World Aquaculture December 2019

WWW.WA S.ORG • WORLD AQUACULTURE • DECEMBER 2019 35 species in stand-alone aquaculture systems as well as in IMTA systems. Conch successfully mated and spawned in captivity in the HBOI IMTA system. Results of this study supported previous results indicating that adults can be stocked at higher female to male ratio without loss of female productivity in regards to the number of egg masses and number of eggs produced per female per week (Gillette 2003). Stocking females at a higher sex ratio (2 to 5 females per male) may also alleviate male guarding and sparring (see sidebar). In this study, variation in sizes of egg masses laid were not different between the two sex ratio treatments (3-19 ml volume displacement). This variation resulted in a broader range of estimated number of eggs per egg mass (41,000-262,000; n=50) compared to a previous study where the range was 76,000-182,000 (n=10) (Shawl and Davis 2004). These range differences were likely due to the number of egg masses sampled or variation of the sizes of egg masses found in each study. Gillette (2003) also showed variation in sizes of egg mass based on measurements of length × width × height (0.48–33 cm 3 ), however, the number of eggs per egg mass was not determined. Egg mass output of Florida fighting conch will vary based on factors such as type of system, stocking density, when conch were placed in the study, matings, and a host of environmental parameters. Cleanliness of the sand substrate in this study also appeared to play a role in egg laying frequency. When sand was siphon-cleaned, egg laying resumed the following day. The mean number of egg masses laid per female per week in this study was lower (0.30 egg masses) compared to 0.56 for Shawl and Davis (2004), but was higher than the 0.10 for Gillette (2003). Females maintained higher egg mass productivity during the first two weeks of the study. Fighting conch store sperm over prolonged periods (Bradshaw-Hawkins and Sander 1981, D’Asaro 1965) and tend to lay a higher number of eggs in captivity after handling from transport (seen in this study and Shawl and Davis 2004). This production peak needs to be taken into consideration when planning a breeding program. In the Gillette (2003) study conch were placed in the study seven weeks after collection and this might explain the lower number of egg masses per female per week. During the last two weeks of the study there was a decrease in female productivity and some egg masses were observed to have egg capsules and portions of egg strands were empty, indicating lack of fertilization. Based on this study and previous studies with conch reproduction in captivity and in the field, pH, ( C O N T I N U E D O N P A G E 3 6 ) FIGURE 15. The effect of sex ratio on mean (+ SD) volume of egg mass per treatment during the four-week study. FIGURE 16. Correlation between the number of eggs per egg mass (y) and volume (mL) of egg mass (x). The values are determined by independent methods (see text). FIGURE 13. Weekly number of egg masses collected per treatment during the four-week study. FIGURE 14. Weekly number of conch egg masses collected for both treatements combined compared with the number of observed daytime matings during the four-week study.