58 



YVES B. PLESSIS 



Size of tank 

 (length x width 



w height) Occupied hy — 



15x10x15cm Scyphistomata, small 



groups of algae, Amphi- 



poda, etc. 

 20x15x20 cm Suitable for a very large 



number of animals of 



small size. 

 30x22x24 cm Small Decapoda, mussels, 



Ophiuroidea, etc. 

 25 liters and above.- Fishes, crabs, etc. 



Air inlet 



O o 



Figure 2. — Bottom of the exhausting device; it 

 consists of a tube of plasticized vinyl. Its 

 lower part is chamfered and perforated by 

 little holes. A, air Inlet. 



Today's techniques make it possible to 

 build tanks of transparent plastic mate- 

 rials. The main advantage is the pos- 

 sibility of having tanks built according to 

 the model chosen, and of fixing water 



712-029 0—64 5 



inlets and outlets without the need for any 

 siphons. The fragility of these tanks is 

 usually rather great, particularly in the 

 large sizes. They must be well constructed 

 so as to prevent the pressure of the water 

 from tearing the seams of the walls apart. 



Tanks with metal corners have the great 

 advantage of being able to be built in large 

 sizes. The metal must be particularly 

 carefully insulated so as to prevent it from 

 being attacked by the sea water. The 

 plastic or bituminous linings that may 

 be used are evidently unsuitable for phys- 

 icochemical investigations of the water. 



There are tanks of 100 to 200 liters' ca- 

 pacity, the frameworks of which are of 

 fiber or cement covered with plastic. The 

 only real inconvenience is the size of the 

 framework. 



In summary, in a particularly detailed 

 study where the chemical elements have 

 been specially studied, it is preferable to 

 use only glass or plastic material. 



Water supply to the breeding tanks is 

 by means of a cascade arrangement. An 

 upper tank receives the water from the re- 

 serve tank through an exhausting device 

 or through a pump, and the excess flows 

 into a tank located at a lower level, and 

 so forth, down to the lowest one, which 

 generally empties itself into the reserve 

 tank by means of a filter. 



"Whenever the arrangement of a tank 

 makes it possible, we have attempted to 

 establish a cross circulation in such a way 

 that the entire water mass is renewed. 

 When there are only very small animals or 

 plants, and when the current of the water 

 is weak, the water may very well pass from 

 the inlet to the outlet without renewing the 

 contents of a tank. In that case, calm 

 zones come into existence where the phys- 

 icochemical conditions of the milieu may 

 be very different from those prevalent 

 within the current of the water. We may 

 cause the water to arrive from the tank 

 at an angle and at the bottom, while we 



