Effects of food type, feeding frequency, and temperature on juvenile survival and growth of Marisa cornuarietis (Mollusca: Gastropoda)

Abstract

The present experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the ramshorn snail, Marisa cornuarietis, in order to identify suitable husbandry conditions for maintaining multi-generation populations in the laboratory for use in ecotoxicological testing. In this paper we focus on the effects of a combination of food types and feeding frequencies (i.e., the frequency with which the snails were offered food) on juvenile growth and survival at different temperatures. Offspring produced in the laboratory by wild specimens of M. cornuarietis, from Puerto Rico, were used to test the effects of three types of food (lettuce, alginate with fish food, alginate with snail mix) fed at three frequencies (given ad libitum on 4/4, 2/4, or 1/4 d) on juvenile survival and growth. The 4-d feeding regimens were repeated four times, giving a total of 16 d for the experiments. The experiments were conducted at two temperatures (22 degrees and 25 degrees C) under a 12 h light:12 h dark photoperiod. Juvenile growth rates increased with increasing feeding frequency for all food types. The most rapid growth rates occurred in the high-frequency lettuce treatments and the slowest growth rates in the low-frequency lettuce and alginate with snail mix treatments. Juvenile snails grew faster at 25 degrees than at 22 degrees C, and mortality was about twice as high at the lower temperature. Growth rates were used to provide a rough estimate of time to maturity, which was determined to take about twice as long at 22 degrees than at 25 degrees C. The results showed that lettuce is the best food if supplied in abundance, but effects on growth are very dependent on feeding frequency and temperature. We conclude that 25 degrees C is a more appropriate temperature for maintaining populations than 22 degrees C, that lettuce provides a suitable food source, and that food should be supplied continuously for husbandry and toxicity testing of populations of M. cornuarietis.

Fig. 1

Individual growth rates for juvenile snails in Experiment 1 (top; 25°C) and Experiment 2 (bottom; 22°C) given a diet of lettuce (circle, solid line), alginate with fish food (triangle, dashed line), or alginate with snail mix (square, dotted line) at low, middle, or high feeding frequencies. No data exist for the low lettuce treatment in Experiment 1 due to 100% mortality. In both cases, the left graph describes growth rate based on snail wet weight (GR_WW), and the right graph shows growth rate based on snail shell diameter (GR_D). Lines are locally weighted scatterplot smooths through the data.

Fig. 2

Individual growth rates for juvenile snails in Experiment 1 (circle, solid line; 25°C) and Experiment 2 (triangle, dashed line; 22°C) given a diet of lettuce (left graph), alginate with fish food (middle graph), or alginate with snail mix (right graph) at low, middle, or high feeding frequencies. No data exist for the low lettuce treatment in Experiment 1 due to a mortality of 100%. Growth rates are based on either snail wet weight (GR_WW) (top graphs) or snail shell diameter (GR_D) (bottom graphs). Lines are locally weighted scatterplot smooths through the data.