Morphometric and meristic variation in two congeneric archer fishes Toxotes chatareus (Hamilton 1822) and Toxotes jaculatrix (Pallas 1767) inhabiting Malaysian coastal waters

A simple yet useful criterion based on external markings and/or number of dorsal spines is currently used to differentiate two congeneric archer fish species Toxotes chatareus and Toxotes jaculatrix.Here we investigate other morphometric and meristic characters that can also be used to differentiate these two species.Principal component and/or discriminant functions revealed that meristic characters were highly correlated with pectoral fin ray count,number of lateral line scales,as well as number of anal fin rays.The results indicate that T.chatareus can be distinguished from T.jaculatrix by having a greater number of lateral line scales,a lower number of pectoral fin rays,and a higher number of anal fin rays.In contrast,morphometric discriminant analyses gave relatively low distinction:76.1% of fish were ascribed to the correct species cluster.The observed morphometric differences came from the dorsal and anal spines lengths,with T.chatareus having shorter dorsal and longer anal spines than T.jaculatrix.Overall,meristic traits were more useful than morphometrics in differentiating the two species;nevertheless,meristics and morphometrics together provide information about the morphological differentiation between these two closely related archer fishes.

Intensity of parasitic infestation in silver carp,Hypophthalmichthys molitrix

Silver carp,Hypopthalmichthys molitrix is one of the most economically valuable fish species in Bangladesh.However,its production is often hindered by parasite-induced mortality.The present study reports the intensity of parasitic infestation in 216 specimens of H.molitrix collected from different fish markets in Rajshahi City,Bangladesh.Nine different parasite species (Trichodina pediculatus,Dactylogyrus vastator,Ichthyophthirius multifilis,Gyrodactylus elegans,Lernaea sp.,Apiosoma sp.,Myxobolus rohitae,Camallanus ophiocephali,and Pallisentis ophiocephali) were recovered from the gill,skin,stomach,and intestine of host fish.The highest level of infection was observed for host skin,while lower levels were observed for host gill,stomach,and intestine.The results also revealed that the intensity of parasite infection in different organs of H.molitrix varied with the season.In particular,the highest levels of infection were recorded during the winter period (November-February),when fish are most susceptible to parasites.The findings of the study will help in the management and conservation of H.molitrix.

Immunocytochemical localization of carbonic anhydrase in the pseudobranch tissue of the rainbow trout Oncorhynchus mykiss

Pseudobranch function has long interested scientists, but its role has yet to be elucidated. Several studies have suggested that pseudobranchs serve respiratory, osmoregulatory, and sensory functions. This work investigated the immunolocalization of pseudobranch carbonic anhydrase （CA） in the teleost fish species rainbow trout （Oncor- hynchus mykiss） to clarify its physiological function. CA was purified from rainbow trout gills O. mykiss and specific antibodies were raised. Immunoblotting between tissue homogenates of pseudobrench and gill CA antibodies showed specific immunostaining with only one band corresponding to CA in the pseudobranch homogenate. Results of im- munohistochemical technique revealed that CA was distributed within pseudobranch cells and more precisely in the apical parts （anti-vascular） of cells. The basal （vascular） parts of cells, tubular system, blood capillaries, and pillar cells were not immunostained. Immunocytochemistry confirmed these results and showed that some CA enzyme was cytoplasmic and the remainder was linked to membranous structures. The results also showed that the lacunar tissue tayers did not display immunoperoxidase activity. Our results indicated that pseudobranch CA may have a function related to the extracellular medium wherein CA intervenes with the mechanism of stimulation of afferent nerve fibers.

Morphometric and meristic variation in two congeneric archer fishes Toxotes chatareus (Hamilton 1822) and Toxotes jaculatrix (Pallas 1767) inhabiting Malaysian coastal waters

A simple yet useful criterion based on external markings and/or number of dorsal spines is currently used to differentiate two congeneric archer fish species Toxotes chatareus and Toxotes jaculatrix.Here we investigate other morphometric and meristic characters that can also be used to differentiate these two species.Principal component and/or discriminant functions revealed that meristic characters were highly correlated with pectoral fin ray count,number of lateral line scales,as well as number of anal fin rays.The results indicate that T.chatareus can be distinguished from T.jaculatrix by having a greater number of lateral line scales,a lower number of pectoral fin rays,and a higher number of anal fin rays.In contrast,morphometric discriminant analyses gave relatively low distinction:76.1% of fish were ascribed to the correct species cluster.The observed morphometric differences came from the dorsal and anal spines lengths,with T.chatareus having shorter dorsal and longer anal spines than T.jaculatrix.Overall,meristic traits were more useful than morphometrics in differentiating the two species;nevertheless,meristics and morphometrics together provide information about the morphological differentiation between these two closely related archer fishes.