Gary J. Burtle

Winter Feeding Frequency for Channel Catfish in Cages

Abstract Cage-stocked channel catfish (Ictalurus punctatus) with an average initial weight of 99 g were fed once a day on alternate days or once weekly throughout the winter (19 November–22 April). Total fish weight per cage on the alternate-day schedule increased by 32.1% over the study period. Less weight gain per cage was produced when fish were fed once weekly (1.7–8.5% weight gain; P < 0.01). Channel catfish weight can be maintained by once-weekly feedings during warm winters (mean water temperature near 16.3°C) by feeding during warming trends.

Water quality in catfish ponds subjected to high stocking density selective harvesting production practice

Abstract Nine 0·1-ha earthen ponds were stocked with 12500, 25000, and 37500 channel catfish ( Ictalurus punctatus ) fingerlings/ha in three replicates. Ponds were fed daily with a commercial feed at a rate up to 3% of the fish weight determined by sampling. They were periodically harvested to remove marketable fish weighing more than 0·25 kg. The harvested fish were replaced by fingerlings. Water quality of all ponds was monitored weekly by analyzing chemical parameters including nitrite-N, nitrate-N, total ammonia-N (TAN), total Kjeldahl nitrogen (TKN), total phosphorus, chloride, chemical oxygen demand (COD), and total and dissolved solids. Concentrations of nitrite-N, nitrate-N, TAN, and total phosphorus were not significantly different among stocking densities at any given time but were significantly different over time. The values of TKN and COD were significantly affected by treatments as well as time. The amounts of total solids were significantly higher for the highest stocking density treatment but the dissolved solids concentrations did not change significantly with stocking density or time. Ranges for chemical parameters were 7·0 to 8·4 for pH, 0·4 to 2·7 mg/litre for NH 3 N, 1·3 to 28·5 μg/litre for NO 2 N, 10·6 to 771·9 μg/litre for NO 3 N, 2·2 to 85·5 mg/litre for TKN, 28·2 to 150·0 mg/litre for COD, and 0·05 to 0·6 mg/litre for total phosphorus. The amount of total solids ranged from 105 to 262 mg/litre. The feed-to-weight-gain ratios were 1·66, 1·64, and 1·82 for high, medium, and low density treatments respectively.

Treatment of Aquaculture Wastewater Using Floating Vegetated Mats

Methods are needed for treating aquaculture wastewater. The goal is to improve water quality sufficiently for it to be recycled to production ponds. One method is to use floating vegetation in treatment tanks. Alternatively, the floating vegetation could be grown directly on the production ponds. A study with floating vegetated mats for improving aquaculture wastewater quality is being conducted at the Univ. of GA Aquaculture Unit in Tifton, GA. The objective is to determine amount of biomass produced, nutrients removed, and quality of the treated wastewater. Wastewater from fish-production ponds is pumped into sets of 1285 L aquaculture tanks. There are three tanks in series in each treatment set, and three replicate sets per vegetative species. Each tank contains a floating platform (1 m2) for growth of vegetation. During a prototype test of wetland, horticultural, and agronomic plants, it was determined that cattail, iris, or soft rush were suitable for growing in aquaculture wastewater. The treatments are three-tank sets of cattail, iris, soft rush, or a control (no plants). The water is circulated every three weeks such that tank 1 receives water from the fish pond, tank 2 receives water from tank 1, tank 3 receives water from tank 2, and tank 3 is drained into a nearby storage pond. Water samples for analyses are collected from each tank prior to transfer to the next tank. Plant biomass is harvested as needed. Measurements are made of total biomass per tank and nutrient content (N, P, and K) of the plant tissue. Water quality measurements include N, P, K, BOD, chlorophyll, O2, turbidity, and pH. This paper presents partial results of the three-year study which started in May 2009.