WWW.WA S .ORG • WORLD AQUACULTURE • JUNE 2022 39 trapped on the filter during weekly filter cleanings, likely due to organics accumulating in the system. All conch observations were made in the morning before feeding or any type of manipulation of animals or the system. Survival rate (= remaining amount of conch/original amount of conch × 100) at the culmination of the study was 92 percent. One mortality was noted for a female 15 days after commencement of the trial, likely due to stress during collection. One male conch was released 39 days after beginning the study due to abnormal behavior such as lack of food grazing, higher than usual mucus production, lethargy to stimuli and receding into its shell. Although the cause of this behavior is unknown, it was unusual and should be monitored. It was not anticipated that adult milk conch would grow during the study because all had flared lips and shell length is terminal after the lip is formed. At the end of the study, shell lengths (cm) of 22 of the original 24 adult milk conch were measured from the apex to the siphonal canal with calipers (Fig. 5). Males had a mean shell length of 9.6 cm ( C O N T I N U E D O N P A G E 4 0 ) and spray bars (Fig. 6), resulted in evaporation that caused salinity to increase over time. To control salinity a partial water change (1/3 of the water volume) was conducted (1/19/21) in the nursery system and this lowered salinity from 41 to 37 ppt. Also, to mediate salinity increase, spray bars were placed lower inside trays. During the study, the pH range was 7.5-7.9 and dissolved oxygen saturation range was 80.9-86.8 percent. Successful system operation such as spraying trays, siphoning tanks and pump filter cleaning schedules were all determined based on feces accumulation, uneaten feed and animal behavior. For instance, a small amount of excess mucus produced by conch was likely from overfeeding and/or high nutrient debris in the tray environment. Mucus observation and feed remaining were used to adjust the frequency of tray spraying and tank siphoning cycles from every three days to every seven days. On the other hand, filter cleaning on the intake side of the pump did not need to be adjusted and therefore was performed once weekly throughout the study. As the study progressed, there was an increase in the amount of debris TABLE 2. Weekly ranges, based on daily observations of remaining feed and milk conch buried percentages throughout the 10-week study. Remaining feed (%)1 Burying (%) Week Tank A Tank B Tank A Tank B 1 0 - 40 0 - 50 0 - 100 0 - 66 2 0 - 15 0 - 20 66 - 100 0 - 100 3 0 - 5 0 - 10 33 - 100 0 - 100 4 0 - 15 0 -10 0 - 100 0 - 100 5 0 - 10 0 - 5 0 - 66 0 - 100 6 0 - 10 0 - 5 0 - 100 0 - 66 7 0 - 5 0 - < 5 0 -100 0 - 66 8 0 0 - 5 0 - 100 0 - 66 9 0 0 - 5 0 - 66 0 - 100 10 0 0 - 10 0 - 100 0 - 33 1 Remaining feed corresponds to an estimated value based on visual observations. FIGURE 12, LEFT. Morning and afternoon temperature (C) during the 10-wk trial (December 8, 2021 – February 16, 2022). FIGURE 13, RIGHT. Salinity (ppt) during the 10-wk trial (December 8, 2021 – February 16, 2022).
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