Relationship between temperature, ovarian recrudescence, and plasma cortisol level in Tilapia aurea (Cichlidae, Teleostei)

Photo-thermal regulation of neuropeptide Y (NPY) expression in ovarian follicles and ovarian activity of the catfish, Clarias batrachus

Authors have recently reported a gradual increase in neuropeptide Y expression in the ovarian follicles of Clarias batrachus with the progression of oogenesis, coinciding with increasing photoperiod and temperature. This indicates the involvement of photoperiod and temperature in controlling NPY expression. Therefore, a study was designed to investigate the role of photoperiod and temperature in regulation of NPY expression in ovarian follicles. The catfish were exposed to different photo-thermal regimes during the late-quiescence and late-recrudescence phases for one month, and the expression of NPY was analyzed along with other ovarian activities. Though the exposure of catfish to long photoperiod induced a marginal increase (1.5 fold) in NPY expression in follicular cells, the high temperature stimulated its expression more effectively (6-10 fold), irrespective of photoperiodic exposures. Exposure to long photoperiod and high temperature together induced NPY expression maximally in granulosa and thecal cells of fully grown oocytes, but exposure to low temperature decreased its expression significantly. The oogenic and steroidogenic activities were also promoted simultaneously after the exposure to high temperature and long photoperiod alone or in combination. However, the low temperature exposure suppressed the ovarian activities leading to atresia of advanced follicles. Thus it is suggested that photoperiod and temperature both affect NPY expression and ovarian recrudescence in fish but the influences of temperature seem to be more prominent.

Survey of the Adrenal Homolog in Teleosts

The adrenal homolog of teleosts is not a compact organ as the adrenal glands of most vertebrates but is composed by aminergic chromaffin and interrenal steroidogenic cells located mostly inside the head kidney that, in this taxon, generally has a hematopoietic function. The two tissues can be mixed, adjacent, or completely separated and line the endothelium of the venous vessels or are located in close proximity. The chromaffin cells in some species are also present in the posterior kidney. Histological and ultrastructural work revealed cytological peculiarities of both types of cells as compared to those of other vertebrate species. In particular, the interrenal ones can show some variations in ultrastructure depending on sex, time of the year, and relation to stress events. A periodic renewal of the whole gland tissue is also sustained by some studies. Research regarding development is scanty as compared to mammals and most studies go back to the early years of the past century. The adrenal homolog of teleosts is under hormonal and neuronal control. Moreover, local paracrine interactions may play an important role in modulating a system involved in stress response and osmoregulation. Most previous studies involved a few species with the object of intensive rearing for commercial purposes; in fact cortisol, the main hormone secreted by the interrenal cells, can also influence reproduction and growth. This review summarizes data from morphocytological work and refers to other excellent reviews regarding physiology. Some of the results are compared to data available from other fishes and vertebrate classes with the aim of including them in an evolutionary and environmental framework.

Semilunar changes in estradiol and cortisol coincident with gonadal maturation and spawning in the killifish Fundulus heteroclitus

Radioimmunoassay techniques were used to measure estradiol-17 beta (E2) and cortisol in the serum and ovarian fluid of Fundulus heteroclitus throughout complete semilunar spawning cycles. The cyclic nature of spawning activity was confirmed by monitoring the gonadosomatic index and noting the times at which ovulated eggs were found within the ovarian lumen. Levels of serum E2, ovarian fluid E2, and serum cortisol all exhibited cycles which paralleled the semilunar cycle of gonadal maturity and spawning in this euryhaline killifish. Elevations of serum cortisol were temporally associated with ovulation, whereas ovarian fluid E2 levels peaked several days prior to ovulation. Serum E2 remained elevated after ovarian fluid E2 levels had returned to baseline. Cortisol concentrations in ovarian fluid did not cycle and no correlation was apparent between serum cortisol and glucose concentrations.

Clearance of corticosteroids in yearling coho salmon, Oncorhynchus kisutch, in fresh water and seawater and after stress

The metabolic clearance rate of corticosteroids determined after a single injection of [3H]cortisol was higher in fish acclimated to seawater (SW) than in those acclimated to fresh water (FW). Uptake and retention of corticosteroids in liver, gill filaments, and gall bladder bile were greater in SW than in FW fish. The stress of long-term (5 days), but not short-term (12 hr), continuous confinement apparently increased the clearance rate of corticosteroids in both FW and SW fish. Chronic, but not acute, administration of exogenous cortisol, yielding cortisol titers close to the physiological range, appeared to increase the clearance rate of corticosteroids in FW fish.

Radioimmunoassay of serum cortisol in the plaice (Pleuronectes platessa L.)

The validity of a radioimmunoassay kit for direct measurement of cortisol in the plaice is described. This technique was used to determine the cortisol concentration in adult male and female plaice in 100 microliter of either plasma or serum. There was no significant difference in the serum cortisol values determined by radioimmunoassay either with or without chromatography. Storage of whole blood at 4 degrees for varying periods up to 24 hr, before removal of the serum, did not affect the cortisol concentration. Decreases also did not occur in serum samples kept at room temperature for up to 5 days, although losses of 1-12% occurred after 7 days and 11-39% after 8 days. The daily variations in serum cortisol levels were examined in fish exposed at 11 degrees to 12 hr light: 12 hr dark over a 32-hr period and the existence of a 24-hr cortisol rhythm was observed. Blood samples were taken from the same six fish every 4 hr, each fish being bled nine times during the experiment. Blood samples were also taken every 4 hr from groups of seven fish, each fish during this experiment being bled only once. Measurement of monthly serum samples throughout 1 year showed cortisol concentrations at a maximum in April, during the peak spawning period. There was no significant difference between cortisol levels in male and female plaice, except in January, and no difference between serum and plasma values in either sex.

The effect of social isolation on androgen and corticosteroid levels in a cichlid fish (Haplochromis burtoni) and in swordtails (Xiphophorus helleri)

The blood androgen and glucocorticoid levels of male Haplochromis burtoni and Xiphophorus helleri were measured in socially isolated individuals (8 and 4 weeks, respectively) and nonisolated controls. In both species social isolation leads to significant reductions of mean concentrations and variances, both for androgens and corticosteroids. It is known for H. burtoni--and new evidence for X. helleri is presented--that social isolation reduces aggressivity in nonescalating situations. It is proposed that social stimuli in both species stimulate the testes to produce more androgenic hormones, and that this can lead to higher levels of aggression. At least in tropical fish species the androgenic optimum for defending a territory or a social status may be much more controlled by social stimuli than previously realized.

Circannual and circadian variations in plasma levels of steroids (cortisol, estradiol-17 beta, estrone, and testosterone) correlated with the annual gonadal cycle in the catfish, Heteropneustes fossilis (Bloch)

Circannual and circadian variations in plasma levels of steroids were estimated by radioimmunoassay in the female and male catfish, Heteropneustes fossilis, over two consecutive annual reproductive cycles. In the female catfish, testosterone (T), estradiol-17 beta (E2), and estrone (E1) were detectable in the plasma only during the reproductively active (preparatory through spawning) period and their levels increased during vitellogenesis. In the fully gravid catfish, when vitellogenesis was nearly complete, levels of E2 declined but those of T continued to increase suggesting a product-precursor relationship between the two steroids. Plasma cortisol (F) was detectable throughout the year and exhibited three peaks coinciding with summer, monsoon, and winter; the first and second peaks coincided with vitellogenesis and spawning, respectively. In the male catfish, changes in plasma T and F levels closely paralleled the seasonal recrudescence and activity of testes and seminal vesicles. After spawning, gonads regressed and levels of sex steroids declined sharply. In the absence of natural spawning due to scanty monsoon rains, as during the second year of this study, gonadal regression was delayed and the sex steroids persisted in the plasma well beyond the normal spawning season. In addition, the first two peaks of F levels merged to form a plateau extending from the preparatory period until the late spawning period. The three sex steroids (T, E2, and E1) exhibited identical circadian rhythms; a major peak occurred at the onset of the dark phase (20:00 hr) and a minor peak was generally observed 4 hr after the onset of the light phase (12:00 hr). The amplitude of rhythms was greatest during the prespawning and the spawning periods. Cortisol peak levels generally alternated with those of sex steroids. Steroid rhythms show rather precise correlations with environmental factors such as photoperiod, temperature, and rainfall as well as with seasonal reproductive activity in both sexes of catfish.