Effect of dietary cortisol administration on growth and reproductive success of channel catfish

The effect of cortisol administration on reproductive performance was investigated in channel catfish Ictalurus punctatus broodfish. Cortisol was added to a commercial catfish feed by dissolving in ethanol and spraying the feed to yield a dietary concentration of 150 mg kg⁻¹ feed. The cortisol diet and the control (no cortisol) diet were offered at a rate of 1% of biomass to three replicate ponds each containing 28 female and 14 male broodfish, respectively, three times per week for 11 weeks. Spawning began 10 days after the start of the experiment, and continued for 10 weeks. In fish fed cortisol, body mass and the hepato‐somatic index were reduced ( P  ≤ 0·02) and concentrations of plasma cortisol and glucose were significantly higher ( P  ≤ 0·0003) compared to those of controls. The relative frequency of spawning was similar between the two treatments; however, cortisol‐fed channel catfish had an average of 47·1% more spawns than the control‐fed fish. On average, there were 25·5 spawns per pond in the treated groups compared to 12·3 spawns per control pond ( P  = 0·10). No effect was observed on egg production, with individual egg mass, fecundity, and hatching success being similar ( P  ≥ 0·27) for both treatments. Despite the observed negative effects of cortisol on somatic and hepatic growth, the increased reproductive output coupled with no observable effects on the eggs or hatching success demonstrates that cortisol does not suppress channel catfish reproduction.     

Cloning and characterization of microsatellite loci in channel catfish, Ictalurus punctatus

Short tandem repeat (microsatellite) loci were cloned from the channel catfish, Ictalurus punctatus , genome for use as molecular markers for genetic improvement of this important agricultural species. Plasmid clones containing catfish genomic DNA inserts were identified, by hybridization with tandem repeat DNA probes, and sequenced using automated laser fluorescence. A feral population of catfish displayed levels of heterozygosity greater than 0·7 for 13 of 22 loci and heterozygosity greater than 0·5 for 20 of 22 loci. Allelic polymorphism ranged from three to 17 alleles per locus in the feral population. Populations of domestic, farm-raised catfish and a research strain displayed levels of heterozygosity similar to the feral population. Non-invasive tissue sampling provided abundant material for the polymerase chain reaction-based genotype assay. The microsatellite loci will be useful in the molecular characterization and genetic improvement of channel catfish populations.     

Effects of in vivo crude human chorionic gonadotropin on ovulation and spawning of the African catfish, Clarias gariepinus Burchell–1822

The effects of increasing dosages of crude human chorionic gonadotropin (cHCG) on ovulation and spawning of Clarias gariepinus Burchell were examined. Four and 5 mg cHCG/100g body weight of fish gave the best response. The activation of the interrenals and stimulation of the ovary are discussed as a possible route of in vivo human chorionic gonadotropin administration on ovulation and spawning in catfish.     

Purification of 5 beta-reductase from hepatic cytosol fraction of chicken

From the cytosol fraction (supernatant fluid at 105,000 g) of chicken liver, 4-en-3-oxosteroid 5 beta-reductase (EC 1.3.1.23) was purified by ammonium sulfate precipitation, followed by Butyl Toyopearl, DEAE-Sepharose, Sephadex G-75 and hydroxylapatite column chromatographies. The enzyme activity was quantitated from amount of the 5 beta-reduced metabolites derived from [4-14C]testosterone. During the purification procedures, 17 beta-hydroxysteroid dehydrogenase which was present in the cytosol fraction was separated from 5 beta-reductase fraction by the Butyl Toyopearl column chromatography. By the DEAE-Sepharose column chromatography, 3 alpha- and 3 beta-hydroxysteroid dehydrogenases were able to be removed from 5 beta-reductase fraction. The final enzyme preparation was apparently homogeneous on SDS-polyacrylamide gel electrophoresis. Purification was about 13,600-fold from the hepatic cytosol. The molecular weight of this enzyme was estimated as 37,000 Da by SDS-polyacrylamide gel electrophoresis and also by Sephadex G-75 gel filtration. For 5 beta-reduction of 4-en-3-oxosteroids, such as testosterone, androstenedione and progesterone, NADPH was specifically required as cofactor. Km of 5 beta-reductase for NADPH was estimated as 4.22 x 10(-6) M and for testosterone, 4.60 x 10(-6) M. The optimum pH of this enzyme ranged from pH 5.0 to 6.5 and other enzymic properties of the 5 beta-reductase were examined.     

Effects of mammalian gonadotropin-releasing hormone analogue, pimozide, and the combination on plasma gonadotropin levels in different seasons and induction of ovulation in female catfish

In the catfish Heteropneustes fossilis , 0.5μg g-¹ B.W. mGnRH-A alone or the low dose of 0.05 μg g^-1 B.W. in combination with pimozide [a dopamine (DA)-receptor antagonist, 5 or l0μg g^-1 B.W.], caused a preovulatory surge in plasma gonadotropin (GTH) and induced a high rate of ovulation. The ovulatory response of the catfish to the low dose of mGnRH-A when given alone was not effective in the early (July) but was effective in the late spawning season (August). Plasma GTH response to these treatments showed seasonal variations. Pimozide administration potentiated the response to mGnRH-A in a season-dependent manner, being effective only in the prespawning and spawning phases. Pimozide treatment alone did not affect plasma GTH. These observations suggest that the release of GTH from the pituitary is subject to seasonal differences in the sensitivity of the GnRH system and the degree of its modulation by dopamine.     

Reproductive biology of hardhead catfish Ariopsis felis: evidence for overwintering oocytes

Hardhead catfish Ariopsis felis are a common marine catfish in the coastal waters of the Gulf of Mexico (GOM). The low economic value of this species has depressed interest and research, and although the species is known for its extremely low fecundity and large oocytes, little else is known about this catfish species. A total of 1230 samples across all months of the year from 2016 to 2018 resulted in 681 females, and analysis of gonado-somatic index (I_G) revealed 1% to be a clear cut-off indicating maturity. Females are considered capable of spawning from April to June when I_G averaged 4–8%. Both atresia and post-ovulatory follicles were present in July, suggesting that spawning ends in July in the northern GOM. The 1% I_G cut-off was used to designate maturity, and from that an L₅₀ of 253 mm was estimated. Batch fecundity from 41 females estimated a mean batch size of 36 oocytes. Perhaps the most interesting finding was the presence of secondary growth stage oocytes (e.g., cortical alveoli) from July through November, well outside the spawning capable period. Furthermore, 78% of females had some early vitellogenic oocytes present during the non-spawning season, and the distribution of these relatively large (2–5 mm) oocytes did not change over time. The results here are not only important as reproductive biology information for a common and abundant species, but also present interesting and unusual patterns of non-spawning season oocyte development that is not commonly seen in Western Hemisphere subtropical fish species.     

Androgen-induced changes in Leydig cell ultrastructure and steroidogenesis in juvenile African catfish, Clarias gariepinus

The present report focuses on the mechanism(s) involved in the steroid-induced decrease of androgen production in immature African catfish testes that was observed in previous studies. Juvenile animals were implanted with Silastic pellets containing different 11-oxygenated androgens (11-ketotestosterone, KT; 11 beta-hydroxyandrostenedione, OHA; 11-ketoandrostenedione, KA), testosterone (T) or estradiol-17 beta (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were either incubated with increasing concentrations of catfish luteinizing hormone (LH), or incubated with [3H]-pregnenolone ([3H]-P5) or [3H]-androstenedione ([3H]-A). Tissue fragments were also prepared for the quantitative assessment of Leydig cell morphology. Most of the parameters studied were not affected significantly by implantation of E2. Implantation of all androgens inhibited both the basal and the LH-stimulated androgen secretory capacity in vitro. This was associated with a reduced size of the Leydig cells and loss of half of their mitochondria. The studies on the metabolism of tritiated steroid hormones indicated that steroidogenic steps prior to 11 beta-hydroxylation, probably C17-20 lyase activity, were affected by all androgens. Although the effects of 11-oxygenated androgens and T on Leydig cells were mostly similar, previous work showed that only the 11-oxygenated androgens stimulated spermatogenesis, suggesting that distinct mechanisms of action are used by 11-oxygenated androgens and T. These mechanisms, however, seem to merge on the same target(s) to impair Leydig cell androgen production. Such a negative feedback mechanism may be of relevance in the context of the decline in androgen secretion per milligram testis tissue that accompanies the first wave of spermatogenesis in pubertal African catfish.     

A standardized microsatellite marker panel for parentage and kinship analyses in channel catfish,Ictalurus punctatus

This research was designed to produce a standardized set of microsatellite loci for parentage and kinship analyses in channel catfish, the leading species of US aquaculture. Three panels of five to six markers each were developed that contained a total of two dinucleotide‐, eight trinucleotide‐ and seven tetranucleotide‐microsatellite loci respectively. The loci had a range of nine to 31 alleles per locus in an outbred population. Based on the allele frequencies measured in commercial randomly bred broodstock, the combined probability of non‐exclusion of an unrelated candidate parent pair was 5.36e‐18. The combined probability of non‐exclusion of unrelated identical genotypes was 2.58e‐08. The microsatellite panels were validated by parentage and kinship evaluation in three populations. A total of 697 spawns were collected from matings of outbred broodstock over three spawning seasons, and parents were determined unambiguously for all but three spawns. Genotype analysis also enabled the identification of half‐sibling and full‐sibling families produced by pond spawning. In a second experiment, parentage was unambiguously determined in nine spawns from a population consisting of broodstock derived from only four families. A third experiment demonstrated that all but one of 374 individuals from 10 full‐sibling families could be assigned to a family after coculture in an earthen pond for 1 year. The standardized microsatellite panels enable the development of pedigreed catfish populations and large‐scale performance evaluations in common environments to support the genetic improvement of cultured catfish through selective breeding.     

Gonadal morphology, enzyme histochemistry and plasma steroid levels during the annual reproductive cycle of male and female brown bullhead catfish, Ictalurus nebulosus Lesueur

The annual reproductive cycle of the brown bullhead catfish, Ictalurus nebulosus Lesueur, was investigated over a two-year period. In females, GSI increased in the spring as follicles enlarged and the granulosa became hypertrophied, dropped during spawning in August, then rose in the autumn as follicles enlarged slightly. 3β-Hydroxysteroid dehydrogenase (3β-HSD) activity was limited to thecal nests of large, vitellogenic follicles. Plasma testosterone and estradiol-17β levels increased in parallel with GSI. Levels of both steroids dropped prior to the spawning period, although a peak in estradiol-17β was evident during the spawning period. No 11-ketotestosterone was detected in female plasma. In males, GSI increased in the spring as spermatogenesis proceeded, and dropped during spawning. 3β-HSD activity was confined to Leydig cells and was most intense prior to spawning. Plasma testosterone and 11-ketotestosterone peaked during the pre-spawning period, dropped prior to spawning, then rose slowly during the autumn. A peak in estradiol-17β occurred during the spawning period. Significant differences in GSI and plasma steroid levels during the pre-spawning and spawning periods were observed between the two yearly cycles; they may be related to differences in rainfall during these periods.     

Spatial and temporal variability of macroinvertebrates in spawning and non-spawning habitats during a salmon run in Southeast Alaska

Spawning salmon create patches of disturbance through redd digging which can reduce macroinvertebrate abundance and biomass in spawning habitat. We asked whether displaced invertebrates use non-spawning habitats as refugia in streams. Our study explored how the spatial and temporal distribution of macroinvertebrates changed during a pink salmon (Oncorhynchus gorbuscha) spawning run and compared macroinvertebrates in spawning (riffle) and non-spawning (refugia) habitats in an Alaskan stream. Potential refugia included: pools, stream margins and the hyporheic zone, and we also sampled invertebrate drift. We predicted that macroinvertebrates would decline in riffles and increase in drift and refugia habitats during salmon spawning. We observed a reduction in the density, biomass and taxonomic richness of macroinvertebrates in riffles during spawning. There was no change in pool and margin invertebrate communities, except insect biomass declined in pools during the spawning period. Macroinvertebrate density was greater in the hyporheic zone and macroinvertebrate density and richness increased in the drift during spawning. We observed significant invertebrate declines within spawning habitat; however in non-spawning habitat, there were less pronounced changes in invertebrate density and richness. The results observed may be due to spawning-related disturbances, insect phenology, or other variables. We propose that certain in-stream habitats could be important for the persistence of macroinvertebrates during salmon spawning in a Southeast Alaskan stream.     

Role of cyclic AMP-dependent protein kinase in oocyte maturation of the catfish,Clarias batrachus

The results of the present study demonstrate the probable involvement of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase (PKA) in the regulation of oocyte maturation in the catfish, Clarias batrachus. A decrease in total PKA activity with a concomitant increase in the percentage of germinal vesicle breakdown (GVBD) was found in oocytes treated with different doses of N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinoline sulfonamide (H-89), a selective, potent inhibitor of PKA and 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17 alpha, 20 beta-DP), the natural maturation-inducing steroid of this catfish. Evaluation of time-course of response to H-89 and 17 alpha, 20 beta-DP revealed that PKA activity decreased, and incidence of GVBD increased at all the time points when compared with their respective controls. The data further indicate that the decrease in PKA activity in H-89-treated oocytes was more prominent, but the induction of maturation was slower than that induced by 17 alpha, 20 beta-DP. Moreover, cyanoketone (CK), an inhibitor of steroidogenesis that blocks the salmon gonadotropin (SG-G100)-induced GVBD, failed to abolish the maturational effect of H-89, suggesting that H-89 directly promotes GVBD by reducing PKA activity in oocytes. Taken together, these results indicate that inhibition of PKA activity in the oocyte of C. batrachus is directly involved in the mechanism leading to oocyte maturation.     

Reproductive ecology of the Far Eastern catfish, Silurus asotus (Siluridae), with a comparison to its two congeners in Lake Biwa, Japan

Spawning activity of the catfish, Silurus asotus, takes place in temporary water (rice fields) from early evening to midnight, generally in connection with rainfall, from late April to late August. Spawning of the catfish was correlated with hydrographic parameters dependent on rainfall: daily precipitation, turbidity, water depth, and water temperature. The spawning habits of the catfish, and in particular the use of temporary waters such as rice fields that become submerged after rainfall or by irrigation, are presumed to be adaptations to the Asian monsoon climate with a pronounced rainy season. The apparent sex ratio of the catfish was extremely biased toward females. Intraspecific variation in the reproductive ecology, particularly mating behavior, of this species is observed among local populations. Factors that may have caused this variation are discussed in the context of a comparison of mating behavior, reproductive environment, and sex ratio between the Lake Biwa population of S. asotus and other conspecific populations, as well as two other species of silurid catfish that occur in the Lake Biwa drainage, S. biwaensis and S. lithophilus.     

Features of the reproductive ecology of the rock catfish Silurus lithophilus

Some aspects of the reproductive ecology of the rock catfish Silurus lithophilus (Siluriformes: Siluridae), a species endemic to the Lake Biwa system, were investigated from April to July in 1989–1994. Field observations were conducted at a rocky shoal, which was also a spawning ground of S. biwaensis, along the shore of the Seta River, the lake's outlet. Spawning of S. lithophilus occurred around midnight at shallow, rocky places on the shoal (5–70 cm in water depth) from early May to mid-July, starting earlier than S. biwaensis (mid-May to mid-July). Spawning tended to occur at low water temperatures irrespective of high-water events, unlike S. biwaensis, and in low densities (fewer than 8 fish per night) compared to S. biwaensis (1–45 fish per night). Although the rock catfish tended to appear and spawn at higher frequencies on nights when S. biwaensis spawned or appeared, it always avoided conflict with the latter species by spawning at sites far from those used by S. biwaensis or after S. biwaensis had left the vicinity. The survival of eggs of S. lithophilus might be favored by a strategy of diverting predator attention from them by synchronizing spawning nights with S. biwaensis. Received: February 27, 2001 / Revised: October 17, 2001 / Accepted: November 8, 2001     

Comparison of fatty acid profiles of spawning and non-spawning Pacific herring, Clupea harengus pallasi

Crude lipid and fatty acid composition from liver, intestine, roe, milt and flesh of spawning and non-spawning Pacific herring (Clupea harengus pallasi) were examined to determine the relative effects of spawning on the nutritional value of herring. Depletion of lipid due to spawning condition was significant (P < 0.01) in all organ tissues and flesh of spawning herring. The lipid content ranged from an average of 1.9 to 3.4% (wet weight basis) in different organ tissues of spawning herring, to 10.5 to 16% in non-spawning fish. The fatty acid profile exhibited many differences in the relative distribution of individual fatty acids among organ tissues and between the two fish groups. Oleic acid (C18:1n-9), a major monounsaturated fatty acid (MUFA) found in all tissue lipids, decreased significantly (P < 0.01) in spawning fish. The two monoenes, C20:1n-9 and C22:1n-11, occurred at high concentrations in the flesh but at only minor proportion in the digestive organs and gonads. Spawning herring also had significantly (P < 0.01) higher polyunsaturated fatty acids (PUFA) content in the organ tissues, particularly in the milt and ovary, with docosahexaenoic acid (C22:6n-3, DHA) having the greatest proportion. Among the n-6 fatty acids, only C18:2n-6 and C20:4n-6 occurred at notable amounts and were present in higher proportions in spawning fish. We concluded that although relatively higher n-3 fatty acid content was found in the organ lipids of spawning herring, they are not an energy-dense prey food source due to the fact that both flesh and gonads contain a very low amount of lipid.     

Adaptive significance of the formation of multi-species fish spawning aggregations near submerged capes

Background

Many fishes are known to spawn at distinct geomorphological features such as submerged capes or “promontories,” and the widespread use of these sites for spawning must imply some evolutionary advantage. Spawning at these capes is thought to result in rapid offshore transport of eggs, thereby reducing predation levels and facilitating dispersal to areas of suitable habitat.

Methodology/Principal Findings

To test this “off-reef transport” hypothesis, we use a hydrodynamic model and explore the effects of topography on currents at submerged capes where spawning occurs and at similar capes where spawning does not occur, along the Mesoamerican Barrier Reef. All capes modeled in this study produced eddy-shedding regimes, but specific eddy attributes differed between spawning and non-spawning sites. Eddies at spawning sites were significantly stronger than those at non-spawning sites, and upwelling and fronts were the products of the eddy formation process. Frontal zones, present particularly at the edges of eddies near the shelf, may serve to retain larvae and nutrients. Spawning site eddies were also more predictable in terms of diameter and longevity. Passive particles released at spawning and control sites were dispersed from the release site at similar rates, but particles from spawning sites were more highly aggregated in their distributions than those from control sites, and remained closer to shore at all times.

Conclusions/Significance

Our findings contradict previous hypotheses that cape spawning leads to high egg dispersion due to offshore transport, and that they are attractive for spawning due to high, variable currents. Rather, we show that current regimes at spawning sites are more predictable, concentrate the eggs, and keep larvae closer to shore. These attributes would confer evolutionary advantages by maintaining relatively similar recruitment patterns year after year.     

Seasonal effects of melatonin on ovary and plasma gonadotropin and vitellogenin levels in intact and pinealectomized catfish, Clarias batrachus (Linn)

Effects of daily administration of melatonin for 15 days were evaluated with respect to ovarian activities and plasma gonadotropin (GtH II) and vitellogenin (Vg) levels in intact (INT) and pinealectomized (Px) female catfish, C. batrachus, during preparatory (April), prespawning (May and June), spawning (July) and post-spawning (September) periods. Px (saline control groups) caused a stimulatory effect during preparatory (with respect to Vg synthesis and incorporation) and prespawning (with respect to Vg synthesis) periods whereas no effect was observed during spawning and post-spawning periods with respect to the reproductive parameters studied. During April, melatonin-treatment significantly decreased plasma GtH II levels and percentage of vitellogenic oocytes without any significant changes in plasma Vg levels and gonadosomatic index (GSI). During early prespawning period, in May, 50microg melatonin brought about a significant reduction in plasma GtH II levels in INT group, whereas 100microg caused a decrease in all parameters; on the other hand, in Px groups both dose levels proved to be inhibitory. In June (late prespawning period) melatonin-treatment could not bring about any change in GSI and plasma Vg levels compared to the control groups regardless of Px but plasma GtH II and mean number of yolky oocytes were significantly reduced in melatonin-treated INT group. During spawning period (July) melatonin inhibited the GSI, mean number of yolky oocytes and plasma GtH II levels without affecting plasma Vg levels. In September (post-spawning period), melatonin did inhibit both GSI and plasma GtH II levels. The results, thus, indicate that melatonin showed variable effects (inhibitory and/or no effect) to GSI, mean number of yolky oocytes and plasma Vg levels but a consistent inhibiton of plasma GtH II levels indicating that melatonin may control the reproduction by blocking the GtH II release from the pituitary via affecting the hypothalamo-hypophysial axis.     

Blood serum chemistry measurements of normal and acutely stressed channel catfish

1. An automated blood serum chemistry analytical system designed for human usage was employed to establish the levels of 26 different components present in sera obtained from various experimental groups of channel catfish. 2. Comparisons of samples from feral and commercial production pond fish during warm months indicated statistically significant differences in the serum levels of sodium, CO2, urea nitrogen, direct bilirubin, cholesterol, creatinine and protein. 3. Laboratory acclimated and production pond fish exhibited differences in serum electrolytes (sodium, potassium, chloride, phosphorus), serum metabolites (urea nitrogen, creatinine, triglycerides), serum enzymes [gamma-glutamyl transferase, glutamate-oxaloacetate transaminase (GOT), lactate dehydrogenase (LDH), alkaline phosphatase, and amylase], and serum iron. 4. Seasonal (temperature?) differences in production pond fish were noted for 12 serum components including potassium, magnesium, CO2, glucose, creatinine, albumin, iron, alkaline phosphatase, and glutamate-pyruvate transaminase (GPT). 5. Comparisons of samples obtained from laboratory-acclimated fish before and 18 hours after acute handling and transport stress revealed significant differences in only three serum parameters: glucose, LDH, and creatine phosphokinase (CPK). 6. These studies suggest that "normal" values established by any method of sera analysis may be different in the same species depending on the diet, season, and presence of environmental stressors.     

Spawning and season affect lipid content and fatty acid composition of ovary and liver in Japanese catfish (Silurus asotus)

The influences of spawning and season on lipid content, lipid classes, and fatty acid composition were assessed in ovary and liver of wild and cultured Japanese catfish (Silurus asotus). The lipid content (7.3+/-1.6 g/100 g wet wt.) of ovary from wild catfish at spawning was higher than that at post-spawn. However, no influence of spawning on the lipid content of liver was observed. Docosahexaenoic acid [DHA, C22:6(n-3)] in ovary lipids was 12.3+/-0.5% of total fatty acids. The percentage of n-7 monounsaturated fatty acids in triacylglycerol from the ovary and liver in the spawning season was high. Percentages of C22:6(n-3) in phosphatidylcholine and phosphatidylethanolamine from ovary were higher during spawning than after spawning. No significant differences were observed in the lipid content of ovary and liver from cultured catfish between seasons (summer vs. winter). Content of arachidonic acid (C20:4n-6) in ovary and liver from cultured catfish was higher in summer than in winter. There were differences in lipid classes of ovary and liver by spawning and season. These results suggest that the lipid metabolism in Japanese catfish is greatly influenced by spawning and season.