Effect of Sperm Ratio and Temperature on Fertilization and Early Larval Development of the Surf Clam Mesodesma donacium (Bivalvia:Mesodesmatidae)

Simple Summary The surf clam Mesodesma donacium, known in the Southeastern Pacific as "macha", has experienced decreased availability for local consumption due to high levels of extraction for many years in Chile and the effect of El Nino Southern Oscillation (ENSO) in Peru. To compensate the population decline, the advancement of the development of technology for cultivation and commercial production is proposed. Therefore, the development of small-scale aquaculture with the participation of artisanal fishermen and small fish farmers is considered. In this work, progress is made in determination of the conditions for fertilization and the effect of temperature on early embryonic and larval development. The effect of sperm ratio on fertilization was evaluated in five sperm:oocytes treatments (10:1, 50:1, 100:1, 500:1 and 1000:1), the effect of temperature on embryonic and larval development in three temperature treatments (13 degrees C, 16 degrees C and 19 degrees C) was recorded and the duration of each stage, the growth rate and survival rate were registered. The oocytes were spherical (67.5 +/- 4.2 mu m) with a defined nucleus. Spermatozoa had a circular head (2 mu m) and a fusiform flagellum (12 mu m). The 500:1 sperm:oocytes treatment presented the lowest % of unfertilized oocytes, and lysis was observed in the 1000:1 treatment. An inverse relationship was observed between temperature and the duration of the stages of embryonic development. At 16 degrees C, veliger D larvae were observed at 41 h 45 ' pf (88 +/- 13.0 mu m). Umbonate larvae were obtained at day 16 in the 13 degrees C culture and at day 10 in the 16 degrees C and 19 degrees C treatment (140 mu m). On day 16 of culture, advanced umbonate larvae with a well-defined stomach (235 mu m) were observed. The larval growth rate was higher in the 19 degrees C treatment (3.6 mu m day(-1)) than the 13 degrees C and 16 degrees C treatment (2, 2.2 mu m day(-1)). The mortality was higher in the 19 degrees C treatment (91%). These results are an initial contribution towards the culture of M. donacium as part of small-scale aquaculture in South America.