Subterranean Fishes of the World

1338

1997

Environmental Biology of Fishes

357-369

50

The population ecology of the trichomycterid catfish, Trichomycterus itacarambiensis, from the Olhos d'Àgua Cave, Itacarambi Co., Minas Gerais, eastern Brazil, was investigated by the mark-recapture method during the dry season of 1994 (April to October). The cave is subject to a pronounced seasonality, and is flooded during part of the rainy period. All individuals captured along the 5000 m long stream gallery (divided in 50 sections) were marked by tattooing, measured and examined for the degree of pigmentation reduction. About one third of the population is truly albinic; the remainder may exhibit partial depigmentation. After five bimestrial collections, 583 specimens have been marked, of which 150 were recaptured at least once. Estimated population size was 1500–2000 individuals longer than 20 mm SL. The total population size of T. itacarambiensis is considered small when compared to those of epigean trichomycterids and of other studied cavefishes as well. Mean population density was 0.15–0.20 individuals m-2 throughout the dry season; it increased with the distance to the stream resurgence, probably due to the higher food availability upstream. This population density may be considered intermediate to those of other troglobitic fishes. Most recaptures (66%) were done in the same section as the previous capture. Active movements, both upstream and downstream, were recorded up to distances of 600 m; a few possibly passive, downstream movements covered distances from 900 to 1500 m. T. itacarambiensis catfishes move more frequently and for longer distances than the Brazilian blind pimelodids, Pimelodella kronei. Individual growth in T. itacarambiensis probably occurs in pulses, during the rainy seasons; interruption of growth in the dry season is attributed to the pronounced food shortage. The mean longevity was estimated as seven years. Differences between pigmented and albino individuals include a higher frequency of downstream movements and slightly higher growth rates in the latter.

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