Chemical addition for accelerated biological filter acclimation in closed blue crab shedding systems

Abstract

Heavy loading of commercial crab shedding systems is a major problem at the beginning of the softshell crab season if the biological filters are not properly acclimated. Thus methods that can be used to accelerate filter acclimation in a commercial setting are desirable. Experimental shedding systems with submerged rock filters impacted by media size, commercial additives containing nitrifying bacteria, and chemical addition were examined. Filters acclimated with crabs took 35 days to adjust to base line water quality conditions. The filters demonstrated the ability to be increased to full design loading if acclimated with 25% of the shedding system design. Filter media size and addition of concentrated nitrifying bacteria did not have any significant effect on acclimation time of the nitrification beds. Addition of ammonia to simulate loading acclimated a biological filter without the use of animals, but did not shorten the acclimation time. The most promising avenue of research is the addition of ammonia and nitrite in combination to stimulate growth in both species of nitrifying bacteria simultaneously. Nitrite addition during startup of a biological filter reduced the acclimation period by 10 days (or 28%).