The global population is projected to expand beyond 9 billion by 2040. Current global human consumption of seafood is 157MT and is projected to grow by 1.1% annually for the next decade. Historically, natural fisheries have sustained population growth, but all are now at risk of collapse due to overfishing. Coupled with climate change induced crop instability, global ability to sustain food supply is threatened. Fortunately, aquaculture has been growing steadily since 1980 and is projected to surpass capture fisheries for all fish production by 2025. To further promote growth in the industry, innovation is paramount. Flowthrough rearing systems for oyster larvae were first described in 1977 and offer the advantage of potential improvements in water quality while simultaneously allowing increased larval densities. Oyster flowthrough system designs follow a similar pattern-- cone-bottom tanks, banjo-sieves, and bubble columns for mixing. Continuous flow through is relatively new, with earliest literature mentions around 2011. During veliger and pediveliger stages, and before transfer to downwelling, the cone may concentrate larvae and risks dangerous densities near the bottom due to the exponentially decreasing surface area.
The updated design reduces risk by utilizing a 750L convex bottom fiberglass tank. A bottom drain will be installed peripherally, and the system will be angled 2.5° for complete drainage. A standpipe shall be inserted in the drain during normal operations to serve as overflow protection. The center standpipe will be used for volume control. Height of the center standpipe will be modular to allow rapid reduction in larvae density through incremental volume increases. Larvae will be retained using a 0.5m2 mesh screen cylinder supported by a ring permanently affixed to the bottom of the tank. Aero-Tube® will revolve around the retention ring to aerate, mix, and reduce larval entrapment. A secondary algae retention tank will provide algae continuously to the culture tank.
Optimal densities will be established and tested using flowthrough protocols developed by Reiner in 2011. Maximum and minimum exchange rates will be determined using data obtained from density trial combined with daily flow rate and NH3-N assessments to develop exchange rate/population curves. Intermittent flow testing will also be performed using an automatic valve and intermittent cycle timer to determine optimal flow and cycle rates to maximize larval survival and growth.