Production of young forms of the species Mesodesma mactroides (Reeve, 1854), in laboratory

Author: Juan Jethro Silva Santos (Currículo Lattes)
Supervisor: Dr Luis Alberto Romano
Co-supervisor: Dr Carlos Henrique Araújo de Miranda Gomes (UFSC)

Abstract

Malacoculture is an activity which contributes to world aquaculture production, highlighting bivalve molluscs. In this context, Latin America has been investing on farming and research of exotic bivalve species and mainly in native ones with potential for production. This investment tends to increase the diversification of farmed species, and consequently implies on overfishing decrease of natural stocks, becoming an alternative for food and income to several regions. Based on this assumption, the yellow clam Amarilldesma mactroides is a sand bivalve of Mesodesmatidae family, with socioeconomic importance in regions where this species is endemic and for several decades is susceptible to excessive exploitation and mortality outbreaks without definite causes. For this reason, many researches are being developed regarding this species, however no one is related to its reproduction in laboratory. Due to yellow clam vanishing in natural environment, seed production may be an alternative to control the environment stock. Nevertheless, to aquaculture development of new species, it is necessary information about biological and ecological requirements toward environmental variables in laboratory to later observe its performance in farming systems. In this way, the chapters of the present work aimed to obtain information on the laboratory production of yellow clam, taking into account initially to describe and describe the larviculture, to later  evaluate the effect of variables such as salinity, temperature and diets, in the stages of development embryonic, larval as well as in the settlement of this species. Chapter 1 demonstrated that it was possible to perform spawning by the stripping technique, in which descriptive analysis was followed by the stages of complete embryonic development, from fertilization to the formation of D larvae, lasting 24 hours. A positive larval development was observed by means of the biometric variables of height and length of shells as a function of time, with formation of pediveliger larvae ready for settlement, in the period of 27 days. In Chapter 2, embryos and larvae of A. mactroides were submitted to and maintained at four different salinities: 20, 25, 30 and 35 ppt, to determine optimal conditions for the species. The results of this experiment indicated that embryos and larvae tolerate salinities between (25-35 ppt), with the best growth and survival at high salinities of 35 ppt. While in Chapter 3, the effect of four different temperatures (18, 20, 23 and 26 °C) on embryonic development, larval growth and survival of yellow clam was evaluated. The results indicated that the embryos of this species are able to tolerate a variation of 18 to 26 °C of temperature, being the effect of this variable a determinant in  the speed of metamorphosis. In view of the experimental conditions adopted, the larvae remained dependent on the lower temperatures (18 and 20 °C) to be able to settle in better  conditions of size and survival. Finally, in Chapter 4, the effect of different proportions,  quantities and concentrations of three live microalgae, consolidated in aquaculture as a  source of feed, was evaluated: Isochrysis aff. galbana (T-ISO) (Iso); Chaetoceros  muelleri (Cm) and Tetraselmis suecica (Ts). In this experiment, the yellow clam fed diets  composed of I. galbana and C. muelleri, offered in isolation or mixed with each other  (several proportions), presented higher growth and survival in the laboratory. Thus, with  these results it can be said that it was possible to carry out a basic protocol for the  cultivation of A. mactroides in the laboratory, in which, this information may contribute  to future programs to repopulate the natural environment and seed production for the  purpose of cultivating this species.

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