Controls 



Discussion and Conclusions 



All of the nickel pins in the aquarium 

 control lot were corroded. In the bent pins 

 the degree of failure ranged from pitting 

 and surface corrosion to hollowing. All of 

 the straight pins were hollowed, and broke 

 when tested with pliers. 



The control pins in the harbor showed 

 varied resistance to corrosion. Two bent 

 pins bore minor surface corrosion at the 

 bend, the other three were unjiffected. Two 

 of the straight pins showed minor surface 

 corrosion and one was unaffected. The 

 remaining two were lost during the experi- 

 ment . 



Stainless Steel Pins 



On Tagged Fish 



The stainless steel pins were almost 

 completely free from corrosion. Three pins 

 showed rust spots and one pin was partially 

 worn through by abrasion from the outer 

 disc. These results agree well with those 

 of Forrester and Ketchen (1955) who used 

 pins of Type 316 stainless steel in a field 

 tagging study. Type 316 differs from the 

 Type 304 used in this experiment mainly in 

 having 15 times as much molybdenum (Anon. 

 1947). 



Controls 



None of the control stainless steel 

 pins were affected by immersion in the 

 aquarium or in the harbor. 



Table 3. -- Summary of the average condition of the nickel 

 used to tag fish 



Time on Fish 

 Days 



Condition 



1 - 21 



22 - 42 



43 - 61 



62 - 64 



Minor corrosion 

 Moderate surface corrosion 

 Moderate to extensive corrosion 

 Extensive corrosion; hollowed pins 



ili 



Most of the structural damage to the 

 pins occurred where the pin contacted fish 

 tissue. Body fluids of the fish may have 

 been primarily responsible for the corro- 

 sion of the nickel pins on fish. Addi- 

 tional factors (Calhoun, Fry and Hughes 

 1951) which may have entered into the pro- 

 cess which caused the pin damage are the 

 galvanic effect produced by dissimilar 

 metcils (i.e., stainless steel, nickel and 

 the iron pipes and drain screens) immersed 

 in the aquarium tanks and/or the concentra- 

 tion-cell effect produced by a metal 

 immersed in a mixture of electrolytes (i.e., 

 fish excretory products and sea water). 

 Electrolysis from either cause, coupled 

 with actual chemical corrosion, would 

 accelerate destruction of the pins. This 

 could explain why the nickel control pins 

 in the tanks were more corroded than the 

 nickel control pins in the harbor which 

 corroded slightly or not at all. 



The airtif iciality of the aquarium 

 tanks as a fish habitat should be con- 

 sidered before any strict conclusions are 

 drawn concerning the usefulness of the pins 

 which were tested in this study. However, 

 since the nickel pins did corrode in the 

 aquarium and to some extent in the harbor, 

 it is reasonable to assume they would 

 corrode in the open sea over a period of 

 months instead of weeks. This conclusion 

 is supported by the number of nickel pins 

 which have corroded in the field tagging 

 of haddock. Similarly, since the stainless 

 steel pins did not corrode in the aquarium 

 or in the harbor they probably would not 

 corrode in field use. Based on the results 

 of these studies we have decided to 

 stop using nickel pins for tagging 

 haddock. 



Since the Type 304 stainless 

 steel pins we tested are resistant 

 to corrosion by the metabolic pro- 

 ducts of the haddock and also 

 resistant to corrosion by raw sea 

 water, we are using them exclusively 

 in field tagging of several marine 

 species. The pins were used in an 

 extensive haddock tagging program 

 conducted in 1956 and 1957. When 

 sufficient returns are available, 

 the relative corrosion resistjuice 

 of the stainless steel and the 

 nickel pins in actual field use will 

 be compared. 



pins 



