Browsing by Author "Bandara, K.V.S.N."

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Effect of glyphosate-based herbicide, RoundupTM on territory deference of male Oreochromis mossambicus (Osteichthyes, Cichlidae) associated with mating behavior
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Bandara, K.V.S.N.; Amarasinghe, U.S.
African cichlids are important constituent species in tropical inland fisheries and Oreochromis mossambicus supports profitable fisheries in many countries of the world. This species exhibits elaborate courtship behaviour. Building of spawning nests by males, aggressive behaviour and breeding colouration are important behavioural patterns of this species associated with reproduction. As O. mossambicus is found in reservoirs of Sri Lanka which are situated in agricultural areas of the country, reservoir populations of this species are vulnerable to exposure to agrochemicals at least at sub lethal levels. As ‘Roundup™’ is one of the widely used herbicides in the agricultural areas of the country, the present study was undertaken to investigate its impacts on territorial behaviour of O. mossambicus. Adult O. mossambicus collected from the wild was acclimatized to laboratory condition and exposed to sub-lethal glyphosate concentrations (0 ppm, 5 ppm, 8 ppm and 10 ppm). The territorial behaviour of males measured as intensity of colour change, chasing distance, chasing occurrence, area of territory maintained by nest builders, dorsal fin erection and status of the bites has altered significantly in the aquaria with all three concentration of herbicide.
Effect of the sub-lethal concentrations 'Glyphosate' on the reproductive behaviour mossombicus (Peters)
(Sri Lanka Association for Fisheries and Aquatic Resources, 2012) Bandara, K.V.S.N.; Amarasinghe, U.S.
African cichlids are important constituent species in tropical inland fisheries and Oreochromis mossambicus supports profitable fisheries in many tropical countries such as Sri Lanka. This species exhibits elaborate courtship behaviour. Building of spawning pits by males, aggressive behaviour and breeding colouration are important behavioural patterns of this species associated with reproduction. Due to improper uses of agrochemicals in Sri Lanka, reservoir populations of O. mossambicus are vulnerable to exposure to them at least at sub lethal levels. As 'Roundup' (Glyphosate) is one of the widely used weedicides in Sri Lanka, the present study was undertaken to investigate its effect on reproductive behaviour of 0. mossambicus. Adult breeding-sized O. mossambicus of both sexes were collected from Negombo estuary and were exposed to four different sub- lethal concentrations (0 ppm, S ppm, 8 ppm and 10 ppm). The colour change in males, aggressive behaviour of nest builders, and approximate area of home range that each nest builder maintained were determined. The experiment was replicated three times. Physico-chemical parameters in water i.e., dissolved oxygen, temperature, conductivity, chemical oxygen demand, biological oxygen demand and pH were determined using standard techniques. Water quality parameters in test aquaria with Roundup were not appreciably different from each other. The three concentration of Roundup tested had significant negative effects on the reproductive behaviour measured as chasing distance of males, chasing occurrence of males, dorsal fin erection of males, frequency of bites of males and area of the home range maintained by nest builders. The highest chasing directions were observed in control tank and the chasing distance decreased with increa'sing Roundup concentration. The degree of colour change of males was also affected by Roundup concentration. As Roundup brings about alteration of reproductive behaviour of O. mossambicus at the concentration which are much lower than the recommended concentration in agricultural lands, there may be long term adverse effects of Roundup on 0. mossambicus populations in reservoirs. Hence, control of Roundup application in agricultural lands is necessary for the proper management of inland fishery of Sri Lanka.
Factors related to nesting sites of Oreochromis niloticus (Cichlidae) in irrigation reservoirs, Sri Lanka
(Asian Fisheries Science, 2017) Bandara, K.V.S.N.; Amarasinghe, U.S.
The nesting sites of Oreochromis niloticus (Linnaeus 1758) were studied in 10 irrigation reservoirs of Sri Lanka from April 2014 to April 2016 to understand the influencing factors. The optimal nesting depth and nest diameter varied across reservoirs. Nest density (ND) was negatively related to slope of the littoral area (in degrees) according to ND = -0.070 Slope + 0.536 (R2 = 0.415) and positively to water turbidity (Turb in NTU) according to ND = 0.033 Turb + 0.083 (R2 = 0.598). The optimal nesting depth (NDPopt in cm) was also negatively related to turbidity as NDPopt = -5.133 Turb + 154.660 (R2 = 0.509). Mean relative reservoir water level fluctuation [RRLF = (Mean reservoir level amplitude/Mean depth) x 100] had a significant negative relationship with ND according to ln ND = -1.185 ln RRLF + 5.231 (R2 = 0.518). As hydrological regimes in reservoirs are mainly influenced by irrigation requirements of command areas, effective dialog between multiple users of reservoirs to achieve a win-win situation could possibly be adopted to optimise fish yield.
Life-History Strategies of Nile Tilapia, Oreochromis niloticus(Linnaeus, 1758) (Teleostei, Cichlidae), in Irrigation Reservoirs of Sri Lanka
(Asian Fisheries Society, 2020) Bandara, K.V.S.N.; Ajith Kumara, P.A.D.; Amarasinghe, U.S.
As in many tropical countries, reservoir fishery of Sri Lanka is dominated by the exotic cichlid, Oreochromis niloticus(Linnaeus, 1758). Oreochromis niloticuspopulations in irrigation reservoirs are expected to be under the influence of various disturbances such as changes in hydrological regimes, trophic conditions and fishing pressure. In the present study, an attempt was made to investigate the effect of biological productivity and fishing pressure on life history patterns of O. niloticuspopulations in 10 irrigation reservoirs of Sri Lanka. Oreochromis niloticuspopulations in environmentally stressed reservoirs, exhibited low age at maturity than those inhabiting reservoirs with relatively low biological productivity. Hydraulic retention time (HRT) in reservoirs also had negative influence on size and age at maturity of O. niloticus. As length at first capture of O. niloticusis positively related to mean length at maturity, these attributes have significant implications on the optimal fishing. Fishing intensity (FI) in O. niloticuspopulations also had negative influences on mean length and age at maturity. Hence, the present study supports the opinion that altricial or opportunistic traits having faster growth and achieving maturity early in the life dominate disturbed environments and that precocial or equilibrium traits exhibiting delayed maturity occur in more stable environments. Possible shifting of life history strategies of O. niloticusto opportunistic traits due to disturbance events could be manipulated by increasing FI for smaller individuals in the population.
Population Dynamics of Nile Tilapia, Oreochromis niloticus(Linnaeus, 1758) (Teleostei, Cichlidae), in Some Irrigation Reservoirs of Sri Lanka
(Asian Fisheries Society, 2020) Bandara, K.V.S.N.; Ajith Kumara, P.A.D.; Amarasinghe, U.S.
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. niloticuspopulations in 10 reservoirs. Length-frequency data of O. niloticusfrom fishlandings 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-1to 0.49 yr-1. As growth performance indices of 10 reservoir populations of O. niloticuswere 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. niloticusalso 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. niloticusin 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.