Gonadotropin-releasing hormone-immunoreactive neuronal structures in the brain and pituitary of the African catfish,Clarias gariepinus (Burchell)

Summary The distribution of gonadotropin-releasing hormone (GnRH) immunoreactivity was studied in the African catfish, Clarias gariepinus, by means of immunofluorescence and immunoperoxidase techniques. Immunoreactive neurons were found throughout the preoptic nucleus (NPO). However, only a portion of the secretory perikarya in the NPO showed a positive reaction by use of an anti-LHRH serum. Numerous immunoreactive fibres were found to enter the pituitary and to terminate in its proximal pars distalis, the site of concentration of the gonadotropic cells. Since GnRH is present in the brain and pituitary of the African catfish, the lack of spontaneous ovulation in captivity is apparently due to an insufficient release of GnRH.     

Sexual steroids during puberty in male African catfish (Clarias gariepinus): serum levels and gonadotropin-stimulated testicular secretion in vitro

Blood serum and testicular tissue samples were collected from 3 to 13-month-old African catfish (groups A-G) in order to study their pubertal development. The sampling covered the period from before the beginning of spermatogenesis until full maturity. Testes of fish in group A contained spermatogonia alone. In testes of group B, spermatogonia, spermatocytes and spermatids were present. Spermatozoa were first observed in group C and became predominant as the fish attained full maturity (group G). Several sex steroids were determined in the blood samples. Testosterone was the quantitatively dominating androgen in the blood serum (3–5 ng·ml^-1) in groups B and C (fish in group A were too small to collect blood samples). In group D, the concentrations of 11-ketotestosterone and 11-hydroxyandrostenedione increased to levels similar to those of testosterone. Androstenedione that was undetectable before (below 0.4 ng·ml serum^-1), also increased to 3–5 ng·ml^-1 in group D. The levels of androgens kept increasing until the fish attained full maturity (group G). In order to monitor the responsiveness to gonadotropic hormone and the steroid secretion capacity, the in vitro secretion of two steroids (11-hydroxyandrostenedione and 17,20-dihydroxy-4-pregnen-3-one) by testicular tissue was quantified at the different stages of development. Testicular maturation was accompanied by changes of both the steroid secretion capacities and of the sensitivity to gonadotropic hormone. The most important changes occurred just after the initiation of spermatogenesis, as spermatocyte/spermatid formation was associated with a drop of the secretory capacity (amount of steroid secreted per milligram of tissue incubated) and with a reduced sensitivity to gonadotropic hormone. At later stages, when the testicular weight substantially increased concurrently with the formation of numerous spermatozoa, both the secretory capacity and the responsiveness to gonadotropic hormone increased again to reach the levels typical of adult fish. The blood levels of androgens appeared to be positively related to the increasing testicular weight in the later phases of development.Abbreviations 17,20P 17,20-dihydroxy-4-pregnen-3-one - A2 androstenedione - A3 androstenetrione - BPG-axis brain-pituitary-gonadal axis - FSH follicle stimulating hormone - GnRH gonadotropin-releasing hormone - GTH gonadotropic hormone - GSI gonado-somatic index - hCG human chorionic gonadotropin - HEPES N-(2-hydroxyethyl)piperazine-N-(2-ethanesulphonic acid) - KT 11-ketotestosterone - LH luteinizing hormone - OHA 11-hydroxyandrostenedione - OHT 11-hydroxytestosterone - PE pituitary extract from adult fish - PE_juv pituitary extract from juvenile fish - RIA radio immunoassay - T testosterone     

Effects of 4-nonylphenol on blood cells of the African catfish Clarias gariepinus (Burchell, 1822)

In the present work, the destructive effects of the 4-nonylphenol on one of the most economically important Nile fishes, namely African catfish (Clarias gariepinus) were studied. Apoptosis, erythrocytes alterations, micronucleus test and blood parameters count were used as biological indicators to detect those effects. After exposure to sublethal concentrations of 4-nonylphenol (0, 0.05, 0.08 and 0.1 mg/l), apoptotic red blood cells with many malformations and micronucleated erythrocytes were recorded. Decrease in the blood parameters such as red blood cells (RBCs), hemoglobin (Hb), package cell volume (PCV), mean corpuscular hemoglobin concentration (MCHC), platelets, white blood cells (WBCs), lymphocytes, basophils, monocytes and increase in mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), neutrophils, eosinophils indicated the negative effects of 4-nonylphenol. It was concluded that, the 4-nonylphenol caused genotoxicity in erythrocytes with many malformations in shape and number indicated with other blood parameters.     

The seminal vesicle of the African catfish,Clarias gariepinus

Summary The seminal vesicle of the African catfish, Clarias gariepinus, consists of 36–44 fingerlike lobes built up of tubules in which a fluid is secreted containing acid polysaccharides, acid-, neutral- and basic proteins, and phospholipids. In this fluid sperm cells are stored. The seminal vesicle fluid immobilizes the sperm cells. After ejaculation, it prolongs the period of sperm activity. The seminal vesicle fluid is secreted by the epithelium lining the tubules. The tubules in the proximal part of the lobes are predominantly lined by a simple cylindrical and those of the distal part by a simple squamous epithelium. These epithelial cells contain enzymes involved in energy-liberating processes, the enzyme activites being proportional to the height of the cells. Interstitial cells between the tubules have enzyme-histochemical and ultrastructural features indicative of steroid biosynthesis. Similar characteristics are found in testicular interstitial cells. The most rostral seminal vesicle lobes and the most caudal testicular efferent tubules form a network of tubules that opens at the point where the paired parts of the sperm ducts fuse with each other. The tubules of most seminal vesicle lobes, however, form a complex system that fuses with the unpaired part of the sperm duct.     

Isolation of gonadotrops from the pituitary of the African catfish,Clarias lazera

Summary Dispersed pituitary cells from male African catfish, Clarias lazera, were fractionated in a density gradient of Percoll. Five fractions were isolated, consisting of about 6, 19, 39, 95 and 83% gonadotrops, respectively. The gonadotrops were identified by their ultrastructural characteristics, by immunocytochemistry, and by measuring their hormone content. After one day in culture, in each fraction the secretion of gonadotropin could be stimulated by a luteinizing hormone-releasing hormone analogue, indicating that the cells had retained their functional integrity. Since the regulatory mechanisms of different cell types from the pituitary have some similarity, purification of the gonadotrops provides a model to study the regulation of gonadotropin secretion.A portion of the results was presented as a poster at the XII^th Conference of the European Society of Comparative Endocrinology, Sheffield, July 31–August 5, 1983     

饵料中添加维生素C对非洲鲶鱼幼鱼生长和营养利用效率的影响

通过研究非洲鲶鱼(Clarias gariepinus)的生长和营养利用来探讨其维生素C的需求量。平均体重为6.02g±0.4g的鲶鱼幼鱼被放置在60cm×45cm×45cm的玻璃缸中,每缸10条鱼,每个处理设3个重复。5组饵料中粗蛋白的含量均为40%,并测定且其基础饲料中维生素C的含量。在第1、2、3、4和5组中,其饵料中维生素C多聚磷酸酯的添加量依次为0(对照)、50、100,150和200mg/kg。每天用这些饵料喂鱼两次,分别在格林尼治时间的9:00和16:00喂食。鲶鱼幼鱼每周称重一次,以便进行统计分析。通过其生长和营养利用效率进行生物学评估。结果表明,特定生长率、食物转换率、蛋白质效率和食物效率在所有组中彼此间都有显著差异。综合所有实验结果看,添加维生素C多聚磷酸酯150mg/kg的第4组,幼鱼的生长和营养利用效率最好。     

Adrenal tissue in the male African catfish,Clarias gariepinus: localization and steroid hormone secretion

Interrenal-like tissue in male African catfish is localized in paired organs, situated retroperitoneally anterior of the kidney. Histological and enzyme-histochemical (3-hydroxysteroid dehydrogenase) reactions were carried out on sections of these organs in order to localize steroid-producing cells. In vitro incubations were carried out to determine the steroidogenic capacity of the interrenal-like tissue. Twenty-one steroids could be identified and quantified in the incubation medium, by means of gas chromatography followed by mass spectrometry. Cortisol, 5-and 5-androstanedione and androstenedione together comprised about 80% of the total steroid content. In a previous study, twenty testicular steroids were detected in plasma after castration. In the present investigation we have shown that most of these steroids can be produced by the interrenal-like tissue, which thus can be considered as an extra-testicular source of gonadal steroids.     

Pheromone detection and olfactory pathways in the brain of the female African catfish,Clarias gariepinus

Summary The olfactory tract of the African catfish, Clarias gariepinus, consists of two tracts, the medial and lateral olfactory tract. Ovulated female catfish are attracted by male steroidal pheromones. Attraction tests with catfish in which the medial and lateral olfactory tract have been selectively lesioned show that the effects of these pheromones are mediated by the medial olfactory tract. The central connections of the medial and lateral olfactory tract have been studied by retro- and anterograde transport techniques using horseradish peroxidase as a tracer. Upon entering the forebrain, the medial olfactory tract innervates the posterior pars ventralis and pars supracommissuralis of the area ventralis telencephali and the nucleus preopticus periventricularis, the nucleus preopticus and the nucleus recessus posterioris. Application of horseradish peroxidase to the olfactory epithelium shows that part of the innervation of the area ventralis telencephali and the nucleus preopticus periventricularis can be attributed to the nervus terminalis, which appears to be embedded in the medial olfactory tract. The lateral olfactory tract sends projections to the same brain areas but also innervates the nucleus habenularis and a large terminal field in the area dorsalis telencephali pars lateralis ventralis. Furthermore, the medial olfactory tract carries numerous axons from groups of perikarya localized in the area dorsalis telencephali. Contralateral connections have been observed in the olfactory bulb, telencephalon, diencephalon and mesencephalon. It is suggested that processes of the medial olfactory tract innervating the preoptic region may influence the gonadotropin-releasing hormone system and in doing so may lead to behavioral and physiological changes related to spawning.     

Reproductive performance of partial gonadectomized male African catfish, Clarias gariepinus broodstocks

This study was conducted to evaluate the effect of partial gonadectomy on reproductive performance of male Clarias gariepinus broodstock. Testes from C. gariepinus broodstock were surgically removed; 25% of the testes (Treatment 1), 50% of the testes (Treatment 2), 75% of the testes (Treatment 3), and removal of the sperm from the testes sac using syringe after the abdominal cavity had been cut open (Treatment 4) {control}. The incisions were sutured and the fish kept inside separate concrete tanks for 4 mo. The incisions closed up within 8 to 9 wk of surgery. The postsurgical survival of C. gariepinus was 100%, indicating the efficiency of the surgical procedure. There was no significant difference (P > 0.05) in sperm production, percentage fertilization, hatchability and survival of the larvae using sperm derived from regenerated testes of the partially gonadectomized C. gariepinus and nongonadectomized C. gariepinus. It also reveals that partial gonadectomy could not alter the quality of sperm production of C. gariepinus. Sperm derived from regenerated testes performed effectively for fertilization of eggs. Based on the results of this study, the removal of 75% of testes during partial gonadectomy proved to be the best as the total number of spermatozoa was more than that of other methods and the sperm was able to fertilize more eggs. Hence the removal of 75% of testis during partial gonadectomy of C. gariepinus is recommended based on the results of this study.     

Origin and destination of globules and irregular masses in the gonadotropin cells from the pituitary of the African catfish,Clarias gariepinus: a morphological study

The possible function of globules and irregular membrane-bound masses in the gonadotropin cells of the pituitary of Clarias gariepinus was studied. Strong secretory stimulation led to the disappearance of the secretory granules from gonadotropin cells but globules and irregular masses remained present. Acid phosphatase was detected enzyme-cytochemically in both globules and irregular masses. Radiolabelling with tritiated amino acids followed by autoradiography demonstrated that globules received radioactive material after secretory granules. The latter received radioactive material within 75 min of administration of radioactive amino acids but globules and irregular masses did not. Although some globules became radioactively labelled within 24 h of the administration of radioactive amino acids, irregular masses remained unlabelled during this period. Secretory granules reacted positively with antisera against and gonadotropin subunits, whereas globules and irregular masses only reacted with the antiserum against the subunit. A moderate anti-7B2 immunoreactivity was demonstrated in secretory granules and globules, whereas irregular masses labelled strongly. The combined cytological results indicate that globules and irregular masses are degradative, possibly crinophagic structures which develop by fusional events from secretory granules to globules and then to irregular masses.     

Effect of GnRHa, pimozide and Ovaprim on ovulation and plasma sex steroid hormones in African catfish Clarias gariepinus

Nine groups each of four fish were injected with a single intramuscular dose of the following preparations: Physiological saline (0.9% NaCl) as a control group, 0.5 ml kg⁻¹ Ovaprim, 20 and 40 μg kg⁻¹ BW of GnRHa, 8 and 16 mL kg⁻¹ pimozide tablets and the following combination of GnRHa with pimozide (GP): 20 μg + 4 mg, 30 μg + 8 mg and 40 μg + 16 mg kg⁻¹ BW. The primary oocyte diameter (POD) before hormone administration ranged from 943.3 to 1071.0 μm. The latency periods (LP) were in the range of 9.0 to 12.0 h after injection. The highest ovulation ratio (OR) was observed in groups Ovaprim, GP(30 + 8) and GP(40 + 16). Other treatments were effective for ovulation, the ovulation ratio in Groups G(40) and GP(20 + 4) were significantly higher than G(20) treatment. The ovulation index (OI) was in the range 62 to 77% and showed significant differences among groups. There was no significant difference in fertilization ratio (FR) among Ovaprim, GP(30 + 8) and GP(40 + 16) groups, while there were significant difference between the previous group and G(20) and G(40) groups. Control, P8, P16 showed negative results in all the parameters LP, OED, OR, OI and FR. Levels of sex steroids were analyzed on 6 and 12 h after initiation of treatments. A significant increase in plasma E₂ with GP(30 + 8) injection was observed 6 and 12 h after injection, while there were no significant increase between all the other groups 6 h after injection. Treatments with GP(20 + 4) resulted in a significant increase in plasma T concentration in females compared with control after 6 h. In contrast, plasma T and E₂ concentrations were lower during the combined GP(20 + 4), GP(30 + 8) and GP(40 + 16) after 12 h than after 16 h of injection. The combined treatments (GnRHa + PIM) are better compared with Ovaprim which gave the same results, they have some advantages, such as reliable response and low cost. Ovaprim is more than 3 to 5-fold of the cost of (GnRH + PIM). Therefore, this method could be useful tool for commercial catfish breeders to ensure spawning success.     

Ontogeny of the hyoid musculature in the African catfish, Clarias gariepinus (Burchell, 1822) (Siluroidei: Glariidae)

Three ontogenetic stages of the African catfish Clarias gariepinus have been used to describe and discuss the ontogeny of the hyoid musculature. During ontogeny, an asynchrony in the development of the muscles is observed: the intermandibularis and protractor hyoidei are the first to develop and which bear their insertions, followed by the hyohyoideus inferior and the sternohyoideus. The hyohyoideus abductor and adductor muscles are the last of the hyoid muscles to develop. In the juvenile stage (136.2 mm SL specimen), the intermandibularis is still present. The protractor hyoidei is well developed, as it may play an important role in the opening of the mouth, the elevation of the hyoid bars and, as a typical catfish feature, the displacement of the mandibular barbels. The protractor hyoidei arises as three pairs of muscle bundles (a pars ventralis, a pars lateralis and a pars dorsalis), of which the pars ventralis and the pars lateralis become fused to each other. This fusion gives rise to four different fields of superficial fibres for the manipulation of the mandibular barbels. The pars dorsalis, with its tendinous insertion, may be of more importance for mouth opening and/ or hyoid elevation. The hyohyoid muscle is well differentiated into an inferior, abductor and adductor muscles, acting on the hyoid bars, the branchiostegal rays and the opercular bone.     

Food composition of Clarias gariepinus (= C. lazera) (Cypriniformes,Clariidae) in Lake Kinneret (Israel)

The feeding behaviour of the freshwater piscivore, Clarias gariepinus (C. lazera) (C & V 1840) was studied over two periods: 1973–1975 and 1981–1982, in Lake Kinneret (Israel). The total number of fish analysed was 264 and their sizes (SL) and weights varied between 238 and 830 mm (146 to 5728 g). More than fifty species of plants and animals from the plankton, benthos and nekton of Lake Kinneret were identified in the intestines of C. gariepinus. Preyed fish were the most abundant food component (81%) and constituted the highest biomass, with Mirogrex terraesanctae representing the majority (although other species were also found). The potential impact of piscivory in the Kinneret ecosystem is considered.     

Mutagenic and physiological responses in the juveniles of African catfish, Clarias gariepinus (Burchell 1822) following short term exposure to praziquantel

Praziquantel (PZQ) is an acylated quinoline-pyrazine originally developed for veterinary application but now one of the most used anti-helminthic drugs for treatment of certain trematodes and cestodes in both human and other animals. The present study investigated the mutagenic and physiological responses in the juveniles of African catfish, Clarias gariepinus following short term exposure to praziquantel. Based on the 53.52 mg/l 96 h LC₅₀ of PZQ obtained, two sublethal concentrations of 5.35 and 10.70 mg/l of the drug were selected and fish were exposed to these concentrations and control for 15 days. Micronuclei induction in the peripheral blood of PZQ-exposed fish was highest on day 10 but the fish morphological parameters were not affected. The packed cell volume (PCV) was significantly reduced (p < 0.05) from day 5 while red blood cells (RBC) and hemoglobin (Hb) significantly declined (p < 0.05) on day 15. Macrocytic anemia was observed on day 1 of study and thereafter microcytic anemia developed on day 5 of study. The white blood cell (WBC) was significantly (p < 0.05) elevated from day 10 of exposure while values of mean cellular volume (MCV), mean cellular hemoglobin (MCH) and mean cellular hemoglobin concentration (MCHC) were not significantly different (p > 0.05) from the control. Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and glucose levels significantly increased while protein reduced (p < 0.05) throughout the exposure period but a mixed trend was observed in the leukocyte differentials. PZQ should be used with caution as sublethal exposure elicited micronucleus induction and alterations of hematological and biochemical parameters in the fish.     

Genetic diversity and population structure of selected lacustrine and riverine populations of African catfish,Clarias gariepinus (Burchell, 1822), in Kenya

Determining the genetic characteristics of natural fish stocks is useful for conservation and aquaculture programs. For African catfish, Clarias gariepinus, genetic characterization could help identify populations suitable as brood stock for culture, and those in need of conservation. This study determined the genetic diversity, population structure, and demographic history of C. gariepinus from Lakes Victoria (LV), Kenyatta (LKE), Kamnarok (LKA), and Rivers Nyando (NR), Tana (TR) and Sosiani (SR) in Kenya. Using 128 DNA sequences of D-loop control region, 34 haplotypes were recovered, of which 79.4% were singletons. Only 7 haplotypes were shared between sites, implying little gene flow between sites. Number of haplotypes was highest in LKE and NR populations and lowest in SR. Haplotype diversity was highest in LV, and lowest in SR, while, nucleotide diversity was highest in LKA and lowest in LV. Phylogenetic analyses revealed five clusters: Lakes Victoria, Kamnarok and Kenyatta, and Rivers Tana and Nyando, from both maximum likelihood tree and minimum spanning network. This, together with significant F _ST values among the sites imply population differentiation. Mismatch distributions were multi-modal in LKA, LKE, NR and TR, signifying demographic equilibria. Neutrality tests Tajima`s D values for the sampled populations were negative and significantly different, suggesting stable populations. These results show the existence of genetically distinct populations of C. gariepinus that require spatially explicit management actions such as reducing fishing pressure, pollution, minimizing habitat destruction and fragmentation for sustainable utilisation of stocks.     

Acute toxicity effects of ibuprofen on behaviour and haematological parameters of African catfish Clarias gariepinus (Burchell, 1822)

Indiscriminate discharge of pharmaceutical waste into the aquatic ecosystem may pose serious health challenges to aquatic biota. The effect of acute exposure to ibuprofen was evaluated using changes in behaviour and haematological parameters under static bio-assay method in Clarias gariepinus. Test specimens were exposed to acute concentrations of ibuprofen (0.28, 0.33, 0.38, 0.43 and 0.48 mg l^?1) for 24, 48, 72 and 96 h durations respectively. Behavioural and phenotypic changes were observed in surviving fish. There were significant (p < 0.05) concentration and duration-dependent increases in erythrocyte (RBC), haemoglobin (Hb), pack cell volume (PCV) and leukocytes (WBC) in treated fish compared to the control. Insignificant decreases (p > 0.05) in mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were observed in treated fish compared to the control. Ibuprofen elicited dose and duration- dependent decrease in neutrophil counts with the decreases being significant (p < 0.05) in the higher doses of 0.43 and 0.48 mg l^?1. Ibuprofen did not elicit any significant changes in monocytes, basophils and eosinophils. Changes observed in this study showed that ibuprofen negatively affected the health of the fish and we recommend that discharge of ibuprofen into the aquatic environment should be monitored and controlled.     

Analysis of production,early growth and survival ofClarias gariepinus (Burchell),Heterobranchus longifilis (Val.) (Pisces: Clariidae) and their F1 hybrids in ponds

Clarias gariepinus andHeterobranchus longifilis were successfully hybridized to produce reciprocal F₁ progeny during a two-year study.C. gariepinus produced significantly heavier spawn thanH. longifilis during the same period. Fertilized eggs were incubated in aerated static-water in fibre-glass troughs, and hatching rates were not found to be significantly different (P<0.05) between any two of the four catfish groups produced. Eight-day old fry of each group were reared in fertilized nursery ponds, and F₁ hybrids fromH. longifilis maternal parent had the best growth and survival rates at the end of 18 days. The reciprocal cross showed intermediate growth rate between both parents. At harvest, differential growth was less pronounced among both hybrids than among the parents.     

Growth response of African catfish, Clarias gariepinus (Burchell) to varied protein and lipid levels

To study the growth response of African catfish (Clarias gariepinus) to the diets containing two protein (30 and 35%) and two lipid levels (12 and 18%) in a closed recirculatory system for 60 days, fish were fed to satiation twice daily. The experiment was carried out in triplicate groups. Fortnightly sampling of fish and water samples was carried out. The best result in terms of growth was obtained with the diet containing 34.62% protein and 12.12% lipid. The protein to lipid ratio was 18.57 in the diet that gave best percentage weight gain. However best survival, food conversion ratio and protein efficiency ratio were recorded in the diet containing 29.86% protein and 18.08% lipid.