Abstract
In this investigation groups of Melongena corona and Nassarius vibex were exposed for extended periods of time, twelve months or longer, to each of four constant temperatures (35(DEGREES), 31(DEGREES), 27(DEGREES), and 23(DEGREES)C) or five unvarying salinities, (30('o)/oo, 25('o)/oo, 20('o)/oo, 15('o)/oo, 10('o)/oo) to determine their growth and survival.Specimens of Melongena corona displayed the best growth both in terms of length added to shell and calculated rate, at high temperatures, 31(DEGREES) and 35(DEGREES)C, was less at 27(DEGREES)C and least at 23(DEGREES)C. Generally, per cent survival of experimental groups appeared inversely related to growth, being greater at 23(DEGREES) and 27(DEGREES)C and smallest in 31(DEGREES)C.Specimens of Nassarius vibex showed the influences of constant temperature both in the formation of an adult lip and by final size attained. Maturity occurred most rapidly in animals held at high temperatures (35(DEGREES)C and 31(DEGREES)C). Because of the delay in adding adult lips, the largest final size, and hence most increase in length, appeared in snails maintained at 23(DEGREES)C.Of the five controlled salinities tested, greatest increase in length occurred at 30('o)/oo and this declined with reducing salinity in snails of both Melongena corona and Nassarius vibex. The per cent survival was high in salinities tested above 25('o)/oo and zero at 10('o)/oo. The number of N. vibex forming adult lips declined with reduction in the controlled salinity.In feeding studies with specimens of Melongena corona at constant temperature, food intake and maintenance requirements and growth were greatest at 35(DEGREES)C and declined in order of treatments; 31(DEGREES), 27(DEGREES), and 23(DEGREES)C. In parallel studies at five controlled salinities, increase in shell length was noted in tests conducted at 30('o)/oo, 25('o)/oo and 15('o)/oo. Growth, food intake and maintenance requirements were smallest at 15('o)/oo and increased with rising salinity.Response surface analyses calculated for groups of Melongena corona and Nassarius vibex after ten day exposures to various combinations of high temperatures and low salinities yielded limits of tolerance correlating well with results of the long term experiments. Temperature-salinity interaction, although slight in specimens of Melongena, indicated that these survived high temperatures better at lower salinities. The interaction effect in snails of N. vibex was greater and this species withstood elevated temperatures best when salinities remained high.