were validated by the use of fish of known age; an error of + 1 year occurred in 17% of determinations. Ages of older fish (14+ to 18+ years) were not overestimated by more than 2-4 years, if at all. Progression of year-classes, and the annual nature of growth-check formation, further validated age determinations. Scale-reading seriously underestimated the age of bass. M. novemaculeata is a long-lived species. The oldest fish was 22+ years, and the mean age of the sample (n = 607) was 4.9 years. There are significant differences in longevity between the sexes; fewer males reach the older age-groups. About 10% of juvenlle fish deposited a growth-check in their otoliths during their upstream recruitment migration. The frequency of this 'migration check' was increased to 20% by capture and relocation of juveniles to isolated waters. A procedure was designed to identify migration checks in wild fish.

Diet of the Australian bass, Macquaria novemaculeata (Perciformes : Percichthyidae), in the Sydney Basin

Stomach contents of Australian bass, M. novemaculeata, sampled from the Hawkesbury River and Georges River in the Sydney Basin, New South Wales, between November 1977 and January 1982 were analysed by the occurrence and points methods. Stomach fullness was also recorded. A total of 143 aquatic and terrestrial animal taxa were present in the diet, and these were grouped into 19 food types for analysis. M. novemaculeata is a euryphagic carnivore. Season and habitat type had significant effects on composition of the diet. Insects were the most important food type, followed by fish and large crustaceans. A large proportion of the diet of bass was derived from allochthonous sources, mainly during summer, and especially in lotic habitats. Mean stomach fullness was highest in spring and lowest in winter. Young M. novernaculeata (TL 11-47 mm) from the Hawkesbury River estuary fed on far fewer prey taxa (mainly chironomids and copepods) than did adults. Dietary overlap occurs between M. novemaculeata and many other carnivorous freshwater vertebrates in the Sydney Basin. However, persistent competitive clashes are generally avoided, either by differences in microhabitat preference and feeding behaviour or by larger-scale habitat partitioning.

The Life Cycle and Morphology of Tetracerasta Blepta, Gen. Et Sp. Nov., And Stegodexamene Callista, Sp. Nov. (Trematoda: Lepocreadiidae) From the Long-Finned Eel, Anguilla Reinhardtii Steindachner.

Two new lepocreadiid digeneans, Tetracerasta blepta, gen. sp. nov., and Stegodexamene callista, sp. nov., are described from the intestine of the long-finned freshwater eel, Anguilla reinhardtii, in the Brisbane River, Queensland, and from the Australian bass, Macquaria novemaculeata, in the Richmond River in New South Wales. Their life cycles have been elucidated and completed in the laboratory, by means of uninfected hosts. Both lepocreadiid species use the prosobranch gastropod, Posticobia brazieri, as their first intermediate host. Cercariae of T. blepta penetrate and encyst in the pharyngeal muscle, external muscle, and viscera of fishes in the genera Gobiomorphus and Hypseleotris, and in several species of tree frog tadpoles. The cercariae of S. callista are often eaten or accidentally inhaled by several small fishes, including Retropinna, Craterocephalus, Pseudomugiland Ambasszs, and encyst in the pharyngeal muscle and viscera. All developmental stages are described and illustrated.