Stock assessment and management Of the stinging catfish (heteropneustes fossilis) in the padma River of northwestern bangladesh considering the Emerging climate change

Abstract

Stinging Catfish, Heteropneustes fossilis (Bloch, 1794) is a precious catfish of the order Siluriformes generally known as shinghi or shinghee in Bangladesh. This fish has significant commercial worth because of its exceptional taste, high medicinal significance with high-quality protein, calcium and iron. It is broadly distributed in Bangladesh, Laos, India, Pakistan, Nepal, Mayanmar, and Sri Lanka. A total of 1170 specimens were collected monthly basis using local fishing gears from the Padma River, Bangladesh, during January 2019 to December, 2020. Male and female specimens were identified by gonadal observation under microscope. Individual total length (TL) and body weight (BW) were measured by measuring board and digital balance with 0.1 cm and 0.01 g precision. The length frequency distribution was calculated by 1.0 cm TL intervals. The length-weight relationship (LWR) was calculated by W=a*Lb. Multiple condition factors (Fulton’s, KF; allometric, KA; Relative, KR and relative weight, WR) were analyzed for assessing the well-being of this species in relation to eco-climatic parameters. To estimate the size at first sexual maturity (TLm), spawning season and peak - spawning season; the GSI (gonadosomatic index in %), MGSI (modified gonadosomatic index in %) and DI (Dobriyal index) were considered. The von Bertalanffy growth function (VBGF) was used to determine asymptotic length (L∞), growth coefficient (K), growth performance index (Ø') and life-span (tmax).Total mortality (Z) was estimated through length-converted catch curve method. Natural mortality (M) was determined by log10M = -0.0066 – 0.279log10 L∞ + 0:6543log10K + 0:0463log10T; where T indicates the mean temperature of the habitat (28.5oC). The fishing mortality (F) was calculated by Z-M. Besides, exploitation rate (E) was assessed as E = F/Z = F / (F + M).Recruitment rate was calculated from the analysis of the total time series of LFDs and growth co-efficients using VBGF models. Finally, MSY (Maximum Sustainable Yield) was determined following the formula of Gulland (1983). The fin formula of H. fossilis is: dorsal, D. 7; pectoral, Pc.1/6-7; pelvic, Pv. 6; anal, A. 62-71; and caudal, C.17-19.The overall sex ratio (male: female=1.00:1.15) varied statistically from the predictable ratio of 1:1 (df = 1, χ2 = 4.85, p < 0.05).The overall growth pattern was possitive allometric (b > 3.00) for both sexes. Total length varied between 8.5-22.3 cm for males and 8.9-37.7 cm for females. The KF was found the best for assessing the well-being of this species. Moreover, KF was found significantly related with temperature for both male and female. The WR indicated that the habitat was in balanced state. Based on GSI, MGSI and DI index, the Lm was documented 15.5 cm in TL. Further, the higher values of GSI, MGSI and DI denoted that the spawning season was extended from May to August, with a peak in June. In addition, GSI was recorded statistically correlated with water temperature.The von Bertalanffy growth function revealed growth coefficient (K = 0.42 year-1), growth performance index (Ø' = 2.84) and life-span (tmax = 4.41year). Further, H. fossilis grew swiftly with an asymptotic length (L∞) of 40.85 cm. We obtained the natural mortality, M =0.93 year-1 is lower than the fishing mortality, F = 1.07 year-1. Therefore, with the current fishing approach, the standing population is not quite sustainable. In addition, the maximum permissible exploitation rate (Emax = 0.450) was less than the calculated exploitation rate (E=0.540). Consequently, overfishing is the major significant risk for the natural stock of H. fossilis in the Padma River of Bangladesh. During the sampling period, the recruitment pattern was more or less continuous with two major peaks (April and August). Lastly, the MSY of H. fossilis was determined as 461.08 metric tons. The results will be very effective and helpful to establish proper fishing policy in the Padma River.