Biology and Stock Assessment of the Threatened Fish Puntius Ticto (Hamilton, 1822) (Cyprinidae) in the Gorai River, Southwestern Bangladesh

Abstract

The present study describes the fisheries biology including length-weight relationships (LWRs), condition factor (Fultonʹs, KF), pre-predator status (based on relative weight, WR), reproductive biology (size at first sexual maturity, spawning season and fecundity), growth parameters (asymptotic length, growth co-efficient, age at zero length) and stock status (fishing mortality, natural mortality, total mortality, exploitation rate) of the threatened fish Puntius ticto (Hamilton, 1822) from the Gorai River, southwestern Bangladesh. A sum of 1200 individuals of P. ticto was sampled during July 2010 to June 2011 using cast net, square lift net and conical trap. Here, the total length (TL) was ranged from 2.77-7.48 cm for male and 2.66-8.00 cm for female. The body weight (BW) ranged from 0.42-6.6 g for male and 0.23-8.94 for female P. ticto. The b values of LWRs ranged from 2.63 to 3.62 for males and 3.04 to 3.76 for females and the overall b values of LWRs indicated negative allometric growth (< 3.00) in both males and females. The KF was higher in January for both genders suggesting that the fish was in good condition in that month. Also, the WR was higher in the month of December-March for male and January-March for female populations of P. ticto indicating that, in these months the predator was in lower and prey was in higher amount. Also, the mean WR was significantly different from 100 for both sexes suggesting the habitat was not in balance condition with lower prey-higher predator. On the basis of gonadosomatic index (GSI) the first sexual maturity was 4.2 cm in TL for male and 4.7 cm in TL for female P. ticto. The higher GSI were found during the month of April-September, which indicates the spawning season of P. ticto in the Gorai River and peak values of GSI were found in the month of June-July, which point out peak spawning season. Also, when temperature increases above 30o C and rainfall starts, then the P. ticto began to spawn. There is a significant correlation between temperature, rainfall and the spawning season. During the study, lowest fecundity was 2021 and highest fecundity was 8623 with mean value of 4600±2037. The length-frequency distribution indicated that male P. ticto were first recruited in the month of September and female P. ticto were first recruited in the month of August. Estimated growth equations showed TL∞ in male is 10.26 cm, and in female is 10.55 cm but female grew faster than male. The growth co-efficient was 1.16 year-1 for male and 1.30 year-1 for female. Also, age at to be calculated as 0.006 for males and 0.007 for females. The growth performance index for males and females P. ticto was 1.80 and 2.16, respectively and longevity was 2.6 year for males and 2.30 year for females. The calculated natural mortality was 1.66 year-1 for males and 2.74 year-1 for females; and fishing mortality was recorded as 2.01 year-1 and 4.40 year-1 for males and females respectively. In addition, the total mortality was 2.67 and 7.14 year-1 for male and female populations of P. ticto. From the estimates fishing and total mortalities, the exploitation rate was calculated as 0.58 or 58% for male and 0.62 or % for female. Therefore, the findings of this study would be very effective for sustainable management and conservation for the stock of P. ticto in the Gorai River and surrounding ecosystems.