Response of channel×blue hybrid catfish to chronic diurnal hypoxia

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 Channel Catfish × male Blue Catfish) may be doubled relative to those achieved with the 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. Although higher stocking rates in those studies did produce greater yields, individual fish growth and feed intake may have been impacted by lower DO levels while appearing to be a direct density effect. In this study, production of hybrid catfish, which were fed daily to satiation in earthen ponds with no water exchange, was compared at low (5,000 fish/acre) and high (20,000 fish/acre) stocking rates while using controlled intensive aeration to maintain a minimum DO over 3.0 ppm in all ponds through the study. We achieved an average net production of 27,704 lb/acre at the higher stocking rate compared to 10,176 lb/acre at the lower stocking rate. Although this is the highest yield reported thus far in traditional static‐water earthen ponds in the southern USA, it may not be the maximum production possible. The average weight of harvested fish was higher at the lower density (2.2 lb versus 1.6 lb), but the feed conversion ratio was identical (1.8) at the two densities. Our data indicate 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 variables unrelated to morning DO—specifically un‐ionized ammonia—may play a role in catfish feed intake and growth but not food conversion.

Section: Resultsmentioning

confidence: 65%

“…) and hybrid catfish (female Channel Catfish × male Blue Catfish; Green et al. ), although hybrid catfish are a bit more tolerant of low DO than are Channel Catfish (Green and Rawles ; Torrans et al. ).…”

mentioning

confidence: 99%

Effects of Density on Production of Hybrid Catfish in Intensively Aerated Earthen Ponds where Dissolved Oxygen is Not a Limiting Factor

Torrans¹,

Ott²

2019

“…In both years of this study, FCRs were not affected by minimum DO concentrations. This was also seen by Torrans (2005Torrans ( , 2008 with Channel Catfish; Torrans et al (2012) with Channel and Blue Catfish; and both Green and Rawles (2011) and Green et al (2012) with Channel and hybrid catfish. Reduced feed intake and decreased growth under moderate hypoxia does not affect FCR in numerous fish species, including Rainbow Trout (Glencross 2009) and Nile Tilapia (Tran-Duy et al 2012), a finding that is presumed to result from decreased energy requirements when feed is restricted.…”

Section: Discussionmentioning

confidence: 73%

“…Torrans et al (2012) similarly showed a decrease in Channel Catfish feed intake of 30% and 44% at similar DOs (data for Channel Catfish interpolated from Figure 5 of Torrans et al 2012). Using a similar experimental design, Green et al (2012) showed an 18% reduction in hybrid catfish feed intake for the June-September growing season when fish were maintained at a minimum DO concentration of 1.6 ppm versus 3.1 ppm in the high-DO controls (B. Green, Agricultural Research Service, personal communication).…”

Section: Discussionmentioning

confidence: 84%

“…This same principle has also been demonstrated in nonaerated warmwater earthen ponds in which the DO concentration normally cycles up to or above air saturation during the day (from photosynthesis) and then drops to lethal levels during the night (from respiration). Torrans (2005Torrans ( , 2008, Torrans et al (2012), Rawles (2011), andGreen et al (2012) demonstrated that Channel Catfish, Blue Catfish, and hybrid catfish do not exhibit a significant reduction in feed intake, growth, or production until the minimum morning DO concentrations are below 3.0 mg/L (i.e., approximately 40% air saturation during the summer months).…”

Section: Discussionmentioning

confidence: 99%

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Impact of Minimum Daily Dissolved Oxygen Concentration on Production Performance of Hybrid Female Channel Catfish × Male Blue Catfish

Torrans¹,

Ott²,

Bosworth³

2015

Hybrid catfish (♀ Channel Catfish Ictalurus punctatus × ♂ Blue Catfish I. furcatus) were reared as single‐batch crops during the growing season (June–September) of two years under two different dissolved oxygen (DO) regimes each year: (1) a high‐DO (control) treatment with minimum daily DO maintained above 3.8 ppm in both years and (2) a low‐DO (test) treatment with minimum DO maintained at 1.6 ppm in the first year and 1.3 ppm in the second year. Fish were fed daily to apparent satiation with a 32% protein commercial feed and harvested each year. In both years, dissolved oxygen concentration significantly impacted gross and net production, final fish weight, and mean fish weight gain due to reduced feed intake. Feed intake was reduced in the low‐DO treatment by 26.6% in year 1 and 29.2% in year 2. Food conversion ratios averaged 1.83 overall and were not affected by minimum DO. Fish in high‐DO treatments gained an average of 44% more weight (1.50 lb/fish) than fish in low‐DO treatments (1.04 lb/fish). Initial weight at stocking also had a significant impact on weight gain: fish stocked at a 0.16‐lb average weight (year 2) gained 37% more weight than fish stocked at a 0.11‐lb average weight (year 1), even though the stocking rate of the larger fish was 50% higher. Hybrid catfish had less reduction in feed intake at reduced DO compared with reported values for Channel Catfish and Blue Catfish.

Effect of Grading Fingerling Hybrid Catfish (♀ Channel Catfish × ♂ Blue Catfish) on Growth, Production, Feed Conversion, and Food Fish Size Distribution

Torrans

Ott

2018

Hybrid catfish (♀ Channel Catfish Ictalurus punctatus × ♂ Blue Catfish I. furcatus) production ponds often produce a wide size range of fish, and payments to farmers may be reduced due to discounts for larger fish. In general, fish under 1 lb or over 4 lb may decrease the price paid to farmers, but this is highly dependent on individual processors. The present study was conducted to determine the effect of grading hybrid catfish fingerlings on the size distribution of harvested food fish. Three 0.25-acre ponds were stocked with ungraded fingerlings (average weight = 0.05 lb; coefficient of variation [CV] = 78.0%) at 8,000 fish/acre. An additional three 0.25-acre ponds were stocked with double-graded fingerlings of the same average weight (0.05 lb) as the ungraded fingerlings but with a significantly reduced size variation (CV = 26.9%). Grading of the fingerlings had no significant effect on any production variable other than final size variation (ungraded fingerlings: CV = 48.2%; graded fingerlings: CV = 26.1%). Final mean weights were identical (1.1 lb) and feed conversion ratios were nearly identical (1.58 and 1.57) between the treatments. Survival and net production were similar between treatments. Overall, 13.5% of ungraded fish and 1.2% of graded fish were less than 0.5 lb at harvest; 5.6% of the ungraded fish and 0.1% of the graded fish were larger than 2.0 lb. Grading of hybrid catfish fingerlings is an effective means of decreasing food fish size variability without impacting production efficiency.