Bartholomew W. Green

Effect of stocking large channel catfish in a biofloc technology production system on production and incidence of common microbial off-flavor compounds.

Density-dependent production and incidence of common microbial off-flavors caused by geosmin and 2-methylisoborneol were investigated in an outdoor biofloc technology production system stocked with stockersize (217 g/fish) channel catfish at 1.4, 2.1, or 2.8 kg/m3. Individual weight at harvest ranged from 658-829 g/fish and was inversely related to stocking density. Net fish yield ranged from 3.8-5.4 kg/m3, and increased linearly as stocking density increased. The percentage of sub-marketable fish (<0.57 kg/fish) increased linearly with increasing stocking rate. Mean total feed consumption increased linearly with stocking density, but feed consumed per fish was inversely related to stocking density. Feed conversion ratio did not differ significantly among treatments. Concentrations of geosmin and 2-methylisoborneol in biofloc water were low throughout the study. All sampled fillets contained low concentrations of geosmin and 2-methylisobornel, but these fillets likely would not be deemed as having objectionable “earthy” or “musty” off-flavors when evaluated by trained processing plant flavor testers because of the low concentrations present. Data from this study combined with data from our two previous studies provide strong evidence that the incidence of geosmin- and 2-methylisoborneol-related off-flavor episodes is low in the BFT production system.

Comparative Production of Channel Catfish and Channel × Blue Hybrid Catfish Subjected to Two Minimum Dissolved Oxygen Concentrations

Abstract The effect of daily minimum dissolved oxygen (DO) concentration on the growth and yield of channel catfish Ictalurus punctatus and channel catfish hybrids (female channel catfish × male blue catfish I. furcatus) sharing the Jubilee strain of channel catfish as the maternal parent was evaluated in a 234-d study in sixteen 0.1-ha earthen ponds (15,113 fish/ha). Ponds were managed to maintain a minimum DO concentration of 25% or 50% of saturation. The total consumption of 32%-protein feed at the high and low DO concentrations was 12,973 and 10,262 kg/ha, respectively, for channel catfish and 12,805 and 11,592 kg/ha, respectively, for hybrid catfish. The net yield of hybrid catfish (8,069 kg/ha) did not differ from that of channel catfish (8,037 kg/ha), but the mean individual weight of hybrid catfish was significantly greater. Net yield (8,740 kg/ha), individual weight (0.75 kg/fish), and feed consumption (12,889 kg/ha) were higher for fish in the high DO than in the low DO concentration treatment (...

The Effects of Harvesting and Hauling on the Blood Physiology and Fillet Quality of Market-Size Channel Catfish

Abstract Commercially produced, food-size channel catfish Ictalurus punctatus that were harvested using routine procedures had significant elevations in plasma cortisol, glucose, and lactate compared with preharvest fish captured from open ponds. Blood samples were taken from 10 fish in each of two treatments (liquid oxygen diffuser- and paddlewheel-aerated holding socks) and four sampling periods (before harvest, after socking, before loading, and before unloading) during each of 10 harvest events. Water column temperatures averaged approximately 27°C during the study. Ten fillet samples were taken from fish held overnight in paddlewheel- and liquid oxygen-aerated holding socks during some harvest events. Mean plasma cortisol levels averaged 3.02 ng/mL before harvest, 84.38 ng/mL immediately after socking, 135.22 ng/mL after 18 h in the sock (i.e., before loading onto the truck), and 128.54 ng/mL after 2–3 h on the truck (i.e., before unloading). Mean plasma glucose levels averaged 34.7 mg/dL before harv...

Evaluation of a Diffused Oxygen Aeration System under On-Farm Harvest Conditions

Abstract The aeration effectiveness of a diffused oxygen system was compared with that of a tractor-powered paddlewheel during eight harvests of channel catfish Ictalurus punctatus at Top Cat II Fishery in Chicot County, Arkansas. Dissolved oxygen and water temperature data were collected from a grading net aerated by the diffused oxygen system, from a grading net aerated by a paddlewheel, and from the open culture pond between the two grading nets and were not significantly different. However, comparison of estimated oxygen consumption by the biomass confined in each grading net indicated that the aeration effectiveness of the diffused oxygen system equaled or exceeded that of a paddlewheel during six field trials. An informal cost comparison indicated that a diffused oxygen system can be placed in service for a smaller capital investment than a tractor-powered paddlewheel and that the hourly operating expense of the diffused oxygen system is comparable to that of the paddlewheel. Results of the study in...

Comparison of Three Methods of Size Grading Channel Catfish Stockers

Abstract The stocking of size-graded catfish into production ponds should increase production efficiency, but grading large numbers of fish with existing technology is laborious. We evaluated the effectiveness of a mechanical grader recently developed at the University of Arkansas at Pine Bluff (UAPB) relative to that of box and sock graders and assessed injuries sustained by stocker channel catfish Ictalurus punctatus during grading. Three 0.25-acre ponds were stocked at 11,777 lb/acre. Initial total length (TL) ranged from 6.3 to 15.7 in, and initial weight of individuals ranged from 0.04 to 1.10 lb. The fish population in each pond was divided into three groups graded with the box grader, UAPB grader, or sock grader. Fish were graded twice with the box and UAPB graders; a bar spacing of 13/32 in was used to grade off small fish and a spacing of 13/8 in to grade off large fish. Sock grader mesh size was 13/8 in. Mean weights and lengths of the size-classes produced by grading (small, medium, and large) ...

Hepatic transcriptomic and metabolic responses of hybrid striped bass (Morone saxatilis×Morone chrysops) to acute and chronic hypoxic insult.

Striped bass (Morone saxatilis), white bass (Morone chrysops), and their hybrid are an important group of fish prized for recreational angling in the United States, and there and abroad as a high-value farmed fish. Regardless of habitat, it is not uncommon for fish of the genus Morone to encounter and cope with conditions of scarce oxygen availability. Previously, we determined that hybrid striped bass reared under conditions of chronic hypoxia exhibited reduced feed intake, lower lipid and nutrient retention, and poor growth. To better understand the molecular mechanisms governing these phenotypes, in the present study, we examined the transcriptomic profiles of hepatic tissue in hybrid striped bass exposed to chronic hypoxia (90days at 25% oxygen saturation) and acute hypoxia (6h at 25% oxygen saturation). Using high-throughput RNA-seq, we found that over 1400 genes were differentially expressed under disparate oxygen conditions, with the vast majority of transcriptional changes occurring in the acute hypoxia treatment. Gene pathway and bioenergetics analyses revealed hypoxia-mediated perturbation of genes and gene networks related to lipid metabolism, cell death, and changes in hepatic mitochondrial content and cellular respiration. This study offers a more comprehensive view of the temporal and tissue-specific transcriptional changes that occur during hypoxia, and reveals new and shared mechanisms of hypoxia tolerance in teleosts.

Effects of solids removal on water quality and channel catfish production in a biofloc technology production system

ABSTRACT Total suspended solids control was evaluated in a channel catfish (Ictalurus punctatus) biofloc technology production system. Settling chamber flow rates were 0.9 (LO) or 2.9 (HI) L/min to reduce total suspended solids to 300 mg/L; solids were not removed from control tanks. Channel catfish yields (7.6–8.7 kg/m3) were not affected significantly, but control fish were skewed toward smaller size classes. Control treatment channel catfish tolerated 1,410 mg/L total suspended solids without adverse effects. LO- and HI-treatment fillet geosmin concentrations were high enough to be designated as off-flavor. Water quality results suggested that nitrification was affected by solids removal.

Comparative water quality and channel catfish production in earthen ponds and a biofloc technology production system

ABSTRACT This 210-day study compared variation in water quality and fish growth for channel catfish (Ictalurus punctatus; 47 g/fish) stocked in earthen ponds (1.5 fish/m2, 14,820/ha) and in a biofloc technology (BFT) production system with high-density polyethylene-lined rectangular tanks (12.6 fish/m2, 126,000/ha). Feed input and culture environment affected water-quality dynamics. In ponds, phytoplankton uptake predominated and little nitrification occurred, whereas in the BFT system phytoplankton uptake and nitrification maintained low ammonia-nitrogen concentrations. Size classes of fish were skewed toward the larger market sizes in ponds and toward smaller market sizes in the BFT system. Mean final fish weight was 630 g/fish in ponds and 542 g/fish in the BFT system. Despite these differences, fish yield was higher in the BFT system (7.7 kg/m3 v. 1.5 kg/m3) because of the greater initial stocking rate.

A Submersible Magnetic Stirrer for Use in Measuring Photosynthesis in a Biofloc Technology Production System

Abstract Measuring photosynthesis or primary productivity in biofloc technology production systems is challenging because the biofloc must be maintained in suspension constantly. Photosynthesis can be measured in external incubators designed to keep the biofloc suspended in the biochemical oxygen demand (BOD) bottle, but primary productivity must be measured in the biofloc technology production system culture unit. Therefore, a submersible device is required to keep the biofloc suspended in the BOD bottle. This report details a submersible, air-powered magnetic stirrer that we designed, fabricated from off-the-shelf materials, and tested in biofloc technology production system tanks. Received November 28, 2011; accepted January 25, 2012