Abentin Estim

Water quality remediation using geotextile in fish hatchery systems.

This study was designed to use Aquamat™ in the daily exchange and flow-through culture systems of fish hatchery for improving the quality of seawater. Aquamat™ is a commercial innovative product fabricated from highly specialized synthetic polymers that forms a three dimensional structure. Results showed that the Aquamat™ reduced ammonia (NH3-N), total suspended solids (TSS) and dissolved oxygen (DO) concentrations in the daily exchange system but not in the flow-through system. Average values of NH3-N (F=0.028; t=-2.006; P=0.047), TSS (F=4.550; t=-2.787; P=0.006) and DO (F=25.085; t=-2.833; P=0.005) concentrations were significantly lower in the culture tank with Aquamat™ than the culture tank without Aquamat™. Fish biomass gain was significantly higher (F=2.177; t=-4.296; P=0.001) in the culture tanks of with Aquamat™ than without Aquamat™. The bacterial density was significantly higher (F=11.437; df=2; P=0.000) on the surface of Aquamat™ than in the seawater of culture tanks with and without Aquamat™. This study suggests that the Aquamat™ provides surface area for fish to hide from cannibalism activity, thereby reducing mortality. It was also found that the extra feeds and fish wastes attached to the surface of Aquamat™, reduced TSS concentration in the water with culture system. The surface of Aquamat™ also provided places for microbes to grow and increased the nitrification process. The nitrification processes converted NH3-N to NO2-N then NO3-N with help from nitrifier bacteria and DO concentrations, which reduced NH3-N toxicity in the culture system. However, result also showed that the Aquamat™ increased the NO2-N and NO3-N concentrations in the culture system. This study suggests that the Aquamat™ is still not capable of eliminating the entire amount of dissolved inorganic nitrogen in the culture system for water quality management in a fish hatchery system.

BEHAVIOR AND RESPONSE OF JAPANESE CATFISH (Silurus asotus) IN CAPTIVITY PROVIDED WITH AN ARTIFICIAL MICROHABITAT MOSAIC

Rearing of Japanese catfish ( Silurus asotus ) requires special considerations for designing of facilities and management. Information on its biology in natural environment provides ideas for developing suitable culture systems. For this species, underwater artificial microhabitat structures are needed to perform its normal behavior. The fish shows distinct preferences for some designs based on visual cues and its decision to make use of these structures is guided by other cues probably related to light and water flow. Microhabitat structures can make a real difference to managing stress of captivity in this species. Absence of a suitable structure causes ‘habitat bottleneck’ that develops aggressive behavior. However, the intraspecific antagonistic behavior gives way to social tolerance among conspecifics. Microhabitat metrics is important in addition to physical attributes of the structure so as to allow social grouping in the fish under favorable conditions.