The evaluation of a short-term holding system for the North American lobster, Homarus americanus

The water quality parameters for use in the design of lobster (Homarus americanus) holding facilities were reviewed from published literature. The review indicated that several parameters (temperature, pH, salinity, dissolved oxygen, oxygen demand, suspended solids, ammonia and nitrite nitrogen) could be of major importance in the design of commercial short-term holding facilities where partial or complete water recycle is required. Of major interest were the changes in water quality immediately following the introduction of lobsters into the system. Monitoring of the changes in water quality for different biomass loading rates and temperatures was carried out at a commercial holding facility. The facility typically holds approximately 1000 kg of lobster in 13 tanks with a system water volume of 17500 1. Normally the water is completely recycled with treatment consisting of drop aeration, sand filtration and UV sterilization. Results indicated that water temperature is the most important factor in the maintenance of water quality and design of a lobster holding facility. It has an impact on lobster metabolism, the dissolved oxygen concentration and biochemical oxygen demand of the holding water, as well as affecting the rate of nitrification of ammonia. It was demonstrated that during the first 0.5 h after lobster introduction at the high experimental temperatures, water quality often deteriorated to a deleterious level, particularly with respect to dissolved oxygen concentration. Acceptable levels were regained gradually after the critical period. At a normal operating temperature of 7°C and a lobster load of 1100 kg, oxygen demand was reduced, as dissolved oxygen dropped from 10.5 to 8.5 mg.1⁻¹ compared to a drop from 9.0 to 5.5 at 13°C and from 8.2 to 3.3 mg.1⁻¹ at 19°C. An attempt to detect nitrification in the sand filters indicated that very limited activity was present at 12 and 17°C. The most important regulating factors were possibly the residence time of the holding water in the filter units and competition from heterotrophic bacteria. Results from experiments designed to establish the effectiveness of the UV sterilizers at controlling bacterial levels in the holding water showed that the units were effective in controlling bacteria at the three test temperatures. General recommendations regarding the design and maintenance of a short-term lobster holding system include: temperature control as an essential design feature; TOC control [the rest of the abstract is missing]Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat