Acute and chronic toxicity of nitrite to Clarias lazera

The present study is an attempt to define acute (96 hr) and chronic (6-months) effects of nitrite on two different sizes of juvenile Clarias lazera. Static bioassays on acute toxicity showed median tolerance limit (TLm) for four days of 28 and 32 mg/l NO2-N for the two sizes respectively. Although nitrite is known to cause hypoxia, as a result of oxidation of haemoglobin to methemoglobin, exposure of both sizes to nitrite resulted in a decreased erythrocyte count haemoglobin content and haematocrit values. Fish exposed to nitrite responded physiologically by producing methemoglobin. A decline in serum total protein levels was recorded during acute and chronic exposure of both sizes to nitrite. This was interpreted as a generalized stress response.     

Stress response of juvenile Clarias lazera elicited by copper

1. Experiments were conducted with juvenile Clarias lazera to investigate the influence of acute copper exposure on bioaceumulation and some haematological constituents (erythrocyte count, haemoglobin content and haematocrit value).2. Analyses of copper residues in liver, kidney, muscle, gills, brain and blood after 96-hr exposure period revealed that liver and kidney accumulated the greatest amount of copper, while the other organs were found to accumulate relatively smaller concentrations.3. All blood samples collected from copper-treated fish showed some haemolysis. In addition, significant decreases in the values of the 3 parameters were noted. The anaemia reported is therefore of the haemolytic type, possibly due to the effect of copper on membrane ATPase, the glycolytic enzymes in the erythrocytes and glutathione.     

革胡子鲶生长激素cDNA克隆与蛋白质结构分析

从革胡子鲶(Clarias lazera(Burchell))的脑垂体组织中提取总RNA, 应用RT-PCR方法, 扩增得到了革胡子鲶生长激素(Growth hormone, GH)基因cDNA的开放阅读框(Open reading frame, ORF)序列。ORF全长为603 nt, 编码由22个信号肽氨基酸和178个成熟肽氨基酸共同组成的生长激素前体蛋白。序列同源比较结果表明, 研究中得到的革胡子鲶生长激素氨基酸序列与GenBank中已报道的其他6种鲶形目鱼类的氨基酸序列同源性高达95.8%。二级结构预测分析结果表明, 革胡子鲶生长激素蛋白中含有a 螺旋、b 折叠和b 转角以及无规卷曲等二级结构, 以a 螺旋为主, 是典型的a 型结构蛋白质。此外, 抗原性分析表明, 在氨基酸序列中的4个区域均可形成优势抗原表位, 其结构特点非常适合改造成为重组生长激素疫苗或单克隆抗体制剂加以开发利用。     

Myxosporean parasites of the catfish,Clarias lazera (Valenciennes)

Summary Five new species of myxosporean were found in the catfish Clarias lazera (Val.) in Israel. These species are described as: Henneguya laterocapsulata n. sp. (cyst-like trophozoites in the skin), H. suprabranchiae n. sp. (cyst-like trophozoites in the suprabranchial respiratory organs), Sphaerospora inaequalis n. sp. (spores in the lumen of the kidney tubules), Myxidium clariae n. sp. (spores in the gall bladder) and Myxobolus heterofilamentatus n. sp. (spores in the kidney, spleen, liver, suprabranchial respiratory organ, gills, heart and urinary bladder). Their taxonomic affinities to other species are discussed. ac]19860407     

Hemoglobin Richmond. Subunit dissociation and oxygen equilibrium properties.

In hemoglobin Richmond (beta102 leads to Lys), amino acid substitution has occurred at the same site as the mutation in hemoglobin Kansas (beta102 Asn leads to Thr), a variant with very low oxygen affinity. Although hemoglobin Richmond has been shown to have increased tetramer-dimer dissociation, its oxygen affinity has been inferred to be normal from studies on hemolysates of carriers. We have isolated hemoglobin Richmond and have further studied its properties. We confirm that the oxygen affinity of pure hemoglobin Richmond under conditions similar to those found in vivo is normal. However, the Bohr effect of the variant hemoglobin is markedly abnormal. Its oxygen affinity is low at high pH and high at low pH, relative to hemoglobin A. The tetramer-dimer equilibrium displays a strong pH dependence such that protons promote dissociation. A model is presented in which the structural change in hemoglobin Richmond results in low oxygen affinity, like hemoglobin Kansas. However, the close linkage between tetramer-dimer dissociation and proton concentration seen with hemoglobin Richmond results in normal oxygen affinity at intracellular pH and hemoglobin concentration, and carriers display no hematological abnormalities.     

The toxicity to Clarias lazera of copper and zinc applied jointly

1. The acute toxicity to juvenile Clarias lazera of a mixture of copper and zinc over a 96 hr exposure period was determined. Fish were exposed to the summation of half the 96 hr TLm value of each toxicant. 2. Percentage survival was much reduced indicating that the metals potentiate each others lethal action. 3. Comparison between metal residues in fish exposed to copper and zinc or to their mixture showed that the uptake of one metal was decreased by the presence of the other. 4. Toxic effects of the mixture on the physiological parameters studied were mainly attributable to copper, indicating that the presence of zinc did not influence the mode of action of copper.     

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     

On the blood sugar in Clarias lazera C. et V.

Summary The normal blood sugar of Clarias lazera was determined and found to have an almost constant value.Whereas starvation hardly affected the blood sugar level, after feeding the blood sugar increases considerably, due to a rise in true glucose. The highest values were found at a time when digestion of the ingested food was almost completed.In animals kept out of water for more than one hour the blood sugar was found considerably higher than in normal fishes. After return to the water, the blood sugar regained its original level after 26 hours.The hypoglycaemia after insulin injections was found to be mild, slow to appear and to subside rather quickly.The author is indebted to Dr. J. J. Mansoub-Bek, for suggesting the problem and for advice during the course of the work.     

The development of the stomach in Clarias lazera and the intestinal absorption of protein macromolecules

Summary The development of the stomach of the teleost, Clarias lazera, during the early posthatching period, is described, and the developing stomach is compared with that of adult Clarias.The stomach develops in two distinct parts: the corpus, which differentiates first, and the pylorus. The corpus contains a mucous surface epithelium, arranged in folds, and a tubular gland system containing only one type of gland cell, to which the secretion of pepsinogen and HCl is attributed. The pyloric region does not contain tubular glands.From the ultrastructure of the gland cells, the ³H-thymidine labeling index, and the onset of acid production (as determined with pH indicators) it is concluded that a functional stomach is present in juveniles with a standard length of ± 11 mm (approximately 12 days after fertilization at 23–24° C).The ultrastructure of the intestinal epithelium has also been studied. The intestine consists of three segments, similar to those described for stomachless teleosts and a number of fish larvae. In larvae as well as in juveniles, the enterocytes of the second segment show pinocytosis of horseradish peroxidase, although in the juveniles the stomach has already developed. This second segment has the same relative length in all studied larvae and juveniles and is also present in adult Clarias.It is therefore concluded that the capacity to absorb protein macromolecules is not specifically related to the absence of a functional stomach in this teleost species.     

Salinity tolerance of young catfish, Clarias lazera (Burchell)

Experiments were conducted to determine the adaptability of young catfish, Claria lazera , to various saline concentrations. Young catfish, total length 52–88 mm, were subjected to abrupt and gradual changes from fresh water (salinity = 0.14‰) to various salinities. Ninetyfour per cent survival occurred when the fish were transferred from fresh water to 25% sea water (salinity = 9.5‰ No fish survived higher salinities even through gradual change.     

Serum transaminases activity and histopathological changes in Clarias lazera chronically exposed to nitrite

Increase in serum transaminases (GOT and GPT) activity attributable to nitrite toxicity was observed in juvenile Clarias lazera after chronic exposure to nitrite. The application of SGOT and SGPT assays for monitoring the effect of nitrite exposure over a 6-month period has shown that changes in activities are correlated with histological effects in Clarias liver. Kidneys from fish exposed to nitrite were not noticeably different histologically from that of control fish. Hypertrophy and hyperplasia were the most consistent lesions that occurred in the gills. Lifting of lamellar epithelium and necrosis of some epithelial cells were also prominent.     

Ultrastructure and immunolabeling of gonadotrops and thyrotrops in the pituitary of the African catfish,Clarias lazera

Summary Pituitaries of the African catfish (Clarias lazera) were studied with immunocytochemical methods, at the light-microscopic and ultrastructural levels, for the characterization and localization of gonadotropic and thyrotropic cells. Two immunostaining procedures with the use of different markers were carried out: (i) with peroxidase-antiperoxidase, (ii) with protein A-gold. In routinely stained sections for light microscopy two types of basophils were identified in the proximal pars distalis: (1) large, round, purple cells, and (2) small, angular, light-blue cells. Both types were immunolabeled with antibodies against Clarias ,-gonadotropin (GTH) and salmon G100-GTH. Only the large basophils were immunolabeled with anti-carp -GTH, whereas the small basophils were the only cells immunolabeled with anti-human thyrotropin beta subunit (anti-h TSH-). It was concluded that the large basophils represent the gonadotrops and the small basophils the thyrotrops. At the ultrastructural level the immunostaining of the GTH-cells was confined to three types of inclusions: (i) secretory vesicles, (ii) globules, and (iii) electron-dense, membrane-bound irregular masses. Especially the protein A- gold method, in combination with the use of a highly diluted homologous antiserum, resulted in a distinct localization of GTH. The presence of two types of nerve fibres, synaptically contacting the gonadotrops, is discussed with regard to the presence of a peptidergic (stimulatory) and an aminergic (inhibitory) control of GTH-secretion.Part of the results were presented as a poster at the IX^th conference of the European Society of Comparative Endocrinology, Jerusalem, August 1981, and published as an abstract (Peute et al. 1982)     

Histochemical evidence for granulosa steroids in follicle maturation in the African catfish,Clarias lazera

Summary The effects of carp pituitary suspension (CPS) and 11-desoxycorticosterone-acetate (DOCA) on 3-hydroxysteroid dehydrogenase (3-HSD) and glucose-6-phosphate dehydrogenase (G6PD) activity in the ovary of Clarias lazera are described. Strong 3-HSD and G6PD activities are localized in the stroma, of both control and treated fish. A single CPS injection stimulates 3-HSD activity in the granulosa of postvitellogenic, maturing and postovulatory follicles, but DOCA has no such effect on the postvitellogenic and maturing follicles, and only stimulates a weak response in the postovulatory ones.     

Toxicity in Tilapia zilli and Clarias lazera (Pisces) induced by zinc, seasonally

Subadult teleosts, Tilapia zilli and Clarias lazera, were exposed in laboratory bioassays to lethal and sublethal concentrations of zinc, seasonally (at range of temperature between 9.3 +/- 1.5 and 25 +/- 1 degree C). It appears that Tilapia is more susceptible to Zn than Clarias and both species are more resistant to Zn toxicity at lower temperature (during winter). To determine the uptake and tissue distribution of Zn in the two species, gill, liver and muscles were analysed at moderate temperature (during spring). After a 96 hr exposure period, Zn was decreased in the following order: gill greater than liver greater than muscle.