Location: Warmwater Aquaculture Research UnitTitle: Effects of density on production of hybrid catfish in intensively aerated earthen ponds where dissolved oxygen is not a limiting factor
Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2019
Publication Date: 7/13/2019
Citation: Torrans, E.L., Ott, B.D. 2019. Effects of density on production of hybrid catfish in intensively aerated earthen ponds where dissolved oxygen is not a limiting factor. North American Journal of Aquaculture. 81(4):417-423. https://doi.org/10.1002/naaq.10110.
Interpretive Summary: Catfish stocked at higher densities typically exhibit reduced growth. However, this effect may be confounded by the fact that ponds stocked at higher densities usually have lower morning dissolved oxygen (DO) concentrations and lower DO can reduce feed intake. We stocked ponds with hybrid catfish at high (20,000/acre) and low (5,000/acre) densities and maintained the DO above the concentration known to show no effect on feed intake. Fish in the high density ponds exhibited reduced growth, indicating that some factor(s) other than DO concentration, such as ammonia and/or behavioral interactions, also affects growth rate.
Technical Abstract: Research has demonstrated that by maintaining the minimum dissolved oxygen (DO) concentration in earthen ponds at or above 3.0 ppm feed intake and growth of Channel Catfish Ictalurus punctatus, Blue Catfish I. furcatus, and hybrid catfish female I. punctatus X male I. furcatus may be doubled over oxygen management regimes typically used on commercial catfish farms. In earlier studies using only emergency aeration or low levels of fixed aeration, the direct effect of stocking rate has been confounded by lower morning DO concentrations in ponds stocked at higher densities due to higher feed input and fish biomass. While higher stocking rates in those studies did produce greater yields, the lower DOs may have impacted feed intake and individual fish growth while appearing to be a direct density effect. In this study we compared production of hybrid catfish at low (5,000/acre) and high (20,000/acre) stocking rates, fed daily to satiation in earthen ponds with no water exchange, while using controlled intensive aeration to maintain a minimum DO over 3.0 ppm in all ponds through the study. At the higher stocking rate, we achieved an average net production of 27,704 lbs/acre, compared to 10,176 lbs/acre at the lower stocking rate. While this is the highest yield reported thus far in traditional static-water earthen ponds in the southern U.S., it may not be the maximum production possible. The average weight of harvested fish was higher at the lower density (2.2 lbs vs. 1.6 lbs), but the FCR was identical (1.8) at the two densities. Our data indicates that when morning DO is maintained above limiting concentrations, other factors such as direct density interactions (aggression and/or inhibitory pheromonal feedback), and/or water quality parameters unrelated to morning DO, specifically unionized ammonia, may play a role in catfish feed intake and growth but not food conversion.