of the Fishery Board for Scotland. 



45 



It is to be noted that the young fish referred to include post-larval 

 forms as well as larvse. Thus, in a table of measurements of the young 

 cod, haddock, and whiting obtained, it is seen that among the cod 204 

 were over 5 mm. in length, and 557 were 5 mm. or less, the largest 

 included being 28 mm. Of 222 young haddocks, 79 were 5 mm. or 

 under, and 143 over that size, the largest being 38 mm. Of 142 whiting, 

 18 were 5 mm. or under, and 124 above 5 mm., the largest being 11 

 cm. It would therefore appear that the proportion of larvse derived from 

 pelagic eggs to the number of pelagic eggs must be considerably less than 

 above stated. 



In Lochfyne, Williamson carried on a series of tow-nettings from 17th 

 January to 9th August, and determined the eggs and youug fishes.* 

 The collections were made at various depths down to 15 fathoms, or to 

 about the same depth as in Dahl's observations. The total number of eggs 

 of the Gadidse obtained was 17,675, and the number of gadoid fishes 103, 

 the ratio being 171*6 eggs to each fish ; the number of eggs of the cod 

 was estimated at 6618, and the number of young cod was 86, the ratio 

 being 77 eggs to each fish. The number of eggs of flat-fishes was 9259, 

 and the number of young flat-fishes was 43, the ratio being 215 eggs to 

 1 fish ; the number of plaice eggs procured was 538, and the number of 

 young plaice was 8, the ratio being 67 eggs to 1 fish. The total number 

 of eggs of the gadoids and flat-fishes was 26,934, and the total number of 

 larval and early post-larval fishes of these groups was 146, the ratio being 

 184-5 eggs to 1 fish. 



As previously indicated, observations are not yet complete enough to 

 allow of an exact comparison being made between the numbers of pelagic 

 eggs and the larval fishes derived from them, as they naturally exist in the 

 sea, but they show at all events that the biologic value of a larval fish is 

 much greater than that of a pelagic egg, and it is probably not overstating 

 the case to say that it is twenty times greater. If that is so, then the 

 100,000,000 larvae of the plaice referred to previously would represent 

 the sexual product not of about 600 female and male fish but of about 

 12,000 living under natural conditions. 



The natural destruction that goes on among the eggs from physical 

 causes and from enemies is continued in the larval stage, and no doubt 

 mainly in the early part of that stage, when the young fish is entirely 

 dependent for its nourishment on the supply of yolk it possesses and is 

 comparatively inert. Later, when it begins to feed and gain in vigour 

 and activity, it is presumably better able to escape its enemies and has a 

 better chance of surviving. 



With regard to the plaice, we have a considerable amount of informa- 

 tion relating to the value of protection in the early stages. The duration 

 of embryonic development within the egg depends upon the temperature 

 of the water; in February it occupies about 24 days, in March about 22 

 days, in April 19 or 20 days. The larval stage, before the yolk is absorbed, 

 endures for seven or eight days, and the duration of the post-larval stage, 

 until the plaice settles on the bottom as a little flat-fish is from 29 to 40 

 days, the mean being 34 or 35 days.t As the young fish are kept in the 

 hatchery, until near the close of the larval stage, protection is thus afforded 

 for about half the period between the spawning of the egg and the 

 completion of transformation, when the young fish lives on the bottom in 

 comparative security ; and there is little doubt that it is in the first half 

 of pelagic life, as egg and as larva, that the greatest destruction occurs. 



* Seventeenth Ann. Rep., Fishery Board, Part 7//.,fp. 79 

 t Fifteenth Ann. Rep., Part III., p. 175. 



D 



