The diet of 1200 adult Sarotherodon mossambicus [16-37 cm total length (T.L.)] in 12 man-made Sri Lankan lakes, belonging to five different irrigational systems were studied over four climatic seasons using volumetric analysis. Food differed between seasons and reservoirs but overall, the diet consisted of 2, 2, 6 and 15 genera of diatoms, blue-green algae, green algae and animal material respectively. However, none of the S. mossambicus populations maintained either a detritivorous, phytoplanktivorous or a zooplanktivorous habit through the year. Detritivory was most common during the rainy season while phytoplanktivory predominated in the dry season. Blue-green algae were not an important constituent of the diet. Out of the 12 reservoir populations. five were predominantly detritivorous, six phytoplanktivorous and one zooplanktivorous. Detritus was completely absent in the ingested material in certain populations when they devoured animal or plant material, indicating the ability of S. mossambicus to switch from deposit to suspension feeding. The mean relative intestinal length (m.r.i.1.) of S. mossambicus ranged between 5.1 and 15.2. The m.r.i.1. decreased significantly with increasing body length: m.r.i.l.= 14.1 -0,018 T.L. ( r = -0.89; P

SynopsisThe dietary composition and the nutritional status and the (digestibility of the diets of Sarotherodon mossambicus from nine reservoirs in Sri Lanka were evaluated. 'The feeding habits of S. mossambicus were variable from reservoir to reservoir; they ranged from herbivory to total carnivory. The protein, total lipid, carbohydrate and total organic matter content of the ingested material were related to the dietary composition and ranged from 18.53% to 35.15% (t-24.18%), 5.94% to 9.84% (X-7.91%), 11.6% to 34.7% (X-22.34%) and 34.4% to 64.4% (t-45.71%), respectively. Irrespective of the feeding habits, the diet contained a significant proportion of organic material which cannot be accounted for by protein, total lipid and carbohydrate. As much as the ingested material was related to the feeding habit, the digestibility of the nutrient components was related to the food material devoured. For example, the mean digestibility of the total organic matter in S. mossambicus feeding on detritus, plants and animal were 36.85, 33.5 and 29.5 respectively, and compared well with observations from elsewhere. It is hypothesised that the favourable nutrient quality of the available dietary material in the reservoirs of Sri Lanka, which could be and is effectively utilized by S. mossambicus, may have been, at least partially, responsible for its almost unprecedented success in Sri Lanka.

SynopsisAspects of the biology of the euryhaline Asian cichlid Etroplus suratensis in a coastal lagoon of Sri Lanka were studied for a period of 15 months. Comparisons are made from the catches from the fishery of manmade, inland freshwater reservoirs. Changes in the stock structure in the sublittoral region of the lagoon indicate that recruitment takes place twice a year, during the high rainfall/low salinity periods. The feeding habits of E. suratensis were different in the two habitats. In the lagoon it fed mainly on molluscs and in the freshwater reservoirs on macrophytes. Feeding chronology based on diurnal surveys indicate that it feeds mainly during the daylight hours. The dentition of E. suratensis is adapted for both tearing and crushing (pharyngeal teeth). Distinct differences in the mean relative intestinal length between populations from the coastal lagoon and inland reservoirs were evident and these differences are correlated to their respective feeding habits. Diurnal changes in feeding activity are associated with changes in the stomach pH. The eggdiameter distribution of mature fish indicate that E. suratensis is a single spawner, that it sheds its mature eggs all at once. It is inferred that E. suratensis breeds twice a year but that an individual female is capable of spawning only once a year.

It is shown that Puntius melanampyx singhala (Duncker, 1911) is identical to juvenile stages of P. filamentosus (Val., in Cuv. & Val., 1844). The taxonomic relationship between the latter species and P. melanampyx (Day, 1865) is briefly discussed. The argument of the present paper is not influenced if the generic name Barbus is adhered to instead of Puntius.