and any depth gauge available and suitable 

 should be used if possible. Experimentation 

 may be desirable such as the use of explosives 

 or fish poison (a seepage container of rotenone) 

 in front of the net entrance, the use of a half- 

 meter plankton net of coarse mesh in place of 

 the cod-end can, or the installation of several 

 truncated cones of netting within the cod end 

 (similar to a fish weir) to prevent fish from 

 escaping the net. 



8-28 Removal of Specimens. — Carefully 

 and immediately remove all specimens from 

 the net. Small specimens should be kept in 

 addition to larger specimens. Immediately 

 place specimens in containers of sea water for 

 subsequent preservation. Color photographs 

 in daylight should be taken of each catch if 

 possible, but must be taken almost immediately, 

 as fish lose their color rapidly when exposed 

 to air or when preserved. Photography may 

 best be done by placing the specimens in sea 

 water in a shallow tray which has been marked 

 off with painted 1-inch squares or other suitable 

 scale. Print the trawl serial number on a slip 

 of paper and place it in a corner of the tray 

 to be photographed, in order to provide 

 positive identification. 



8-29 Preservation of Specimens. — Preser- 

 vation should be made immediately after 

 photographs have been taken. The specimens 

 should be placed in suitable containers as 

 described in sections 8-33 and 8-34. A Mid- 

 Water Trawl Sample label (N. H. O. 1338) 

 should be filled out and placed inside the jars 

 or containers, facing out. These labels (fig. 

 8-4) are printed on a special linen paper which 

 will last many years in preserving solutions. 

 They must be filled out with pencil (No. 2)i 

 or 3H is most desirable), and not ink nor indel- 

 ible pencil. If samples are split into more than 

 one container, label each container and note 

 in the Remarks column. Fish over 3 inches 

 in length should also have some of the formalin 

 injected into their body cavity. 



If bottles are not available, contents of 

 various trawls may be tied up in porous cloth 

 and placed in a larger container of preservative, 

 and each bag thus formed properly marked. 



8-30 Shipping Instructions. — ^Pack sample 

 containers in wooden cases for shipment to the 



U. S. Navy Hydrographic Office (Code 5430), 

 along with all log sheets and photograph 

 negatives. 



8-31 Precautions.^ — ^After using the net, it 

 is not necessary to rinse it in fresh water, but 

 it should be spread and thoroughly dried; 

 never store it in a damp condition. 



8-32 PRESERVATION OF BIOLOGICAL 

 SPECIMENS. — Specimens taken by plankton 

 tows are stored in quart or pint-size mason 

 jars. Those specimens taken by midwater 

 trawls that are too large to fit in glass jars may 

 be wrapped in cloth and placed in a container 

 after the preservative has been injected. 

 Specimen jars should be nearly full to prevent 

 damage to the specimens due to sloshing, but 

 leave a small air space to allow for expansion 

 within the closed jar. Do not overcrowd 

 specimens in the jars as this will prevent keep- 

 ing enough sea water in the container. Over- 

 crowding will also cause fish to harden in 

 distorted shapes. Fill the jars only one-third 

 full of specimens then add sea water to about 

 1 inch from the top. If the bucket and net 

 contain more samples, use additional jars. 



8-33 Preservative Used. — The best and 

 most easily prepared preservative is a 5-per- 

 cent solution of commercial formalin (37- to 

 40-percent solution of formaldehyde gases). 

 The specimens are preserved by adding to 

 the sea- water-filled sample jar a pinch of sodium 

 bicarbonate (baking soda) and the following 

 amounts of formalin (which will give approx- 

 imately a 5-percent solution) : 



to a pint jar, add 20 ml. of formalin; 

 to a quart jar, add 40 ml. of formalin. 

 Insert the special sample label, face outward, 

 before sealing the jar. 



8-34 Preservation of Fishes. — Small fishes 

 are stored in jars and preserved in the same 

 manner as described for plankton. Specimens 

 more than 3 inches long should have some of the 

 5-percent solution of formalin inserted into 

 the body cavity with a syringe before storing 

 in the solution. If the fish is too large to be 

 stored in a jar, it should have the body cavity 

 filled, be wrapped in formalin-saturated cheese- 

 cloth, and be packaged in a waterproof ma- 

 terial. Long thin fish may be stored tempo- 

 rarily in preservative-filled coring tubes. 



H. O. 607 



350676 O- 



85 



