aboard our collecting vessel, R. V. Shrock. Approxi- 

 mately 150 fish were transported to the holding 

 facility at the New England Aquarium. 



The holding facility (Fig. 1) incorporated three 

 biological filters to break down nitrogenous waste 

 products and a mechanical filter to remove particu- 

 late matter. Water was gravity siphoned into the 

 biological filters, and then air lifted back into the 

 tank. The mechanical filter pumped water from the 

 bottom center of the tank through a sand filter and 

 back into the tank at about 60 gal/min flow. This 

 return line helps in aeration of the tank as well as 

 creation of a current which appears to aid in the 

 schooling behavior of the fish. The walls of the 

 holding facility were painted black, a technique 

 which reduces the likelihood of fish colliding with 

 the walls (Hettler). The fish were fed finely grained 

 food 4 to 5 times a day; total daily intake was 

 approximately 5% of their body weight. Experimen- 

 tation with various food sizes indicated that Purina® 

 tropical fish food gave the most efficient feeding 

 since it remained in the water column long enough 

 for maximum consumption. 



No immediate losses were noted due to handling 

 and transfer. However, during the first 2 weeks a total 

 of 34 fish, or 22%, died, possibly from the effects of 

 net damage. Since that time only three additional 

 fish have died. Standard water quality parameters 

 were measured on a regular basis. During July and 

 August the temperature remained about 20°C, but 

 as cold weather set in the temperature steadily 

 dropped to 13°C, and an abrupt color change 



RAPID SAND FILTER 



60 GAL/MIN 



BIOLOGICAL 



FILTERS 



12 GAL/M IN/FILTER 



FIG. 1 Menhaden holding facility. 



82 Clay, Barker, Testaverde, Marcello, McLeod 



occurred in some fish, from bright silver to black, 

 possibly indicating thermal stress. Reduced feeding 

 behavior and sluggishness were also noted. Salinity 

 remained between 30 and 32 ppt, pH was maintained 

 between 7.5 and 7.8, and dissolved oxygen between 

 6 and 7 ppm. Ammonia levels rose for 3 weeks to a 

 maximum of 3.5 ppm until the bacterial population 

 in the biological filter was established. Values then 

 steadily declined to a stable level of 0.225 ppm and 

 the nitrate levels subsequently rose from 0.5 ppm 

 to a maximum of 2.5 ppm. Nitrite also rose from 

 0.006 ppm to 1.5 ppm during the same period. 

 Water changes were made as necessary to keep 

 nitrate and nitrite levels below 3 ppm NOT and 

 1.5 ppm NOI. 



TESTING PROCEDURE 



Fish were removed as needed to perform tests, 

 and a control was run at each saturation. Twelve 

 fish were used in each experiment, six in the test 

 tank and six in the control. The test and control 

 tanks were 145-gal capacity with the test tank 

 attached to a 50-gal pressure chamber detailed 

 in Fig. 2. The pressure chamber was constructed 

 of 60 cm diameter PVC pipe. A 3/4 hp pump provided 

 water circulation through the pressure chamber and 

 a ball valve on the return line to the test tank pro- 

 vided control of pressure and water flow. Original 

 experiments used a venturi method of aeration in 

 the pressure chamber; however, in later experi- 

 ments an air compressor was added to allow for 

 higher saturations. 



The temperature, dissolved oxygen, and dis- 

 solved gas pressure were measured at regular 

 intervals during the experiment in both the control 



BALL VALVE <& 



PUMP 



AIR VENT 



© 



SATURATION CHAMBER 

 50 GALLONS 



3/4 H. P., 26psi 



AIR 

 COMPRESSOR 



40 psi 



PRESSURE 

 GAUGE 



FIG. 2 Supersaturation testing system. 



