Development and population growth of Hydra viridissima Pallas, 1766 (Cnidaria, Hydrozoa) in the laboratory

Fc Massaro,O Rocha

doi:10.1590/s1519-69842008000200020

Abstract

Hydras, the most representative freshwater Cnidaria, are of common occurrence in bodies of water in every continent except Antarctica. This study was planned with the aim of maintaining a population of Hydra viridissima in laboratory culture to enable the determination of the individual and population growth-rates of this species, as well as its population doubling time and generation time, with a view to employing these common animals as test-organisms in ecotoxicological assays. The organisms were maintained in reconstituted water at 20 +/- 2 degrees C, illuminated at 800 lux with a photoperiod of 12 hours light: 12 hours dark, and were fed on neonates of the cladoceran Ceriodaphnia silvestrii (3 or 4 neonates per hydra, 3 times a week). The individual growth-rate (k) of the species was 0.43, the maximum length of the column 2.53 mm and the generation time 6.6 +/- 1.5 days on average. The hydra population showed an intrinsic growth-rate (r) of 0.0468, according to the fitted curve, and a doubling time of 14.8 +/- 2.63 days. Hydra viridissima is easy to grow in the laboratory and performs well in the conditions used in this study. It is thus a promising candidate test-organism for ecotoxicological studies.

Highlights

The freshwater Cnidaria of São Paulo State, of Brazil as a whole, are relatively little known in comparison with the members of this phylum in the USA or Europe, in spite of being common organisms in most freshwater habitats (Silveira and Schlenz, 1999)
The water was changed and the culture cleaned twice a week. In both the population and individual growth experiments, the hydras were maintained under the same culture conditions, with 10 replicates for each test, but in the individual growth experiment only the individuals of seven replicates had survived until the end of the experiment
The curve has been fitted to the data, assuming the Von Bertalanffy model for individual growth

Summary

Introduction

The freshwater Cnidaria of São Paulo State, of Brazil as a whole, are relatively little known in comparison with the members of this phylum in the USA or Europe, in spite of being common organisms in most freshwater habitats (Silveira and Schlenz, 1999).In particular, hydras are common in bodies of water in every continent except Antarctica (Holstein, 1995).They are strictly carnivorous, feeding mainly on small crustaceans, including cladocerans and copepods, insects and annelids. The freshwater Cnidaria of São Paulo State, of Brazil as a whole, are relatively little known in comparison with the members of this phylum in the USA or Europe, in spite of being common organisms in most freshwater habitats (Silveira and Schlenz, 1999). Hydras are common in bodies of water in every continent except Antarctica (Holstein, 1995). They are strictly carnivorous, feeding mainly on small crustaceans, including cladocerans and copepods, insects and annelids. Four species of Hydra (Class Hydrozoa, Subclass Anthomedusae, Family Hydridae) are known in Brazil: Hydra viridissima Pallas, 1766

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