Fish can either be raised in a staggered or batch method just like the crops. Almost all commercial aquaponics systems are based around batch production of fish, but there may be benefits to choosing staggered designs in certain markets. With staggered production, groups of fish of different ages are grown in separate or shared tanks and harvested continuously as they reach maturity. For batch production, fry or fingerlings are added all at once to fill all the tanks and then harvested at one time as well.

Benefits of Staggered Production

Staggered production works best for commercial aquaponics businesses that sell the fish directly to consumers through a farmer’s market stall, membership arrangement, farm store or other outlet. Buyers can pick up fish on a monthly or bi-monthly basis rather than only being able to make purchases every few months or less than once a year. This flow of income can be life-saving during the first few years of running the business. Mixing fish of different sizes and ages in the same stocking tanks also reduces food waste because the younger fish eat particles missed by their bigger counterparts.

Drawbacks of Staggered Production

Mixing fish of different ages doesn’t work well for carnivorous fish like perch and barramundi because the larger fish will eagerly eat the smaller ones. With these fish, you must grade the tank to remove slow-growing and smaller fish even when using batch stocking to avoid this kind of cannibalism. Staggering production also increases the total amount of work necessary to raise each pound of harvested fish and makes it harder to reach the production volume required for wholesale contracts.

Benefits of Batch Production

Batch fish stocking is the primary method used in aquaponics because it’s easier and more convenient. There’s no need to pick up new fingerlings every six weeks for months at a time, fewer issues between the smaller and larger fish, and easier calculations of feeding rates. Because smaller fish eat much more than larger fish by percentage of body weight, staggered stocking makes it tricky to ensure every fish is eating just the right amount for rapid growth without waste.

Drawbacks of Batch Production

Some aquaponics businesses find it difficult to move the sheer amount of fish harvested all at once in a batch production system if they don’t have a wholesale buyer. Fish can only be held for so long after harvesting without losing quality, even when flash frozen, and therefore may end up being wasted if buyer demand wanes. It’s also easier to lose an entire fish population in a batch system than in a staggered system with multiple rearing tanks. Separate rearing tanks reduce the spread of disease, preserving some of your stock when one or more tanks experiences a full die-off.