Eco-Biology of Puntius Gonionotus with Reference to Its Fishery at Pabna

Abstract

Puntius gonionotus is a fresh water food fish of Bangladesh which is locally known as Thai sharpunti, Thai silver barb or Raj puti. It was introduced in Bangladesh in 1977 from Thailand because of its high yielding potential and has become increasingly popular for its high growth, good taste and bright silvery appearance. It is a suitable species for culturing in the seasonal ponds and rice fields in monoculture. It is also a recommended species for polyculture with some other species. In this circumstances, the cultivation of Thai sharpunti can take an important place in our country. The present study describes some biological and ecological parameters including morphometric and meristic analysis (size frequency distribution, length-length, length-weight relationship and condition factor), food and feeding habit, reproductive biology, and the physico-chemical condition, fishery and marketing system of the habitat of P. gonionotus in Pabna . A total of 1440 specimens of Puntius gonionotus were collected randomly from January 2011 to December 2012 from different ponds of Atghoria Upazila under Pabna District. The smallest specimens measured are female 6.5 cm and male 6.3 cm in total length. The largest specimens are female 43 cm and male 39 cm in total length. The weight of the smallest and largest male and female were 8 g, 11 g and 607 g, 757 g respectively. Total-length (TL) and other body lengths were measured to the nearest 0.01 cm using digital slide calipers, and total body weight (BW) was measured using an electronic balance with 0.01 g accuracy. The relation between the total length and other body lengths were shown a highly positive correlated. The length-weight relationship was calculated using the expression: W = aLb, where W is the BW, L is the TL, a intercept of the regression and b is the regression co-efficient.

In the present study, the length weight relationship (TL/TW) showed curve linear regression line in both sexes in the male, female and in combined sexes. The value of ‘b’ of P. gonionotus was observed in male = 2.952 (negative allometric growth), in female = 3.253 (positive allometric growth) and the combined sex = 3.135 (positive allometric growth) and the value of ‘a’ in male, female and combined sexes were as 0.049, 0.041 and 0.047 respectively. The Fultion’s condition factors KF = 100  (W/L3), The relation condition factors KR = W/a  Lb, where W is the BW, L is the TL and a and b are the LWR parameters. The values of condition factor (KF and KR) showed fluctuation. The mean values of KF were obtained as 1.336  0.597, 1.300  0.680 and 1.258  0.596 for the male, female and combined sexes. The mean values of KR were obtained as 0.743  0.225, 0.797  0.306 and 0.698  0.241 for the male, female and combined sexes respectively. From the results marked fluctuation in the condition factor were observed. During the study period meristic count, the following distribution of fin rays were observed dorsal fin ray, 9-10; pectoral fin ray,13-15; pelvic fin ray, 7-9; anal fin ray, 6-8; and caudal fin ray, 13-19. The analysis of gut contents revealed that the fish is very efficient phytoplankton eating surface feeder and a very little liking for zooplankton. The stomachs of 480 fishes were studied for the analysis of food and feeding habit. All the stomachs examined were classified into 17.58% full, 18.49% ¾ full, 17.57% ½ full, 15.22% were ¼ full, 12.98% stomachs were 1/8 full and 18.16% empty. From the present finding, it was obseved that the feeding intensity in mature fish was very poor during the spawning season (April to July). Food item of this fish consisted of chlorophyceae (27.30%), cyanophyceae (17.50%), Bacillariophyceae (15.48%), Euglenophyceae (10.99%), Crustaceae (2.59%), Copepoda (1.56%), Rotifera (3.64%), Animal part (4.61%), Plant part 17.98%, debris and unidentified food materials

(4.67%). The relation between total length (TL) and alimentary canal length (ACL) was established. The mean TL and ACL ratio is 1:4.21 which confirms the herbivorous nature of the fish. The reproductive biology of Puntius gonionotus including ovarian maturation, maturation stage of ova,size at sexual maturity, spawning season , fecundity estimation and sex ratio. Ovarian maturity stage were classified in to five stages(immature, maturing, mature, ripe and spent). The ova were also divided in to four stages on the basis of ova diameter and colouration as immature stage, maturing stage, mature stage and ripe stage. The diameter of the ova ranged from 0.130mm to 1.025mm. The size at sexual maturity was estimated to be 16cm in total length. The gonadosomatic index (GSI) showed a significant increase with progressing ovarian maturity stage and most of the females with GSI≥7.12% were found to be matured. The spawning season was estimated to April to August with a peak during June and July. The fecundity ranged from 13192 to 98325 eggs and mean value was 58660.33±29288.44. The relation between fecundity with total length, standard length, total weight, ovary length, ovary weight of the female showed straight line linear regressions. The value of co-efficicnt of correlation (r) was highly significant. The sex ratio of the specimens collected during 24 months of study has been determined. The total male and female ratio was 1:1.36. Females were prominent in natural population of the fish. 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 P. gonionotus was influenced by physicochemical factors mainly water temperature, turbidity, pH, dissolved oxygen and free carbondioxide and bicarbonate. The two years’ mean values of different parameters were recorded. The ovary weight and length of Puntius gonionotus 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, monthwise landing, existing marketing channel and price analysis of P. gonionotus were studied. To collect the specimen different traditional fishing gears were used such as Khepla jal, Ber jal etc. and transport the fish by Van, Cycle, Boat, Ricksha and Bus in different fish market of Pabna. The marketing system of P. gonionotus was studied in three fish markets (Atghoria bazar, Tabunia bazar and Masum bazar) of Pabna district. During the survey period, interviews were taken from different intermediaries in a marketing channel such as “Baparies, Aratdars, Retailers, Consumers and Growers or Producer. During the years from January 2011 to December 2012 (24 months), the total landings of P. gonionotus were 18460, 8710, 6088 in three sampling areas respectively.