A drop in ambient temperature results in a transient reduction of interrenal ACTH responsiveness in the gilthead sea bream (Sparus aurata, L.)

This study investigated the effects of a drop in water temperature (18 °C to 9 °C in 24 h) on the pituitary and interrenal hormones of the gilthead sea bream Sparus aurata. The in vitro sensitivity of the interrenal tissue to ACTH, plasma levels of cortisol, ACTH, -MSH, GH, glucose, lactate and ions were determined. In vitro ACTH, stimulated the release of cortisol from isolated interrenal glands from control gilthead sea bream in a concentration dependent fashion. However, the interrenal cells were less sensitive to ACTH as soon as 24 h following the onset of the temperature drop. At this time, plasma cortisol and ACTH levels were raised, and plasma GH concentrations were decreased, whereas no significant changes were found in plasma -MSH. After 96 h plasma ACTH levels had recovered whereas plasma cortisol levels were still higher than controls after 8 days of the beginning of the experiment. Interrenal sensitivity had recovered after 8 days. The results may help to clarify the relationship between the stress response and the aetiology of the winter syndrome in sea bream.     

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.     

Protein kinase C in the spleen of the turbot (Scophthalmus maximus L.)

PKC activity was detected in spleen extracts from the turbot, Scophthalmus maximus, a teleost flatfish that is farmed commercially in several countries, in assays with the substrate EGF- R651–658 as phosphate acceptor. The activity was purified about 700-fold by a three-step chromatographic procedure (DEAE-cellulose, phenyl-Sepharose and threonine-Sepharose). Maximal activity was obtained in the presence of the typical PKC cofactors Ca2+ (0.1 mM) PtdS (20 g ml–1) and either DAG (2 g ml–1) or PMA (2 g ml–1). Activity was dose-dependently inhibited by H7 and by the PKC-specific inhibitors PKC19–36 and N-myristoylated PKC19–31. The rate of phosphorylation was highest with the PKC-specific substrate MARCKS161–175. In immunoblotting, MC5 (a mouse monoclonal antibody raised against bovine PKC) recognized bands of 80 and 100 kDa. Immunoblotting with antibodies raised against mouse PKC isozymes (, , , , , , and ) indicated the presence of all these isozymes in turbot spleen.     

The nature of hematological response in fish

Hematological status was examined in rainbow trout,Oncorhynchus mykiss, held for 3–4 weeks under temperature, photoperiod and P_{O 2} conditions approximating those of their winter, spring and summer habitats. The most striking change observed was in red cell population composition. In winter fish mature cells were predominant; juvenile and developing erythrocytes characterized spring and summer animals. Hemoglobin, hematocrit and both mean erythrocytic volume and hemoglobin were modestly lower in spring and summer than in winter fish. Red cell numbers were not significantly affected. These observations suggest that avoidance of viscosity-based increases in circulatory work cost is more advantageous than elevation of blood O₂-carrying capacity. Although hemoglobin isomorph profiles were significantly altered, there is little evidence that such changes are of critical adaptive importance. Given presumed age-based reduction in gas transport effectiveness, the replacement of mature and senescent cells by more metabolically-competent juvenile cells appears to be the pivotal event in hematological response. Leucocyte counts were significantly elevated in spring and summer as compared to winter fish. Lymphocyte/heterophil ratios declined from 8.27 in winter fish to 3.13 in summer trout. Thrombocyte, monocyte, eosinophil and basophil abundances were little changed.     

Diurnal variations in hypothalamic monoamine levels in the teleostChanna punctatus (bloch) in response to melatonin under two photothermal conditions

Hypothalamic dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) levels exhibited marked day-night variations under ambient photoperiod and temperature (12L12D; 17±1°C) with peak values at mid-light phase. The 16L8D; 22±1°C treatment reversed the diurnal rhythm of 5-HT, but not that of DA and NA. However, there was an overall increase in the levels of the catecholamines on exposure to the long photoperiod and high temperature. The administration of melatonin in the fish held on 16L8D; 22±1°C regime restored the 5-HT rhythm to that of the 12L12D; 17±1°C control group, but with elevated mid-photophase value. However, there was no effect of the indole treatment on the 5-HT rhythm under the 12L12D; 17±1°C regime. Melatonin causes a significant reduction of NA level in both the groups, while DA level did not change in either group.     

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     

Incorporation and metabolism of 14C-labelled polyunsaturated fatty acids in juvenile gilthead sea bream Sparus aurata L. in vivo

The incorporation, and the capacity for desaturation and elongation in vivo, of intraperitoneally-injected, ¹⁴C-labelled n–3 and n–6 C₁₈ and C₂₀ PUFAs were investigated in juvenile gilthead sea bream, Sparus aurata. The results indicate that juvenile gilthead sea bream have only limited ability to convert CH PUFAs to C₂₀ and C₂₂ HUFAs in vivo. The data are consistent with the results from nutritional studies on larvae, postlarvae and fingerlings that have shown that gilthead sea bream require the provision of preformed eicosapentaenoic and docosahexaenoic acids in the diet. The impairment in the desaturase/elongase pathway was quantitatively and qualitatively similar to that found in turbot, Scophthalmus maximus, being at the level of the 5-desaturase. The low activity of 5-desaturase combined with the consistent finding that arachidonic acid is selectively retained in membrane phosphatidylinositol suggests that, in addition to eicosapentaenoic and docosahexaenoic acids, gilthead sea bream may also have a requirement for preformed arachidonic acid in the diet.Abbreviations AA 5,8,11,14-eicosapenaenoic acid (arachidonic acid, 20:4n–6) - CPL diradyl (diacyl + alkenylacyl + alkylacyl) glycerophosphocholine - DHA 4,7,10,13,16,19-docosahexaenoic acid (22:6n–3) - EPA 5,8,11,14,17-eicosapentaenoic acid (20:5n–3) - EPL diradyl (diacyl, alkenylacyl + alkylacyl) glycerophosphoethanolamine - HUFA highly unsaturated fatty acids ( C₂₀ and with 3 double bonds) - LA 9,12-octadecadienoic acid (linoleic acid, 18:2n–6) - LNA 9,12,15-octadecatrienoic acid (-linolenic acid, 18:3n–3) - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acid(s)     

Inhibition of HPI axis response to stress in gilthead sea bream (Sparus aurata) with physiological plasma levels of cortisol

This study investigates the effect of corticosteroid (cortisol) administration on the stress response of the gilthead sea bream Sparus aurata subjected to a 48 h confinement. The effect of (in-vitro and in-vivo ) cortisol administration on the in-vitro ACTH sensitivity of the interrenal tissue; the plasma levels and tissue concentration of cortisol; and the plasma levels of ACTH, -MSH, -endorphin and glucose were determined. Confinement caused a transient and concomitant increase in plasma cortisol and ACTH levels. However, in cortisol-fed fish the plasma ACTH levels were lower, indicating a suppresion of the ACTH release from the corticotropes by cortisol. In contrast to the activation of the corticotropes, the levels of plasma melanotrope derived peptides were not affected. In spite of the fact that interrenal cells of cortisol-fed gilthead sea bream released less cortisol than controls, the interrenal sensitivity to ACTH was not affected by in-vivo and in-vitro cortisol administration. This suggests that the interrenal sensitivity to ACTH in stressed (confinement) sea bream is probably not regulated by -MSH, N-ac--END, or by cortisol. Thus, in gilthead sea bream the interrenal sensitivity to ACTH could be regulated at the hypothalamus and/or pituitary and communicated via circulating ACTH levels.     

Progestogen metabolism by ovaries of the roach (Rutilus rutilus L.) and the rudd (Scardinius erythrophthalmus L.)

Roach ovaries converted 17-hydroxyprogesterone to 17,20-dihydroxy-4-pregnen-3-one (17,20P) and to glucuronides of testosterone and 17,20P. Small amounts of 5-pregnane-3- and -3, 17, 20-triols, 7-hydroxy-5-reduced metabolites and 17,20-dihydroxy-4-pregnen-3-one (17,20P) were also formed. Rudd ovaries converted this substrate mainly to 17,20P, 5-pregnane-3- and -3,17,20-triols, 17,20-dihydroxy-5-pregnan-3-one and testosterone glucuronide. The main metabolites of progesterone with both species were 17,20P, 5-pregnane-3,17,20-triol and 7-hydroxy-5-reduced steroids. Rudd ovaries formed, in addition, 17,20-dihydroxy-5-pregnan-3-one from progesterone. The pattern of metabolites was markedly altered when the concentration of substrate was increased from 42ng to 1 µg or 100 µg. At the highest concentration, glucuronides and polar steroids were not detectable, while at low concentrations they accounted for over 50% of the metabolites. 20-Hydroxysteroid dehydrogenase was shown to have a very high capacity, producing 21–47 µg 17,20P from 100 µg 17-hydroxyprogesterone substrate with 200 mg ovarian tissue in 5h.     

Modulation of glycoprotein hormone α- and gonadotropin IIβ-subunit mRNA levels in the pituitary gland of mature male African catfish, Clarias gariepinus

The cDNAs encoding the glycoprotein hormone -subunit (GP) and the gonadotropin II-subunit (GTH II) were cloned from the pituitary gland of the African catfish, Clarias gariepinus. Using RNase protection analysis, we studied the steady-state mRNA levels of GP as well as GTH II in the pituitary gland of adult male catfish. Castration of adult male catfish resulted in a significant decrease of GTH II mRNA levels, whereas there was no change in the GP mRNA levels. Treatment of intact males with a single dose of 11-ketotestosterone (11-KT) resulted in dose-dependent increases in mRNA levels of both GP and GTH II. We conclude that 11-KT, a prominent, non-aromatizable teleost androgen, has a stimulatory effect on the pituitary mRNA levels of GP and GTH II of adult male fish.     

Synthesis and regulation of 17α-hydroxy-20β-dihydroprogesterone in immature males of Oncorhynchus mykiss

Three experimental approaches were chosen to study the question if the progestin 17-hydroxy-20-dihydroprogesterone (1720OHP) is synthesised in testes of young Oncorhynchus mykiss, in which the absence of spermatozoa was verified histologically: first, in order to detect 20-hydroxysteroid dehydrogenase activity (20HSD), testes homogenates were incubated with ³H-labeled 17OHP.Metabolites were analysed by TLC, HPLC, and repeated crystallization to constant isotope ratios. One of the metabolites was identified as 1720OHP-³H, indicating that already immature testes contain 20HSD activity and are able to produce 20-reduced steroids. Second, 1720OHP was quantified by radioimmunoassay in incubates of testes fragments. The sensitivity of the gonads to gonadotropin II (GtH II) became evident when comparing incubations in the absence and presence of GtH II. Third, plasma levels of 1720OHP were significantly higher in animals injected with partially purified salmon gonadotropin, compared to controls. Thus, for the first time, it could be shown that 20HSD is present in testicular cells other than spermatozoa. Furthermore, 1720OHP is indeed secreted at a very early stage of testicular development; 1720OHP secretion is also responsive to GtH II. Future studies will have to show if the functions of this progestin include the stimulation of spermatogenesis.     

Variation in content of Ω3 fatty acids in farmed Atlantic salmon,with special emphasis on effects of non-dietary factors

The main aim of the present study was to examine the impact of some biological and environmental factors on the lipid and fatty acid compositions of farmed Atlantic salmon (Salmo salar), with special emphasis on 3 fatty acids. Two year groups of salmon at nine fish farms distributed along the Norwegian coast were fed the same diet and were sampled every second month. The data are believed to give a representative characterization of lipid and fatty acid content of salmon farmed in Norway.Multiple regression analysis revealed that variation in lipid content and body weight explained 80% of the variation found in 3 fatty acids in farmed salmon, and 22:6 3 showed greater variation than other 3 fatty acids. Further analysis of lipid-corrected values revealed only minor effects of latitude on the per cent content of highly unsaturated 3 fatty acids, and hardly any effect of seawater temperature, with the exception of 22:6 3, which decreased slightly with increasing temperature.The per cent 22:6 3 in the fillet became gradually reduced with increasing fish age and body weight, whereas the content of 20:5 3 and other 3 fatty acids remained relatively constant. The per cent content of 22:6 3 of young salmon was higher than in the feed, but approached the feed value gradually as body weight increased. The lipid content of the salmon increased with fish age, and the absolute quantitative contents of both 22:6 3 and 20:5 3 increased meanwhile, even though the per cent content of 22:6 3 decreased quite pronouncedly.The per cent 22:6 3 and other 3 fatty acids was higher in wild than in farmed salmon, but the absolute quantitative content was higher throughout in farmed salmon, which had higher lipid contents. The 3/6 ratio, which is important in human health evaluation, was lower in farmed than in wild salmon. The large flexibility of 3 fatty acids and lipid content of farmed salmon leave us with the option of producing a wide variety of salmon qualities requested by the market. Both per cent and absolute quantitative 3 contents, as well as the 3/6 ratio, may readily be manipulated.     

Optimal dietary carbohydrate to lipid ratio in African catfish Clarias gariepinus (Burchell 1822)

An 8-week feeding trial was conducted in a recycling water system at 28±1°C to investigate carbohydrate to lipid ratio (CHO:L ratio) in African catfish Clarias gariepinus (12.32±0.04g). Five isonitrogenous (40% crude protein) and isoenergetic (20kJg^–1 gross energy (GE)) fishmeal based diets with varying carbohydrate to lipid (CHO:L g/g) ratios of 0.74, 1.13, 1.66, 2.47 and 3.42 for diets 1–5, were tested, respectively. The diets containing a fixed protein to energy ratio (P:E ratio) of 20-mg proteinkJ^–1 GE were fed to triplicate groups of 20 fish (per 30-L tank). Fish were fed 5% of their body weight per day adjusted fortnightly. Diet 1, containing 14% carbohydrate and 21% lipids with a CHO:L ratio of 0.74 produced the poorest (P<0.05) growth rates, feed and protein efficiency. Increasing carbohydrate content in the diets to 27% concomitant with a reduction in lipid content to 16% with a CHO:L ration of 1.66 of diet 3 significantly improved (P<0.05) growth rates, feed and protein efficiency. A further increase in dietary carbohydrate up to 38% and a decrease in lipids levels to 11% with a CHO:L ratio ranging from 1.66 to 3.42 (diet 3 – 5) did not significantly improve the fish performance. Apparent net protein utilisation (ANPU) of fish fed diet 4 was higher (P<0.05) than for diets 1–3 but did not differ from diet 5. Higher lipid deposition (P<0.05) in whole body and liver were observed with decreasing dietary CHO:L ratios as increasing lipid levels. Whole body protein and liver glycogen content, digestive enzyme activities (protease and lipase) and histological examination of intestine and liver of fish fed varying CHO:L diets did not show any discernible changes among the dietary treatments. However intestinal -amylase activity increased (P<0.05) with increasing dietary carbohydrate levels. This study revealed that African catfish can perform equally well on diets containing carbohydrate ranging from 27 to 38% of the diet, with lipid content ranging from 16 to 11% or at CHO:Lg/g ratio of 1.7–3.4.     

Fatty acid compositions of the major phosphoglycerides from fish neural tissues; (n−3) and (n−6) polyunsaturated fatty acids in rainbow trout (Salmo gairdneri) and cod (Gadus morhua) brains and retinas

The fatty acid compositions of brain phosphoglycerides from a freshwater fish, the rainbow trout (Salmo gairdneri), and a marine fish, the cod (Gadus morhua), were determined and compared with those from a terrestrial mammal, the rat. Fish brain lipids were characterized by a higher degree of unsaturation encompassing increased percentages of (n–3)PUFA (226 and 205) and lower percentages of (n–6)PUFA (204 and 224). However the distribution of fatty acids and specific PUFA between different phosphoglycerides was essentially similar in rat and fish brain tissue. PE and PS contained the highest percentages of 226(n–3), PI was characterized by higher 180 and 204(n–6)/205(n–3), and PC had higher 160 and the lowest percentage of PUFA in all species. A generally similar pattern was found in the fish retinal phosphoglycerides except that PC was also rich in 226(n–3). Overall trout brain phosphoglycerides were slightly more unsaturated than the cod lipids but with lower (n–3)/(n–6) ratios whereas cod retinal lipids were more unsaturated than the trout retinal lipids.     

Turnover of α-, γ, and δtocopherol and distribution insubcellular and lipoprotein fractions indicate presence of an hepatic tocopherolbinding protein in Atlantic salmon (Salmo salar L.)

The purpose of this work was to study the turnover of a, andtocopherol (TOH) in Atlantic salmon (Salmo salar, L.). Fish induplicate tanks were fed a diet containing 150 mg kg^-1-TOH and 100 mg kg^-1 each of and TOHadded as tocopheryl acetates. After fillet TOH concentrations had adjustedto the dietary supplementation levels, samples were taken from fish that hadbeen deprived of feed for 100 h, and from fish that had been fed regularlyuntil sampling. The retained levels of tocopherols in plasma correspondedgrossly with their biological activities, as found in experiments withmammals (::100: 20:3). The plasma concentrationsof -, and TOH amounted to 65, 44 and 15%,respectively, in unfed compared to fed fish. Very low density lipoprotein(VLDL), appeared to contain a greater fraction of plasma -TOH than ofplasma TOH. The mitochondrial fraction of liver, but not that of darkmuscle, was highly enriched in -TOH, and less in andTOH. The concentration ratios in liver and bile indicate that, and to some extent, TOH are excreted in the bile at a higherrate than -TOH. The data fit the hypothesis that Atlantic salmonliver contains a tocopherol binding protein with higher affinity for-TOH than for the other tocopherol homologues. This appears toprevent excretion of -TOH in the bile, and stimulate incorporation of-TOH in VLDL for subsequent secretion into the blood stream. As aconsequence, -TOH is retained in the body to a greater extent than and -TOH.     

Antioxidant effect of dietary tocopherol and ascorbic acid on growth and survival of Litopenaeus vannamei postlarvae

The nutritional effect of vitamin E in dietsfor Litopenaeus vannamei postlarve (PL19)was investigated. Four formulated diets withdifferent combinations of -tocopherylacetate (-TA), ascorbic acid (AA) andhighly unsaturated fatty acids (HUFA) weretested, using four replicates.No significant differences in survival wereobserved among treatments after 34 days offeeding. However, shrimp fed with a dietcontaining 2% fish oil (low n-3 HUFA content),200 mg.kg^–1 -TA and100 mg.kg^–1 AA (diet H/E/C) showedsignificantly better growth than those fed adiet supplemented with 5% fish oil (high n-3HUFA content), 200 mg.kg^–1 -TA and100 mg.kg^–1 AA (diet H+/E/C). Shrimp fedwith a diet containing 5% fish oil,900 mg.kg^–1 -TA and100 mg.kg^–1 AA (diet H+/E+/C) showed a significantly higher tissue level of n-6 PUFAthan postlarvae fed diet H+/E/C. No definiteconclusion could be drawn about a possibleinteraction between -TA and AA, since acomparison of the diet containing 5% fish oil,200 mg.kg^–1 -TA and700 mg.kg^–1 AA (H+/E+/C+) and the dietH+/E/C did not show any significant differencesin any of the measured parameters. Theantioxidative status of the shrimp tissue(measured by means of the thiobarbituric acid(TBA) assay and expressed as nM malonaldehyde(MA) per gramme dry weight) was equal for alltreatments. Nevertheless, there was a slightlylower MA value with the diet H+/E/C+,indicating that AA may be an effectiveantioxidant in the aqueous phase and at thewater/lipid interface of the tissue. The tissuelevels of -T and AA were highlydependent on the amounts in diets and nocorrelation between -T and AAincorporation could be observed.     

Effects of the aromatase inhibitor Fadrozole on plasma sex steroid secretion and oocyte maturation in female coho salmon (Oncorhynchus kisutch) during vitellogenesis

17-estradiol, 17-20-dihydroxy-4-pregnen-3-one (17-20-P), and testosterone levels were measured in plasma samples obtained from vitellogenic coho salmon (Oncorhynchus kisutch) before and 32 days after injection of the aromatase inhibitor Fadrozole (AI). Plasma 17-estradiol levels decreased significantly 6 h after injection in all AI treated fish. The higher the dose the longer the maintenance of low plasma 17-estradiol levels. Inversely, plasma 17-20-P increased significantly 6 h after injection in all AI treated fish, and the higher the dose the longer the maintenance of high plasma 17-20-P levels. At 48 h after injection plasma testosterone levels were significantly higher in the AI treated groups. The oocyte maturation index showed that multiple injections with AI retarded oocyte development. Besides, oocyte diameter and GSI were lower in the same group, which presented high incidence of atresia of vitellogenic oocytes. The ovarian follicles and brain of the fish which received multiple injections secreted less 17-estradiol, in vitro. These findings suggest that aromatase inhibitors such as Fadrozole may have a potential as a tool to regulate sexual development in salmon.     

17α,20β,21-trihydroxy-4-pregnen-3-one and 17α,20β-dihydroxy-4-pregnen-3-one stimulated spermiation in protandrous black porgy, Acanthopagrus schlegeli

The objective of this study was to investigate the effects of sex steroids on spermiation in protandrous male black porgy, Acanthopagrus schlegeli. Experiments on common carp (Cyprinus carpio) were also conducted for comparison. Fifty male black porgy were divided into 5 groups and injected with a superactive analogue of mammalian luteinizing hormone releasing hormone (LHRH-A), 17,20,21-trihydroxy-4-pregnen-3-one (20-S), 17,20-dihydroxy-4-pregnen-3-one (17,20-DHP), 11-ketotestosterone (11-KT) or saline. The dosage of the sex steroids given on days 0, 2, 4 and 6 was 330, 330, 990 and 1980 µg kg^-1 body weight, respectively. Milt volume and sperm concentrations were measured on days 0, 2, 4, 6, 8 and 10. Similar treatments were also conducted in 45 male common carp. Milt volume was significantly increased in black porgy after treatment with 20-S and 17,20-DHP; 17,20-DHP had stimulatory effects on spermiation at a lower dose (900 µg kg^-1 body weight, p < 0.05) as compared to 20-S (1980 µg kg^-1 body weight, p < 0.01). In the common carp, milt volume was also increased after treatment with LHRH-A and 17,20-DHP but not with 20-S. 17,20-DHP stimulated spermiation at a lower dose in common carp (330 µg kg^-1 body weight) than in black porgy (990 µg kg^-1 body weight). However, 11-KT did not stimulate spermiation in black porgy or common carp. The concentrations of plasma 11-KT could immediately reflect to the administration of exogenous 11-KT in black porgy.     

Seasonal,reproductive, and nutritional influences on muscle “buffering capacity” in yellow perch (Perca flavescens)

Effective non-bicarbonate buffering capacity (or buffer value) was measured in white muscle of yellow perch (Perca flavescens) by titrations with mineral acid and base in a carbon-dioxide free, closed system. Yellow perch were collected at three month intervals throughout 1983 from an acidic lake (pH 4.6) and two alkaline lakes (pH 7.8) in northern Wisconsin. Buffering capacity was also determined for white muscle of perch kept in the laboratory under different regimes of temperature and ration. The mean buffering capacity of white muscle from yellow perch taken directly from natural environments ranged from 40.7 ± 3.1 (SD) slykes in March of 1983 to 53.7 ± 2.8 (SD) slykes in July of that year. These changes in buffering capacity were strongly correlated with water temperature. Egg production and thirty-day laboratory starvation produced significant decreases in buffering capacity and increases in the water content of yellow perch muscle. Fed perch in the laboratory had a temperature dependent buffering capacity similar to field caught fish. Buffering capacity of white muscle did not differ between yellow perch from acidic and alkaline lakes. Investigators using buffering capacity as a gauge of species differences in metabolic potential, should be wary of seasonal and reproductive factors that might alter their conclusions.     

Steroidogenesis during induced oocyte maturation and ovulation in the African catfish,Clarias gariepinus

Changes in ovarian steroidogenesis accompanying oocyte maturation and ovulation were studied in the African catfish,Clarias gariepinus. Laboratory-reared females with postvitellogenic ovaries were treated with pimozide and LHRH-analogue. The plasma gonadotropin levels were determined by means of a homologous radioimmunoassay, the condition of the ovaries was studied by histological examination of the follicles, and the steroidogenetic capacity of the ovaries was analyzed byin vitro incubation of tissue fragments for 3 h with [³H]-pregnenolone and [³H]androstenedione as precursors. Data were collected at regular intervals between 0 and 16 h after pimozide-LHRH analogue administration.Until 4 h after the beginning of the experiments the plasma gonadotropin levels did not rise above 25 ng/ml, the ovaries remained in the stage of postvitellogenesis, and testosterone was the main end product of steroidogenesis. Four hours later the gonadotropin concentration in the blood had risen to more than 150 ng/ml, and the ovaries had entered the stage of germinal vesicle migration. At the same time steroidogenesis shifted towards the production of 17,20-dihydroxy-4-pregnen-3-one, 5-pregnane-3, 17-diol-20-one, 5-pregnane-3,6,17-triol-20-one, 5-pregnane-3,17,20-triol and 5-pregnane-3,6,17,20-tetrol. During the subsequent stage of germinal vesicle breakdown the plasma gonadotropin level remained high, and the synthesis of the C₂₁-steroids showed a further increase. Simultaneously, the production of some C₁₉-steroid glucuronides was enhanced. The preovulation and especially the postovulation stages were accompanied by a gradual decrease in steroidogenic capacity of the ovaries, even though the plasma gonadotropin level remained high. It is concluded that the prematuration surge of gonadotropin influences the activity of enzymes involved in steroidogenesis, leading to a reduced C_17,20-lyase and to an augmented activity of the enzymes 20-hydroxysteroid dehydrogenase (HSD), 5-reductase, 3-HSD, 6-hydroxylase and UDP-glucuronosyltransferase. During ovulation the activity of all steroidogenic enzymes, including such key enzymes as 3-HSD and 17-hydroxylase, gradually decreases.Not only 17,20-dihydroxy-4-pregnen-3-one, but also the 5-reduced pregnanes may be involved in inducing oocyte maturation and/or ovulation. The very polar triol and tetrol products may function, together with the steroid glucuronides as sex pheromones.A preliminary account of these results was presented at the XIII Conference of European Comparative Endocrinologists, Belgrade, September 7–12, 1986