Living Silver 



inhabitants of the upper water, very active inhabitants w^ho hunted 

 down the sw^ift-moving nektonic fauna of these regions and did not 

 content themselves w^ith allow^ing plankton to drift into their 

 mouths. Herring, he thought, might easily be their main prey. 

 And the sw^ift forw^ard thrust of the low^er jaw^ confirmed his imag- 

 inations. It w^as so obviously designed to catch prey that w^as act- 

 ively sw^imming aw^ay from it. Yet, vs^hen either saithe or lythe 

 came up in a travel, they came up by the shoal, never individually, 

 never a few^ at a time. When they w^ere present, indeed, there 

 w^as usually nothing but them in the cod- end. There was no room 

 for anything else. And they were seldom found together: it was 

 either all saithe or all lythe. If you could tell the difference be- 

 tween them. Jan simplified matters for himself by saying the lythe 

 was *more so'. Its back was blacker ; its muscles were more obvi- 

 ously enormous ; its mouth jutted further forward ; its lateral line 

 was more highly developed. 



That was the other most conspicuous anatomical feature of both 

 fish, the highly developed lateral line. It was present in most fish, 

 though almost atrophied in many, a kind of sluice of nerve endings 

 that ran down both sides of the animal from the back of the head 

 to the beginning of the tail fin. The gadoids all showed it very 

 clearly, as in the black line that marked its course along the sides 

 of the haddock. But, in the saithe and lythe, it was perhaps the 

 most immediately obvious characteristic, as inalienably present as 

 the stripes of a tiger. Since these fish were caught in large num- 

 bers, though very irregularly, over large tracts of the sea, Jan was 

 inclined to believe that they were both shoaling species ; and he 

 could not refrain from imagining that their conspicuous lateral 

 lines had something to do with their shoaling behaviour, even 

 though he was aware that some other shoaling fish, like the herring 

 and the mackerel, had under-developed lateral lines. The sense 

 organ itself was built to receive vibrations and, although very little 

 else was known about it, it was known to be highly sensitive. It 

 seemed sensible to suggest that each fish in the shoal registered 

 vibrations from its companions who were swimming beside it, and 



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