Eco-Biology of Mystus Vittatus (Bloch, 1794) with Reference to Its Fishery at Rajshahi

Abstract

Mystus vittatus (Bloch, 1794) is a small indigenous fish species of Bangladesh which is known as Tengra. This important fish species is very much famous food fish item and can also be used as medicinal fish. This fish is undoubtedly praised for its taste and is one of the commercially high nutritional valuable food fish in Asian countries including Bangladesh, India, Nepal and Myanmar but the natural populations are seriously decreasing due to degradation of environmental condition of the natural habitat and high fishing pressure, leading to an alarming condition and deserving to high conservation importance. The present study describes some biological and ecological parameters including size frequency distribution, length-length, length-weight relationship and condition factor and food and feeding habit, reproductive biology, fishery and marketing system and the physico-chemical condition of this valuable fish of M. vittatus in Rajshahi area. A total of 2415 specimemens of M. vittatus were collected randomly from different water bodies (Padma river, Kornohara boro beel and Pond) and different fish market of Rajshahi during June, 2010 to May, 2012. Lengths of fishes were varied from 6.00 to 12.05 cm for male and 6.02 to 12.63 cm for female and the weight was varied from 2.83 to 14.40 g for male and 3.00 to 22.08 g for female. The allometric coefficient of the LWR was close to the isometric value (b = 3.058), although it suggested positive allometric growth for female (b = 3.121) whilst positive allometric growth for males (b = 2.735). The LLRs were highly correlated. Fulfon’s and Relatives condition factors showed significant variations (p < 0.001) among the populations. During the study period meristic count the following distribution of fin rays were observed DR, 7-8; PR, 5-6; PlR, 5; AR, 9-10; CR, 20-22. Food and feeding habits of M. vittatus were investigated by examining the gastro-intestine contents and it revealed that the fish is very efficient zooplankton eating and a very little liking for phytoplankton. Their diet consisted of a broad spectrum of food types but insects were dominant group (39.40%), other diatom (20.35%), Green algee (14.49%). Fish larvae (6.86%), Copepode (3.29%), Rotifera (2.93%) Cladocera (1.33%) and Others (8.72%). Analysis of monthly variations in stomach fullness indicated that feeding intensity fluctuated through the year with a low during June and August corresponding to the spawning period. The mean total length (TL) and Alimentary canal length (ACL) ratio is 1:0.71 which confirms the carnivorous nature of the fish. The reproductive biology of M. vittatus including ovarian maturation, maturation stage of ova, size at sexual maturity, spawning season , fecundity estimation and sex ratio. Ovarian maturity stages were divided into five categories (immature, maturing mature, ripe and spent) based on the visual observation of ovaries and oocyte diameter. The size at first sexual maturity was estimated to be 7.8 cm in total length. The gonado somatic index (GSI) showed a significant increase with progressing ovarian maturity stage and most of the females with GSI > 5.8% were found to be matured. The spawning season was estimated to April to September with a peak during June and July. The total male female ratio was 1:1.22, female were prominent in natural population of the fish. The fecundity ranged from 6023.33 to 29800.15 eggs and the relationship between fecundity and morphometrics measurements indicated that body weight and fecundity was related isometrically with female body size. According to the change of month and season the physico-chemical condition of the study areas, which were the habitats of the fish exhibited more or less variations. In all the studied areas 4 physical and 4 chemical parameters were studied. The occurrence of M. vittatus was influenced by physico-chemical factors mainly water temperature, turbidity, pH, dissolved oxygen, free carbon dioxide and bicarbonate. The two years’ mean values of different parameters were recorded. The ovary weight and length of M. vittatus varied from month to month and season to season. Fluctuation in the distribution of different forms of gonad within a year was attributed to the disturbance of their habitats. The change of the condition of gonad was affected by factors like different existing ecological parameters. In the present study calculated values of correlation coefficient (r) for the developmental stages of both ovary weight and length were found. The values of ‘r’ showed both positive and negative correlations. The fishing methods and marketing system included the fishing gears, month wise landing, existing marketing channel and price analysis of M. vittatus were studied. To collect the specimen different traditional fishing gears were used such as, Dharma jal, Khepla jal, Ber jal, Moi jal, Dohair, Kholson, Bana, Barshi etc. and transport the fish by Van, Cycle, Boat, Ricksha and Bus in different fish market of Rajshahi. The marketing system of M. vittatus was studied in three fish markets (Shaheb bazar, Laxmipur bazar and Binodpur bazar) of Rajshahi city. During the survy period interviews were taken form different intermediaries in a marketing channel such as “Farias, Baparies, Aratdars, Retailers, Consumers and Growers or fishermen. By the interviewed it was observed that the basic channel for marketing system is formed between growers and consumer including a number of intermediaries. The producers were found to distribute M. vittatus to different markets through a more or less distinguished channel. Supply of M. vittatus in Rajshahi fish markets is continuous throughout the year. During the years from June 2010 to May 2012 (24 months) the total landings of M. vittatus were 6380, 1772, 1650 (kg) in three sampling areas respectively i.e. Shaheb bazar, Laxmipur bazar and Binodpur bazar.