The idea behind this structure is it would sit on the water, its first tier depositing five fish to a random shoal within its radius every 5 minutes and, once fully upgraded, would then act like a Silo; able to replenish five shoals at once. This means it would take at least a day before a sizeable batch of fish were available again to be harvested.
Given its function, however, I recommend the item be purchasable only through the Merchant, at the Silo's current cost of 750 gems.