CULTURE OF RAINBOW TROUT Oncorhynchus mykiss IN A SMALL-SCALE, DEEPWATER, AIRLIFT DRIVEN AQUAPONICS SYSTEM  

Over the last several years we have been operating two 9,500-L, airlift driven, deep-water aquaponic systems in a greenhouse growing several species of fish in combination with plants.  To date, cultured fish species include tilapia (Oreochromis niloticus) and largemouth bass (Micropterus salmoides).  Plants cultured within this system include basil, romaine lettuce, radishes, red leaf lettuce, mustard greens and arugula.  

In Delaware, little to no rainbow trout culture is performed resulting in the need to import trout for early spring pond/stream stockings from surrounding states.  Rainbow trout (Oncorhynchus mykiss) are a cold-water fish with an optimal culture temperature between 12 and 15°C.  Because it is costly to import large fish, and due to a lack of data on trout culture in Delaware, we decided to assess:

(1)      How rainbow trout would perform in our aquaponics system, and

(2)      Whether or not we could produce rainbow trout large enough for local pond/stream stocking between October and by April by utilizing a single fall/winter/early spring growing season.  

In mid-November 2014, approximately 500(32 g average weight) O. mykiss were stocked into the two aquaponics systems 250 fish/system).  .  Fish were raised along with romaine lettuce for the duration of the 140 day grow-out trial.  Other than fish feed, no inputs were added to either system.  Dissolved oxygen, temperature and pH were measured daily.  Alkalinity, ammonia, nitrite, and nitrate were measured weekly.  Fish were sampled once a month for growth and feed ration adjustments.  Backwashing was performed once weekly when fish were small and as they grew, twice weekly.  Water levels on the systems were maintained by topping off of water due to evaporation or after a backwash event.  

Overall, while romaine lettuce production slowed down over the winter months to just two harvests during the 140 day culture trials, O. mykiss growth and survival was excellent over this same duration.  Rainbow trout grew to an average weight of 240 g and 237 g in the two aquaponics systems and survival was 92 % and 88 %, respectively.  Coupled with the fact that the rainbow trout in this project were stocked one month later than water temperatures would dictate, these results suggest that O. mykiss can be raised in Delaware over a fall/winter/early spring grow-out season to a size suitable for pond/stream stocking.  Further, it is suggested that O. mykiss is a suitable species for culture in an airlift, deep-water aquaponics system over winter months.