A First Insight into the Gonad Transcriptome of Hong Kong Catfish (Clarias fuscus)

Hong Kong catfish (Clarias fuscus) exhibit sexual dimorphism, particularly in body size. Due to the fast growth rate of males, the sexual size dimorphism of Hong Kong catfish has become an economically important trait. However, limited knowledge is known about the molecular mechanisms of sex determination and sex differentiation in this species. In this study, a first de novo transcriptome sequencing analysis of testes and ovaries was performed to identify sex-biased genes in Hong Kong catfish. The results showed that a total of 290,291 circular consensus sequences (CCSs) were obtained, from which 248,408 full-length non-chimeric (FLNC) reads were generated. After non-redundant analysis, a total of 37,305 unigenes were predicted, in which 34,342 unigenes were annotated with multiple public databases. Comparative transcriptomic analysis identified 5750 testis-biased differentially expressed genes (DEGs) and 6991 ovary-biased DEGs. The enrichment analysis showed that DEGs were classified into 783 Gene Ontology (GO) terms and 16 Kyoto Encyclopedia of Gene and Genome (KEGG) pathways. Many DEGs were involved with sex-related GO terms and KEGG pathways, such as oocyte maturation, androgen secretion, gonadal development and steroid biosynthesis pathways. In addition, the expression levels of 23 unigenes were confirmed to validate the transcriptomic data by quantitative real-time polymerase chain reaction (qRT-PCR). This is the first investigation into the transcriptome of Hong Kong catfish testes and ovaries. This study provides an important molecular basis for the sex determination and sex control breeding of Hong Kong catfish.

The mating ritual and patterns of monopolar electrical pulses in Hong Kong catfish Clarias fuscus (Clariidae, Siluriformes)

Laboratory experiments were performed to compare the electrical activity and behavior in Clarias fuscus during spawning. Each of the multiple matings of the male and female was preceded by an amplexus - a mutual pose in which the male tightly covers the females head and remains in close contact with it until the end of mating. The spawning behavior of C. fuscus was accompanied by monopolar electrical pulses (MP) of two types: single MPs, similar to those observed in other behavioral situations (aggression, hunting) and specific MPs, observed only during spawning bursts of serial MPs (burst MPs), at intervals which are comparable with their duration. Each recorded burst MPs (71) corresponded to one mating, and each recorded single MP (63) corresponded to an attack of one fish on another. In different behavioral situations (matings and attacks), MPs differ significantly in amplitude and duration; and for MPs in bursts, in their degree of asymmetry. It can be assumed that the involvement of MPs in the spawning behavior of C. fuscus is similar to that studied earlier in Clarias macrocephalus, and is a common feature for Clariidae.

Effects of Fish-Derived Biological Preservatives on Cold Storage of Grass Carp (Ctenopharyngodon idellus) Fillets

ABSTRACT Two kinds of fish-derived natural antimicrobial substances, protamine and catfish (Clarias fuscus) epidermal mucus extract (CEME), were evaluated for their effect on the quality of grass carp fillets. Fillets were atmosphere packaged in cast polypropylene bags and were stored at 4°C in a low-temperature incubator without light. Solutions (0.5%, wt/vol) of CEME and protamine were used for dip pretreatment, respectively. Bacteriological (aerobic plate count, Shewanella putrefaciens, Pseudomonas fluorescens) and physicochemical (pH, total volatile basic nitrogen, K value, surface color, texture profiles, water distribution) parameters and volatile odor compounds were measured on days 0, 3, 6, 9, 12, and 15. The results indicated that CEME and protamine could improve all bacteriological and physicochemical indexes, except water distribution within muscle. In comparison, CEME had a more inhibitory effect, as determined by the aerobic plate count, and was more effective in inhibiting the growth of P. fluorescens; however, protamine was more effective in preventing the production of sulfur-organic (H2S) group substances. Protamine was more effective in inhibiting the growth of S. putrefaciens. This research suggests that protamine and CEME have the potential to improve the quality and extend the shelf life of grass carp fillets.

Seasonal population dynamics of the monogeneans Quadriacanthus kobinensis parasitising Clarias fuscus in Pearl River, China

SummaryThis paper describes the population dynamics of Quadriacanthus kobinensis on the gills of Clarias fuscus following a field investigation from June 2012 to May 2013 in Pearl River, China. The results showed that in Q. kobinensis prevalence was highest (70.13 %) in the summer and Mean intensity reached a peak in the autumn. The maximum number of Q. kobinensis in a fish was 474. The maximum abundance occurred during summer (25.8) and the minimum values during spring. Q. Kobinensis exhibited an aggregated distribution in all seasons. The highest prevalence was in hosts of 28 cm<L and the infection intensity was also the highest in this group. In terms of infection intensity, host of 28 cm<L differed significantly from those of 24<L≤26 cm, but no significant differences existed in other body length groups.