Chinese Longsnout Catfish Research Articles

Effects of mixed starter cultures and exogenous L-Lys on the physiochemical and sensory properties of rapid-fermented fish paste using longsnout catfish by-products

Fermentation is a good way to utilize fish by-products. In this study, the effects of mixed starter cultures and exogenous L-Lys on the physiochemical and sensory properties of fermented longsnout catfish minced meat were investigated. Fish pastes were divided into three groups, including a treated group (sample A), a mixed starter culture-treated group (sample B), and a L-Lys and mixed starter culture-treated group (sample C). The pH and total volatile base nitrogen in the sample C were the lowest among the tested samples. At the final stage of fermentation, the total acidity, amino acid nitrogen content, and free amino acid content in the sample C were the highest among the tested samples. No significant differences in the histamine content or antioxidant activities were observed among the three samples (p < 0.05). An electronic nose test showed that the odors of the samples B and C were similar, but different from those of the sample A. The sample C exhibited a strong umami and fermented flavor and had the best flavor. All the results demonstrated that the mixed starter cultures and L-Lys can improve the flavor and nutritive value of the fish pastes made with Chinese longsnout catfish by-products by fermentation.

Development of SNP markers in Leiocassis longirostris Günther using high-throughput sequencing

The Chinese longsnout catfish (Leiocassis longirostris Gunther) is a semi-migratory freshwater species. Leiocassis longirostris is mainly inhabiting the main stream of the Yangtze River and rarely found in lakes due to over fishing, environmental pollution and other human disturbances. Novel single nucleotide polymorphisms (SNPs) were screened based on high-throughput sequencing in Leiocassis longirostris. In this study, 40 SNP markers were developed successfully with 30 individuals from the Yangtze River segment of Nanjing, China. The observed heterozygosity (Ho) ranged from 0.0003 to 1.0000, while the expected heterozygosity (He) varied from 0.3367 to 0.9390. The minor allele frequency ranged from 0.0167 to 0.2500. Thirty-four SNPs have been confirmed to fit Hardy–Weinberg equilibrium after Bonferroni correction (P < 0.0013). The first set of SNP makers developed from Leiocassis longirostris will provide valuable informating in population genetics and resource conservation.

Effect of Dietary Lipid Sources on Body Fatty Acid Composition of Chinese Longsnout Catfish Leiocassis longirostris

Abstract We investigated the effects of dietary lipid sources on growth and fatty acid composition of juvenile Chinese longsnout catfish. Triplicate groups of fish (initial average weight, 3.8 g) were fed four diets containing either fish oil (FO), soybean oil (SO), linseed oil (LO) and lauric acid (LA) for 10 weeks. There were no differences among the groups in body weight, feed intake, feed effi-ciency, protein efficiency ratio, and body proximate composition of fish fed the diets containing different lipid sources ( P > 0.05) during the study. However, fatty acids compositions of the whole body were influenced by dietary lipid source. Fish fed the SO diet had high concentration of linoleic acid, whereas those of fish fed the LO diet were rich in linolenic acid and arachidonic acid. Fish fed the FO diet had significantly ( P < 0.05) higher levels of monounsaturated fatty acids such as 18:1n-9 and 20:1n-9 than those of fish fed the SO and LO diets. Eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) composition of body were not influenced by dietary lipid source. The results suggest that each of FO, SO, LO or LA can be used as a lipid source in the diets of Chinese longsnout catfish without any negative effects on growth and feed utilization and these data demonstrate the potential impact which dietary fat composition can change the body fatty acid profile.

Cloning and structure of a histocompatibility class IIA gene (Lelo-DAA) in Chinese longsnout catfish (Leiocassis longirostris)

Here, the major histocompatibility complex (MHC) class II alpha chain gene in the Chinese longsnout catfish (Leiocassis longirostris) was characterized through cloning, sequencing, polymorphism analysis, and expression patterns in various tissues. The full-length LeloDAA cDNA comprises 1,114 bp with a 5′-UTR region of 79 bp, an open reading frame of 714 bp and a 3′-UTR of 302 bp. The deduced protein sequence shows the following important features: leader peptide, α1, α2, and CP/TM/CYT regions. Using long PCR techniques, the genomic sequence was further identified to be 2,093 bp in length, containing four exons and three introns. Three class IIA alleles were identified from four individuals. Two different alleles observed (at most) in each individual suggest the existence of a single locus of class IIA gene in the Chinese longsnout catfish genome. This locus is polymorphic and most of the amino acidic changes occurred in the α1 domain containing the peptide-binding region. Lelo-DAA mRNA expression was mainly found in the intestine, gills, spleen, head kidney and liver; minor expression was detected in the stomach, skin, heart and muscle. Our results yield insight into Chinese longsnout catfish T cell immune responses and will aid future work on the genetic status of this economically important species.

Histological Observations and Regeneration of Barbels in Juveniles of the Chinese Longsnout Catfish Leiocassis longirostris

Barbel structure and regenerated barbel length in the juvenile Chinese longsnout catfish Leiocassis longirostris (G<TEX>$\ddot{u}$</TEX>nther), were evaluated. The barbles consisted of an epidermis, a dermis, and a central rod. The epidermis harbored taste buds, granular cells and epidermal cells. The taste buds were basophilic and situated along the distal portion of the epidermis. The dermis was composed of loose connective tissue containing blood vessels pigment cells. The innermost central region was cartilage enclosed within layers of muscle layers. After 30 days, the regenerated barbel length measured <TEX>$0.92{\pm}0.404mm$</TEX> at <TEX>$15^{\circ}C$</TEX> (regenerated growth curve: y = 0.5085x + 4.0678, <TEX>$r^2$</TEX> = 0.9654, where y is regenerated length and x is experimental period in days), <TEX>$1.88{\pm}0.521mm$</TEX> at <TEX>$20^{\circ}C$</TEX> (y = 0.1806x + 4.808, <TEX>$r^2$</TEX> = 0.9822), and <TEX>$6.44{\pm}0.751mm$</TEX> at <TEX>$25^{\circ}C$</TEX> (y = 0.0914x + 4.9918, <TEX>$r^2$</TEX> = 0.9944). Fifteen days after amputation, the regenerated length was significantly longer at <TEX>$25^{\circ}C$</TEX> than at 15 or <TEX>$20^{\circ}C$</TEX> (P < 0.05). The barbels of the Chinese longsnout catfish was the tender and flexible type, and our experimental findings provide evidence of temperature-dependent regeneration. Additional investigation of the behavior and physiology of the Chinese longsnout catfish is needed, particularly histological studies of regenerated barbels and the measurements of the numbers of taste buds per barbel under various environmental conditions.

Genetic variation of the Chinese longsnout catfish Leiocassis longirostris in the Yangtze River revealed using mitochondrial DNA cytochrome b sequences

The mitochondrial DNA cytochrome b of 132 Leiocassis longirostris collected from 12 localities in the upper to lower reaches of the Yangtze River were amplified and partially sequenced using the PCR technique. The results showed that 27 nucleotide sites were variable along 817bp length of homologous sequence (3.3%), base substitutions happened mostly at the third codon position. A total of 22 haplotypes were identified, which were characterized with moderate haplotype diversity (h=0.5417±0.0519), but low nucleotide diversity (π=0.0019±0.0012). Median-joining network analysis revealed star-shaped patterns with one common central haplotype (H3), whereas mismatch distribution analysis found that the Chinese longsnout catfish fitted a smooth unimodal distribution, which suggested that this species underwent population expansion following bottlenecks and/or they originated from a small number of founding individuals. The time that the total population of Chinese longsnout catfish in the Yangtze River expanded was estimated 169,000–337,000years before present. The analysis of molecular variance (AMOVA) and phylogenetic reconstructions did not detect significant geographic structure between different river sections, especially between above and below the Gezhouba Dam and the Three Gorges Dam, which suggested that these recently developed dams might have not significantly resulted in population genetic differentiation in the Chinese longsnout catfish.

Effects of different weaning strategies on survival and growth in Chinese longsnout catfish (Leiocassis longirostris Günther) larvae

The effects of different weaning strategies during the larval rearing of Chinese longsnout catfish were determined in two trials. In the first trial, the effect of abrupt-weaning from live prey (Artemia nauplii) to microdiet at 5, 6, 7, 8, 10dph, respectively was investigated. The second trial examined the effect of weaning with co-feeding at different ages (6, 8 and 10dph).The survival, growth, digestive enzymes, coefficient of variation of final body weight (CVFBW) and body length (CVBL), digestive enzyme activities, fish body lysozyme and fish body glucose were significantly influenced by abrupt-introducing of microdiet (P<0.05). When weaning with live prey, only the fish body lysozyme significantly increased in the group introduced to microdiet on 8 and 10dph (P<0.05).The study showed that abrupt-weaning of Chinese longsnout catfish should be obtained after 10dph. Co-feeding could reduce the stress to larvae and therefore the weaning could start at 6dph with co-feeding.

Characterization of pathogenic Aeromonas veronii bv. veronii associated with ulcerative syndrome from Chinese longsnout catfish (Leiocassis longirostris Günther)

273 bacterial strains were isolated from 20 Chinese longsnout catfish samples. The biochemical characteristics of all strains conformed to the species description of Aeromonas veronii bv. veronii on the basis of Vitek GNI+ card. Furthermore, 16S rDNA, gyrB and rpoD sequences of the representative strain PY50 were sequenced and showed high similarity with A. veronii bv. veronii in Genbank. Antibiotic-resistance of the representative strain PY50 was assessed by the Kirby-Bauer disk diffusion method, and the results showed it was susceptible and moderately susceptible to 13 and 4 of the 21 antimicrobial agents tested. Extracellular products of strain PY50 contained gelatinase, lecithinase, elastase, most of lipase and lipopolysaccharide. Virulence of strain PY50 and extracellular products to Chinese longsnout catfish were also tested, and LD50 were about 3.47×10(4) CFU per fish and 11.22 μg per fish in intraperitoneal injection respectively. This is the first report that A. veronii bv. veronii was the pathogenic agent of ulcerative syndrome in Chinese longsnout catfish.

Characterization of pathogenic Aeromonas veronii bv. veronii associated with ulcerative syndrome from chinese longsnout catfish (Leiocassis longirostris Günther).

273 bacterial strains were isolated from 20 Chinese longsnout catfish samples. The biochemical characteristics of all strains conformed to the species description of Aeromonas veronii bv. veronii on the basis of Vitek GNI+ card. Furthermore, 16S rDNA, gyrB and rpoD sequences of the representative strain PY50 were sequenced and showed high similarity with A. veronii bv. veronii in Genbank. Antibiotic-resistance of the representative strain PY50 was assessed by the Kirby-Bauer disk diffusion method, and the results showed it was susceptible and moderately susceptible to 13 and 4 of the 21 antimicrobial agents tested. Extracellular products of strain PY50 contained gelatinase, lecithinase, elastase, most of lipase and lipopolysaccharide. Virulence of strain PY50 and extracellular products to Chinese longsnout catfish were also tested, and LD50 were about 3.47×104 CFU per fish and 11.22 μg per fish in intraperitoneal injection respectively. This is the first report that A. veronii bv. veronii was the pathogenic agent of ulcerative syndrome in Chinese longsnout catfish.

Genetic variation at mtDNA and microsatellite loci in Chinese longsnout catfish (Leiocassis longirostris)

Genetic variability and population structure of the Chinese longsnout catfish Leiocassis longirostris Günther in the Yangtze River was examined with mitochondrial control region sequences and nuclear microsatellite markers. A 705-bp segment of the mitochondrial DNA control region was sequenced from 132 samples, which identified a total of 61 haplotypes. The Chinese longsnout catfish in the Yangtze River was characterized with high haplotype diversity (h=0.9770±0.0041) but low nucleotide diversity (π=0.0081±0.0043). Median-joining network analysis revealed a star-shaped pattern and mismatch distribution analysis found a smooth unimodal distribution, which suggested that this species in the Yangtze River underwent a population expansion following bottlenecks and/or they originated from a small size of founding population. It was estimated that the possible time of population expansion was 139,000-435,000years before present, a time period in the middle Pleistocene. The analysis of molecular variance and phylogenetic reconstructions did not detect significant geographic structure between different river sections. This pattern of genetic variation was further evidenced with nuclear microsatellite markers. The genetic differentiation between above and below the Gezhouba Dam and Three Gorges Dam is very small at mitochondrial and nuclear levels, which suggested that these recently developed dams might have not significantly resulted in population genetic fragmentation in the Chinese longsnout catfish. However, the potential exacerbation of genetic structuring by the dams should not be overlooked in the future.

Physiological responses of Chinese longsnout catfish to water temperature

We evaluated the effect of water temperature on the growth and physiology of the Chinese longsnout catfish (Leiocassis longirostris Gunther). The fish were reared at four temperatures (20, 25, 30, and 35°C) and sampled on days 7, 20, and 30. We measured plasma levels of insulin, free thyroxine (FT4), free 3,5,3′-triiodothyronine (FT3), lysozyme and leukocyte phagocytic activity. The optimum water temperature for growth was 27.7°C. The plasma levels of insulin and FT4 declined significantly (P<0.05) on day 30 at temperatures above 20°C. Lysozyme activity was significantly (P<0.05) lower at 25°C than at other temperatures. We conclude that final weight, insulin, FT4, and lysozyme were significantly affected by water temperature.

Effects of dietary oxidized fish oil on growth performance and skin colour of Chinese longsnout catfish (Leiocassis longirostris Günther)

A 61-day experiment was carried out to investigate the effect of dietary oxidized fish oil on growth performance and skin colour of Chinese longsnout catfish (Leiocassis longirostris Günther). Seven diets (Diet 1–7) containing different levels of oxidized fish oil (0, 10, 20, 30, 40, 50 and 60 g kg−1 dry diet) were evaluated at same dietary lipid level (60 g kg−1 diet). Fish skin colour (CIE L*a*b*) and melanin content was measured at three zones of fish body: back (Zone I), belly (Zone II) and tail (Zone III). The results showed that there were no significant differences in growth or feed utilization. Apparent digestibility coefficient of energy (ADCe) decreased while those of dry matter (ADCd), protein (ADCp) or lipid (ADCl) were not affected. Lightness (L*) of Zone I or II were not influenced while L* of Zone III decreased. Oxidized oil increased melanin content of Zone III. No apparent effects on the thiobarbituric acid reactive substances (TBARS) values of blood serum, liver and muscle were observed. In conclusion, dietary oil oxidation did not affect fish growth performance. Fish tail skin lightness was lower in the fish fed with high dietary oxidized fish oil and was positively correlated to melanin content.

Molecular cloning, expression pattern, and 3D structural analysis of the MHC class IIB gene in the Chinese longsnout catfish ( Leiocassis longirostris)

Major histocompatibility complex (MHC) class I and class II molecules encode glycoproteins which mediate the specificity of the vertebrate adaptive immune response. In this study, MHC class IIB gene from the Chinese longsnout catfish ( Leiocassis longirostris) was cloned and sequenced, which encoded a predicted protein of 248 amino acids (28.06 kDa) containing a signal peptide, a beta 1 domain, a beta 2 domain, a connecting peptide, a transmembrane region, and a cytoplasmic tail. Using PCR with primers designed from known fish MHC class IIB sequences followed by elongation of the 5′ and 3′ ends using rapid amplification of cDNA ends (RACE), the full-length cDNA of longsnout catfish MHC class IIB was identified to be 1293 bp, consisting of a 26 bp 5′-terminal untranslated region (UTR), a 520 bp 3′-UTR, and a 747 bp open reading frame (ORF) bearing characteristics of the immunoglobulin C-type 1 (IGc1) family. The deduced amino acid sequences of the Chinese longsnout catfish MHC class IIB gene had 58–75% identity with those of other fishes. Six class IIB alleles were identified from five individuals. At most two different alleles observed in each individual may infer the existence of a single locus of class IIB gene in the Chinese longsnout catfish genome. An extensive study of polymorphism was examined in 60 individuals. A total of 11 haplotypes of exon 2 were detected in the sampled Chinese longsnout catfish. The rates of nonsynonymous substitutions ( d N) occurred at a higher frequency than that of synonymous substitutions ( d S), suggesting the polymorphism of exon 2 seemed to be maintained by the balancing selection. By using long PCR technique, the genomic sequence was further identified to be 2345 bp in length, which contained six exons and five introns. Interestingly, a 98 bp intron 5 cut the 3′-UTR into two parts. Real-time quantitative RT-PCR demonstrated high expression of MHC IIB in gills, spleen, head kidney, and intestine, moderate expression in liver and stomach, and low or negligible expression in heart. Homology modelling has been applied to create a 3D model of longsnout catfish MHC class IIB, with features evaluated and discussed to investigate its interaction with CD4 participating in antigen recognition. The present findings will provide valuable information for understanding structure, function, expression, and molecular polymorphism of MHC class IIB in adaptive immunity of the Chinese longsnout catfish and teleost.

The complete mitochondrial genome of the Chinese longsnout catfish Leiocassis longirostris (Siluriformes: Bagridae) and a time-calibrated phylogeny of ostariophysan fishes

The complete mitogenome sequence of the Chinese longsnout catfish Leiocassis longirostris was determined using long-polymerase chain reaction (long-PCR) and directly sequenced with primer walking method. The complete mtDNA was 16,534 bp in length and contained 13 protein-coding genes, two rRNA genes, 22 tRNA genes, and a control region (D-loop), the gene composition/order of which was identical to that observed in most other vertebrates. Phylogenetic relationship of 15 ostariophysan fishes was reconstructed using Bayesian inference and maximum likelihood methods based on a total of 15,658 nucleotides from all the 13 protein-coding, two rRNA, and 22 tRNA genes, using recently developed models of rate autocorrelation, which resolved the phylogenetic relationship of the major ostariophysan lineages with a high statistical support. The present result was consistent with some previous molecular cladistic work which supported the grouping of (((((Characiformes, Gymnotiformes), Siluriformes), Cypriniformes), Gonorynchiformes), outgroup). The Chinese longsnout catfish together with the Bagrid catfish (both from the same family Bagridae) had a closer affinity with Amblycipitidae than with other four analyzed catfish families. The relaxed molecular clock method incorporated into the program BEAST vl.5.3 was used to estimate divergence dates among ostariophysan lineages, which revealed that the major ostariophysan lineages diversified in the middle Jurassic (around 164.5 million years ago (Mya)) and the split of Leiocassis/Pseudobagrus occurred in the Oligocene to Miocene (8.9-25.1 Mya). The time-calibrated tree generated in this study would provide a powerful evolutionary tool for broad-scale comparative studies of the catfishes and the ostariophysan fishes.

EFFECTS OF DIFFERENT DIETARY VITAMIN C LEVELS ON CHINESE LONGSNOUT CATFISH (&lt;I&gt;LEIOCASSIS LONGIROSTRIS GUNTHER&lt;/I&gt;)

Vitamin C is ail essential micro-nutrient for most fish and plays an important role in immunity and physiology. The deficiency of dietary vitamin C can result in the damage on fish. The study on the deficiency symptom and the sensitive indicator of vitamin C could provide useful information for fish feed industry. This experiment was conducted to investigate the effects of dietary Vitamin C levels oil growth performance, immune and physiological responses in Chinese long-snout catfish (Leiocassis longirostris Gunther), which is ail high value aquaculture fish in China. Three practical diets containing 38, 364 and 630mg/kg vitamin C were fed to Chinese longsnout catfish (23.19 +/- 0.58g) for 8 months. Vitamin C was used in the form of L-ascorbyl-2-polyphosphate. The results indicated that the Chinese longsnout catfish in 38mg/kg vitamin C groups showed typical vitamin C deficiency symptom : skin color turning darker, spinal deformities and scoliosis, erosion of fins, anaemia. SGR and the serum lysozyme activities decreased significantly (p 0.05). The inductive HSP70 in liver was not detected by western-blotting in all groups. In conclusion, serum cortisol and hepatic HSP70 were not the sensitive indicators for vitamin C deficiency symptom, but the serum lysozyme, hepatic SOD activity, hepatic MDA content and the haematological index ( red blood cell number and hemoglobin content) were the more reliable makers to indicate the physiological status in Chinese longsnout catfish.

Effect of water temperature on the growth performance and digestive enzyme activities of Chinese longsnout catfish (Leiocassis longirostrisGünther)

The present study was carried out to investigate the influence of water temperature on the growth performance and digestive enzyme (pepsin, trypsin and lipase) activities of Chinese longsnout catfish. Triplicate groups of Chinese longsnout catfish (35.6±0.48 g, mean±SE) were reared at different water temperatures (20, 24, 28 and 32 °C). The feeding rate (FR), specific growth rate (SGR) and feed efficiency ratio (FER) were significantly affected by water temperatures and regression relationships between water temperature and FI, SGR as well as FER were expressed as FR=−0.016T2+0.91T−10.88 (n=12, R2=0.8752), SGR=−0.026T2+1.39T−17.29 (n=12, R2=0.7599) and FER=−0.013T2+0.70T−8.43 (n=12, R2=0.7272). Based on these, the optimum temperatures for FR, SGR and FER were 27.66, 26.69 and 26.44 °C respectively. The specific activities of digestive enzymes at 24 or 28 °C were significantly higher than that at 20 or 32 °C. In addition, there was a significant linear regression between FR or SGR and specific activities of pepsin and lipase, which indicated that pepsin and lipase played important roles in regulating growth through nutrient digestion in Chinese longsnout catfish.

Isolation and characterization of 17 microsatellite loci for the Chinese longsnout catfish (Leiocassis longirostris)

We describe the isolation and development of 17 polymorphic dinucleotide microsatellite loci for the Chinese longsnout catfish (Leiocassis longirostris). All loci were polymorphic in the 30 individuals tested. The number of alleles per variable locus ranged from 6 to 18, with a mean of 11.71. Observed and expected heterozygosities ranged from 0.467 to 1.000 and from 0.540 to 0.929, respectively. Eight loci were found to have deviated from HWE in the sampled population after Bonferroni correction. Linkage disequilibrium tests revealed significant linkage between two loci (LLW5 and LL27). These microsatellite loci will be useful for revealing population structure, genetic diversity, and phylogeography of the Chinese longsnout catfish.

Effects of dietary ascorbic acid supplementation on the growth performance, immune and stress response in juvenileLeiocassis longirostrisGnther exposed to ammonia

This experiment was designed to investigate the effect of dietary supplemental ascorbic acid (AA) on the feed intake, growth, serum lysozyme, hepatic superoxide dismutase (SOD) and handling stress response in Chinese longsnout catfish (Leiocassis longirostris Günther) exposed to three levels of unionized ammonia nitrogen (UIA-N). Juvenile Chinese longsnout catfish were reared in 54 fibreglass tanks with a 3 × 3 factorial design treatment consisting of three supplemental AA levels in ascorbyl 2-monophosphate (38, 364 and 630 mg AA equivalent kg−1 diet) and three UIA-N concentrations [0.004 (the control), 0.037 and 0.292 mg L−1]. The fish were sampled on the 11th, 32nd and 60th day. On the 62nd day, the remaining fish were subjected to an acute stress by being held in a dipnet out of water for 60 s, and sampled at 30 min post handling. The results showed that the specific growth rate (SGR) in 32 days significantly decreased with increased water UIA-N (P=0.0476) but was not affected by dietary supplemental AA (P>0.05). After 60 days, SGR, feeding rate (FR) and feed conversion efficiency (FCE) significantly increased with increased dietary supplemental AA (P<0.001) while remaining unaffected by water UIA-N (P>0.05). There was no significant interaction between dietary AA and UIA-N for growth responses (P>0.05). The serum lysozyme activity on the 11th day and the hepatic SOD activity on the 32nd day were significantly affected at high (0.292 mg L−1) water UIA-N. On the 62nd day, the increase in cortisol resulting from acute stress significantly decreased by higher UIA-N (P=0.038). It is suggested that Chinese longsnout catfish displayed an adaptive response after long-term UIA-N exposure, and AA had beneficial effects on the growth and feed intake of catfish and alleviated the negative effects of chronic ammonia stress. A chronically higher ammonia level shows a tendency to inhibit the cortisol response to another acute stressor.

Effect of dietary carbohydrate-to-lipid ratios on growth and feed utilization in Chinese longsnout catfish (Leiocassis longirostrisGünther)

An 8-week growth trial was carried out in a semi-recirculation system at 26 +/- 0.5 degrees C to investigate the optimal dietary carbohydrate-to-lipid (CHO:L) ratio for carnivorous Chinese longsnout catfish (Leiocassis longirostris Gunther). Triplicate tanks of fish were assigned to each of five isocaloric and isonitrogenous diets with different carbohydrate-to-lipid ratios (0.75, 1.48, 1.98, 2.99 and 5.07). The results showed that a higher specific growth rate (SGR) and feed rate (FR) were observed in the fish fed diet ratios of 1.98 CHO:L (P 0.05). High dietary CHO:L ratio caused pathological changes in fish morphology and liver histology. Based on maximum growth, the optimal carbohydrate-to-lipid ratio was 1.98 for Chinese longsnout catfish.

Genetic Structure and Low-genetic Diversity Suggesting the Necessity for Conservation of the Chinese Longsnout Catfish, Leiocassis longirostris (Pisces: Bagriidae)

Genetic variation and phylogenetic relationship of Leiocassis longirostris populations from the Yangtze River were investigated at mitochondrial DNA level. The samples were collected from the upstream and mid-downstream of the Yangtze River. Three mitochondrial DNA fragments, ND5/6, cytochrome b (Cyt b) and control region (D-loop), were amplified and then digested by 10 restriction endonucleases. Twenty-three D-loop fragments randomly selected were sequenced. Digestion patterns of ND5/6 by AluI and HaeIII, D-loop by HinfI and RsaI, and Cyt b by HaeIII were polymorphic. Ten and eighteen haplotypes were obtained from RFLP data and sequence data, respectively. The individuals from upstream and mid-downstream of the Yangtze River were apparently divided into two groups. The average genetic distance was 0.008 and 0.010 according to the two data. Low diversities and decreasing abundance indicated that Leiocassis longirostris may be in severe danger and reasonable measures of fishery management should be taken.