Population dynamics of Nile Tilapia Oreochromis niloticus (Linnaeus 1758) (Teleostei Cichlidae) in some irrigation reservoirs of Sri Lanka

Ajith Kumara P. A. D., . and Bandara K.V. Sandun N., . and Amarasinghe Upali S., . Population dynamics of Nile Tilapia Oreochromis niloticus (Linnaeus 1758) (Teleostei Cichlidae) in some irrigation reservoirs of Sri Lanka. pp. 192-204. ISSN 0116-6514

Oreochromis niloticus (Linnaeus 1758) exhibits differences in demographic parameters across the reservoirs resulting in inconsistencies in optimal fishing strategies. This study aimed at investigating O. niloticus populations in 10 reservoirs. Length-frequency data of O. niloticus from fish landings of 10 irrigation reservoirs in Sri Lanka were corrected for multi-mesh gillnet selection and were analysed by FiSAT II stock assessment software. Asymptotic total length ranged from 42.8 cm to 53.4 cm and growth constant ranged from 0.20 yr- to 0.49 yr-. As growth performance indices of 10 reservoir populations of O. niloticus were within the range reported previously and as the estimated growth parameters fall within the growth space� of the species these estimates were consistent with those reported in the literature. Length-converted catch curves of 10 reservoir populations of O. niloticus also gave reliable estimates of total mortality. Exploitation rates of the 10 populations ranged from very low (0.14) to very high (0.76) values. From the relative yield-per-recruit analyses it was apparent that in some reservoirs long-term fish yields can be optimised using gillnet mesh sizes of 7.6 cm. While optimal long-term fish yields of O. niloticus in other reservoirs could be achieved by increasing the permissible gillnet mesh size above the legal mesh size of 8.4 cm. Hence the gillnet mesh regulations in the Sri Lankan reservoir fishery should not be uniform but reservoir-specific. Accordingly site-specific management options which are defined in consultation of resource users are necessary to be implemented in reservoir fisheries of the country.

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Abstract

Oreochromis niloticus (Linnaeus 1758) exhibits differences in demographic parameters across the reservoirs resulting in inconsistencies in optimal fishing strategies. This study aimed at investigating O. niloticus populations in 10 reservoirs. Length-frequency data of O. niloticus from fish landings of 10 irrigation reservoirs in Sri Lanka were corrected for multi-mesh gillnet selection and were analysed by FiSAT II stock assessment software. Asymptotic total length ranged from 42.8 cm to 53.4 cm and growth constant ranged from 0.20 yr- to 0.49 yr-. As growth performance indices of 10 reservoir populations of O. niloticus were within the range reported previously and as the estimated growth parameters fall within the growth space� of the species these estimates were consistent with those reported in the literature. Length-converted catch curves of 10 reservoir populations of O. niloticus also gave reliable estimates of total mortality. Exploitation rates of the 10 populations ranged from very low (0.14) to very high (0.76) values. From the relative yield-per-recruit analyses it was apparent that in some reservoirs long-term fish yields can be optimised using gillnet mesh sizes of 7.6 cm. While optimal long-term fish yields of O. niloticus in other reservoirs could be achieved by increasing the permissible gillnet mesh size above the legal mesh size of 8.4 cm. Hence the gillnet mesh regulations in the Sri Lankan reservoir fishery should not be uniform but reservoir-specific. Accordingly site-specific management options which are defined in consultation of resource users are necessary to be implemented in reservoir fisheries of the country.

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Item Type:	Article
AGROVOC Term:	Tilapia
AGROVOC Term:	Oreochromis niloticus
AGROVOC Term:	Nile River
AGROVOC Term:	Inland fisheries
AGROVOC Term:	Population control
AGROVOC Term:	Reservoirs
Depositing User:	Mr. AFANDI ABDUL MALEK
Last Modified:	24 Apr 2025 00:54
URI:	http://webagris.upm.edu.my/id/eprint/9136

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