Seasonal changes in the hypothalamo-hypophyseal-ovarian system in the catfish,Heteropneustes fossilis (Bloch)*

The annual reproductive cycle of the catfish, H. fossilis (Bloch) is divided into the preparatory period (February-April), the prespawning period (May-June), the spawning period (July-August) and the postspawning period (September-January). During the early postspawning period (September-November), the hypothalamo-hypophyseal-ovarian system shows a gradual regression. In January, the hypothalamic nuclei, the pars magnocellularis (PMC), the pars parvocellularis (PPC) of the nucleus preopticus (NPO), and the nucleus lateralis tuberis (NLT) show renewed activity, as shown by a significant increase in their nuclear diameters and an accumulation of neurosecretory material (NSM) in their cell bodies. The hypophysis and the ovary remain quiescent. During the preparatory period, all the hypothalamic neurons studied indicate decreased activity but simultaneously show an accumulation of NSM in their cell bodies. The number of granulated basophils in the proximal pars distalis (PPD) of the hypophysis remains low but ovarian weights increase, presumably due to the multiplication of oogonia. In the prespawning period, there is a marked accumulation of NSM in the cell bodies of the hypothalamic neurons and at the same time the number of granulated basophils in the PPD of the hypophysis dramatically increases with concomitant increase in vitellogenic activity in the ovary. During the spawning period, the hypothalamic neurons continue to store NSM in their cell bodies and simultaneously there is a tremendous increase in the number of granulated basophils in the PPD of the hypophysis and the ovary has a large proportion of yolky primary oocytes. Spawning is associated with a significant degranulation of the granulated basophils in the PPD of the hypophysis. The significance of the results is discussed in relation to the environmental and hormonal regulation of seasonal ovarian activity.     

Steroid hormone profiles and correlative gonadal histological changes during natural sex reversal of sobaity kept in tanks and sea-cages

The gonadosomatic index of sobaity Sparidentex hasta fits well with the natural spawning season of February-March. At 12 and 24 months all the population matured as males. However, during this time, between April-September intersex gonads were seen. From October of the third year of life, females were seen for the first time. These changes in the histology of the gonads were correlated with the hormonal profile. Testosterone showed no significant correlation with sex but 11-ketotestosterone correlated very well with the mature male gonads and thus can be used for sexing. Oestradiol-17β higher in sex reversed individuals (females) in the spawning season than in males. The sequence of events in the protandrous sex change of this fish during the first two spawning seasons is male → intersex → male. However, during the third spawning season (age 36–37 months) this sequence is male →intersex → male or female (10–17%).     

Seasonal changes in the corpuscles of Stannius and the gonads of the catfish, Heteropneustes fossilis (Bloch).

The seasonal changes in the corpuscles of Stannius (CS) and the gonads of the catfish, Heteropneustes fossilis were studied. The annual sex cycle of the fish has been divided into 4 phases on the basis of the variations in the gonosomatic index and histocytological features displayed by the testes and ovaries. There is a rise in the percentage of aldehyde fuchsin (AF)-positive cells in the CS and an increase in the nuclear diameter, at the beginning of preparatory period (February). In the prespawning period (May--June) the AF-positive cells undergo degranulation. A slight regranulation and rise in the percentage of AF-positive cells occurs during early spawing period (July). During the postspawning phase (September--January) the corpuscles remain predominated by AF-negative cells and show histolytical changes; the nuclear indices are reduced. In view of the concomitant changes occurring in the CS and the gonads the possibility of some direct or indirect relationship between the two has been discussed, although it is difficult to ascertain whether the changes in the corpuscles are cause or consequence of the gonadal cycle.     

Urine of reproductively mature female rainbow trout, Oncorhynchus mykiss (Walbaum), contains a priming pheromone which enhances plasma levels of sex steroids and gonadotrophin II in males

Urine of reproductively mature female rainbow trout was shown to contain a priming pheromone which raised the levels of 17 a ,20β-dihydroxy-4-pregnen-3-one (17,20β-P), testosterone and gonadotrophin II in the blood plasma of reproductively mature male rainbow trout. Milt volumes, however, were unaffected.
Because it had been established in a previous study that the sulphated form of 17,20β-P is abundant in the urine of spawning rainbow trout, synthetic 17 a ,20β-dihydroxy-4-pregnen-3-one 20-sulphate was also tested for pheromonal activity. It was found to have only a smalt and inconsistent priming effect on steroid levels and did not alter the orientation or spawning activity of males.
It was also shown that, in the majority of experiments, there was a significant drop, over the course of 24 h, in the levels of 17,20β-P and testosterone in the control groups of males.     

Responses of the genital system and the urinogenital papilla of the female catfish,Heteropneustes fossilis (Bloch) to sex hormones

Summary Intraperitoneal injections of diethylstilbestrol and testosterone propionate into the catfish,Heteropneustes fossilis (Bloch) elicited pronounced changes in the female reproductive system and the urinogenital papilla. Considerable gonadal and oviducal hypotrophy occurred in the hormone recipients. Marked histological alterations were also encountered in the genital system of the experimental females. Another interesting response was the inhibition of the urinogenital papilla of the treated fishes. It is suggested that the changes in the ovary and the oviduct were induced by the sex hormones throught the inhibition of the gonadotrophic activity of the anterior hypophysis. The changes in the urinogenital papilla proved that this structure in the female catfish is a true secondary sexual character and is under the estrogenic control of the ovary.

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Zusammenfassung Intraperitoneale Injektionen von Diäthylstilböstrol und von Testosteronpropionat haben bei Heteropneustes fossilis ausgesprochene Veränderungen an den weiblichen Geschlechtsorganen und an der Urogenitalpapille zur Folge. Bei den Hormonempfängern kommt es zu einer beträchtlichen Hypotrophie der Keimdrüse wie des Ovidukts. Im Genitalsystem der Versuchstiere sind auch deutliche histologische Veränderungen nachzuweisen. Eine bemerkenswerte Folgeerscheinung ist die Hemmung der Urogenitalpapille der behandelten Fische. Es ist anzunehmen, daß die Veränderungen im Eierstock und im Eileiter durch die Geschlechtshormone über eine Hemmung der gonadotropen Aktivität der Hypophyse veranlaßt werden. Die Veränderungen an der Urogenitalpapille beweisen, daß dieses Organ beim weiblichen Heteropneustes den Charakter eines wahren sekundären Geschlechtsmerkmales besitzt und unter der östrogenen Kontrolle des Eierstocks steht.

     

Changes in ovarian development and plasma levels of sex steroid hormones in the wild female Japanese sardine (Sardinops melanostictus) during the spawning period

In order to clarify the spawning pattern of Japaneses sardine ( Sardinops melanostictus ) during the spawning period, changes in ovarian histology, frequency distributions of oocyte diameter and plasma levels of oestradiol-17β (E₂) and 17 a ,20β-dihydroxy-4-pregnen-3-one (17 a ,20β-diOH-P) were examined in female fish captured in the region off Kyushu and Shikoku in Japan. With the development of the ovary, the gonadosomatic index (GSI) increased gradually and the size of oocytes became larger. When the GSI exceeded 13, the translucent hydrated eggs began to dominate and ovulation subsequently occurred. After ovulation, GSI decreased to less than 3. Post-ovulatory follicles were found only in the lower GSI ranges and atretic oocytes were always observed in the ovary. Plasma E₂ levels increased along with ovarian development but decreased after completion of yolk accumulation. On the other hand, 17 a ,20β-diOH-P showed the highest level just before and after ovulation. Ovarian histology and hormonal profiles suggest that the sardine spawns repeatedly during the spawning period. Based on the concentration of 17a,20β-diOH-P, the female Japanese sardine was estimated to ovulate before the middle of the night.     

Thermal influences on temporal changes in plasma testosterone and oestradiol-17β concentrations during gonadal recrudescence in female common wolffish

Temperature treatment during ovarian recrudescence influenced temporal changes in plasma testosterone (T) and oestradiol-17β (E₂). In fish exposed to 8 and 12° C early in the cycle the peaks of both T and E₂ were delayed by 4 weeks in comparison with those of fish held at 4° C throughout the experiment. These differences were accompanied by corresponding shifts in the timing of ovulation.     

Surface ultrastructure of the olfactory rosette of an air-breathing catfish,Heteropneustes fossilis (Bloch)

The surface architecture of the olfactory rosette ofHeteropneustes fossilis (Bloch) has been studied by scanning electron microscopy. The olfactory rosette is an oval structure composed of a number of lamellae arranged pinnately on a median raphe. The raphe is invested with epithelial cells and pits which represent goblet cell openings. On the basis of cellular characteristics and their distribution the lateral surface of each olfactory lamella is identified as sensory, ciliated non-sensory and non-ciliated non-sensory epithelium. The sensory epithelium is provided with receptor and supporting cells. The ciliated non-sensory epithelium is covered with dense cilia obscuring the presence of other cell types. The non-ciliated non-sensory epithelium is with many polygonal areas containing cells.     

Seasonal effects of pinealectomy on testicular recrudescence and secretory activity of seminal vesicles in the catfish Heteropneustes fossilis (Bloch)

The effects of pinealectomy on testicular activity and secretory activity of seminal vesicles were examined in the catfish Heteropneustes fossilis under various combinations of photoperiod and temperature during different periods of the annual reproductive cycle. Pinealectomy had no effect on gonadal activity during the preparatory, prespawning and spawning periods of the reproductive cycle. However, during the postspawning period, under long (LD 14:10) or short (LD 9:15) photoperiod at 25° C or at gradually increasing ambient temperature, pinealectomy accelerated testicular recrudescence and secretory activity of the seminal vesicles. Nevertheless. during this period the presence of the pineal facilitated the recrudescence of testes and seminal vesicles in catfish exposed to continuous light (LL), continuous darkness (DD) and 12 hL:l2 hD (LD) at 25° C. These findings suggest that the role of the pineal in catfish reproduction is variable and depends upon the photoperiod and temperature regimes to which the fish are exposed, as well as on the time of the year and the state of the reproductive cycle. The results also suggest that the effects of pinealectomy in catfish are mediated through an influence on the hypothalamo-hypophyseal gonadal axis.     

Plasma levels of C18-, C19- and C21-steroids in captive and feral female sea bass

Morphometric analysis of the gonads of sea bass Dicentrarchus labrax revealed that captive fish matured 1 month later than feral fish, but levels of gonadal steroids were identical in both groups at the same stage of sexual development. 17β-oestradiol (E₂) (up to 3 ng ml-1) and testosterone (T) (up to 4 ng ml-1) were highest during the gametogenetic period while 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P) (free and sulphated) were maximal during the spawning period. Free 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) was very low and did not change (c. 0·5 ng ml⁻¹) while 17,20β-P-sulphate increased during the spawning period in both groups (up to 2 ng ml⁻¹). In contrast cortisol levels were higher in captive fish and increased during the spawning period (up to 100 ng ml⁻¹). These results suggest that captivity delays vitellogenesis and spawning in sea bass without affecting the final levels of the gonadal steroids and further indicates a role for cortisol in the latter period. The increased levels during the spawning period suggests a pheromonal role for 17,20β-P-sulphate and 17,20β,21-P-conjugates and the involvement of 17,20β,21-P in final ooccyte maturation.     

Inhibition of hCG-induced spawning by alpha-methylparatyrosine, a tyrosine hydroxylase inhibitor, in the catfish Heteropneustes fossilis (Bloch)

In this study, the effect of pharmacological inhibition of catecholaminergic activity on hCG-induced spawning was evaluated and correlated with tyrosine hydroxylase (TH) activity, the rate-limiting enzyme in catecholamine biosynthesis. Gravid female H. fossilis collected in both prespawning and spawning phases were given alpha-methylparatyrosine (alpha-MPT: 250 microg/g body weight, ip, an irreversible inhibitor of TH) and human chorionic gonadotropin (hCG: 100 IU/fish, ip) alone or in combination. The fish were sampled at different intervals for measuring hypothalamic and ovarian TH activity and checking spawning response. The administration of hCG resulted in ovulation and spawning in both phases with a higher response in the spawning phase. The administration of alpha-MPT did not induce any response, like the control fish. In the hCG + alpha-MPT groups, the spawning response of hCG was significantly inhibited and delayed by the inhibitor. The spawning response of hCG was accompanied by a significant increase in both hypothalamic and ovarian TH activity at 6 and 12 h of the injection. However, at 24hr the activity decreased except in the spawning phase. The alpha-MPT treatment inhibited TH activity significantly in a duration-dependent manner. In the hCG + alpha-MPT groups, enzyme activity was inhibited at all duration. The results indicate the involvement of catecholamines during the hCG-induced spawning and the specific functional nature of the involvement needs further investigation.     

Variations in hepatic estradiol-17beta receptor concentrations during the annual reproductive cycle of diploid and triploid female catfish, Heteropneustes fossilis (Bloch)

Concentrations of hepatic estradiol-17beta (E2) receptors (ER) in cytosolic and nuclear fractions were evaluated in diploid and triploid female catfish Heteropneustes fossilis (Bloch) during four different reproductive periods of a complete reproductive cycle. Basal level of ER concentration was noted in the resting period of both diploids and triploids. Receptor level gradually elevated through the preparatory period and reached a peak in the pre-spawning period in both diploids and triploids. However, ER concentrations were overall reduced in triploid to that of diploid females. In a single point assay, in diploids, ER concentration showed about a 3-fold rise (p<0.001) in the cytosolic and a 4-fold rise (p<0.001) in the nuclear extracts from resting to the pre-spawning period. In triploids, only a 2-fold rise was observed both in cytosolic (p<0.01) and nuclear (p<0.05) ER concentration during the same span. Finally, a sudden fall of receptor level was observed in the spawning period in both the ploidy groups with a lower concentration in the triploids. The K(d) value did not differ between the females of diploids (cytosolic 1.12+/-0.21 nM and nuclear 6.9+/-0.9 nM) and triploids (cytosolic--1.13+/-0.17 nM, nuclear--6.8+/-2 nM). However, B(max) of the diploid showed about double the value than triploid females both in the cytosolic (diploid--367.4+/-33.24 pmol/mg protein, triploid--187.3+/-13.20 pmol/mg protein, p<0.001) and nuclear extracts (diploid--946+/-66 pmol/mg DNA, triploid-558+/-98 pmol/mg DNA, p<0.01) of liver. Lower E2 binding capacity and lower amount of E2 receptors of triploid catfish liver with a stunted vitellogenic status could be one of the major causes for reduced gonadal development and sterility in female triploids.     

Effect of starvation on tissue and serum gluconeogenic enzymes, alkaline phosphatase and tissue glycogen in the freshwater catfish, Heteropneustes fossilis (Bloch).

The influence of starvation has been studied on tissue and serum G-6Pase F-D-Pase and alkaline phosphatase activities and on the muscle and liver glycogen content of the freshwater catfish H. fossilis (Bloch). A marked increase in G-6Pase and F-D-Pase activities and a fall in the muscle and liver glycogen content recorded during 40 day starvation. The rise in gluconeogenic enzymes during starvation may be due to glucocorticoid stimulation. Alkaline phosphatase activity was found to decline markedly during starvation. The decline in enzyme activity is attributed to some factors like a fall in the rate of synthesis caused by lowered metabolic demands and to electrolyte imbalance caused by tissue overhydration. The fall in glycogen content may be related to the starved condition of the fish. Elevation in glycogen content and alkaline phosphatase activity and a fall in gluconeogenic enzymes were noted when feeding had been resumed.     

Effect of salicylate and adrenocorticotropin on the hepatic and serum cholesterol in catfish, Heteropneustes fossilis (Bloch).

A single injection of salicylate or salicylate plus ACTH was able to lower the hepatic cholesterol content within one hour after the treatment. However, their daily injection for eight days caused significant rise in the hepatic cholesterol. ACTH alone could not significantly alter the liver cholesterol content after similar treatment. A single injection of salicylate produced hypocholesterolemia within one and three hours after the treatment. ACTH or salicylate plus ACTH also brought about 50 per cent reduction in serum cholesterol level from its initial control value within one hour. Similar treatments, however, raised the serum cholesterol after three hours. The rise in the serum cholesterol level was about twofold in animals five hours after salicylate plus ACTH treatment. Daily administration of salicylate, ACTH or salicylate plus ACTH for eight days caused, however, hypocholesterolemia.     

Role of pineal in the regulation of some aspects of circadian rhythmicity in the catfish, Heteropneustes fossilis (Bloch)

The findings reported here indicate that the pineal organ in catfish is involved in the regulation of locomotor activity rhythms and in some aspects of osmoregulation. Under LD 12:12 regimen, catfish is nocturnally active, with the maximum activity just before dawn. However, under conditions of continuous darkness (DD), the locomotor rhythm became free-running. Pinealectomy abolished the activity rhythm under DD and resulted in arrhythmicity. Circadian rhythms in plasma cortisol, osmolality and electrolytes (Na+ and K+) were also observed. Pinealectomy, though, increased the amplitudes of the rhythm; however the differences were not statistically significant. Removal of pineal significantly increased the mesor values of plasma osmolality and electrolytes, but there were no significant differences in the mesor values of plasma cortisol.