World Aquaculture December 2019

34 DECEMBER 2019 • WORLD AQUACULTURE • WWW.WA S.ORG Study Results Except for pH, water quality parameters in this study were within acceptable ranges for conch reproduction (Gillette 2003, Shawl and Davis 2004). Temperature and pH values in the study tanks were statistically different between the morning (lower values) and the late afternoon (higher values). Mean pH value was 7.4 ±0.1 in the morning and 8.0±0.3 by late afteroon. Likewise, mean morning temperature (28.8 ±1.0 C) increased to a maximum (30.5±1.1 C) by late afternoon. Salinity fluctuated over the course of the study and it was significantly lower in week 1 with mean 35.5±0.6 ppt and was significantly greater in week 3 with mean of 39.1±0.8 ppt (one-way ANOVA, p<0.05). Total ammonia nitrogen, nitrite, alkalinity and dissolved oxygen remained relatively constant throughout the study period (Table 1). The mean shell length of female fighting conch (8.5 ± 0.5 cm; n=42) was significantly greater than that of males (7.9 ± 0.8 cm; n=18) (t-test, p < 0.05). All conch survived to the end of the four- week study. Egg masses were produced over 6-8 hour periods, primarily during the night or early morning hours. Fifty-one egg masses were collected during the study period with 32 from the 1:5 treatment and 19 from the 3:3 treatment. Egg mass production decreased over time in both treatments during the study period (Fig. 13). For both treatments, a greater number of observed matings coincided with a greater production of egg masses during the first two weeks (Fig. 14). Based on daytime observations, there were approximately double the number of matings in the 3:3 treatment (29 observed) compared to the 1:5 treatment (13 observed). However, daily egg mass production, standardized as egg masses per female per day was 0.04 ± 0.05 (n=6) for the 1:5 treatment and 0.06 ± 0.06 (n=4) for the 3:3 treatment, were not statistically different between sex ratio treatments (Kruskal-Wallis test, p < 0.05). The number of egg masses per female per week ranged from 0.03-0.80 for the 1:5 treatment and 0.08-1.10 for the 3:3 treatment, with the greatest productivity during the first two weeks of the study (Table 2). Egg mass data, including egg mass volume, number of eggs per mm of egg strand and number of eggs per egg mass is summarized in Table 3. Egg mass volume varied between 3-19 mL. The mean volume of the egg masses was 9.5 ± 2.5 mL for the 1:5 treatment and 7.6 ± 3.1 mL for the 3:3 treatment and there were no statistical differences between treatments (Kruskal-Wallis test, p < 0.05) (Fig. 15). The relationship between eggs per egg mass (y) and egg mass volume (x) can be expressed as y = 13775 x – (1 × 10 -10 ) (Fig. 16). Discussion This study supports the concept that Florida fighting conch is a promising newmarketable species that can be included as a TABLE 1. Water quality of the IMTA seawater before entering the study tanks (6/20 – 7/17, 2019). Results are expressed as mean + standard devition (n=number of samples) and range for dissolved oxygen. Parameter Results Temperature (°C) 29.6 ± 1.0 (60) pH 7.7 ± 0.2 (60) Salinity (ppt) 37.5 ± 1.4 (60) Total Ammonia Nitrogen (mg/L) 0.07 ± 0.07 (12) Nitrite (mg/L) 0.11 ± 0.03 (12) Alkalinity CaCO3 (mg/L) 137 ± 10 (12) Dissolved Oxygen (% saturation) 87.1 - 99.8 LEFT, FIGURE 10. Different size egg masses covered in sand from seven Florida fighting conch in the study. Photo: Megan Davis. MIDDLE, FIGURE 11. Measuring the displacement volume of a subsample of an egg mass to determine a correlation of egg mass volume with number of eggs per egg mass. Photo: Megan Davis. RIGHT, FIGURE 12. Measuring the egg strand length of a 1-mL subsample of the egg mass to determine a correlation of volume with number of egg per millimeter of egg strand. Photo: Megan Davis.