Temperature and salinity are among the critical factors affecting the survival and growth of bivalve larvae. The combined effects of temperature and salinity on the embryonic and larval development of the rock oyster Saccostrea cuccullata (von Born, 1778) in culture conditions were investigated in a laboratory study on Inhaca Island, Mozambique. A factorial experimental design tested three temperatures (24, 30 and 34 ºC) and three salinities (30, 35 and 40 parts per thousand) over a seven-day period. Larval survival and growth (in height and length) were assessed by regular sampling by counting and measurement of larvae under an optical microscope equipped with a micrometric scale. Significantly higher larval survival was observed at the combination of 30 °C and 35 salinity. However, the mid-range temperature (30 ºC) and highest salinity (40) resulted in faster growth of the larvae. The lowest temperature (24 ºC) negatively affected growth regardless of salinity level and survival decreased linearly with increasing salinities. The present results will aid in the understanding of the environmental factors behind the natural recruitment of spat of S. cuccullata and contribute to the optimization of rearing protocols for the larval culture of this oyster species.

Broodstock conditioning involves maintaining adult animals in optimal environmental conditions to ensure that the largest number of breeders reach maturity. We evaluated the gonadal development and the occurrence of spawns in the yellow clam (Amarilladesma mactroides) and estimated the duration of conditioning that results in the highest maturity rate. Clams were kept buried in a 10 cm sand bed within Ø = 15 cm containers. A concentrate of Isochrysis galbana and Chaetoceros muelleri was supplied daily. Four conditioning periods (14, 28, 45 and 60 days) with four replicates were used. On the day of collection and at the end of each conditioning period, clams were induced to spawn with thermal shocks (16.7 °C to 26 °C) and sperm. The first spawns were observed on day 28, but only 50% of the males and 33% of the females were mature, and their mean oocyte diameter (36.33 µm) was smaller than the minimum (45–50 µm) considered for ready-to-spawn clams. However, on day 45, all males and females were mature (mean oocyte diameter = 45.14 µm) and 1102 × 10³ eggs were released. To ensure a high maturity rate, yellow clams should be conditioned in captivity for 45 days. Monitoring gonadal development in the wild to collect clams at advanced stages of gonadal development may be a less expensive strategy worth considering.