SEA-WATER SYSTEMS FOR REARING FISH LARVAE 



85 



POLYTHENE 

 INCUBATOR 



INCUBATOR 

 EXHAUST 



TRAY WITH 

 GREEN ALGAE 



GLASS WOOL 

 FILTER 



HATCHERY 

 AIR HEATER 



INCUBATOR 

 SUPPLY 



SEAWATER 

 HEATER 



CONCRETE 

 RESERVOIR 



Figure 2. — Closed sea-water circulation for rearing plaice : 3,500-gallon capacity. 



A greenhouse covers the reservoir, so it 

 receives natural lighting during the day. 

 Low-wattage immersion heating panels, 

 embedded in epoxy resin and controlled by 

 floating thermostats, counteract excessive 

 cooling of reservoir water during cold 

 weather. For 2 years there were no safe- 

 guards against rapidly rising water tem- 

 peratures in spring and early summer. A 

 separate cooling circulation combined with 

 filtration and bacterial control was instal- 

 led in 1961 (fig. 3). Sea water is pumped 

 at a fast rate from the far end of the reser- 

 voir into three plywood boxes irradiated 

 with ultraviolet light. After treatment, 

 water overflows out of the boxes, through 

 glass-wool filters, into three 100-gallon as- 

 bestos-cement tanks, each containing two 

 refrigeration coils made up from 50-foot 

 lengths of %-inch steel tubing. All six 

 coils are connected to a 3-horsepower 

 motor and compressor controlled by a 

 thermostat in the reservoir. Water over- 

 flows from the cooling units back into the 

 main tank. 



ULTRA VIOLET 

 LIGHT ASSEMBLY 



COMPRESSOR 



Figure 3. — Reservoir cooling circulation com- 

 bined with filtration and ultraviolet irradia- 

 tion. 



