Macrognathus aral (Bloch and Schneider 1801): Growth, condition, age, mortality, recruitment and exploitation in running and stagnant ecosystems in Gandak Basin, India

Life history of M. aral under running and stagnant ecosystems

Abstract

Growth and fishery of Macrognathus aral were studied from an oxbow lake Matwali-Majhariya
maun and the river Dhanauti in Gandak Basin, India based on 367 and 451 specimens
collected from the oxbow lake and the river, respectively through weekly sampling from
June 2020 to May 2021 . The length-weight relationship revealed negative allometric growth
(b<3.0) as W= 0.0051*L (2.82) in lake and W= 0.0045*L (2.85) in the river. The relative condition
factor Kn was found to be ≈1.0 in both the ecosystems. The age at length zero and the
maximum age Tmax were estimated to be -0.312 year and 9.4 years in the lake and -0.328
year and 8.8 years in the river respectively. Growth parameters L∞ and ‘K’ were estimated
to be 37.7 cm and 0.32 year-1 in the lake, and 34.3 cm and 0.34 year-1 in the river, indicating
slow growing nature of the species. The mortality rates ‘M’ ‘Z’ and ‘F’ were determined to
be 0.78, 0.95 and 0.17 per year in lake and 0.81, 97 and 0.16 per year in river. Recruitment
analysis showed a single peak during August in both the ecosystems. Lopt was estimated
as 20.8 cm in lake and 19.2 cm in river. Virtual population analysis (VPA) revealed highest
fishing mortality observed in the length groups above 30.0 cm in both the ecosystems. The
optimum level of exploitation (E0.5) was found to be 0.32 in lake and 0.34 in river, which was
lesser than the current level of exploitation. The above finding will be useful for sustainable
management and conservation of the species.

Keywords:
Age, Exploitation, Gandak Basin, Growth, Mortality,
Macrognathus aral, Recruitment