6io 



NA TURE 



{Aprd 2^, 1881 



in a year, the shoals of each spawning season would be 

 the fry of the twelvemonth before. However, no direct 

 evidence can be adduced in favour of this supposition, 

 and it would be extremely difficult to obtain such 

 evidence." • 



1 believe that these conclusions, confirmatory of those 

 of previous careful observers - are fully supported by 

 all the evidence which has been collected, and the fact 

 that this species of fish has two spawning seasons, one 

 in the hottest and one in the coldest months of the year, 

 is very curious. 



Another singular circumstance connected with the 

 spawning of the herring is the great variety of the 

 conditions, apart from temperature, to which the fish 

 adapts itself in performing this function. On our own 

 coasts, herrings spawn in water of from ten to twenty 

 fathoms, and even at greater depths, and in a sea of full 

 oceanic saltness. Nevertheless herrings spawn just as 

 freely, not only in the narrows of the Baltic, such as the 

 Great Belt, in which the water is not half as salt as it is 

 in the North Sea and in the Atlantic, but even in such 

 long inlets as the Schlei in Schleswig, the water of which 

 is quite drinkable and is inhabited by freshwater fish. 

 Here the herrings deposit their eggs in two or three 

 feet of water ; and they are found, along with the eggs 

 of freshwater fish, sticking in abundance to such fresh- 

 water plants as Potamogeton. 



'Nature seems thus to offer us a hint as to the way in 

 which a fish like the shad, which is so closely allied to 

 the herring, has acquired the habit of ascending rivers 

 to deposit its eggs in purely fresh water. 



If a full female herring is gently squeezed over a vessel 

 of sea-water, the eggs will rapidly pour out and sink to 

 the bottom, to which they immediately adhere with so 

 much tenacity that, in half an hour, the vessel may be 

 inverted without their dropping out. When spawning 

 takes places naturally the eggs fall to the bottom and 

 attach themselves in a similar fashion. But, at this time, 

 the assembled fish dart wildly about, and the water 

 beco:nes cloudy with (the shed fluid of the milt. The 

 eggs thus become fecundated as they fall, and the de- 

 velopment of the young within the ova sticking to the 

 bottom commen :es at once. 



The first definite and conclusive evidence as to the 

 manner in which herring spawn is attached and becomes 

 developed that I know of, was obtained by Prof. 

 AUmin and Dr. MacBain in 1862," in the Firth of 

 Forth. By dredging in localities in which spent herring 

 were observed on the 1st of March, Professor Allman 

 brought up spawn in abundance at a depth of fourteen to 

 twenty-one fathoms. It was deposited on the surface of 

 the stones, shingle, and gravel, and on old shells and 

 coarse shell-sancl, and even on the shells of small living 

 crabs and other Crustacea, adhering tenaciously to what- 

 ever it had fallen on. No spawn was found in any other 

 part of the Forth ; but it continued to be abundant on 

 both the east and the west sides of the Isle of May 

 up to the 13th of March, at which time the incuba- 

 tion of the ovum was found to be completed in a great 

 portion of the spaw 1, and the embryos had become free. 

 On the 25th scarcely a trace of spawn could be de- 

 tected, and nearly the whole of the adult fish had left 

 the Forth. 



Prof. Allman draws attention to the fact "that the 

 deposit of spawn, as evidenced by the appearance of 

 spent herrings, did not take place till about sixty-five 

 days after the appearance of the herring in the Firth,'' 

 and arrives at the conclusion that "the incubation probably 

 continues during a period of between twenty-five to thirty 



* '■ Report of the Royal Commission on the operation of the Acts relating 

 tj Trawling fjr Herrings on the Coast of Scotland (1863)," p. 2S. 



2 Brandt and Ratzebnrg. for example, in 1S33 strongly asserted that the 

 herring has two spawning seasons. 



3 " Report of the Royal Commission on the Operation of the Acts relating 

 to Trawling for Herring on the Coast of Scotland, 1863." 



days," adding however that the estimate must for the 

 present be regarded as only approximative. It was on 

 this and other evidence that we based our conclusion that 

 the eggs of the herring " are hatched in at most from two 

 to three weeks after deposition.'' 



Within the last few years a clear light has been thrown 

 upon this question by the labours of the West Baltic 

 Fishery Commission, to which I have so often had oc- 

 casion to refer.' It has been found that artificial fecun- 

 dation is easily practised, and that the young fish may 

 be kept in aquaria for as long as five months. Thus, a 

 great body of r.ccurate information, some of it of a very 

 unexpected character, has been obtained respecting the 

 development of the eggs, and the early condition of the 

 young herring. 



It turns out that, as is the case with other fishes, the 

 period of incubation is closely dependent upon warmth. 

 When the water has a temperature of 53° Fahrenheit, the 

 eggs of the herring hatch in from 6 — 8 days ; the aver- 

 age being seven days. And this is a very interesting fact 

 when we bear in mind the conclusion to which the in- 

 quiries of the Dutch meteorologists, and, more lately, 

 those of the Scottish Meteorological So:iety appear to 

 tend, namely, that the shoals prefer water of about 55°. 

 At 50° Fahrenheit, the period of incubation is length- 

 ened to eleven days ; at 46° to fifteen days ; and at 38° it 

 lasts forty days. As the Forth is usually tolerably cool 

 in the month of March, it is probable that Prof. AUman's 

 estimate comes very near the truth for the particular 

 case which he investigated. 



The young, when thsy emerge from the egg, are from 

 one-fifth to one-third of an inch in length, and so ex- 

 tremely unlike the adult herring that they may properly be 

 termed larv;e. They have enormous eyes and an exceed- 

 ingly slender body, with a yelk bag protruding from its 

 forepart. The skeleton is in a very rudimentary condi- 

 tion ; there are no ventral fins; and instead of separate 

 dorsal, caudal, and anal fins, there is one continuous fin 

 extending from the head along the back, round the tail, 

 and then forwards to the yelk bag. The intestine is a 

 simple tube, ciliated internally ; there is no air-bladder, 

 and no branchire are yet developed. The heart is a mere 

 contractile vessel, and the blood is a clear fluid without 

 corpuscles. At first the larva; do not feed, but merely grow 

 at the expense of the yelk, which gradually diminishes. 



Within three or four days after hatching, the length 

 has increased by about half the original dimensions, the 

 yelk has disappeared, the cartilaginous skeleton appears, 

 and the heart becomes divided into its chambers ; but 

 the young fish attains nearly double its first length 

 before blood corpuscles are visible. 



By the time the larva is two-thirds of an inch long (a 

 length which it attains one month after hatching), the 

 primitive median fin is separated into dorsal, caudal, 

 and anal divisions, but the ventral fins have not ap- 

 peared. About this period the young animal begins to 

 feed on small Crustacea ; and it grows so rapidly that, at 

 t wo months, it is \\ inch long, and, at three months, has 

 attained a length of about two inches. 



Nearly up to this stage the elongated scaleless little fish 

 retains its larval proportions ; but, in the latter part of the 

 third month, the body rapidly deepens, the scales begin 

 to appear, and the larva passes into the " imago " state 

 — that is, assumes the form and proportions of the adult, 

 though it is not more than two inches long. After this, it 

 goes on growing at the same rate (i I millimetres, or nearly 

 half an inch) per month, so that, at six inonths old, it is 

 as large as a moderate-sized sprat. 



The well-known "whitebait" of the Thames consists, 



" See the four valuable memoirs, Kupffer, " Ueber Laichen und Entwick- 

 elung des Herings in der westlichen Ostsee"; Idem, "Die Entwickelung 

 des Herings im Ei " ; Meyer, " Beobachtungen iiber den 'Wachsthum 

 des Herings " ; Heincke, " Die Varietaten des Herings," which are contained 

 in the Jahresbericht der Commission in Kiel fiir 1874-75-76 — 1878. 

 ■yVidegren's essay " On the Herring," 1871, translated froin the Danish in 

 U.S. Commission Reporis, 1873—75, als;. contains important information. 



