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Sexually mature female striped trumpeter Latris lineata (Forster, 1801) were sampled monthly for two spawning seasons until the start of gonadal recrudescence, and then fortnightly until ovulations ceased. Oocyte size and ovarian length, measured by inserting a semi-rigid biopsy catheter to the full extent of insertion, were recorded at each sample time. Ovarian length was expressed as proportion of fork length to provide a gonad index (GI). In non-ovulating females, there was little change in GI throughout the year. However, in ovulating females, GI increased from 18.3 five months before the first spawning season to 27.6 at the peak of the season in October, decreasing to 19.1 the following May and then increasing again to a maximum of 31.1 the following October, in concert with annual changes in reproductive condition. There was a positive linear correlation between GI and oocyte size during the period of oocyte growth ( r = 0.75, n = 302). Based on the range of GI values for each stage in oocyte development (primary, cortical alveoli, vitellogenic, maturing and hydrated), GI was 90% accurate at assessing fish as pre-vitellogenic and 83% accurate at assessing fish as undergoing final oocyte maturation. This study demonstrated that measurement of GI by catheterization provides a rapid and non-destructive method for assessing maturational status of striped trumpeter broodstock. [ABSTRACT FROM AUTHOR]

Seasonal change in temperature has a profound effect on reproduction in fish. Increasing temperatures cue reproductive development in spring-spawning species, and falling temperatures stimulate reproduction in autumn-spawners. Elevated temperatures truncate spring spawning, and delay autumn spawning. Temperature increases will affect reproduction, but the nature of these effects will depend on the period and amplitude of the increase and range from phase-shifting of spawning to complete inhibition of reproduction. This latter effect will be most marked in species that are constrained in their capacity to shift geographic range. Studies from a range of taxa, habitats and temperature ranges all show inhibitory effects of elevated temperature albeit about different environmental set points. The effects are generated through the endocrine system, particularly through the inhibition of ovarian oestrogen production. Larval fishes are usually more sensitive than adults to environmental fluctuations, and might be especially vulnerable to climate change. In addition to direct effects on embryonic duration and egg survival, temperature also influences size at hatching, developmental rate, pelagic larval duration and survival. A companion effect of marine climate change is ocean acidification, which may pose a significant threat through its capacity to alter larval behaviour and impair sensory capabilities. This in turn impacts on population replenishment and connectivity patterns of marine fishes. [ABSTRACT FROM AUTHOR]

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., (Copyright © 2010 Elsevier Inc. All rights reserved.)

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.

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).

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 (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.

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., (Copyright 1999 Academic Press.)

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.

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.

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)

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)

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.