Growth, mortality, and fish stock of dominant fish species in Pondok Reservoir, East Java, Indonesia

This study aimed to determine the long-term optimal fishing strategies of several dominant fish in Pondok Reservoir. The study procedures were conducted in the Pondok reservoir, East Java, from January to November 2021. Fish stock estimation was carried out using acoustic tools, while recording fish catch data and size were determined by enumerators. Subsequently, recording of monthly length frequency data was conducted for the selected dominant fish, namely Cichlid (Oreochromi niloticus) and Minnows (Barbonymus gonionotus). The growth equations for Minnows and Cichlids were Lt = 29 (1 − e−0.56(t+0.3)) and Lt = 31 (1 − e−0.7(t+0.2)), respectively. The population dynamics parameters of Barbonymus gonionotus were L∞ 29 cm, K = 0.56, Lc50 = 13.25 cm, Lm = 18.6 cm, F = 1.34, M = 1.23, Z = 2.57, and E = 0.52. Meanwhile, the parameters for Oreochromi niloticus were L∞ = 31 cm, K = 0.7, Lc50 = 9.51, Lm = 19.7 cm, F = 2.25, M = 1.4, Z = 3.65 and E = 0.62. The results showed that the exploitation rates of both species were greater than 0.5, which was an indication of overfishing. The length at first capture (Lc50) of Minnows and Cichild was less than the length at the first gonad maturity (Lm), indicating that fishing had been intensive and could lead to growth overfishing. Based on the results, it was necessary to regulate fishing gear, especially the Bagan (lift net) and Jaring (gill net), as their usage was increasing and the mesh size was less than 2 in. In addition, it was necessary to restock native fish, such as B. gonionotus.