Rainbow trout larvae production in an airlift-based recirculating system

Abstract

Replacement of traditional flow-through (FT) systems with recirculating aquaculture systems (RAS) can reduce fresh water demand and environmental effects of aquaculture practices. Thus, we investigated the utility of a simple airlift-based recirculating egg incubation system with low initial construction costs and low demand for fresh water to incubate rainbow trout (Oncorhynchus mikiss) eggs and produce advanced larvae. An airlift-based recirculating system, consisting of a trough with four trays was designed, and a flow-through California trough with four trays was used as control. In each tray of the flow-through and recirculating systems, 5000 fertilized eggs were introduced. Water flow rates were 6–7 l/m in both systems. Physicochemical conditions, quality of eggs, and number of yolk-sac larvae were surveyed during the 42-day experimental period. In both systems, eyed eggs occurred at 14 days after fertilization. In the FT system and the RAS, all of the fertilized eggs hatched at 28 and 29 days after fertilization, respectively, and yolk-sac depletion occurred at 41–43 days after fertilization. In the FT system and RAS, percentages of eyed eggs were 79.75% and 79.01% respectively, and hatching rates were 70.31% and 63.65%, respectively. The survival rate of fry was 68.26% in the FT system and 61.07% in the RAS. There were no significant differences between two systems in terms of wet weight or dry weight at hatching time (p > .05), while final length (25.53 mm), wet weight (161.19 mg) and dry weight (30.78 mg) of larvae in the FT system were significantly higher than in the RAS (25.09 mm, 149.99 mg and 29.37 mg, respectively). In conclusion, the simple airlift-based system could be used effectively in the egg incubation period, while growth performance of larvae was little affected by this system as compared with the FT system.