156 



NATURE 



IJune 13, 1889 



have been, and are now, supplying electricity by over- 

 head wires without statutory powers, and being convinced 

 of the undesirability of allowing this to be continued, 

 would venture to suggest that, in any further legislation 

 on electric lighting, the supply of electricity in any district, 

 before obtaining statutory powers for such district, should 

 be prohibited under penalty." 



To this we see no objection, now that the Electric 

 Lighting Act is so modified that it is possible for an 

 electric lighting company to reap commercial success by 

 working under it. 



THE LIFE-HISTORY OF A MARINE 

 FOOD-FISH} 



II. 



'T^HE larval salmon enters the world of a size — though 

 -*- small — that is readily recognizable, viz. about three- 

 fourths of an inch in length, but the marine forms under 

 consideration, from their minute size and glassy trans- 

 lucency, are almost invisible to the naked eye — just a 

 gleam of light broken by the passage of a different 

 medium, or a tinge of pigment, arresting attention. Only 

 in the cat-fish (which is not much — though it ought to be 

 more — of a food-fish) with its large egg, have we a size 

 nearly reaching that of the salmon at birth. 



We had left the larval fish tossed about by the currents 

 and unable to struggle against them, now floating with 

 its yolk-sac uppermost, or hanging in the water with its 

 head downward, and again making spasmodic darts 

 hither and thither. Soon, however, it gathers strength, 

 and at the end of a week or ten days it glides actively 

 through the water, and avoids both obstacles and enemies, 

 the young cod nimbly escaping the forceps, poising 

 itself in the water with its large pectoral fins (Fig. 1 1), and 



Fig. II. — Ventral view of the interior region of larval cod (magnified). 



evincing both intelligence and dexterity. Moreover, this 

 activity greatly promotes respiration in those like the 

 gunard with a motionless mandible, the water being thus 

 sent through the mouth and over the branchial region. 

 Its mouth has now opened and the yolk-sac has been 

 absorbed, while it feeds on the most minute of the little 

 Copepods, especially those almost microscopic in size, 

 that swarm in the surrounding water. The provision 

 whereby such tiny fishes find in the ocean food suited to 

 their capacities is one of the most striking features in 

 Nature, but it has only recently been carefully investigated. 

 It is a notion no longer tenable that during the winter 

 and spring the sea, to a large extent, is devoid of the 

 wealth of pelagic life so characteristic of the summer 

 months — ^just as it is of the genial waters of the tropics. 

 For several years, however, it has been found that a vast 

 abundance of minute fife of all kinds is present through- 

 out the entire year — and from the surface to the bottom. 

 Moreover, during the warmer months a constant succes- 

 sion of young forms rises from the eggs both of the seden- 

 tary and creeping animals on the bottom to the surface, 

 where they sport in the summer sun, undergo certain 



'A Discourse delivered by Prof. W. C. Mcintosh, F.R.S., at the Royal 

 Institution, on Friday, February i, 1889. 



changes, and again descend as they assume the form of 

 the adult. The pelagic young food-fishes — swimming 

 freely in the ocean — thus have a double chance at them ; 

 first in their very early stage as they rise, and again in 

 their larger and later condition as they descend. The 

 enormous numbers, countless variety, and ever-changing 

 nature of the small animals either directly or indirectly 

 constituting the food of these little fishes form an im- 

 portant feature in the economy of the sea. Such animal 

 forms comprise those long known in the British seas, 

 besides others more familiar to Arctic voyagers, or to the 

 sunny waters of the Mediterranean, for, with modern 

 apparatus and persistent efforts (thanks to the enlightened 

 views of the Government acting through the Fishery 

 Board), our knowledge is always extending. 



It is a remarkable fact that it is primarily to plants in 

 inshore waters that the abundance and variety of animals 

 are in many respects due, especially if estuaries also 

 debouch in the neighbourhood. Thus nowhere are the 

 swarms of Sagittal, Appendicularians, Crustaceans, and 

 other forms of fish-food more conspicuous than in the 

 midst of a sea teeming with Diatoms, Rhizosoleniae, and 

 other Algoid structures. ^ These nourish many of the 

 lower forms upon which the Crustaceans and other higher 

 types feed, the latter again falling a prey to the fishes. 

 Moreover, while the larger forms of the Copepods and other 

 Crustaceans, for example, afford suitable nourishment for 

 the more advanced post-larval fishes, the multitudes of 

 larval Crustaceans {Naiiplii) are adapted to the needs of 

 the smallest larval food-fishes. Now this plant-life is 

 specially abundant in April and May, just when the larval 

 and very young post-larval fishes appear more abundantly 

 in the inshore waters, so that the cycle is nearly complete, 

 viz. from the inorganic medium through microscopic plant 

 and larval Crustacean to the post-larval fish. I have 

 mentioned the neighourhood of an estuary as a prolific 

 source of food for young fishes, and I need only explain 

 further by instancing the case of mussel-beds, which for 

 months pour countless myriads of larval mussels into the 

 adjoining sea, far beyond the needs of the area as regards 

 mussel-culture, but which form a favourite food of the 

 little 'fishes at all stages, but especially from an inch 

 and a half to three inches in length. These fishes feed 

 on the young mussels as they settle down on the sea- 

 weeds, rocks, and zoophytes in August, after a free- 

 swimming larval existence. Like some of the forms indi- 

 cated above, mussels live to a considerable extent on micro- 

 scopic plants and various minute organisms contained in 

 the mud of the estuaries and other sites, so that a rich 

 and favourite food, universally liked by fishes, is the pro- 

 duct of these uninviting flats. Moreover, in passing, it 

 may be remarked that, while everywhere preyed on by 

 the food-fishes, it occasionally happens that in turn the 

 mussel proves a source of inconvenience to them, for, 

 settling on the gill-arches of haddocks, the mussels 

 flourish on a site so suitable for aeration and food that 

 they by and by press out the gill-cover and impede 

 respiration, just as the shore-crab (which is also fond of 

 mussels) has its eye-stalks wrenched out by the slow but 

 sure growth of the young mussels which have fixed them- 

 selves in their sockets. Nemesis thus, by a chance of 

 anchorage, converts a favourite food into a permanent 

 inconvenience. 



Again, in connection with the pelagic food of fishes, it 

 is a well-known fact that adult cod are extremely fond of 

 sea-anemones,^ and some of the rarest species may be 

 procured in their stomachs, a feature by no means sur- 

 prising when we remember that Abbe Dicquemare cooked 

 and ate his sea-anemones with great relish, and wrote in 

 their favour, as also did Mr. Gosse in our own country. 

 Now, the pelagic young fishes, instead of roaming near 



'^ The fact that certain fishes feed on Infusoria has not been overlooked. 

 ^ A favourite bait for cod in some parts ; and from the fact, amongst others, 

 that star-fishes do not molest them on the hooks, no bait is more successful. 



