Seasonal variations in growth, condition and gonads of Dormitator latifrons (Richardson) in the Chone River Basin, Ecuador

Abstract

Growth in length, condition, and gonads of a food fish, Dormitator latifrons, were studied in the Chone River basin, Ecuador, in 1981. The river was bordered by floodplains in the upstream freshwater zone, and by mangrove swamps and shrimp farms in the downstream estuarine zone. The climate was marked by wet (January to April) and dry (May to December) seasons. During the dry season, an earth dam in the river prevented movement of water and fish between upstream and downstream zones. At the end of the dry season, most of the upstream floodplains were dry, and the main fish refuges were in downstream areas in deep pools in the river upstream. During the floods, fish migrated from downstream areas towards upstream floodplains. Growth rates and condition increased when water levels were high or salinity was low and decreased when water levels were low or salinity was high. Seasonal changes in gonads and abundance of juveniles indicated that reproduction occurred during the floods, but there was some reproduction in the dry season. Reproduction occurred in upstream and downstream zones and appeared to be stimulated by a complex of factors, including water levels, currents and salinity. The yield in flood plain sites was estimated as c. 115 kg ha−1 in 1981.