دانلود رایگان مقاله مناطق اکسیژن دهی در برکه خاکی و معمولی گربه ماهی

Abstract

Dissolved oxygen (DO) is one of the most important water quality variables associated with catfish culture. Understanding the oxygen dynamics in commercial catfish aquaculture ponds is important for understanding when oxygen problems could arise throughout the growing season. Oxygenation zones (OZ, here defined as the area with DO reaching 2.5 mg/L or greater) in both conventional (CP) and split (SP) earthen ponds were determined and compared in July and August, 2013. Hach Hydrolab data sondes were placed in the ponds, and DO concentrations were measured hourly from 9:00 P.M. to 9:00 A.M. for three consecutive nights. Variables including OZ volume, total DO mass in OZ, kg of DO/m3, fish density in OZ, and kg of fish/m3 in the OZ, and DO isopleths were determined using average DO concentrations. The smallest sizes or lowest volumes of the OZs occurred at 5:00 A.M. in both systems. The OZ volumes at 5:00 A.M. showed no significant difference between systems in both months. The entire fish zone was completely oxygenated in August in the SP ponds. The CP system was considered completely oxygenated at both 12:00 A.M. and 9:00 A.M. in both months, and the OZ volumes were significantly larger than those in the SP system at the same time slots. The fish density and kg of fish/m3 in the OZ reached the highest at 5:00 A.M. in both systems in both months but without system difference. These results could help farmers evaluate the overall water quality performance of the two pond production systems.

4. Discussion

The SP and CP systems have similar OZ volumes at the 5:00 A.M. sampling times. Although they were equipped with the same number of aerators and the water had the ability to disperse farther throughout the larger CP system, the OZ in the SP was actually larger in terms of the OZ volume and total mass of DO within it. The fish zone of the SP was completely oxygenated (entire area >2.5 mg/L) at all sampling times with the exception for SP-1 at 5:00 A.M. in July and SP-2 when at 12:00 A.M., 5:00 A.M., and 9:00 A.M. in July. This was likely caused by an exceptionally large algal bloom for SP-2. Chlorophyll a data gathered from this pond one day prior to placing data loggers in the pond averaged 4874.45 g/L. The consumption of oxygen by this large phytoplankton bloom may have reduced oxygen in the fish zone to below 2.5 mg/L. Therefore, the size of the OZ and the amount of oxygen in it shrunk, and increased the fish density and kg fish/m3. Another possible explanation for the low DO in the fish zone of the SP system, particularly SP-1, could be the suspension of sediment that can cause DO depletion (Steeby et al., 2004). This resuspension of sediment could be caused by the high aeration rates in the relatively small fish zone of the SP, which could disturb the sediment and increase clay particles in water (Hollerman and Boyd, 1980). While almost every night in the fish zone of the SP system was fully oxygenated, there is a chance placement of the aerators near one of the sluiceways contributed to some loss of water with high DO. It is likely a minimal loss, but placement of aerators might have an influence on the oxygen dynamics of the OZs in the SP system. DO depletions in the fish zone of the SP system could also be the result of increased feeding rate compared to the CP system. Higher feeding rate is associated with longer durations of lower DO concentrations (Hargreaves and Steeby, 1999).