Comparative analysis on microbial community associated with different gastrointestinal regions of wild northern snakehead Channa argus Cantor, 1842

Microbial communities in different gastrointestinal regions （stomach, foregut, midgut, and hindgut） of the northern snakehead Channa argus （Cantor, 1842） were compared by polymerase chain reaction and partial 16S rDNA sequencing. A total of 194, 140, 212, and 122 OTUs were detected in the stomach, foregut, midgut, and hindgut, respectively. Significant differences were found in the Sobs, ACE, Shannon, and Simpson indices among samples （P〈0.05）. The gastrointestinal microbial community of C. argus consisted predominantly of Proteobacteria with either Halomonas, Shewanella, Plesiomonas, or Sphingomonas. Fusobacteria, Firm!cutes, and Bacteroidetes also existed in the gastrointestinal tracts. However, significant＇differences were found in the compositions of microbial community among the four regions （P〈0.05）. Cyanobacteria and Spirochetes were significantly higher in the midgut and hindgut （P〈0.05）. Fusobacteria and Firmicutes were dominant in the hindgut and foregut, respectively （P〈0.05）. Proteobacteria was the lowest in the hindgut （P〈0.05）. At genus level, Cetobacterium and Plesiomonas were significantly higher in the hindgut than in the other three samples （P〈0.05）. Clostridium and Prevotella were the highest in the midgut （P〈0.05）. Halomonas, Shewanella, and Sphingomonas were the highest in the foregut （P〈0.05）. Paracoccus and Vibrio were the highest in the stomach. Several genera were only detected in certain regions, as follows： stomach, Paracoccus and Hbrio; foregut, Halomonas, Shewanella, and Sphingomonas; midgut, Clostridium and Prevotella; and hindgut, Cetobacterium and Plesiomonas （P〈0.05）. At the species level, Acinetobacter rhizosphaerae was only detected in the stomach. Prevotella copri and Clostridium perfring were not detected in the foregut and midgut, respectively, whereas Prevotella copri and Faecalibacterium pra were not detected in the hindgut. These findings provide valuable information on the microbial community in each gastrointestinal region of C. argus. Moreover, this study indicated that microbial community was not only related to rearing environment but also to the physico-chemical characteristics of each gastrointestinal region.

How big can a walking fish be?A theoretical inference based on observations on four land-dwelling fish genera of South Vietnam

Comparative study of terrestrial locomotion of 4fish genera including Anabas,Channa,Clarias,and Monopterus,was performed in experimental setting with the substrate surface of wet clay.No special adaptations for terrestrial locomotion were found.Everyfish uses for propulsion on land what it already has.Eel-shaped Monopterus crawls by body undulations in a serpentine or sidewinding technique,the latter of which was not previously observed beyond snakes.The other 3fish genera walk by body oscillations using stiff appendages as propulsors.When they are located anteriorly,as the serrate operculum in Anabas and the preaxial spine of the pectoralfin in Clarias,the propulsion is termed prolocomotor,when posteriorly,as the spiny analfin in Channa—metalocomotor.Channa is the heaviestfish walking out of water in our days,quite comparable in size withfirst Devonian tetrapods Acan-thostega and Tulerpeton.A theoretical calculation is suggested for the upper size limit of afish capable of terrestrial walking without special locomotor adaptations.It should be roughly 20 cm in the vertical dimension of the trunk,which is just a little above the known size of Devonian tetrapodomorphfishes Panderichthys and Elpistostege.The metalocomotor walking technique of Channa is suggested as the closest extant model for terrestrial locomotion at thefish-tetrapod transition.The major difference is that the metalocomotor propulsor in Channa is represented by the analfin,while in tetrapodomorphs by the pelvicfins.The sprawled pelvicfins were advantageous in respect of reduced requirement for side-to-side tail swinging.

Assessment of genetic diversity, detection of strain-specific single nucleotide polymorphisms and identification of the Bangladesh and Vietnam strain of Channa striata by PCR-RFLP analysis of the mitochondrial COI gene fragment

Striped snakehead(Channa striata)has enormous fisheries and aquaculture importance due to its high market demand and food value.Recently,Vietnam strain of the species has been introduced to Bangladesh for aquaculture.Therefore,it is essential to develop a reliable molecular technique that can distinguish the Bangladesh strain from the Vietnam ones as biological invasion by feral exotic fish to the wild may cause enduring damage to ecosystem and species diversity.Fin clips from snakehead samples were collected from six locations and total DNA was extracted.The cytochrome oxidase c 1(COI)gene fragment was amplified by PCR using the Fish F1/R1 primer set and sequenced for analysis of intra-and inter-strain genetic diversity and detection of single nucleotide polymorphism to distinguish the Vietnam strain from Bangladesh ones.A total of 15 haplotypes were identified with an overall haplotype diversity of 0.888.The median-joining network created based on COI gene sequences clearly differentiated the Bangladesh strain from the strain of Vietnamese origin by a total of 18 single nucleotide polymorphisms.An In silico restriction analysis revealed AluI was the most suitable restriction enzyme that produced diagnostic restriction profiles of the two strains of C.striata.PCR-RFLP analysis by the restriction enzyme AluI created distinguishing restriction profile similar to that in the In silico analysis.This work illustrates a simple,reliable and inexpensive molecular tool for the identification of the Bangladesh and Vietnam strains of C.striata by one-step PCR and restriction of the COI gene fragment.