Plasma profiles of fourteen ovarian steroids before,during and after ovulation in African catfish,Clarias gariepinus,determined by gas chromatography and mass spectrometry

The plasma concentrations of fourteen ovarian steroids were measured in postvitellogenic African catfish,Clarias gariepinus, which had been injected with pimozide and LHRHa. Postvitellogenesis persisted for at least four hours after pimozide and LHRHa administration. During this stage a limited rise in the plasma gonadotropin (GTH) level was accompanied by an increase in the testosterone concentration. The estradiol level was high and remained high except for a passing drop during the stage of germinal vesicle migration. At the stage of germinal vesicle migration a strong increase in the plasma GTH level coincided with a maximum in the testosterone concentration and a concomitant increase in the levels of 17,20-dihydroxy-4-pregnen-3-one and of five 5-reduced pregnanes. During germinal vesicle breakdown the GTH concentration remained high, the plasma level of 17-hydroxyprogesterone tended to increase, and the levels of 5-pregnane-3, 17-diol-20-one, 5-pregnane-3,17,20-triol and 5-pregnane-3,17,20-triol reached a maximum. At pre-ovulation the GTH concentration did not change, and peak levels were reached of 17,20-dihydroxy-4-pregnen-3-one and 5-pregnane-3,6,17-triol-20-one. Shortly after ovulation the GTH concentration slightly decreased together with a sharp decline in the concentrations of 17,20-dihydroxy-4-pregnen-3-one and the 5-reduced steroids, with the exception of 5-pregnane-3,17,20-triol, 5-pregnane-3,6,17,20-tetrol and 5-dihydrotestosterone. The plasma concentrations of androstenedione, estrone, etiocholanolone and 5-androstane-3,17-diol showed marginal fluctuations during oocyte maturation and ovulation. Apart from 17,20-dihydroxy-4-pregnen-3-one, the 5-reduced pregnanes might be candidates for the function of oocyte maturation inducing hormone inC. gariepinus.     

Accumulation of zinc from diet and its release in common carp

High zinc diet of 2000 mg kg^–1 was fed to common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idellus) and tilapia (Oreochromis aureus) for 8 weeks to compare the accumulation of Zn in fish. It was found that accumulation of zinc from diet by grass carp and tilapia was low when compared to common carp. The largest difference occurred in digestive tract tissue. The digestive tract tissue of common carp had a large pool of stored zinc, the mean storable capacity is about 1500 g Zn g^–1 fresh tissue, and the time needed to saturate the tissue when feeding 2000 mg Zn kg^–1 diet is about 8 weeks. The accumulated Zn in the digestive tract tissue of common carp was released when the dietary Zn was reduced to normal level (50 mg kg^–1) or deficient level (4 mg kg^–1) for 4 weeks.Subcellular fractionation results indicate that Zn accumulated in digestive tract tissue of common carp was accumulated mainly in the nuclei/cell debris fraction. Exposure to a high Zn diet induced some metallothionein-like substance in the digestive tract tissue and the hepatopancreas of common carp, but the amount was very low when compared with the amount of Zn accumulated in the nuclei/cell debris fraction.     

Gonadotrophin-releasing hormone agonist raises plasma concentrations of progestogens and enhances milt fluidity in male Atlantic halibut (Hippoglossus hippoglossus)

In two separate spawning seasons, spermiating male Atlantic halibut were implanted with pellets containing gonadotrophin-releasing hormone agonist (GnRHa). Males were bled repeatedly, and milt samples were collected. Blood samples were assayed for free and conjugated steroids: testosterone, 11-ketotestosterone, 17,20-dihydroxy-4-pregnen-3-one (17,20-P), 17,20-dihydroxy-4-pregnen-3-one (17,20-P), 17,20,21-trihydroxy-4-pregnen-3-one and steroids with a 17,20 configuration. Towards the end of the first season, pellets were implanted into three wild-caught and three hatchery-reared males. No control fish were available. The major progestogen in plasma was identified as sulphated 5-pregnane-3,17,20-triol (3,17,20-P-5-S). Concentrations of this steroid were stimulated by the GnRHa. Sulphated 17,20-P was also identified in the plasma, but at 10-fold lower concentrations than 3,17,20-P-5-S. In the middle of the second season, pellets were implanted into five hatchery-reared males; five unimplanted males were used as controls. Levels of androgens fell following GnRHa treatment, levels of progestogens rose briefly, and there was a significant increase in the fluidity of the milt. Of all the measured steroids, free and sulphated 17,20-P showed the best correlation with milt fluidity.     

Effects of diet on spontaneous locomotor activity and oxygen consumption in Adriatic sturgeon (Acipenser naccarii)

Adriatic sturgeon (Acipenser naccarii) were maintained on a commercial diet enriched either in long chain polyunsaturated fatty acids of the 3 series (3 LCPUFA) or in saturated fatty acids (SFA). The effects of dietary fatty acid composition on spontaneous locomotor activity in normoxia and hypoxia (O₂ tension = 10.5 ± 0.8 kPa), and on oxygen consumption (M^O ₂) in normoxia, in hypoxia (O₂ tension = 6.6 ± 0.8 kPa) and during recovery were then investigated. The effects of adding supplementary vitamin E to the fat-enriched diets were also studied.Dietary fatty acid composition had effects on spontaneous locomotor activity and M^O ₂ in normoxia. Activity levels were higher in all sturgeon fed extra dietary fats (without vitamin E), when compared with control animals, but fish fed 3 LCPUFA had a significantly lower M^O ₂ than those fed SFA, with intermediate M^O ₂ in controls. In hypoxia, sturgeon 3 LCPUFA did not alter activity or M^O ₂ whereas those fed SFA reduced both and controls reduced M^O ₂. During recovery, both animals fed SFA and controls had a higher M^O ₂ than sturgeon fed 3 LCPUFA. The data indicate that fish fed 3 LCPUFA are more tolerant of hypoxia than controls or those fed SFA, as they did not reduce either activity or M^O ₂, and consumed less O₂ during recovery.Vitamin E supplements modified the effects elicited by dietary fats. All sturgeon fed vitamin E had low activity levels in normoxia and hypoxia. Sturgeon fed vitamin E with 3 LCPUFA had a higher M^O ₂ in normoxia than those fed 3 LCPUFA alone; reduced M^O ₂ in hypoxia, and during recovery increased M^O ₂ to a rate higher than that of animals fed 3 LCPUFA alone. In normoxia, sturgeon fed vitamin E with SFA had a similar M^O ₂ to those fed SFA alone but did not change M^O ₂ in hypoxia or during recovery. Thus, the effects of vitamin E were dependent on fat composition of the diet. Vitamin E with 3 LCPUFA removed the beneficial effects on M^O ₂ and responses to hypoxia obtained with 3 LCPUFA alone, but vitamin E with SFA allowed sturgeon to maintain aerobic metabolism in hypoxia, a more effective response than that observed in fish fed SFA alone.     

Effects of steroid hormones on in vitro oocyte maturation in white sturgeon (Acipenser transmontanus)

The in vitro effects of several steroids on the maturation of intact white sturgeon (Acipenser transmontanus) ovarian follicles were investigated. At the highest concentration (1024 ng ml^–1 for the C21 steroids and 1139 ng ml^–1 for the C19 steroids), all of the C21 steroids tested, progesterone (P4), 17-hydroxyprogesterone (17OHP), 17,20-dihydroxy-4-pregnen-3-one (17,20-P), 17,(20,21-trihydroxy-4-pregnen-3-one 20-S), 11-deoxycortisol (S) and cortisol (F), as well as testosterone (T) induced germinal vesicle breakdown (GVBD) at 14 and 22 h. At 6 h, only P4 and 17,20-P induced maturation at the highest concentration (1024 ng ml^–1). At 14 and 22 h, 11-deoxycortisol was the most potent steroid inducer of GVBD followed by P4, 17OHP, 17,20-P, and 20-S. The steroid 11-hydroxytestosterone (11OHT) was completely ineffective at all concentrations and exposure times. The C21 steroids induced oocyte maturation at concentrations ranging from 4 to 1024 ng ml^–1, whereas T induced GVBD at 225 to 1139 ng ml^–1. Calculation of the mean effective concentration that induced 50% GVBD (EC50) from the 22 h incubations revealed the following order of potencies: S > P4 > 17OHP > 17,20-P > 20-S >> F > T. These bioassay results, together with previous findings on the endogenous production of steroids by ovarian follicles from gonadotropin-primed females, indicate that more than one steroid has a biological role in the resumption of meiosis in sturgeon oocytes and provides empirical evidence for P4, 17OHP, S, 20-S, and 17,20-P as maturation-inducing steroids in white sturgeon.     

Smoltification induced by a ‘skeleton’ photoperiod in underyearling coho salmon (Oncorhynchus kisutch)

Underyearling coho salmon fry were subjected to three initial photoperiod treatments (6L18D, 10L14D, 14L10D) for two months and subsequently to three final treatments (16L8D, 9L6D1L8D, 10L14D) in a factorial design. Growth rates and seawater adaptability were monitored regularly. The groups that were exposed initially to 6L18D or 10L14D and then to 16L8D grew faster and had lower plasma sodium ion levels after seawater challenge tests than any of the other groups. Fish which were initially exposed to 6 L or 10 L daylength and then to a 9L6D1L8D skeleton photoperiod, showed a slightly lower growth rate and seawater adaptability than those given the corresponding complete 16L8D photoperiod. However fish maintained on skeleton photoperiods had significantly greater growth rates and seawater adaptability than those kept on the 10L14D photoperiod. This indicates that it is not the accumulated number of hours of exposure to light that initiates smolting, but rather the time during the day when light is experienced. Fish exposed initially to 14L10D showed little or no response to subsequent changes in photoperiod, suggesting that responsiveness to inductive photoperiods depends on the initial photoperiod treatment.     

Immunohistochemical investigation of the pituitary of the sturgeon (Acipenser baeri,Chondrostei)

An immunohistochemical study of the sturgeon (Acipenser baeri) pituitary was undertaken using antisera directed against hormones from various classes of vertebrates, including the only pituitary hormone available from sturgeon, gonadotrophin. A positive reaction was obtained after application of antisera towards the following hormones 1–24 synthetic ACTH (1-24 ACTH), melanophore stimulating hormone (MSH), ovine prolactin (oPRL), ovine growth hormone (oGH), salmon growth hormone (sGH), carp gonadotrophin (cGTH) and its beta subunit (cGTH), sturgeon gonadotrophin (aciGTH), carp thyrotrophin (cTSH) and subunit of the human thyrotrophin (hTSH). The results demonstrate that, in general, the sturgeon pituitary resembles that of teleosts as regards the distribution of the different cell types: ACTH and PRL cells in the rostral pars distalis, GTH, TSH and GH cells in the proximal pars distalis and MSH and PAS-cells in pars intermedia. In addition to the topographical organization of the sturgeon pituitary, this study provides data on the immunological relationships between sturgeon pituitary hormones and those of other vertebrates.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Induced meiotic gynogenesis in shovelnose sturgeon

Gynogenesis was induced in three shovelnose sturgeon (Scaphirhynchus pIatorynchus) by heat shock after egg activation with UV-treated paddlefish (Polyodon spathula) milt. Ultraviolet dosage (J m–2) for the pooled milt samples was calculated using the following linear regression equation: Dosage = 2405.27 – 352.80X 19.78X2 (X = percent transmittance of milt). Activated eggs were incubated at 18 °C until shocking at 35 °C. Shock duration was applied at 0.050 intervals from 0.15 to 0.40 0 (8.25 to 22.00 min post-fertilization; 0 at 18 °C = 55 min). The highest yield of gynogenotes (16%) was observed at 0.25 0 for female 3, 10 % at 0.30 0 for female 2 and 12% at 0.35 0 for female 1. The percentage of viable gynogenotes responded quadratically to the tau index (s/0) when shock treatments were applied. The higher yields of viable diploid sturgeon gynogenotes were achieved when eggs were heat shocked at embryological ages ranging from 0.25 to 0.35 0 (approximately 14 to 19 min post-activation at 18 °C). No viable hybrids were produced in the control fertilization of sturgeon eggs with intact paddlefish sperm which verified the gynogenetic origin of the offspring produced. © Rapid Science Ltd. 1998     

Effect of feeding schedule on growth of rainbow trout

Rainbow trout (Oncorhynchus mykiss) fingerlings were reared for 2 months under one of two different feeding regimes (one and two diurnal peaks) and under a constant feeding regime as a control in order to find out if it is possible to fit the feeding to the assumed circadian rhythm. The differences in the specific growth rates observed between the different feeding treatments were not significant, but the tank-effect and the effect of the genetic background of the fish were highly significant. The conclusion that no beneficial effects are achievable through alteration of the feeding regime and the significance of a possible genotype-feeding-regime interaction are discussed.