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

Abstract

AbstractAge, 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 Yaxhá and Petén 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 Yaxhá and from 0 to 5 years in Lake Petén Itza. Within both lakes, males were larger than females, although the difference was slight in Lake Petén Itza. Lake Yaxhá Giant Cichlids had faster growth rates than those from Lake Petén Itza, and fish over 2 years old from Lake Yaxhá were larger at age than fish from Lake Petén Itza. This is counter‐intuitive because Lake Petén Itza is heavily exploited, whereas Lake Yaxhá is unfished. However, long‐term exploitation in Lake Petén Itza may have resulted in selection for fish with reduced growth rates. Alternatively, the mesotrophic state of Lake Yaxhá may explain the differences in growth, although areas of Lake Petén 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 Yaxhá, with most of the age structured on 2–4‐year‐old fish, and 1.05 for Lake Petén Itzá, 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 Yaxhá.