Black Bream Acanthopagrus Butcheri Research Articles

A comparison of sex steroid binding protein (SBP) in four species of teleost fish.

A sex steroid binding protein (SBP) binding E2 with high affinity has been detected in a pleuronectid (greenback flounder Rhombosolea tapirina), two sparids (black bream Acanthopagrus butcheri and snapper Pagrus auratus), and its presence has been confirmed in a salmonid (rainbow trout Oncorhynchus mykiss). SBP binding characteristics were measured using a hot saturation assay for trout, bream and snapper, and a cold saturation assay for flounder. Bound and unbound steroid were separated by incubation with dextran-coated charcoal (DCC). Affinity for E2 was highest in trout (kD=0.44 nM), followed by bream (kD=3.39 nM) and snapper (kD=10.7 nM). The lowest affinity was found in flounder (kD=84.7 nM). Binding capacity, however, was greatest in flounder (Bmax=164 nM), followed by trout (Bmax=92 nM), and then bream and snapper (Bmax=50 and 39 nM, respectively). Binding of E2 to SBP had a very rapid rate of association, and most dissociation occurred within 5 min. To confirm that the plasma protein measured here was SBP, the relative binding affinities of SBP for a range of steroids were measured. In trout, bream and snapper, SBP bound E2 with the highest affinity, followed by T. In contrast, the relative affinity of T for flounder SBP was more than twice that of E2. The rank orders of affinity of binding indicate the importance of an unhindered 17β-hydroxyl group, and a 3-hydroxyl or 3-ketone group for high affinity binding to SBP. These requirements for high affinity binding are present in most animals possessing SBP and indicate conservation of the SBP molecule through evolution.

Stress‐induced changes in concentrations of plasma sex steroids in black bream

Cortisol levels of black bream Acanthopagrus butcheri at capture did not change with time of day, gonadal stage or season and were 1·9±0·2 and 2·8±0·4 ng ml−1 for male and female fish, respectively. Confinement resulted in significantly elevated cortisol levels at all time periods; however, levels after 24 h of confinement were significantly lower than peak cortisol levels (15 min for males and 1 h for females). Confinement stress resulted in reduced levels of 17β‐oestradiol (E2) and testosterone (T) within 1 h in sexually mature females. In mature males, suppression of T and 11‐ketotestosterone (11KT) occurred after 30 min and 6 h of confinement, respectively. The relationship between confinement stress and levels of 17,20β‐dihydroxy‐4‐pregnen‐3‐one (17,20β P) was more complex, with levels in males being elevated after 15 min and 24 h and suppressed after 6 h of confinement. In contrast, 17, 20β P levels in females were elevated after 1 h of confinement. In regressed females, plasma E2 and T concentrations were low at capture and were not affected by confinement stress whereas plasma 17, 20β P was elevated within 1 h. This study indicates that stress exerts a rapid inhibitory effect on gonadal steroidogenesis.

Comparisons between the reproductive biology of black breamAcanthopagrus butcheri (Teleostei: Sparidae) in four estuaries with widely differing characteristics

The reproductive biology ofAcanthopagrus butcheri has been studied in the permanently open Swan River and intermittently open Moore River estuaries on the lower west coast of Australia (31–32°S) and in the permanently open Nornalup Walpole and normally closed Wellstead estuaries on the southern coast of Western Australia (34–35°S). Trends exhibited by gonadosomatic indices, gonadal maturity stages and the sizes and developmental stages of the oocytes demonstrate thatA. butcheri typically spawns in spring and early summer. However, spawning occurred in salinities ranging from as low as 3.5–8 gL−1 in the Moore River Estuary to as high as 41–45 g L−1 in the Wellstead Estuary. Furthermore, water temperatures during spawning were greater in the two northern estuaries (19.7–28.5°C) than in the two southern and cooler estuaries (17.5–23.4°C). Histological studies strongly indicate thatA. butcheri spawn more than once in a breeding season and demonstrate that the development of its oocytes exhibits group synchronysensu de Vlaming (1983). The ages and total lengths at which, on average, female and maleA. butcheri both first attain maturity in the Swan River Estuary were ca 2 years and ca 215 mm. However, the age at which individual fish in that system reach maturity was influenced by body size. This suggests that the attainment of first maturity at an older age but smaller length in the Moore River and Nornalup Walpole estuaries than is the case in the Swan River Estuary is a consequence of the slower growth rates ofA. butcheri in those estuaries. The combination of the young age (ca 2 years) but small length (ca 145 mm) at which maturity is first attained in the Wellstead Estuary could have resulted from selection pressures brought about by high mortality rates and/or heavy fishing pressure in this estuary. The mean fecundity ofA. butcheri, based on the combined number of yolk vesicle and yolk granule oocytes found in ovaries just prior to the onset of spawning, was 1580×103. The significance of the sizes at first maturity, minimum legal length for capture, mesh selectivity data and closure of certain regions of estuaries to fishing for the management of the recreational and commercial fishery forA. butcheri is discussed.

Optics of the developing fish eye: comparisons of Matthiessen's ratio and the focal length of the lens in the black bream Acanthopagrus butcheri (Sparidae, Teleostei)

Matthiessen's ratio (distance from centre of lens to retina: lens radius) was measured in developing black bream, Acanthopagrus butcheri (Sparidae, Teleostei). The value decreased over the first 10 days post-hatch from 3.6 to 2.3 along the nasal and from four to 2.6 along temporal axis. Coincidentally, there was a decrease in the focal ratio of the lens (focal length:lens radius). Morphologically, the accommodatory retractor lentis muscle appeared to become functional between 10–12 days post-hatch. The results suggest that a higher focal ratio compensates for the relatively high Matthiessen's ratio brought about by constraints of small eye size during early development. Combined with differences in axial length, this provides a means for larval fish to focus images from different distances prior to the ability to accommodate.