• Journal of Life Science
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• v.26 no.3
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• pp.296-301
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• 2016

An antibacterial peptide from skin extract of the catfish Silurus asotus was purified and characterized. The acidified skin extract was put through a Sep-Pak C18 solid phase extraction cartridge using a stepwise gradient and divided into flow-through (F.T.), 10% methanol-elute (RM10), 60% methanolelute (RM60), and 100% methanol-elute (RM100) fractions. RM10, RM60, and RM 100 showed antimicrobial activity against Escherichia coli D31. On the other hand, the F.T. fraction did not show antimicrobial activity. Among the various fractions, RM 60 had the highest activity. RM 60 was partially purified on a cation exchange column (CM52) by a stepwise gradient. The ammonium acetate (pH 5.15) 0.02 M – 0.8 M fraction showed antimicrobial activity. Then an antimicrobial peptide was purified using a 0.6M fraction with strong antibacterial activity through a series of five C18 reversed-phase HPLC columns. For the characterization of the purified peptide, the molecular weight and amino acid sequence were analyzed by MALDI-TOF MS and Edman degradation. The molecular weight of this peptide was about 4182.1 [M+H]⁺. The amino acid sequence of this peptide was partially determined as follows: PALXXKARREAKVKF. These findings suggest that this peptide plays a significant role in the innate defense system of catfish skin.

• Journal of Aquaculture
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• v.13 no.4
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• pp.359-362
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• 2000

Mitotic gynogenesis was induced in the far eastern catfish, Silurus asotus using UV-irradiated heterospecific sperm and cold shock treatment. Eggs were activated with the sperm of mud loach, Misgurnus mizolepis which has been irradiated with UV at dose of 9,000 ergs/$mm^2$. To determine the optimum duration required to prevent the first cleavage, a cold shock at 4$^{\circ}C$ with duration of 20, 30 or 40 min was applied to the eggs 50 min after activation. To induce diploidization of mitogenesis, the most effective protocol was to apply cold shock to 50-min old (after activation) eggs at 4$^{\Circ}C$ for 30min.

• Journal of Aquaculture
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• v.15 no.4
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• pp.275-277
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• 2002

To obtain baseline data required for ploidy induction in Silurus asotus, a species with enormous aquacultural potential, histological events related to early embryonic development at 24$\pm$0.5$^{\circ}C$ are described. The histological location of the one-celled embryos indicated that metaphase stage of the first cleavage occurs at 31 min after insemination, when the highest yield can be obtained for the chromosome set manipulation.

• Asian-Australasian Journal of Animal Sciences
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• v.27 no.10
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• pp.1478-1486
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• 2014

The present experiment was conducted to evaluate the efficacy of dietary fermented by-product of mushroom, Pleurotus ostreatus, (FBPM) as a fish meal (FM) replacer in juvenile Amur catfish, Silurus asotus. A total number of 225 fish averaging $5.7{\pm}0.1g$ ($mean{\pm}standard$ deviation) were fed one of the five experimental diets formulated to replace FM with FBPM at 0%, 5%, 10%, 20%, and 30% ($FBPM_0$, $FBPM_5$, $FBPM_{10}$, $FBPM_{20}$, and $FBPM_{30}$, respectively). At the end of eight weeks of the experiment, average weight gain (WG) of fish fed $FBPM_0$ or $FBPM_5$ were significantly higher than those of fish fed $FBPM_{20}$ or $FBPM_{30}$ diets (p<0.05). However, there was no significant differences in WG among the fish fed $FBPM_0$, $FBPM_5$ or $FBPM_{10}$, and between fish fed $FBPM_{10}$ or $FBPM_{20}$, and also between those fed $FBPM_{20}$ or $FBPM_{30}$ diets. Lysozyme activity of fish fed $FBPM_0$ or $FBPM_5$ were significantly higher than those of fish fed $FBPM_{10}$, $FBPM_{20}$ or $FBPM_{30}$ diets (p<0.05). The chemiluminescent response of fish fed $FBPM_5$ was significantly higher than those of fish fed $FBPM_0$, $FBPM_{20}$ or $FBPM_{30}$ diets (p<0.05). Broken line regression analysis of WG suggested that the maximal dietary inclusion level for FBPM as a FM replacer could be 6.3% without any adverse effects on whole body composition and on serological characteristics. Therefore, these results may indicate that the maximal dietary inclusion level of FBPM as a FM replacer could be 6.3% in juvenile Amur catfish.

• Korean Journal of Ichthyology
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• v.13 no.4
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• pp.248-253
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• 2001

An histological study was conducted to determine the initial treatment time and treatment duration in the use of sex-reversal hormones in relation to gonadal development and sexual differentiation in the bagrid catfish, Leiocassis ussuriensis. The primordial germ cell, which could be recognized from one-day-old fry, began to protrude into the peritoneal cavity between the mesonephric duct and the gut. The primordial gonad with a genital ridge was developed at 5~10 days after hatching. Sex differentiation of the ovary was identified by the ovarian cavity and meiotic oocytes from 20-day-old larvae. Testicular differentiation was also identified by spermatogonial cells from 20-day-old larvae. It may therefore be concluded that this species belongs to the differentiated type of gonochoristic teleost.

• Journal of fish pathology
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• v.5 no.2
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• pp.143-152
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• 1992

Metallothionein is an essential and common protein to regulate the intracellular concentration of heavy metals, which exist in most organisms from bacteria to vertebrates. Although the detailed function of metallothianein has not been fully identified until yet, it may be involoved in the cellular protection against the heavy metal toxicity and in the global regulation of several other genes and the expression of metalloproteins. We have cloned the full cDNA clone of metallothionein gene in Channel Catfish by Reverse Transcriptase-Polymerase Chain Reaction(RT-PCR) starting from poly(A)-containing mRNAs. All PCR fragments have been subcloned into EcoRV site of pBluescript SK+ and dT-tailed at Smal site of pUC19, then PCR products are recovered by the double digestion of recombinant plasmids wiht EcoRI and HindIII, which are adjacent to EcoRV site in multicloning sites or by rapid PCR screening. The nucleotide sequence analysis of pMT150(one of the PCR clones) showed high homology with several other piscine metallothionein cDNA genes.

• Journal of fish pathology
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• v.9 no.1
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• pp.79-85
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• 1996

The effect of $\beta$-glucan administration on the resistance of Korean catfish(Silurus asotus) to experimental Edwardsiella ictaluri and Aeromonas hydrophila infection was evaluated. Fish were either intraperitoneally received $\beta$-glucan($200\sim1000{\mu}g$/100g body weight) dissolved in physiological saline once or twice at an intervals of 3 days, or placed in $\beta$-glucan bath($100{\mu}g/m\ell$) prepared with filtered tap water for 30 or 60 min. Bacterial challenge was performed by intraperitoneal injection of 0.1 ml of bacteria suspension($2{\times}10^7 CFU/m\ell$) 3 days after $\beta$-glucan administration. The $\beta$-glucan injected fish showed an significantly enhanced resistance against experimental infections. The resistance was much higher in the twice-injected fish than in the once-injected fish. But glucan bath did not affect survival rate after the challenge. The protective effect in the $\beta$-glucan injected fish was higher to A. hydrophila than to E. ictaluri. These results indicate that $\beta$-glucan injection can increase the resistance of Korean catfish against experimental E. ictaluri and A. hydrophila infection and that twice injection of $\beta$-glucan at an 3 day-intervals is more effective to the resistance.

• Asian-Australasian Journal of Animal Sciences
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• v.18 no.5
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• pp.671-676
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• 2005

A total of 50 individual catfish, the Tra (Pangasius hypophthalmus) cultivated in either floating cages (Tra-c) or in ponds (Tra-p) and the Basa (Pangasius bocourti) raised in three floating cages, were collected in two of the Mekong Delta provinces. The caudal fin of each individual fish was used for protein electrophoresis employing the SDS-PAGE method. The one fillet sides were used as a representative sample to determine the dry matter (DM), crude protein (CP), ether extract (EE) and amino acids (AAs). The catfish oil was extracted from the belly fats, and the fatty acid (FA) composition was analyzed. There were 21 bands of the Tra and the Basa. Protein bands of the two varieties were 28.6-33.3% polymorphic, while polymorphic individuals of the Tra ranged from 80.0 to 100.0%, and the Basa was 90.0% polymorphic. The phenotypic diversity (Ho) of the Tra ranged from 1.71 to 1.80, while the Basa ranged as high as 2.14%. Diversity values (H$_{EP}$) for genetic diversity markers were equal in the Tra and the Basa. The sum of the effective number of alleles (SENA) of both varieties ranged from 3.40 to 3.83 for the Basa and the Tra, respectively. The lower values of Ho and SENA, as compared with those of the fresh water prawn (Macrobrachium equidens) in the area, would suggest that the species with the low values will become extinct due to inbreeding; the gene pools of each observed population were below a suitable threshold. Many of the differences in the nutritional values of the Tra-c, the Tra-p and the Basa were measured; their nutrient values were comparable to fishmeal or fish oil. Most of the DM, CP, and EE were higher in the Tra, especially in the Tra-c. The essential AA content, especially that of lysine, was highest in the Tra-c, next highest in the Tra-p, and lowest in the Basa. Therefore, the amino acid patterns were closer to the ideal patterns in the same sequences. In contrast, the essential FAs were concentrated in the Basa fish oil. It was found that suitable selection of parents for seed production is required to avoid inbreeding. Catfish may be valuable sources of nutrition for both humans and animals, and the differences in their nutritional values by variety and/or management must be taken into account.

• Fisheries and Aquatic Sciences
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• v.1 no.2
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• pp.192-200
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• 1998

This study was carried out to evaluate the effect of feeding higher protein feeds with lesser amount, but feeding the constant total protein input for all treatments, on water quality and nitrite toxicity in channel catfish ponds. There was no significant difference in survival rate among treatments $(P>0.05)$. Specific growth rate (SGR) for Treatment 1$(28\%\;protein\;and\;100\%\;of\;satiation)$ was significantly higher $(P>0.05)$ than for Treatment 3$(36\%\;protein\;and\;87.5\%\;of\;satiation)$, but not significantly higher than for Treatment 2 $(32\%\;protein\;and\;77.8\%\;of\;satiation)$ at constant digestible energy (DE), 3.08kcal/g (treatments 1, 2 and 3). At constant DE/P (treatments 4, 2 and 5), no significant difference in SGR was observed among treatments. Feed conversion ratio (FCR) slightly improved or improved as dietary protein level increased from $28\%$ to $32\%$ and feed allowance decreased by $12.5\%$, but did not improve as dietary protein level increased from $32\%$ to $36\%$ and feed allowance decreased by $22.2\%$, at constant DE and constant DE/P. There was no significant difference in water quality variables, such as total ammonia nitrogen (TAN), nitrite, chlorophyll a, soluble phosphorous concentrations among treatments, but significant difference in water quality variables over time as amount of feed fed increased $(P<0.0001)$. There was a trend toward increase in TAN and nitrite over time. A strong linear regression was observed between mean total ammonia nitrogen and nitrite for all treatments Y (Nitrite) =$0.04\times (TAN)+0.01$, $R_2=0.89$. Methemoglobin percent in the blood of catifish was not significantly different among treatments. And its mean value was $7.5\%$, which was relatively low, so that it was not serious problem in catfish production pond under these experiment conditions. There was the stronger linear regression between the percentage of Methemoglobin and the molar ratio of nitrite to chloride rather than nitrite alone: $Y\;(Methemoglobin\;\%)\;=\;58.45\;\times\;(NO^{2-}/Cl^-)\;+\;0.41,\;R^2=0.60$. These results indicate that deterioration of water quality has no strong impact on poor weight gain for $36\%$ dietary protein in this study.

• Journal of Aquaculture
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• v.15 no.1
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• pp.49-60
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• 2002

Research on practices for improving water quality in channel catfish Ictalurus punctatus ponds was conducted at the Auburn University Fisheries Research Station, Auburn, Alabama, in 1998 and 1999. The objective of this two-year study was to determine better management practices to enhance water quality and improve production efficiency. In the first year, oxidation of bottom soil by drying, tilling, and applying sodium nitrate was performed (dry-till and dry-till with sodium nitrate treatments). The second year, based on the results obtained during the first year, precipitation of phosphorus (P) from water by applying gypsum was compared to the dry-till treatment (dry-till and dry-till with gypsum treatments). Control ponds were not subjected to bottom drying, tilling, sodium nitrate, or gypsum treatment. Channel catfish fingerings were stocked at 15,000/ha. In the first year, water in ponds from dry-till and dry-till with sodium nitrate treatments had lower concentrations (P < 0.01) of soluble reactive P, nitrate ($NO_{3} ^{-}) and nitrite ($NO_{2} ^{-}) nitrogen (N), total ammonia ($NH_3$) nitrogen, total suspended solids and turbidity, and higher values of pH, Secchi disk visibility, total alkalinity, total hardness, and calcium ($Ca^{2+}) hardness than water in control ponds. Ponds of the dry-till treatment also had lower concentrations (P < 0.01) of total P and total N than control ponds. Total fish production and survival rate did not differ among the treatments (P > 0.05). The findings suggested that drying and tiling pond bosoms between crops could achieve water quality improvement. Applying sodium nitrate to dry, tilled pond bosoms did not provide water quality improvement. In the second year, the treatment with the best results from the first year, dry-till, was compared with a dry-till with gypsum treatment. Enough gypsum was applied to give a total hardness of about 200 mg/L, and gypsum was reapplied as needed to maintain the hardness. Compared to the control, dry-till and dry-till with gypsum treatments had lower concentrations (P < 0.01) of total and soluble reactive P, total N, and total $NH_3$-N, and higher concentrations (P < 0.01) of dissolved oxygen. Ponds of the duty-till with gypsum treatment also had lower concentrations (P < 0.01) of chlorophyll $\alpha$, chemical oxygen demand, and total alkalinity than the control. Total fish production and survival rate did not differ (P > 0.05) among the treatments. These findings suggest that drying and tilling pond bosoms between crops and treating low hardness waters with gypsum could achieve water Quality improvement.