The endocrinology of stress in fish: an environmental perspective.

Much of the understanding of the endocrine basis of stress in fish comes from studies of cultured stocks of teleosts; there is comparatively little information on stress responses in wild stock, and less still on chondrosteans and elasmobranchs. This understanding is being refined through increasing understanding of molecular processes underlying endocrine events, with molecular tools offering ready examination of parts of the endocrine pathway that have been resistant to easy measurement of hormone products. An assessment of the timecourse of activation of the hypothalamic-pituitary-interrenal axis shows generally strong independence of temperature, with most teleosts showing measurable increase in plasma cortisol within 10 min of stress. Chondrostean and elasmobranch responses are less well described, but in chondrosteans at least, the response pattern appears to be similar to teleosts. The short latency for increases in corticosteroids following exposure to a stressor means that sampling of wild fish needs to occur rapidly after encounter. Several techniques including underwater sampling and rapid line capture are suitable for this, as is measurement of steroid release to the water by undisturbed fish, albeit possibly with a reduced range of applications. Basal cortisol values in wild teleosts are typically <10 ng mL(-1), but a number of species show values orders of magnitude higher in unstressed fish. Variability in corticosteroid levels arises from a range of factors in addition to stress including, sex and maturity, time of day or since feeding, and season. These factors need to be understood for the sensible assessment of stress responses in wild fish. Studies on free-living birds suggest that environmental stress resides mainly around unpredictable change, and the limited data available for fish support this view. The effect of unpredictable event such as floods or storms are difficult to assess in wild fish due to the difficulty in sampling at these times, and would be predicted to impose environmental stress as in terrestrial systems; however, this has yet to be demonstrated. There is scope for use of stress responses to be used as a measure of environmental quality but only if the basic response to environmental stress is well understood first. Development of this understanding remains a priority for this field of research.

Temperature and salmonid reproduction: implications for aquaculture.

Fish reproduction is likely to be affected by increasing water temperatures arising from climate change. Normal changes in environmental temperature have the capacity to affect endocrine function and either advance or retard gametogenesis and maturation, but above-normal temperatures have deleterious effects on reproductive processes. In Atlantic salmon Salmo salar, exposure to elevated temperature during gametogenesis impairs both gonadal steroid synthesis and hepatic vitellogenin production, alters hepatic oestrogen receptor dynamics and ultimately results in reduced maternal investment and gamete viability. Exposure to high temperature during the maturational phase impairs gonadal steroidogenesis, delaying or inhibiting the preovulatory shift from androgen to maturation-inducing steroid production. There are also deleterious effects on reproductive development of female broodstock of rainbow trout Oncorhynchus mykiss and Arctic charr Salvelinus alpinus when they are exposed to elevated temperature. Less is known about temperature effects on male fishes but inhibition of spermiation has been observed in S. salar and O. mykiss. Among wild stocks, the response to elevated temperature will involve behavioural thermoregulation with consequent change in geographical ranges and the possibility of local extinctions in some regions. For domesticated stocks, containment in the culture environment precludes behavioural thermoregulation and aquaculturists will be required to develop adaptive strategies in order to maintain productivity. The most direct strategy is to manage the thermal environment using one or more of a range of developing aquaculture technologies. Alternatively, there is potential to mitigate the effects of elevated temperature on reproductive processes through endocrine therapies designed to augment or restore natural endocrine function. Studies largely on S. salar have demonstrated the capacity for synthetic luteinizing hormone-releasing hormone to offset the inhibitory effects of elevated temperature on maturational events in both sexes, but the potential for hormone therapy to provide protection during gametogenesis is still largely unexplored.

Habitat-related variation in reproductive endocrine condition in the coral reef damselfish Acanthochromis polyacanthus.

Spiny damselfish Acanthochromis polyacanthus are brood protectors with no larval dispersal stage, with the result that characteristics of local populations are likely to reflect local habitat conditions. In order to assess the possible effect of habitat on reproductive characteristics, spiny damselfish were captured by divers in 1999 and 2001 from reefs around Lizard Island in the northern section of Australia's Great Barrier Reef, chosen to represent a range of coral cover characteristics. Fish were bled underwater immediately after capture, then blood and fish were placed on ice at the end of the dive for transport to the laboratory where plasma was separated for subsequent measurement of testosterone (T) and 11-ketotestosterone (11KT) in males, and T and 17beta-estradiol (E2) in females. Ovaries from fish captured in 2001 were dispersed to isolate vitellogenic follicles, fecundity and follicle size were determined, then follicles were incubated in Leibowitz L15 medium alone or with human chorionic gonadotropin (hCG), to assess steroidogenic capacity. In 1999 there were significant site to site variations in plasma T and E2 levels in females, and in 2001, in E2 in females, and in T and 11KT in males. Highest hormone levels were recorded from sites of both low and high coral cover (a measure of presumptive habitat quality), but there was consistently low steroid production in fish from a site of high coral cover and fish density. An initial expectation that poor reproductive condition might be associated with degraded coral sites was not met. Vitellogenic follicles from fish captured in 2001 showed increased in vitro production of E2 and to a lesser extent, T, with increasing follicle size, and this was further augmented by treatment with hCG. Comparison of regression slopes of log E2 production versus follicle size showed that fish from sites where there were generally low levels of plasma steroids also had impaired in vitro steroidogenic capacity, and that this effect partially disappeared when follicles were stimulated with hCG. Reduced steroidogenic capacity was strongly associated with low fecundity, indicating that low in vitro and in vivo E2 production were reflected in reduced reproductive capacity. As the effect was most consistent at a site where fish density (and subsequent competition for planktonic food) was high, it is suggested that nutritional status associated with habitat characteristics may regulate reproductive endocrine condition in spiny damselfish. It is clear that local factors other than coral cover can generate site variation in reproductive performance.

In vitro effect of vitellogenin on steroid production by ovarian follicles of greenback flounder Rhombosolea tapirina.

Ovarian follicles from vitellogenic greenback flounder (Rhombosolea tapirina) were incubated in L15 medium alone, or containing human chorionic gonadotropin (hCG), dibutyryl cyclic AMP (dbcAMP) or the steroid precursors testosterone (T), 17-hydroxyprogesterone (17P) and androstenedione (A) in the presence of vitellogenin (Vtg) at 0.1-5.0mg mL(-)(1). Medium concentrations of 17beta-estradiol (E(2)) and T were measured by radioimmunoassay. HCG generally stimulated follicular E(2) but not T production, whereas 17P, A and T stimulated production of E(2), T, and E(2) respectively. Treatment of follicles with dbcAMP inhibited follicular E(2) production, but increased follicular T production at high doses. The effect of low concentrations of Vtg on follicular steroid production was variable; however, higher doses of Vtg significantly suppressed basal, hCG-, dbcAMP- and steroid precursor-stimulated follicular E(2) and T production. The results of this study show that high concentrations of Vtg may suppress follicular steroid production by interfering in the steroidogenic pathway. This suggests that Vtg may regulate its own production by limiting the ovarian production of E(2).

Differential effects of temperature and maturity stage on hepatic estrogen receptor characteristics of Atlantic salmon.

In order to determine if elevated temperature during vitellogenesis had a detrimental effect on hepatic estrogen receptors of Atlantic salmon (Salmo salar), 3H-estradiol saturation binding analysis, using one- and two-site binding models, was carried out on extracts of hepatic cytosols from fish held at 14, 18 or 22 degrees C over the austral period of peak vitellogenesis (February to April). With one-site binding analysis, no temperature related difference in either receptor affinity (Kd) or number (Bmax) was found at each sampling point, but there was an apparent decrease in both affinity and number at each temperature over the period of the study. However, some analyses, notably at 22 degrees C during February, were best described using a two-site binding model. At this temperature and time, there was a clear separation of binding affinity into high and low components (Kd = 0.67+/-S.E. 0.05 and 20+/-S.E. 5.6 nM, respectively) (n = 4), which suggests that February was a critical time of temperature related hepatic sensitivity to estrogen. These results support those of other studies where we found that February was also a sensitive time with respect to temperature impairment of in vitro follicular estrogen synthesis, and the greatest period of in vivo temperature sensitivity.

Vitellogenin isolation, purification and antigenic cross-reactivity in three teleost species.

Vitellogenin (Vtg) was isolated from male greenback flounder (Rhombosolea tapirina), rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar) plasma, following induction by estradiol (E(2)) inoculation. The molecular weight of each native molecule, as determined by gel filtration, was 540, 383 and 557 kDa, respectively. With sodium dodecyl sulphate polyacrylamide gel electrophoresis under reducing conditions, Atlantic salmon and greenback flounder Vtg appeared as three major bands (approximately 159, 117, 86 kDa and 155, 104, 79 kDa, respectively), whereas rainbow trout Vtg appeared as one major band (approximately 154 kDa). Several minor bands were also present in each Vtg isolate. Polyclonal antisera, produced against only the highest molecular weight band from each species following excision from reducing gels, were reactive with all major bands in Western blots. In competition ELISA, parallel binding slopes were demonstrated between purified Vtg and plasma from vitellogenic females of the same species, but there was no reaction with plasma from untreated males. These antisera were highly species-specific and little cross-reactivity was noted, even between the two salmonid species. These data suggest that excision of bands from gels is a simple procedure for the preparation of species-specific antisera, and confirm that cross-species assays give highly variable results.

Differences in binding characteristics of sex steroid binding protein in reproductive and nonreproductive female rainbow trout (Oncorhynchus mykiss), black bream (Acanthopagrus butcheri), and greenback flounder (Rhombosolea tapirina).

The binding characteristics of sex steroid binding protein (SBP) were investigated in vitellogenic and nonreproductive female rainbow trout (Oncorhynchus mykiss), black bream (Acanthopagrus butcheri), and greenback flounder (Rhombosolea tapirina). The binding capacity of rainbow trout and black bream SBP was significantly greater in vitellogenic than in nonreproductive-stage fish. A decrease in binding affinity was observed in male trout injected with estradiol (E(2)) compared to control fish. This difference was not observed after partial purification of the SBP by gel filtration and may have resulted from competitive inhibition of E(2) binding by vitellogenin. No differences in flounder SBP binding characteristics were observed.

Characterization of parameters for in vitro culture of isolated ovarian follicles of greenback flounder Rhombosolea tapirina.

Isolated ovarian follicles of greenback flounder Rhombosolea tapirina were incubated with a variety of gonadotropins (GtHs) and steroid precursors for periods of up to 42 h, and levels of free and glucuronated testosterone (T) and 17beta-estradiol (E(2)) in the medium, and free T and E(2) from inside follicles were measured by RIA. Short incubations (6 h) generated increases in T and E(2) in response to steroid precursors, but not human chorionic GtH (hCG), or salmon or carp GtH. At incubation times of 18 h, all GtHs stimulated T and, or E(2) production, whereas after 42-h incubation, GtH effects on E(2) production had disappeared. Steroid precursors remained effective at 18 and 42 h. T and E(2) glucuronides were formed in small quantities but did not account for loss of treatment effects at long incubation times. Instead, this could be explained by accumulation of E(2) in controls as a result of continued basal steroid production. Follicles absorbed substantial amounts of both endogenous and exogenous steroid from the medium, however, this did not appear to have any influence on changes in treatment effects with incubation time. Flounder follicles were most sensitive to hCG, followed by salmon and carp GtH at approximately 10-fold higher concentrations. Ovarian segments were not sensitive to any GtH but did convert exogenous steroid precursors indicating that tissue access by GtH may be a limiting factor under certain in vitro conditions. HCG augmented the conversion of 17-hydroxyprogesterone (17P) to T but not T to E(2), consistent with the relative GtH-insensitivity of aromatase in other species. Follicles converted a range of steroid precursors with equal competence, indicating that no step in the cleavage pathway is strongly rate-limited, and that choice of precursor is unlikely to affect the assessment of steroidogenic activity.

The effect of short term confinement stress on binding characteristics of sex steroid binding protein (SBP) in female black bream (Acanthopagrus butcheri) and rainbow trout (Oncorhynchus mykiss).

The effect of short term confinement stress on sex steroid binding protein (SBP) binding characteristics was examined in female black bream (Acanthopagrus butcheri), and rainbow trout (Oncorhynchus mykiss). Black bream were sampled immediately after capture from the wild and again after 1, 6 or 24 h confinement. Rainbow trout were sampled before and after 5 h confinement. Confinement of black bream for 6 h after capture significantly reduced the binding capacity of SBP. Binding affinity also tended to be lower after confinement. There were no differences in binding affinity or capacity of black bream SBP after 1 or 24 h confinement, or rainbow trout SBP after 5 h confinement. Plasma from rainbow trout at 3 and 6 h after treatment with cortisol was compared to plasma from saline-injected controls. No significant differences in binding characteristics were detected, but there was a trend of decreased binding capacity in cortisol-injected fish compared to controls at 6 h post-injection. Relative binding studies indicated that plasma cortisol at concentrations 100x or more greater than plasma estradiol (E(2)) may displace E(2) from SBP in black bream, and act to reduce circulating levels of E(2) through increased clearance of free steroid. Physiological levels of cortisol did not displace E(2) from SBP in trout. The observed changes in SBP and the competition of physiological concentrations of cortisol for SBP binding sites may generate a component of the stress-induced falls in plasma levels of E(2) reported across a range of species.

Evidence that acute stress inhibits ovarian steroidogenesis in rainbow trout in vivo, through the action of cortisol.

Sexually mature (preovulatory) rainbow trout exposed to confinement stress showed a transitory increase in plasma cortisol levels that was accompanied by a similarly brief depression in plasma testosterone (T) levels. Plasma levels of maturational gonadotropin (GtH) and 17beta-estradiol (E(2)) were unaffected by stress. A similar pattern was displayed by fish exposed to stress in midvitellogenesis. Treatment of vitellogenic fish with exogenous cortisol resulted in significant increases in plasma cortisol at 1 and 3 h postinjection (p.i.). This was associated with significant depression of plasma T levels at 1 and 3 h p.i. and plasma E(2) levels at 3 and 6 h p.i. Plasma levels of GtH were unaffected by treatment with cortisol. Treatment of fish at an earlier stage of vitellogenesis with two different doses of cortisol resulted in very high elevations of plasma cortisol, but no effect on plasma levels of E(2) or GtH. In contrast, plasma T levels showed a stepwise decline over time. These results suggest that the inhibitory effects of stress on reproduction are mediated by cortisol and that the effect does not involve inhibition of GtH secretion and possibly acts at the level of GtH signal-transduction.

Reproductive condition and behavior in relation to plasma levels of gonadal steroids in the spiny damselfish Acanthochromis polyacanthus.

Gonadal condition and plasma levels of gonadal steroids were measured in relation to behavior in the biparental brood-protecting spiny damselfish Acanthochromis polyacanthus. Fish were captured by SCUBA divers from natural populations on Australia's Great Barrier Reef and immediately bled underwater, following diver or video observation of precapture behaviour. In winter (July), most fish were nonterritorial, with a low proportion of mature males, or vitellogenic females present. In spring (November), most fish were territorial with broods of young at varying stages of maturity, and all stages of gonadal development were represented. Territorial males were larger than nonterritorial fish, but territorial fish that had large (older) young (the end of the brooding phase) had lower condition factors than fish at other stages. Males of all gonad stages had a high proportion of spermatozoa in the testis, but this was higher in November than in July. Ovaries of females commonly had several classes of developing follicles present, although fish that were brooding large young had regressed ovaries with a high incidence of atresia. Plasma levels of testosterone (T) and 11-ketotestosterone were elevated in males of advanced gonadal maturity, and also in relation to recent or imminent spawning behaviour, but there were no changes in plasma 17, 20beta-dihydroxy-4-pregnen-3-one (17,20betaP), which was near assay detection limits at all times. Females had elevated T and 17beta-estradiol (E2) in association with vitellogenesis and elevated T in relation to spawning activity in some fish, but as in males, 17,20betaP levels were low and unchanging. Territorial females without young had lower cortisol levels than nonterritorial fish, or females protecting young. The results confirm the importance of elevated androgens to spawning activity in territorial male fish, but not females where endocrine activity is more closely related to stage of ovarian development. Extended brooding appears to inhibit vitellogenesis, perhaps via a stress-related mechanism.

Evidence that the inhibitory effects of stress on reproduction in teleost fish are not mediated by the action of cortisol on ovarian steroidogenesis.

Ovarian follicles of goldfish, common carp, and the sparid Pagrus auratus (New Zealand snapper) were incubated in vitro to assess the effects of cortisol (F) on ovarian steroidogenesis. Unstimulated goldfish follicles produced little testosterone (T) or 17 beta-estradiol (E2), whereas both carp and snapper follicles spontaneously produced E2 and to a lesser extent T. Goldfish follicles produced increased amounts of E2 in response to treatment with human chorionic gonadotropin (hCG), whereas carp and snapper follicles did not. However, stimulation of carp follicles with maturational carp gonadotropin (cGTH-II) resulted in dose-dependent increases in production of E2. Treatment of follicles of all three species with T resulted in E2 production to levels as high as or higher than those following treatment with hCG or cGtH-II. Cotreatment of follicles with T and hCG or cGTH-II did not result in higher E2 production than treatment with T alone. Goldfish follicles treated with 25-hydroxycholesterol showed increases in E2 production that were similar to those occurring following treatment with T. Treatment of follicles with F at a range of doses up to 1 microgram.ml-1 had no inhibitory effect on T or E2 production in any treatment combination in any of the species examined. In several cases, follicles incubated with T and/or hCG produced more E2 in the presence of F than they did without F. The results suggest either that the observed inhibitory effects of stress in a range of teleost species are not mediated by F or that they arise higher in the endocrine pathway than at the level of ovarian steroidogenesis.

Changes in plasma levels of gonadal steroids and gonad morphology during the spawning cycle of male and female demoiselles Chromis dispilus (Pisces: Pomacentridae).

This study examined the relationship between gonad morphology and endocrine function of male and female demoiselles Chromis dispilus. Gonad samples were collected over two successive seasons and staged macroscopically and histologically. Blood samples were assayed for the gonadal steroids 17 beta-estradiol (E2), testosterone (T), 11-ketotestosterone (11KT), and 17 alpha,20 beta-dihydroxy-4-pregen-3-one (17,20 beta P) by radioimmunoassay. Histological examination indicated that demoiselles are multiple spawners with group synchronous gamete development, and gonad changes are synchronised within local populations. Gonad morphology does not differ between nonterritorial and territorial males. Plasma levels of E2 and T increased with vitellogenesis in female demoiselles. Plasma levels of 17,20 beta P did not change in association with final oocyte maturation, but 17,20 beta P was not excluded as the possible maturation inducing steroid. However, 17,20 beta P was elevated in females in association with spawning activity. Plasma levels of T and 11KT were not consistently associated with spermiation in male demoiselles but were elevated in association with spawning behaviour. Androgen levels were significantly higher during spawning in territorial males than in nonterritorial males. There was no association between 17,20 beta P and spermiation. Plasma levels of 17,20 beta P were elevated during the display and spawning period in territorial males only. The results of this study provide further evidence for the association of plasma levels of gonadal steroids and behavioural status in demoiselles.

Uncoupling of visual and somatic growth in the rainbow trout Oncorhynchus mykiss.

Hatchery reared juvenile rainbow trout of common parentage were reared on measured low or high rations, or fed ad libitum for 4.3 months to produce fish with different growth rates. Fish from the different groups differed in size by up to 40 and 290% for length and weight, respectively, by the end of the trial. Slow somatic growth was not accompanied by correspondingly slow growth of either the eyes, optic tectum or the cerebellum, suggesting that above a certain maintenance ration, growth of these parts of the CNS is strongly age-dependent. Retinal characteristics were also found to be age-dependent and not affected by the somatic growth rate of the fish. The corollary that age-dependent ocular growth should also be reflected in different relative eye sizes in fish with differential growth rates in the wild was tested by comparing fish of known age from lakes in which fish have markedly different growth profiles. Fish stocked from a single hatchery were recaptured from Lakes Okataina and Tarawera (rapid fish growth) and Lake Taharoa (slow fish growth) at times up to 5 years after release. As predicted, eye sizes of fish from Lakes Okataina and Tarawera were smaller for any given body size, than those of fish from Lake Taharoa. Absolute eye size was correlated with fish age, although there was some variation in eye size for any given age. Taken together, these results show that up to a certain level of food deprivation, growth of the eye is maintained at the expense, or in spite, of low somatic growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of population density, territorial interaction and plasma levels of gonadal steroids in spawning male demoiselles Chromis dispilus (Pisces: Pomacentridae).

Territorial male demoiselles Chromis dispilus were captured and bloodsampled underwater by scuba divers, from reef areas of low, medium, and high population density, over five spawning seasons. Measurements of densities of territory-holding males and the water-column population (females and nonterritory-holding males) were made from the same sites. Behavior of territory-holding males was assessed in relation to phase of the reproductive cycle and population density, using a remote underwater video system. Plasma levels of testosterone, 11-ketotestosterone (11KT), and 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) were measured by RIA. Territory density was found to be proportional to population size. Males from high density sites spent more time chasing conspecifics and spawning during the phase of courtship display and spawning (spawning phase), but there were no differences in behavior between males from different density sites during periods of egg-brooding and defence (nesting phase). Plasma levels of all three steroids were elevated during the spawning phase, and low during the nesting phase. Absolute levels of gonadal steroids were higher in fish from areas of high population density during the spawning phase, than in fish from lower population densities. In one case, plasma 11KT and 17,20 beta P were also elevated at high density during the nesting phase. The results of the study indicate that steroid hormone levels are labile in response to changes in population density, and frequency of territorial interaction. Changes in levels of plasma androgens are consistent with the "challenge" hypothesis of social regulation of territorial aggression.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of behavioural and morphological measures of visual acuity during ontogeny in a teleost fish, Forsterygion varium, tripterygiidae (Forster, 1801).

Ocular morphology was examined in larval, juvenile and adult F. varium. There was a 26-fold increase in eye size from 0.28 mm in the smallest larva (5.0 mm in length) to a maximum diameter of 7.2 mm in a 110 mm long adult. Larval fish had pure cone retinae at hatching, however, putative rod precursor cells were also present. Juvenile and adult fish had a duplex retina with cones arranged in a square mosaic in which 4 equal double cones surrounded a central single cone. Hypertrophy of cone ellipsoids with increasing eye size resulted in maintenance of a closely packed array in fishes of all sizes. Theoretical sensitivity, assessed in terms of convergence of rods:bipolars, rod density, and photoreceptor outer segment length, increased during the juvenile phase but was constant across the adult size range. Angular density of cones increased with increasing eye size such that theoretical spacial acuity was poor in smallest fish (1 degree 8') and improved to an asymptotic value of about 9' in adults. Behavioural acuity of a 1-day-old larva determined using the optokinetic response (29 degrees), was very much poorer than histological estimates (1 degree 8'). Behavioural acuity improved to 4 degrees 18' at 14 days of age, compared to a theoretical value of 54'. An estimate of Matthiessen's ratio based on histological measurements suggests that the larval eye is initially strongly myopic, and grows into focus. Development of the retractor lentis muscle was first apparent 7 days after hatching with the result that larval eyes are incapable of accommodative lens movements to correct for a refractive error. This apparent myopia is thought to account for at least part of the mismatch between theoretical and behavioural spatial acuity.

Ocular morphology of the sweep Scorpis lineolatus and the spotty Notolabrus celidotus (Pisces: Teleostei) grown in low intensity light.

Adults of two species of teleost fishes, the New Zealand sweep (Scorpis lineolatus) and the spotty (Notolabrus [formerly Pseudolabrus] celidotus), were recovered from dark, sealed sea water storage tanks after an extended period of residence (physical constraints meant that fish could only have entered the system as larvae or small juveniles). Individuals of both species had proportionately larger eyes than normal fishes of similar body size. Age estimation, based on unvalidated annual increments in otoliths indicated that fishes from the water tanks were all older (i.e. slower-growing) than normal fishes of similar size. This suggests that the increase in relative eye size in tank fishes may have been the result of maintenance of ocular growth, in the face of reduced rates of somatic growth, and raises the question as to whether eye growth in fishes generally, is a temporal function. In addition to ocular enlargement, sweeps from the water tanks also showed reduced densities of cones, rods, ganglion cells and, in some cases bipolar cells compared to normal fishes of similar body size. Cone, rod and bipolar cell densities of tank fishes were not different when compared with normal fishes of similar eye size; however, ganglion cell numbers were still lower than in normal fishes. This suggests that changes in cone, rod and bipolar cell densities in tank fishes resulted from the normal changes that occur with ocular growth, whereas low ganglion cell densities were a direct result of the abnormal photic environment. In contrast to the sweeps, most of the spotties from the water tanks did not show differences in retinal cell densities relative to normal fishes.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in plasma levels of gonadal steroids during spawning behaviour in territorial male demoiselles Chromis dispilus (Pisces: Pomacentridae) sampled underwater.

Males of the demoiselle Chromis dispilus (a species endemic to New Zealand) were hand-netted from nest territories by scuba divers and blood sampled in situ. Reproductive condition and behaviour prior to capture were compared with plasma levels of testosterone (T) and 17 alpha,20 beta dihydroxy-4-pregnen-3-one (17,20 beta P). Spawning cycles of about 7 days, consisting of 1-2 days of spawning activity followed by 4-5 days of brooding behaviour, were observed. Plasma levels of T and 17,20 beta P were elevated (4-6 and 1-1.5 ng.ml-1, respectively) in fish that were engaged in courtship display, spawning, or guarding freshly spawned eggs. Levels of both hormones fell to less than 1 (T) and less than 0.4 ng.ml-1 (17,20 beta P) at the end of spawning episodes and remained low through the subsequent brooding period. T levels increased slightly toward the end of the brooding phase. Samples taken at 2- to 3-hr intervals during daylight hours showed similar correlation of steroid levels and activity; however, there was a marked fall in 17,20 beta P in spawning fish with the onset of shelter seeking at dusk. Values returned to high levels with the resumption of spawning the next day. Plasma steroid levels were not consistently correlated with reproductive condition (degree of spermiation). It is concluded that there is a strong correlation between plasma T and 17,20 beta P levels and the male spawning cycle, but not brooding or territorial behaviour per se.

Endocrine changes during gonadal maturation and spawning in the orange roughy (Hoplostethus atlanticus Collett), a teleost from the midslope waters off New Zealand.

Orange roughy were sampled at all stages of the reproductive cycle by trawling at depths of 700-1200 m off the coast of New Zealand. Blood samples were collected from live fish, and changes in plasma levels of gonadal steroids were correlated with gonadal development and spawning. Plasma androgens were low in spent and regressed fish of both sexes and increased during gametogenesis to peak early in the spawning period at 6.6 and 9.4 ng.ml-1 for males and females, respectively. Androgen levels dropped to near basal levels over successive days during the first week of spawning in both prespawning and ovulated or spermiated fish. Falls in plasma androgens were not accompanied by increasing levels of plasma 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17 alpha,20 beta P) which remained at or near assay detection limits throughout. 11-Deoxycortisol (11-DOC) was present in the plasma of both sexes but did not change in concert with reproductive development. 17 beta-Estradiol was present in low concentrations (maximum 0.9 ng.ml-1 plasma) in recrudescing females, whereas estrone was detectable but not elevated at any stage. 17 alpha-Hydroxyprogesterone was not detectable in the plasma of any fish at any time. It is suggested that neither 17 alpha,20 beta P nor 11-DOC were active as maturation-inducing steroids (MIS) in orange roughy and that androgens may act as MIS. If the recorded fall in androgens was due to synthesis of another steroid from a common precursor, then the unidentified steroid does not appear to have been involved in stimulating final gamete maturation, but may have some action in initiating spawning behavior.

Seasonal changes in reproductive condition and plasma levels of sex steroids in the blue cod,Parapercis colias (Bloch and Schneider) (Mugiloididae).

Gonad and plasma samples were taken from blue cod captured throughout the reproductive cycle, gonad condition was assessed, and plasma levels of 17α-hydroxyprogesterone (17αOHP), 17α,20Β-dihydroxy-4-pregnen-3-one (17α,20ΒP), testosterone (T), 17Β-estradiol (E2) and estrone (E1) were measured by radioimmunoassay. It was confirmed that spawning occurred over an extended period in late winter and spring, with individual fish being involved in multiple spawning events. Plasma levels of T were bimodal in both sexes with peaks (maximum of 6.0 ng.ml(-1)) occurring 2 months prior to, and also during the early part of the spawning period. 17α,20ΒP was elevated in males (2.1 ng.ml(-1)) in mid-spermatogenesis coinciding with the first T peak (4.9 ng.m.(-1)). 17α,20ΒP was detectable but not significantly elevated (0.6-1.2 ng.ml(-1)) at any sample time in females. E2 was elevated in mature females (1.0 ng.ml(-1)) early in the spawning period but remained at assay detection limits (0.3 ng.ml(-1)) at all other sample times. Neither 17αOHP nor E1 were detectable in the plasma of either sex. It is suggested that bimodal increases in sex steroids prior to spawning may be a feature of species with rapid recrudescence.