Age, Growth, and Mortality Rates of the Giant Cichlid in Guatemala

Age, growth, and mortality were assessed in Giant Cichlids Petenia splendida from lakes in northern Guatemala by using cross-sectioned sagittal otoliths. Marginal increment and edge analyses of Giant Cichlid otoliths indicated that one annulus formed per 12-month period in Lakes Yaxha and Peten Itza. Opaque zone formation was associated with the peak of the rainy season from May to September. Ages ranged from 0 to 8 years for Giant Cichlids in Lake Yaxha and from 0 to 5 years in Lake Peten Itza. Within both lakes, males were larger than females, although the difference was slight in Lake Peten Itza. Lake Yaxha Giant Cichlids had faster growth rates than those from Lake Peten Itza, and fish over 2 years old from Lake Yaxha were larger at age than fish from Lake Peten Itza. This is counter-intuitive because Lake Peten Itza is heavily exploited, whereas Lake Yaxha is unfished. However, long-term exploitation in Lake Peten Itza may have resulted in selection for fish with reduced growth rates. Alternatively, the mesotrophic state of Lake Yaxha may explain the differences in growth, although areas of Lake Peten Itza are changing from oligotrophic to meso-eutrophic due to rapid cultural eutrophication. Total mortality (Z) estimates for Giant Cichlids were 0.81 for Lake Yaxha, with most of the age structured on 2-4-year-old fish, and 1.05 for Lake Peten Itza, where the age structure was dominated by 0-2-year-old fish; these results were consistent with expectations based on the low fishing pressure in Lake Yaxha.