DISTRIBUTION OF FISH AND OTHER ANIMALS. 29 
The question has often been raised as to 
how far the young fishes brought up in the shrimp 
trawl, if not actually dead, are so seriously 
injured, that they would not recover, even if 
promptly returned to the sea. We have made 
many experiments, and kept many records bearing 
upon this matter. In 1893, we devised a series 
of ‘‘ vitality’ experiments, which were carried out 
on the Fisheries’ steamer ‘‘ John Fell,” for several 
years. Sample fish from the various hauls, were 
placed, after their condition had been recorded, 
in a large tub, through which there flowed a 
constant circulation of sea water. The condition 
of the fish at stated intervals, half-an-hour and 
then hourly, was noted, and the ultimate recovery Fic. 8.—Boat working a Shrimp Trawl. 
or death. The result, naturally, depended greatly upon the kind of haul, the length of the 
drag, the weight of the catch, the muddiness, and other particulars; but it was also found 
that some fish are much more delicate than others, and can stand less knocking about and 
pressure. Flat fish on the whole can stand more than round fish. Soles seemed to be 
specially hardy, about 95 per cent. surviving ; while Plaice came next, 81 per cent. of those 
caught, some with the fish and others with the shrimp trawl, haying recovered after being in 
the tub on the average for about an hour. It is obvious, then, that under ordinary circum- 
stances the majority of such fish caught might still live if returned promptly to the sea. But 
even if one puts the most favourable interpretation upon such experiments, it is obvious that 
there is an immense amount of destruction going on in the Lancashire fish ‘‘ nurseries.” 
These extensive ‘‘nurseries” are an important link in the life-cycle of the more 
sedentary fish of the Irish Sea. They depend upon the off-shore spawning grounds for 
their supply, and in their turn they give recruits to the stock of adolescents and adults 
on the fishing grounds. 
Taking the Plaice as a typical sedentary flat-fish, and the one to which attention has 
been largely directed in our district,* we find that the females become mature in our seas at a 
size of from 13 to 15 inches, and the males at about 11 inches ; they are probably at that time 
about 3 or 4 years old. The spawning of the plaice takes place from February to the 
end of May and the female fish lays from 300,000 to 400,000 ova. The egg is of 
diameter. The spawning takes place in deep water, say 20 to 30 fathoms, at a distance 
from land, and the egg floats at or near the surface of the sea during its development. 
At a temperature of 10° C., the embryonic development, from the fertilisation of the egg 
till the larva is hatched, takes about 12 days; and then there emerges from the egg- 
covering a little plaice larva of about 6°5 mm. in length. At first the larva does not 
eat, and subsists upon the remains of the nourishing matter that was in the egg; but 
this yolk sac only lasts for about a week, and shortly before it has disappeared the 
larva begins to feed, at first upon Diatoms and minute larval Molluscs. A 
fortnight later, three weeks from hatching, it measures about 7°5 mm., and now feeds 
relatively large size, as edible fish-eggs go, being from 1°6 mm. to nearly 2 mm. in 
*See the Memoir on the Plaice by F. J. Cole and J. Johnstone, appended to the Lancashire Fisheries 
Laboratory Report for 1901. 
