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.     

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.     

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.     

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.     

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.     

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.     

Universal antisera for immunocytochemical identification of two different gonadotrophs in acanthopterygian fishes

Pituitaries of various teleosts belonging to 25 orders were immunostained with antisera raised against synthetic fragment peptides corresponding to conservative regions of gonadotropin subunits (mummichog FSH 50-60 and mummichog LH 91-106). Both immunoreactive FSH cells and immunoreactive LH cells were successfully identified in the fishes of almost every order of the superorder Acanthopterygii and several species of the superorders Paracanthopterygii and Polymixiomorpha, such as mullet, alfonsino, flyingfish, mackerel, flounder, cod, beardfish, etc. These antisera are therefore considered as universal antisera for immunocytochemical application to acanthopterygian fishes. Extensive diversity in the abundance of the FSH cells and the LH cells among species was noted even in fishes with similar gonadal stages, indicating the possibility that the respective roles of FSH and LH may vary considerably among species in advanced teleosts.Evident but generally weak immunoreactivities to anti-mummichog LH 91-106 were observed in the fishes of the superorder Cyclosquamata; and slight or weak immunoreactivities to the antiserum were observed in the fishes of several more primitive taxa (superorder Stenopterygii, Protacanthopterygii, Ostariophysi, subdivision Clupeomorpha, and subdivision Elopomorpha). No immunoreactivity to anti-mummichog FSH 50-60 was observed in these fishes. These results are consistent with the phylogenetic status of the fishes and the degree of conservativeness in the amino acid sequences of the antigen regions.     

Effects of cortisol and triiodo-L-thyronine on the steroidogenic capacity of rainbow trout ovarian follicles at two stages of oocyte maturation

The in vitro basal and salmon gonadotropin (sGTH)-stimulated steroidogenic capacity of rainbow trout follicles was examined at four stages [early (EV)-, mid (MV)- and peak-vitellogenic (PV), and pre-ovulatory, post-vitellogenic (PO)] of gonadal recrudescence using radioimmunoassays (RIAs) to measure 17-estradiol (E₂) and testosterone (T) production. In addition, follicles were incubated in the presence of [³H]pregnenolone ([³H]P⁵) and the radiolabelled steroid metabolites produced were separated using high performance liquid chromatography (HPLC). Peak basal and sGTH-stimulated E₂ and T production was found in PV stage follicles and lowest in PO stage follicles, and there were marked differences in the HPLC profiles of steroid metabolites. For EV stage follicles the major metabolite eluted as a peak that co-eluted with the androstenedione (A₄) and 17-hydroxyprogesterone (17-OHP) standards. A smaller peak that co-eluted with 11-hydroxyandrostenedione (11-OHA₄) and very small peaks co-eluting with 20-dihydroprogesterone (20-DHP) and E₂ were also seen. MV and PV stage follicles produced predominantly E₂, together with a small combined A₄ + 17-DHP peak, traces of 11-OHA₄ and two peaks that did not co-elute with any of the reference standards. The PO stage follicles produced only 17, 20-dihydroxy-4-pregnene-3-one (17,20-P).In addition, the effects of cortisol and triiodothyronine (T₃) on steroidogeneis were investigated in PV and PO stage ovarian follicles. For PV stage follicles, cortisol at 100 ng ml^–1 in the incubation medium significantly suppressed both basal and sGtH- stimulated T and E₂ production relative to control treatments. T₃ at 10 ng ml^–1 in the medium had no significant effect on either basal or sGtH-stimulated T or E₂ production compared to the controls, nor did it have any beneficial effect over the suppressive effect of cortisol. PO phase follicles taken 1 to 2 weeks prior to anticipated spawning had very low E₂ and T production, and there was no effect of cortisol or T₃, alone or in combination, on E₂ or T production. For PV stage follicles incubated in the presence of [³H]P⁵, cortisol suppressed T and E₂ production, but did not block the steroid pathway at any specific level; T₃ had no apparent affect on the metabolism of [³H]P⁵. The PO stage follicles produced little or no E₂; the major metabolite was 17,20-P. Cortisol and T₃ had no apparent effect on either basal or sGtH-stimulated 17,20-P production by the follicles at this stage of maturation.     

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.     

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.     

Survival and Growth of Bighead Carp Fry Exposed to Low Salinities

Bighead carp (Aristichthys nobilis Oshima) fry of various ages (11, 18, and 35 days post-hatch) were exposed to the low salinities encountered during the annual intrusion of seawater in Laguna Lake, Philippines. Practical indices of salinity tolerance assessed the effect of a 96 h direct exposure to low salinities (0–16). Mean (MST) and median survival times (MST50) of fry decreased as salinity of rearing medium increased. Younger fry were less able to tolerate exposure to these salinities than their older cohorts. Median lethal salinity after 96 h (MLS) revealed higher tolerance among 35–day old fry (7.6) than 11 (2.3) and 18–day old fry (6.0), demonstrating that survival in saline water depends on their age at initial exposure to low salinities. Mean body weight of 18–day old fry reared in 0 and 2 for 3 and 4 weeks was higher than for those reared in 4 and 6 for the same period. Growth over these periods was inversely related with the range of salinities tested. These results demonstrate that, despite their known stenohalinity, bighead carp fry possess some degree of osmoregulatory capability, allowing them to survive and grow in lakes subjected periodically to saltwater inflow.     

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.     

Variations on stress defences and metallothionein levels in the Senegal sole, <Emphasis Type="Italic">Solea senegalensis</Emphasis>, during early larval stages

The biochemical status of antioxidant defences of larvae from the commercial, benthic fish, Solea senegalensis, were studied over a period of 28days from hatching. The parameters studied were: catalase (EC 1.11.1.6), total glutation peroxidase activity (sum of the selenium dependent and independent forms) (EC 1.6.4.2), DT-diaphorase (EC 1.6.99.2), and as an indication of conjugative detoxifying metabolism, the enzyme glutathione S-transferase (GST; EC 2.5.1.18). Oxidative damage was evaluated by the formation of malondialdehyde (MDA) as an indication of lipid peroxidation (LP). Metallothionein (MT) levels were measured by differential pulse polarography and stress proteins (HSP 70 and HSP 60) were detected by immunoblotting, using commercial antibodies. The presence of catalytic activities was observed from hatching day and tended to increase during larval development. Significant changes were seen in most enzymes at day 3, when the larvae finished their endogenous feeding and started to feed on rotifers. DT-diaphorase activities were similar in both NADH and NADPH-dependent forms and, in turn, were about 10-times lower than their correspondent reductases. LP sharply increased at 19 and 28days post-hatch (dph), suggesting a saturation of the antioxidant defences during metamorphosis. MT showed high values during the endogenous phase and the lowest value corresponded to day 3, when the egg-yolksac was fully reabsorbed; a steady-state value was reached thereafter. Stress proteins were present at all stages, showing distinctiveness in the molecular weight of HSP60 at hatching day and 1dph. Quantitatively, both forms were significantly elevated at 3dph, with their ratio (HSP70/HSP60) decreasing over time.     

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.     

Brackishwater carp culture in potentially waterlogged areas using animal wastes as pond fertilizers

In order to assess the possibilities of utilizing drainage effluents (salinity range 5.0–12.5), fish culture experiments were carried out. Experiments on polyculture using cow dung (24 000 kg ha^–1 y^–1) as pond fertilizer were conducted at five different salinity levels (0.3–8.5). Studies have revealed that carp perform well in salinities up to 7.5 and reasonably high fish production has been obtained. Even though the ponds had a high trophic status, higher salinities ( > 7.5) appear to repress fish growth probably due to low dissolved oxygen (DO), high BOD and high NH₄-N. Experiments on monoculture of common carp (Cyprinus carpio) conducted at two different salinity levels (0.3–0.9 and 6.0–7.0) using four different organic fertilizers (cow dung at 24 000 kg and 20 000 kg, poultry at 1500 kg, duck at 6000 kg and sheep/goat at 1500 kg ha^–1 y^–1) have revealed the highest fish growth to be in poultry-treated ponds, followed in decreasing order by duck and sheep/goat wastes. Similar trends in fish production were observed both in fresh- and salt-water ponds. However, fish production was lower in ponds having higher salinities ( > 7.5). Nevertheless, these studies indicated that inland saline waters can be utilized for fish culture. With minor modifications in the existing technology of fish culture in stagnant freshwater fish ponds, animal wastes could be used to fertilize brackishwater fish ponds.     

Oocyte maturation inClarias batrachus. III. Purification and characterization of maturation-inducing steroid

Maturation-inducing steroid (MIS) in the Indian female catfish,Clarias batrachus, was purified and characterized from the incubation medium in which fully grown but immature folliculated oocytes were incubated with salmon gonadotropin (SG-G100) for 36 h. Maturation-inducing (MI) activity of residues obtained at various steps of extraction and purification was assessed byin vitro germinal vesicle breakdown (GVBD) assay using folliculated oocytes ofC. batrachus. The post incubation medium was extracted with diethyl ether. The ether phase was partitioned using 50% methanol plus n-hexane. The methanol phase which had MI activity was fractionated into 7 fractions using reverse-phase high-performance liquid chromatography. Of these 7 fractions, fraction 3 was found to be active in having MI ability and identified as 17 ,20-dihydroxy-4-pregnen-3-one (17,20-diOHprog). The authenticity of 17,20-diOHprog as the major follicular mediator of gonadotropin-induced oocyte maturation was further confirmed by thin-layer chromatography (TLC) in which fraction 3 was run along with authentic 17,20-diOHprog standard. This investigation gives a direct evidence that 17,20-diOHprog is the major naturally occurring MIS in Indian female catfish,C. batrachus.     

Dexamethasone receptors and their distribution in the brain of the red tilapia

Cytosolic extracts of liver and brain showed specific, saturable binding with [³H]dexamethasone: Scatchard plots were linear. Cortisol and 11-deoxycortisol acted as competitors, whilst 17,20-dihydroxy-4-pregnen-3-one was relatively much less effective. There was a four-fold range of differences in specific binding capacity between dissected brain regions, the order being telencephalon > hypothalamus > rhombencephalon > optic tectum (thalamus + tegmentum + torus semicircularis) when N_max was calculated in terms of DNA content. There was no evidence for any binding of [³;H]dexamethasone with membrane fractions.     

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.     

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.