ICHTHYOLOGICAL NOTES ON: I. OPHIODON ELONGATUS GIRARD; II. ONCORHYNCHUS KETA WALBAUM; III. THE DIAGNOSIS OF FISH BY MEANS OF THE SCALES; IV. MALLOTUS VILLOSUS MÜLLER. BY C. MCLEAN FRASER, PH.D., Curator of the Marine Biological Station, Nanaimo, B.C. I. OPHIODON ELONGATUS GIRARD. Fishes in general pay little attention to the well-being of their progeny. In oviparous forms the eggs are shed, provision is made for fertilisation and that is the end of it as far as the parent is concerned, Among the exceptions to the general rule is Ophiodon elongatus. commonly known as the Blue or Green Cod. The eggs of this species are very adhesive so that after they are shed they are collected into a large mass which becomes attached to a rock, usually in a crevice or some other unevenness, a short distance below low water or occasionally in such a position that they may be exposed during a low spring tide. Over the mass the parent fish keeps guard so well that no intruder has much chance of meddling. In no case have I found the female engaged in this protective duty, but if she does not take any part, the male must have a weary vigil, as the period of incubation is about two months. In the first instance my attention was directed rather forcibly to this characteristic of the Blue Cod. While collecting at low tide near the Biological Station, Departure Bay, I saw a mass of eggs under a rock about a foot and a half below the surface of the water. Wishing to examine some of them I managed to force off a small bunch with the blade of an oar-they stick so solidly together that this is not an easy matter-immediately after which I put down a dip net to catch them before they would sink to the bottom and was somewhat surprised with a sudden jerk that almost took the dip net out of my hand. A little later I discovered that the jerk came from a large cod that appeared from under the rock to resent the intrusion. When I thought of the sharp teeth of Ophiodon I was much better satisfied that the net rather than my hand received the force of the attack. The satisfaction was by no means decreased when further experiment showed how savagely he could attack starfish, nudibranchs, etc., that were lowered to test his watchfulness. Since that time the dip net has received many a jerk for a similar reason when it has been poked among the rocks in collecting. When the tide is low and the surface of the water is smooth, it is an easy matter in certain localities to see several of these fish on duty, as the opaque whiteness of the mass of eggs makes discovery an easy matter. In the vicinity of Nanaimo spawning takes place during the latter part of January or early in February. The eggs, about 2.8 mm. in diameter, differ from the eggs of many other species in that they are so opaque that nothing can be seen of the development of the embryo with a lens or microscope, hence the early stages can be studied only by sectioning. I have not made such studies, because I considered it would be of little use to do so unless the earliest stages could be studied hour by hour, and in no case have I been certain within a day when the eggs were fertilized. Moreover, I have not had the same success in hatching out blue cod eggs in the laboratory that I have had with the eggs of other species. They seem to go bad very easily. Although I have not got these earliest stages, I have been fortunate enough to get some embryos just hatched out. When the eyes are developed they show as dark spots in the eggs. After development had proceeded thus far I examined the eggs at intervals and thus managed to get a number hatched out shortly after they were brought into the laboratory. This was on March 25th. The newly-hatched embryo or alevin as it may now be called, is 11-12 mm. in length, with development well advanced. A certain amount of color is produced by a number of fine dark spots on the head, bands of them on each side of the dorsal fin and a less pronounced band below the lateral line. There is no break in the continuity of the median fin except at the anal opening, but there is little of it anterior to that opening. The pectoral fins are present, but they are not well developed. They do not seem to be used at all to assist respiration. There is no sign of the ventral fins. There is not much sign of skeletal tissues. A broad plate of cartilage extends for some distance under the cerebrum, but it soon narrows and disappears before the optic chiasma is reached. At the anterior end of the notochord it again appears, forming an irregular plate of considerable size. A portion of it extends out to form part of the capsule of the ear and posteriorly it grows up around each side of the medulla almost to the mid-dorsal line, but this lasts only for a very short distance. Laterally it connects up with the articular portion of the mandible, which is slightly developed. There is a cartilaginous rod in each gill arch. The skeleton of the pectoral girdle is but slightly developed, and this only in the part some distance from the middle line, in the fin itself. The notochord is relatively rather small, and at this period is entirely vacuolated. The nervous system is well developed. In the brain the cerebral hemispheres are almost distinct; the optic lobes are large, with the cavity separating as it passes backward; the epiphysis and the pineal body show up well; the hypophysis and the saccus vasculosus are relatively of large size, and the cranial nerves show distinctly. Judging from their appearance, the sense organs must be almost as well suited for action as they are in the adult. The nasal pits are quite deep and possess a large sensory surface, the eye has the structural characteristics and the nerve supply of the adult, while the ear is relatively of large size, and is extensively chambered with the ampullæ showing distinctly. Although much of the yolk-there is an oil globule present-remains unabsorbed, the digestive system is apparently of high enough development to look after food taken directly from the sea. At any rate in certain other fishes there is not so high a development when the yolk is all absorbed. The mouth is of large size, with the posterior portion of the cavity in direct connection with the outside through the large gill-clefts. The digestive tube does not vary much in size throughout, but it is bent on itself to form a loop of considerable length. The anal opening is quite far forward, a short distance posterior to the yolk-sac. The lobed liver is of large size with well developed hepatic tissue. The pancreas shows up distinctly. The excretory organs must be strongly functional, as the kidneys. have got much beyond the single tubule stage and the ducts are relatively of large size. In the circulatory system, the heart has become quite muscular, with the chambers and general shape much the same as in the adult. The aorta with its branches through the gill arches can be traced easily, and many other of the large arteries and veins have become distinct. Taking it as a whole the young Ophiodon, as it emerges from the egg, is in good condition to look after itself, although, as in the majority of young fishes, it will have enemies in plenty, enough to require the use of all its powers, no matter how fully they are developed. II. ONCORHYNCHUS KETA WALBAUM: "DOG SALMON" Plate X, figs. 26-29 One of the characteristic sights in the shallow waters of Departure Bay near the Biological Station, during the spring months, is the continuous bubbling of the water due to the presence of myriads of young dog salmon, Oncorhynchus keta. This year they appeared as early as March 4th, when a few straggling schools of from 8 or 10 to 20 or 30 appeared in the shallow water near the shore. These were 30-35 mm. long, and several retained part of the yolk, although already they had the characteristic parr-marks in the majority of cases. Some of them, even when much older than this, or perhaps rather when they are much older, have no sign of the bars, so that they look very much like humpbacks. It seems scarcely possible that they are anything but dog salmon, as they are found in the same school with the barred forms, although at certain times they seem to predominate. After watching these fry for some time, the wonder that they grow so rapidly after they reach sea water gradually disappears, as it would be hard to imagine a more active mass of condensed hunger than each of these appears to be. Watch them at any time during the day and the restless movement goes on. A snap is made at a desirable morsel here and another there, with no intermission of any length. At night when other sounds are stilled, the continuous jumping and splashing makes a ripple like that of a brook bubbling over a pebbly bed, so that it can be heard distinctly many rods away from the shore. Looking down over the water one sees them pass on in their illumined way as they disturb the various phosphorescent forms, some of which become phosphorescent no more. Occasionally when a large fish comes up with a splash to devour some of them, those fortunate enough to escape the cruel jaws, make such a speedy departure from the spot that the phosphorescence becomes more noticeable, looking like a meteoric shower in miniature. Catch them when you will, their stomachs are gorged with food, and one would think that their digestive systems would have to work overtime to get everything assimilated. They are not particular as to their diet. Apparently anything that can be swallowed goes. If one edible species is abundant that serves very well; if there is great variety that seems to do just as well. On one occasion I found them eating nothing but dipterous insects, at another nothing but barnacle larvæ, at another nothing but appendicularia. At one time they were filled with cladocera and mollusc eggs; a few days later this was changed to amphipods and mollusc eggs. The greatest variety found at any one time appeared in two salmon caught on June 12th, 1913. In these two there were cladocera, barnacle larvæ, copepods, crustacean sloughs and mollusc eggs in abundance, a dipterous insect, a crab larva and a young mussel. I know of no reason for their being here in such numbers unless there is an especially abundant supply of food for them. This may be so, as the waters eddy into the Bay a good deal and many of the smaller forms are apt to be brought in with the currents. Although some of them linger around the mouth of the stream near by, others remain some distance away where the water is as salt as it is out in the open, hence it seems that salinity can have nothing to do with it. They are not hatched out very near by. So far as I am aware none are hatched nearer than the Nanaimo River, the mouth of which is four miles distant. That is quite a distance for the young salmon to come through the salt water before they are out of the alevin stage. When the yolk disappears there is no indication of any scales in the skin. About the middle of May when the fry are 40-45 mm. long, the scale makes its first appearance. It is round or oval, 0.14 to 0.2 mm. in diameter, smooth and withouc rings. It is the nucleus of the large scale. In a week or two the first ring appears, soon followed by others, until by the end of June, when the fry disappears from this locality, there are 8 or 9 rings surrounding the central nucleus. Occasionally a few larger fish appear with the small ones, but I have not been able to obtain any of them. They are three or four inches long, and in all probability are dog salmon that have remained in the fresh water until the second spring instead of coming down the first spring. If one is to judge from the number that appear here, the proportion of second year fish is so low as to be almost negligible. III. DIAGNOSIS OF FISHES BY MEANS OF THE SCALES A system of identification of fishes by means of their scales has been advanced by Prof. T. D. A. Cockerell, but so far the system does not seem to have met with very great favor. Yet it is quite possible that the scale can be relied upon for identification purposes at least as fully as any other single characteristic if not as fully as all others combined. Since it has been discovered that the appearance of the scales may serve as a reliable indication of the age of the fish, the study of fish scales has become almost a science in itself, and there is no doubt but that it will add materially to the means of attacking the many problems connected with the life history. Two cases of personal interest may be quoted to show the value of the study of the scales in diagnosis. For some time after taking a special interest in the life-history of the herring, I knew nothing of the development between the time when the yolk was just absorbed and the time when the young fish was 6 cm. or over in length and had taken on the general appearance of the mature herring. On June 6th, 1913, there were numerous young fish, 35-40 mm. long, around the Government wharf on Gabriola Island. By June 12th |