Volume 04 No. 01 July 1992

Species Composition, Distribution and Economic Importance of Fishes in the Bolgoda Lagoon

1992-01-01T00:00:00Z

Species Composition, Distribution and Economic Importance of Fishes in the Bolgoda Lagoon Jinadasa, J.; Jayantha, H.D.S.; Perera, W.V.J. There are 55 species of fin fishes belonging to 33 families in the Bolgoda Lagoon, of which about 30 are commercially important. Sardinella melanura, Caranx sansun, Leognathus. sp, Mugil cephalus, Etroplus suratensis and Trachysurus cae/us are the dominant species. The mean annual fin fish production is 30 mt/year and it is on the decline.

Some Interesting Features of an "Impromptu Test" set up to Evaluate the Minimum Level of Competence in Mathematical Manipulation

1992-01-01T00:00:00Z

Some Interesting Features of an "Impromptu Test" set up to Evaluate the Minimum Level of Competence in Mathematical Manipulation Fernando, P.C.B.; Mapalagama, C. This paper essentially examines ihe predictive nature of an "impromptu test" iff respect of future performance in Physics at the B.Sc. (B.S.) degree.

Seasonal Diurnal and Vertical Distribution Patterns of Cyclopid copepods in Kotmale Reservoir

1992-01-01T00:00:00Z

Seasonal Diurnal and Vertical Distribution Patterns of Cyclopid copepods in Kotmale Reservoir Chandrananda, W.P.N.; Piyasiri, S. Vertical distribution of cyclopid copepcds was studied in Kotmale reservoir, in order to determine the variation in zooplankton at different depths. Their seasonal distribution and migratory patterns were also studied. Vertical and horizontal sampling were done at monthly intervals from August 1990 to December 1991. Two diurnal samplings were done; one when water level was low (40m) and the other when it was high (62m). The two cycIopid species identified were Mesocyclops leukarti and Thermocyclops crassus. CycIopid adults and their immature stages were abundant at all depths. However their population density decreased with increasing depth. Highest density was found within the range of surface to ten meters. They showed striking diurnal migration which was independent of the intensity of sunlight. The migratory pattern of adults and young was not much different. The seasonal variation observed did not show the same pattern during both sampling years. During the latter part of the study (October to December 1991)a large decrease in cyclopid population was observed which was correlated with the collapse of green algae population and the appearance of algal bloom caused by blue green algae (Microcystis aeruginosa).

Present Status of the Seine Fishery in Negombo Lagoon of Sri Lanka

1992-01-01T00:00:00Z

Present Status of the Seine Fishery in Negombo Lagoon of Sri Lanka Wijeyaratne, M.J.S.; Perera, W.M.D.S.K. Studies on the seine fishery of Negombo Lagoon in the west coast of Sri Lanka (7°10' Nand 79°50' E) were carried out for a period of one year from May 1989 to April 1990. In the operation of this gear, 2 or 4 standard nets, each with a length of 32 m are used. Each net was made up of 4 or 5 vertically joined pieces of nets, with a stretched mesh size of 1.25 em. 3 and 5 men are involved in 2 net and 4 net operations respectively. Total production from this gear was estimated to be around 36,000 kg/year. During the present study, 82 species of fish ranging in size from 2.5 em to 130.0 em were encountered together with 6 species of commercially important penaeid prawns. The catch and fishing effort were low from August to December. Catch per unit effort was high from February to May. Salinity and fish catch showed a significant positive correlation probably due to immigration of allochthonous marine organisms into the lagoon with increasing salinity. Fishing effort also showed a significant positive correlation with salinity. Significant difference between the catches of 4 net-piece and 5 net-piece nets was not observed (P>0.05). Although the catch and catch per fisherman were significantly higher in 4 net operations than in 2 net operations (P <0.05), significant difference in catch per net between the two operations was not observed (P > 0.05). 2 Net operations were observed to provide more employment opportunities and better distribution of income than 4 net operations. Threat of overexploitation of the resource was observed to be high in 4 net operations.