Optimizing Trout Farm Effluent Treatment by Stabilizing Trout Feces: A Field Trial

The following study investigates the effect of adding guar gum binder to a commercial extruded trout diet (Select P/Trouvit) in a land-based water-flow-through trout farm, analyzing the effects of binder-mediated fecal stabilization with respect to particle size distribution, nutrient retention, and the effectiveness of drum filtration of effluent. The experiments took place in a facility with two raceways of similar size and water flow rate and with similar stocks of rainbow trout Oncorhynchus mykiss. Fish in one raceway were fed Select P, while those in the other raceway received the same diet with the addition of guar gum. When the fish were given feed containing the dietary binder, feces were discharged in visibly and significantly larger particles. Furthermore, in effluent from the raceway in which fish were fed the diet plus binder, the particle-bound fractions of phosphorus and Kjeldahl nitrogen were increased at the expense of the respective dissolved fraction by about 18% and 8%, respectively, possibly reflecting a reduced leaching of nutrients from the larger particles. Drum filter removal efficiency was significantly higher for the effluents from the fish fed the binder-containing diet; for both total suspended solids and total phosphorus there was an improvement of about 40%. For total Kjeldahl nitrogen the improvement was about 17%. For the particulate fraction, removal values were even higher, efficiency improving about 47% for particulate phosphorus and 34% for particulate Kjeldahl nitrogen. The addition of the binder to the trout diet proved to be an effective means of improving mechanical effluent treatment and thus to developing environmentally sound fish production opportunities.