tags were fastened with nickel pins. Three 

 fish tagged with stainless steel pins and 

 three fish tagged with nickel pins were 

 placed in each tank. 



Control Pins 



In addition to pins attached to the 

 fish, two groups of control pins were set 

 up to distinguish the effects of the raw 

 harbor water, the aquarium water and the 

 body fluids of the fish. A group of 10 

 stainless steel pins and 10 nickel pins 

 were put in the aquarium water with the 

 fish and a similar group was placed in the 

 harbor. Half of these pins were bent as in 

 tjigging and half were left straight to see 

 if bending affected the resistance to cor- 

 rosion. 



rising until it reached 70° F. on July 1. 

 The last fish succumbed on July 12. These 

 data are shown in table 2. 



Although 36 fish had been tagged, 

 only 34 tags were recovered from fish dur- 

 ing the course of thg. experiment . The tags 

 which had fallen off two fish were later 

 recovered from the bottom of the tank. 

 When a fish died its tags and pin were re- 

 moved intact and washed in fresh water. 

 The tag number, the date and the condition 

 of the tagging wound were noted. At the 

 end of the experiment the control pins were 

 removed from the tanks and the harbor and 

 washed in fresh water. All pins were exam- 

 ined under a binocular microscope for 

 evidence of corrosion. 



Fish Survival 



RESULTS 



There was some mortality throughout 

 the experiment, but 20 fish survived for 

 eight weeks. All these died during the 

 ninth week, probably from lethal water tem- 

 peratures. Previous studies at Woods Hole 

 have shown that haddock do not survive well 

 at water temperatures higher than 65° F. 

 The temperature in the tanks was 53° F. on 

 May 9 and reached 65° F. on June 19, six 

 _weeks later. The temperature continued 



Table 2. -- Abstract of the experimental log 



Nickel Pins 



On Tagged Fish 



Date 



May 9 

 16 

 23 

 30 



June 6 

 13 

 20 

 27 



July 4 

 12 



Water 



Temperature 



(degrees Fahrenheit) 



&3 

 54 

 57 

 59 

 60 

 62 

 67 

 69 

 70 

 70 



Number of 

 fish alive 



All the nickel pins were corroded 

 except one pin that was on a fish which 

 died the day after tagging. Most of the 

 nickel pins were corroded where they passed 

 through the operculum and were in contact 

 with tissue. The degree of corrosion vaxied 

 from minor (staining and shallow 

 etching on the surface metal) to 

 extensive (deep etching and weaken- 



ing of the metal). Two pins were 



partially worn through from abrasion 

 by the tag discs, one was abraded 

 by the inner disc, the other by the 

 outer disc. 



36 

 32 

 27 

 26 

 25 

 25 

 22 

 22 

 20 

 AU dead 



Three pins appeared sound on 

 the surface but broke when bent, 

 revealing a hollow corroded interior 

 covered by a thin skin of apparently 

 unaffected metal. This phenomenon 

 has also been noted by Calhoun, Fry, 

 and Hughes (1951) and Forrester and 

 Ketchen (1955). In one case the 

 nickel pin weakened and broke, allow- 

 ing the pin head and inner disc to 

 fall off the fish. The rest of the 

 pin and the outer disc remained 

 attached to the fish. This probably 

 explains the loss of both tags by 

 two fish on which nickel pins had 

 been used. Table 3 summarizes the 

 condition of nickel pins on tagged 

 fish. 



