Length-weight relationship and exploitation of Macrobrachium species in the Burhi Gandak River, North Bihar, India

Three species of the Palaemonidae family, namely Macrobrachium dayanum (Henderson, 1893), Macrobrachium lamarrei (Milne Edw., 1837) and Macrobrachium malcolmsonii (H. Milne Edw., 1844) were investigated for their length-weight relationship and exploitation status in the Burhi Gandak River between July 2020 and June 2021. A total of 907 specimensof M. lamarrei, 942 M. dayanum and 962 M. malcolmsonii were collected using trap net (locally named Ghana Jal), Saalbhar Jal, Pelni, Dhonijal and Khorjal and traditional boats such as Nauka and Donga. M. lamarrei was found to be the dominant species among them in the catch composition. Peak landing was observed from June to August. The maximum length was recorded for M. malcolmsonii (16.8 cm) followed by M. dayanum (8.0 cm) and M. lamarrei (6.1 cm). The length-weight relationship of M. lamarrei, M. dayanum and M. malcolmsonii indicated negative allometric growth with slope (b) values of 2.7692, 2.6027 and 2.7513, respectively. The von Bertalanffy growth parameters viz., asymptotic length (L∞), growth coefficient (K) and age at zero length (to) were 5.67 cm, 2.3 y-1 and -0.5913 y-1 for M. lamarrei ; 10.08 cm, 0.990 y-1 and 0.6684 y-1 for M. dayanum and 16.59 cm, 0.730 y-1and -0.7289 y-1 for M. malcolmsonii , respectively. Fishing mortality was lower than natural mortality which was estimated as 1.71 for M. lamarrei, 0.15 for M. dayanum and 0.18 for M. malcolmsonii. The present study revealed that the smaller length groups had higher natural mortality, whereas larger length groups had higher fishing mortality. The current exploitation rate was 0.26 for M. lamarrei, 0.06 for M. dayanum and 0.09 for M. malcolmsonii. The research fills a critical gap providing essential insights into the population dynamics and exploitation of the three prawn species in the Burhi Gandak River, revealing their underexploited status, highlighting opportunities for sustainable harvesting and informed fishery management to support biodiversity conservation and local livelihoods. Keywords: Bihar, Burhi Gandak River, Length-weight relationship, Macrobrachium, Stock assessment