Fish Migration 203 



to the sea, which is usually about six 

 months after." A very good effort in 

 days before steam or petrol were dreamed 

 of, and any avowed naturalist was re- 

 garded with suspicion. To-day fish are 

 marked with discs of vulcanite attached 

 near the dorsal fin, both above and 

 below, with silver wire, which disc bears 

 cryptic numbers and letters referring to 

 longitude, latitude, date, depth and 

 temperature of water. The actual mark- 

 ing occupies a few seconds only and 

 entails no bloodshed. The specimens ; 

 with their passports, are kept in tanks 

 aboard the ships of the fishery board 

 until they have recovered from the 

 shock of being caught up and are fit for 

 return to the sea. Much valuable data 

 has thereby been obtained. It is known 

 that a plaice lives to fifty years of age 

 and that only three per cent, of these 

 fish caught by trawlers are of marketable 

 size. A vigorous flat-fish, striking bad 



