Body condition and nutritional ecology of Oreochromis mossambicus (Pisces, Cichlidae) populations of man-made lakes in Sri Lanka

The nutritive quality of ingested material of adult Oreochromis mossambicus wild populations from 12 perennial, man-made lakes were evaluated for four climatic seasons. The seasonal variation in condition of each population, and the overall condition of each population, considered as the theoretical weight of a 20cm individual, was computed from the length-weight regressions, which were curvilinear. The mean overall condition of the O. mossambicus reservoir population was 152.6 g ( s.d. ± 9.5) and ranged between 139.8 and 167.8 g. Distinct patterns in the seasonal changes in condition of an individual population were not apparent. The mean percentage of protein and total organic matter (TOM) and calorific content (kJg⁻¹) of the ingested material were 20.7% ( s.d. ± 3.7; range 9.6–35.2%), 46.0% ( s.d. ± 9.8; range 20.9–73.7%) and 11.6 ( s.d. ± 3.4; range 4.6–20.9) respectively. The amount of each of the above components for any one population varied seasonally in relation to the changes in feeding habit. The protein content of the ingested material of those populations devouring predominantly detritus also showed seasonal variability. The amount of protein (mg) in the digestible total organic matter (DTOM) and the calorific content (Cal) in the ingested material were related to the TOM content as follows: The overall body condition (BC) of O. mossambicus populations was linearly rebated to the digestible protein: energy ratio (PER) thus: The study indicates that a mixed diet was superior in nutritional quality to a single-component diet. especially with respect to detrital material.