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Volume 67, 1938
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The Structural characters of New Zealand Rainbow Trout.

[Read before the Canterbury Branch, September 2, 1936; received by the Editor, May 15, 1937; issued separately, December, 1937.]

Contents.

  • Introduction.

  • Material and Methods of Examination.

  • Structure and Taxonomy.

  • Habits.

  • Literature Cited.

  • Appendix.

Introduction.

The primary purpose of this paper is to record particulars of the structure of New Zealand rainbow trout and to indicate the extent to which the various characters have been found to be variable. A consideration of the taxonomic position of this fish is also attempted, but this has been handicapped by the scarcity of systematic literature dealing with the various rainbow trouts, and the incomplete, and in some instances, contradictory descriptions of some American authors. The confusion that has always surrounded this group of fishes has in no way been lessened by the popular practice of declaring a “steel-head trout” to be merely a “ rainbow trout” that has gone to sea. The term steelhead appears to be have been originally applied to Salmo gairdnerii, which is a sea-going fish; but it has been robbed of whatever definitive value it may have possessed by the action of those zoologists who apply it indiscriminately to all sea-going forms and regard it as more indicative of an anadromous habit than of any particular species or variety of trout. Under this system the various forms of sea-going rainbow trout are admitted to be distinct so long as they remain in fresh water, but they become united as steelheads after a sojourn in the sea, although the structural characters that previously distinguished them obviously remain unchanged by a marine existence. The sea-dwelling fish are blue and silver in colour, but when they return to fresh water to spawn they resume the red lateral band and some of the general colouration of the river-dwelling forms, and are then called rainbow trout. In popular terms an adult fish of this type is a steelhead trout for about ten months of the year, and a rainbow trout for the remainder. The term steelhead is not even reserved for sea-going members of the rainbow trout group, but is applied also to sea-going specimens of Salmo clarki and its allies—a group of fishes intermediate between the trouts and the chars which might, with some propriety, be excluded from the genus Salmo on account of the presence of teeth on the hyoid bone. Used in this sense, the term steelhead merely implies that the fish to which it is applied is anadromous, and it could advantageously be abandoned in favour of the latter term. As any attempt to re-establish it as a definition for a particular species or variety of trout will tend to delay the clarification of the present confusion, it would be better if it were abandoned in this sense also.

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Some particulars of the habits of New Zealand rainbow trout are included in this paper, but these deal principally with those peculiarities of habit that might be expected to throw light on the derivation of this fish. The unreliability of local records, together with the confusion in popular nomenclature that has existed in the country of the fishes' origin, precludes any possibility of determining ths point from historic data.

Material and Methods of Examination.

The material examined during the present investigation consists of 16 specimens from Lake Taupo in the Thermal Lakes district of the North Island, 14 from Lake Lyndon in Canterbury, 24 from Lake Coleridge, also in Canterbury, and a mixed group of 8 from various lakes in the same district. The anatomical data of these specimens have been individually recorded in order to indicate the extent of variation, and an explanation of the methods of examination is given below to facilitate comparison with the results of other workers.

The total length is measured from the tip of the snout to the extremity of the middle rays of the caudal fin and differs from the standard length which extends only to the hypural joint, a point somewhat in advance of the posterior limit of the scale covering.

The branchiostegals have been counted on each side and the numbers are shown in the tables separated by a hyphen. The frequent inequality of the two numbers is due to one side of the branchiostegal curtain overlapping the other at the junction and causing degeneration of one or two rays on the under side, but where this has been only partial and sufficient development has occurred to render the rays definable they have been counted. The minimum of three recorded for No. 8, Table 2 is the result of congenital deformity and may be disregarded.

The number of rays in the dorsal fin is indicated by two numbers separated by an inclined line, the first representing the single or simple rays and the second those that are branched. The last of the single rays is usually the longest in the fin, but the anterior ones are often extremely short and can be detected only by dissection. It has become the practice in North America to count only the longest of the single rays in addition to all of the branched ones, and refer to the result as the number of “developed rays.” This method makes for simplicity and has been adopted in the table of averages given in the text.

The same particulars apply to the anal fin.

The point of insertion of the dorsal fin is indicated by a decimal representing the portion of the standard length before the anterior of the fin. A figure of less value than 0.5 indicates that the point of insertion is nearer to the snout than to the hypural joint, while a figure of greater value indicates the opposite.

The longitudinal scale count has been made actually in the lateral line, and all scales have been counted irrespective of whether the pores are fully functional or imperfectly developed. While some workers adopt this method, others count the transverse series of scales on the upper part of the body, either immediately above the

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lateral line or at various and varying distances from it. It appears to be the custom in western North America to count the number of oblique rows of scales running in a downward and backward direction from the dorsum to the lateral line, and to regard the series as terminating at the hypural point. It is usually possible to count about eight more or less irregularly placed scales beyond this point, and in the American method these are omitted, but the loss is just about compensated by the advantage gained through the multiplication of the cross rows above the lateral line. Tests made with New Zealand rainbow trout show that the results obtained by the American method may be directly compared with the lateral line count without the introduction of serious error. It has been fqund, however, that the count of the cross rows of scales gives greater variation between the two sides of a single specimen than is obtained by counting the scales in the line itself, and the advantage of the former method appears to be, at least, questionable. In the present investigation both sides of the fish have been counted except where this has been impossible owing to injury or deformity.

It is usual, when counting the scales in the adipose fin series, to follow a series extending from the rear of the fin obliquely forward and downward to the lateral line, but the scales of New Zealand rainbow trout are frequently arranged so that no definite forward series exists, and even the rearward series, which is always the more distinet, is not so well defined as in brown trout. The rearward series has been followed in the present investigation, and in most instances both sides of the fish have been counted, but these data are too uncertain to be of much value.

In counting the vertebrae all bones possessing a joint at each end have been counted irrespective of whether these joints are or are not capable of movement. The first vertebra is somewhat triangular in lateral aspect and is normally coalesced to the rear of the cranium, while several of the posterior bones forming the upturned portion of the vertebral column are greatly modified. As a standard for comparison it may be stated that the vertebrae of brown trout, when counted in the manner described, usually number 56 or 57, but range occasionally to 55 and 58.

The number of gill-rakers has been counted on the anterior gill arch and includes all examples however rudimentary. The result is shown in the tables as two numbers separated by a plus sign, the first representing the rakers on the upper limb together with the one that is usually located in the angle of the arch, and the second those on the lower limb. In most specimens both sides have been counted, two sets of numbers being shown in the tables with a hyphen between them.

The enumeration of the pyloric caeca is a simple matter requiring no explanation.

Structure and Taxonomy.

The following table gives the averages for the four groups listed in the appendix. For greater convenience in tabulation the differentiation between the upper and lower gill-rakers has been abandoned, and the process of averaging the fin rays has been simplified by recording only the “developed rays.”

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[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Averages of Structural characters of Rainbow Trout from Lakes Taupo, Lyndon, Coleridge and sundry.
Locality. Branchiostegals Developed rays in dorsal fin. Developed rays in anal fin. Dorsal fin insertion ratic. Scales in lateral line. Vertebrae. Gill-rakers. Pyloric caeca.
Taupo 11.31 10.56 10.31 .5008 128.468 61.062 19.625 54.857
Lyndon 11.04 10.92 10.42 .4875 128.038 61.142 19.867 50.500
Coleridge 10.92 11.30 10.91 130.000 60.869 20.050 53.833
Sundry 11.60 10.62 10.37 130.571 61.875 19.687 49.000

A comparison of these data reveals a close agreement between the four groups. Not only does it seem probable that the rainbow trout of all waters that have been investigated have been derived from the same source, but the small amount of variation in the whole collection suggests that the present fish are descended from a pure race capable of consistent perpetuation.

Of the characters that are of use in determining the identity of the various forms of rainbow trout, the number of scales in the longitudinal series is generally regarded as the most valuable, but the validity of this character is questioned by Mottley (1934), who claims that in Salmo kamloops it is modifiable by temperature variation in the early stages of life, and that definite changes may be effected in a single generation. An average difference of about five scale rows was obtained by dividing the eggs of a pair of trout and subjecting one lot to a temperature about 5 degrees C. above the other, but it must be noted that the trout of Kootenay lake with which Mottley worked are so variable in the number of scale rows as to suggest a population of mixed ancestry, and it is conceivable that the offspring of parents in which genetic complications exist would react to temperature variation in a manner that would not be possible in those of a pure and constant race. Under normal circumstances the influence of temperature, if potent in structural modification, seems more likely to operate through the slow processes of evolution than as a levelling agent which would bring extreme forms together in a few generations. The results obtained by Mottley are not sufficiently definite to justify the belief that the Golden Trouts of the Upper Sacramento would reduce the number of their scales from 200 to 130 if bred for several generations in coastal waters, and it will still be necessary to regard the more distinct forms of rainbow trout as valid species or varieties. It is of little consequence which distinction is applied so long as the differences existing between the various forms are recognised.

Unfortunately the systematic literature of these fishes is somewhat contradictory and a good deal of confusion has resulted in

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consequence. While Jordan and Evermann (1896) credit the steel-head trout Salmo gairdnerii with the possession of about 160 scales in the lateral line, and state “the scales in gairdnerii are always smaller than in typical rainbow trout,” Kendall (1920) says, “The steelhead trout is the one that has the coarser scales. The scales run about 130, a few more or less according to locality. The McCloud River rainbow has scales numbering about 160 in the lateral line.” The McCloud River rainbow referred to is S. shasta. Snyder (1933) when describing the coast rainbow or steelhead trout S. irideus, of which he regards S. gairdnerii a synonym, states, “The scales are large, the lateral series numbering 120 to 150 or so.” The same author (1925) states that the lateral series of fourteen small specimens from the Eel River numbered from 124 to 138 and that these specifications agree with those of the large steelheads from the Klamath. Dynmond (1932) states that the scales in S. gairdnerii are usually in 131 to 134 diagonal rows but that there is considerable variation, the lower limit being about 124 and the upper 146. The number of scale rows of other forms of rainbow “trout is stated by Snyder (1933) to be as follows:—

S. stonei syn. shasta 150—165; S. gilberti about 155; S. roosvelti about 200; S. whitei about 200; S. agua-bonita 165—180; S. aguilarum 136—140; S. regalis 144—150.

Other modern authors concur in the view that the coastal, migratory forms, S. gairdnerii and its derivatives, are coarse scaled and that the river dwelling group of which S. shasta may be regarded as typical, is fine scaled, but not all agree upon the question of nomenclature. Snyder (1933) maintains that the coarse scaled coastal types should be called irideus, but if the original description of this species is consulted it will be found to be too vague to enable any fish to be identified with it, and moreover, it includes the statement that the scales are small. The original description of gairdnerii is little more definite, and the adoption of this name in the present paper is chiefly in conformity with the trend of modern usage.

Reference to the tables given in the appendix will show that the New Zealand specimens agree with gairdnerii in being definitely coarse scaled, the lowest number recorded being 115 and the maximum 135, but it is to be noted that they come within narrower limits of variation than Snyder and Dymond accord this species. The moderate amount of variation in the present collection suggests a well-defined and constant race, and, incidentally, raises the question whether the wide limits of American authors may be the result of including in a general specification particulars of several more or less distinct forms.

The number of vertebrae is regarded by some ichthyologists as of considerable importance in determining the identity of rainbow trouts. Kendall (1920) states that the specimens examined by him invariably showed 60 vertebrae for S. gairdnerii and 63 for S. shasta, but if these specifications are valid and these fishes are absolutely constant in the number of vertebrae, they differ from all members of the family Salmonidae that have been examined in New Zealand. The acceptance of this specification would identify some of the New Zealand rainbows with gairdnerii, a few with shasta, while the

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majority would be intermediate. Such determinations would be discredited by the number of scales, which, as already shown, invariably comes within the limits prescribed by Kendall and others for gairdnerii. It will be found on examination of the tables that there is a slight tendency for the higher numbers of vertebrae to be associated with the higher numbers of scales, but the latter character in no instance approaches the specification of shasta. Unfortunately, few other particulars of the vertebrae of rainbow trouts are available. Snyder (1926) gives a comprehensive table showing a variation from 60 to 65 for S. irideus syn. gairdnerii, but it is to be noted that this author inclines to the view that all rainbow trouts belong to a single species, and precisely what fishes are included in his definition of irideus is not clear. There is a tendency for American ichthyologists, when determining the identity of trouts, to place too much reliance on colour, the number of spots and characters other than those that are purely structural, and to widen the structural specification to whatever limits these superficial determinations require. While Snyder's specification may be unduly plastic, Kendall's appears to err in the direction of excessive rigidity and until further work is done on the vertebrae of rainbow trouts, and some degree of unanimity is reached by investigators, it would be useless to attempt to determine the status of the New Zealand fish from this character.

There are two specimens in the present collection requiring special mention, No. 9 and No. 23, Table 3. The count of 57 vertebrae recorded for No. 9 is questionable as there was considerable deformity of the vertebral column and several of the bones were coalesced. In No. 23, although the count is definite, about ten of the vertebrae after the fourteenth were reduced in size, and in view of this abnormality it would be unsafe to attach much importance to the specimen. The number of vertebrae recorded (56) is common in brown trout, with which species the present specimen agrees fairly well in the number of scales, but the identity of the fish appears to be established by the form of the cranial bones, which is typical of rainbow trout. The propriety of including these specimens in the collection is, perhaps, questionable, as the average number of vertebrae in the Coleridge group has been slightly affected thereby, but as specimens are listed individually in the tables, these two may be disregarded if desired. Their exclusion would bring the average to 61.285, which would then agree closely with those of the other groups.

The dorsal fin insertion ratio was not investigated in the early stages of the present work and particulars of only 28 specimens are recorded. Few specifications of this character have been published and in those that are available there is little to indicate the extent of variation recognised by individual authors. A figure of S. shasta given by Smith and Kendall (1921) shows the origin of the dorsal fin to be slightly nearer to the hypural joint than to the tip of the snout, so far as the former point may be estimated from the illustration. Dymond (1932) shows a figure of S. gairdnerii in which the dorsal insertion is much nearer to the snout than to the hypural joint. Snyder (1926) gives the average of 10 specimens of S. irideus (syn. gairdnerii) as 50, but in a figure of this species presented

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by the same author (1933) the dorsal fin is shown well to the rear. Reference to the present tables will show that the lowest dorsal insertion ratio is 461 and the highest 535. The variation is, therefore, considerable, but the average obtained by combining the Taupo and Lyndon groups is 496, which agrees very well with Snyder's average for irideus (syn. gairdnerii). Beyond this statement it is not possible to go, as the averages for other forms are not available.

An instance of extreme variation is to be noted in the number of pyloric caeca of No. 16, Table 1, which is nearly 50 per cent. greater than the next highest number and over 100 per cent. greater than the minimum. Investigation of this character in brown, trout has shown that the number does not vary with age or the nature of the food, and, although differences have been observed in the trout of different localities, these have been found to be associated with other modifications which seem to suggest a racial influence. Unfortunately no particulars of the caeca of the various forms of rainbow trout are available, and no use can be made of this character in determining the identity of the New Zealand race.

The number of rays in the anal fin, while serving to distinguish the rainbow trout group from the European representatives of the genus Salmo, and also from Oncorhynchus, is of little assistance in determining the specific or varietal identity of forms within the group. Many of these, both fine scaled and coarse scaled, agree in the number of anal fin-rays with the specification given in the present tables, and this is true also of most of the remaining characters of which data are given. Of the characters that have not been dealt with in the tables perhaps the most important are the dentition and the form of the maxillary. The vomerine teeth in New Zealand rainbow trout are arranged in two rows which are much more distinctly separated than in brown trout, and are remarkably persistent. Occasionally old specimens are observed in which some teeth are missing, but the loss of teeth is just as likely to occur in the middle of the vomer as at the rear, and appears to be merely the result of general decadence. The maxillary varies greatly with age; in young specimens it is straight, short and narrow, approaching the form of S. salar, while in the old individuals it extends far beyond the eye and assumes a sinuous form posteriorly. These characters appear to agree equally well with the gairdnerii and shasta groups, so far as published descriptions indicate, and are of little use in a fine classification of these fishes.

The taxonomic deductions from the foregoing discussion are, briefly, that the New Zealand rainbow trout are definitely not S. shasta, S. gilberti or any of the allied, fine-scaled, river-dwelling forms, but belong to the coarse-scaled, migratory group. There is an upland fish, S. nelsoni, described by Snyder (1926) as having coarse scales (about 130 in the longitudinal series), but the local specimens are disqualified for admission to this species by the possession of about 20 gill-rakers; S. nelsoni is described as having 12. The New Zealand rainbow trout must therefore be placed in the species gairdnerii, but the precise strain or race to which they belong has not been clearly indicated.

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Habits.

The introduction of rainbow trout appears to have been first effected in the North Island of New Zealand, from which ova were subsequently obtained for the purpose of stocking other waters. The practice of the Canterbury Acclimatisation Society has been to procure ova from the Thermal Lakes district and either liberate the whole of the resultant fry or retain a quantity in ponds as stock fish for egg production. Occasionally the second generation fish have been used for breeding, but the process has not been carried further and the stock has been regularly renewed by the procurement of fresh ova. Since the fish-ponds in the Christchurch Domain were abandoned, wild fish have sometimes been stripped at Lake Coleridge and the fry liberated in the district, but the greater part of the stocking has been done with fry reared directly from North Island ova.

This fish appears to be successfully established in the Thermal Lakes district, but it has not shown itself to be capable of maintaining its existence in any Canterbury water. Lake Lyndon is one of the most productive rainbow trout waters in Canterbury, but the maintenance of the stock is dependent on artificial culture. This lake has an altitude of approximately 2750 feet and shows considerable temperature variation, the surface frequently becoming frozen in winter and reaching 68° F. in summer. A small creek at the north-east end sometimes carries fry of rainbow trout, and it is possible that these have been hatched in the stream, but there is no evidence that this is so or that natural reproduction ever occurs in the lake itself. The majority of the adult fish existing in this water are spawn-bound, and even those that succeed in getting rid of their eggs or milt cannot be regarded as having spawned in a natural manner. Many of the younger fish taken in early summer contain free eggs which will flow from the body during handling, and as the season advances individuals in which no mature eggs remain are found, but this condition is reached through the involuntary loss of eggs long after ripeness has occurred and not through natural spawning. Older fish usually contain ova or milt belonging to two different seasons, and specimens are sometimes observed in which the whole of the current season's ova, the degenerate remains of that of the previous year and the partly developed roe of the coming season are present. Such fish fall off in condition and become dark in colour with the red lateral band particularly vivid. There is nothing to suggest that they ever regain a normal condition and it is probable that all perish prematurely after a period of gradually increasing debility.

While the absence of suitable spawning streams appears to account for the failure of many Lyndon fish to deposit their ova, this explanation is not applicable to Lake Coleridge, where a spawn-bound condition is by no means uncommon. This lake has an altitude of approximately 1670 feet and is not subject to extreme temperature variation, the monthly average of the surface water varying steadily between 47° F. in August and 56° in February. It possesses six tributaries, most of which produce fry of rainbow trout, brown trout or lake-dwelling quinnat salmon in quantities

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that seem to indicate the existence of satisfactory spawning conditions, but notwithstanding this about half of the adult rainbow trout taken in the lake are spawnbound. It is scarcely conceivable that mature fish would overlook a stream of such size as the Harper channel if the desire to spawn were present, and some explanation other than lack of suitable accommodation is necessary. The circumstances seem to indicate imperfect development of the reproductive organs, and, while this in its turn would suggest unsuitability of habitat, it must be pointed out that no adverse influence is manifest till the fish attain their first maturity. The scales of Lake Coleridge rainbow trout indicate excellent growth during immature life, but thereafter a severe check occurs, and it is seldom that free growth is resumed either in fish that become eggbound or in those that apparently spawn in a natural manner. In some seasons the natural hatch is considerable, but despite this fact the majority of the fish taken by anglers agree in age with some definite liberation and appear to be the result of artificial stocking. A certain amount of natural reproduction occurs in most Canterbury waters in which rainbow trout exist, but throughout the district indications are that this fish would dwindle away and become extinct if left to itself. When liberated in Canterbury streams rainbow trout usually disappear before reaching maturity and, so far as is known, never return. This movement is not a definite migration comparable to that made by quinnat salmon smolts, but appears to be a gradual evacuation of an unsuitable habitat. There is nothing to show that these fish find favourable conditions in the sea, or elsewhere, and so far as the present investigation has shown, there is no evidence of rainbow trout adopting a marine existence in any part of New Zealand. The scales of these fish exhibit structure that is typical of lake-dwelling salmonoids, and differs from that formed in New Zealand seas by either brown trout or quinnat salmon. They differ also from those of sea-dwelling rainbow trout existing in their native habitat, the general characters of which conform to those of anadromous brown trout in New Zealand. A micrograph of a scale from a Klamath River steelhead is shown by Snyder (1933) and is reproduced in fig. 1 as an example of sea-formed structure. This photograph was originally published as a negative, the ridges, which appear dark in the projected image, appearing in the print as white lines, while the valleys, which are normally light, were correspondingly reversed, and it is reproduced here as a positive in order to render it comparable with the Lake Taupo scale shown in fig. 2. These photographs have been arranged so that the structure of each is presented at approximately similar magnification, and although a complete correction is not possible owing to the complication introduced by erosion the difference in the spacing of the ridges in corresponding zones is so definite as to render the possibility of a slight error in magnification of no consequence. The inner part of fig. 1 is occupied by a section representing approximately three years of river life (marked 1, 2 and 3 in the illustration), after which the spacing of the ridges in the summer zones becomes coarse while the winter zones show the structural contractions typical of the scales of most sea-dwelling salmonoids. The spawning marks shown at A and D also agree with those of other anadromous species, in most

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of which there is a complete cessation of growth and severe disintegration of the edge of the scale when maturity occurs. The principal features in which the scales of most lake-grown trout differ from those of sea-dwelling fish are the comparatively poor definition between summer and winter zones in the section formed between the parr stage and the attainment of maturity, and the much less severe erosion forming the spawning mark. It is also to be noted that the pre-maturity winter band, when visible at all, is broader than in sea-dwelling fish and appears to represent a considerable period during which the growth-rate has been only slightly less than the maximum. The outer edge of such a band is marked W.B. in fig. 2. This tendency to uniformity of structure is characteristic of the scales of rainbow trout from such lakes as Te Anau, Coleridge and Taupo, while in smaller lakes it is modified according to the nature of the habitat and disappears altogether in waters that are physically opposite to those mentioned. Many of these lakes are either land locked or extremely difficult of access, but where other features approach equality the scales from closed and open waters show no difference that would suggest that any of the rainbow trout existing in New Zealand are sea-going. In those localities in which this fish has established itself, as in the Thermal Lakes district, it is, for the greater part, lake-dwelling, but whether this habit is inherited or of recent adoption is not clear. So far as the writer's observations have shown the habits of the salmonoid fishes that have been successfully introduced have not been changed by New Zealand conditions, and where aberrations have occurred, as in the freshwater-dwelling quinnat salmon of various lakes, indications are that existence will not be indefinitely perpetuated but that the fish will degenerate to the point of extinction. If this rule applies also to the New Zealand rainbow trout, it would appear that this fish has been derived from a strain of Salmo gairdnerii that has accommodated itself to a lake existence, either in consequence of enforced isolation or in the normal evolution of a freshwater race.

Literature Cited.

Dymond, J. R., 1932. The Trout and other Game Fishes of British Columbia, Dept. of Fisheries, Ottawa.

Jordan, D. S., and Evermann, B. W., 1896. The Fishes of North and Middle America, Part 1, Bull. U.S. Nat. Mus., 47 (1).

Kendall, W. C., 1920. What are Rainbow Trout and Steelhead Trout? Trans. American Fisheries Society, vol. L., pp. 187–190.

Mottley, C. McC., 1934. The Effect of Temperature During Development on the Number of Scales in Kamloops Trout, Salmo kamloops, Jordan. Contributions to Canadian Biology of Fisherics, vol. VIII, no. 20 (Series A, General, no. 41), Toronto.

Smith, H. M., and Kendall, W. C., 1921. Fishes of the Yellowstone National Park, Appendix III, Rep. U.S. Comm. Fisheries.

Snyder, J. O., 1925. The Half-pounder of Eel River, a Steelhead Trout, California Fish and Game, vol. II, no. 2, pp. 50–55.

— 1926. The Trout of the Sierra San Pedro Martir, Lower California. University of Cal. Publications in Zool., vol. 21. no. 17. pp. 419–426.

— 1933. California Trout, California Fish and Game, vol. 19, no. 2, pp. 81–112.

Picture icon

Fig. 1—Scale of sea-grown [ unclear: ] trout from [ unclear: ] Length of fish. 25 ½in. Reproduced from a photograph published by Dr. Snyde [ unclear: ] (1933).
Fig. 2—Scale of lake-grown rainbow trout + Lake Taupo. N Z Length of fish. 23 ½ inches
Fig. 3— Male [ unclear: ] from Lake London N.Z. Length 19 inches.

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[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table 1. 16 Rainbow Trout from Lake Taupo.
Sex. Total length (in inches). Branchiostegals. Dorsal fin rays. Anal fin rays. Dorsal fin insertion ratio. Scales in lateral line. Scales in adipose fin series. Vertebrae. Gill-rakers. Pyloric caeca.
1 F 22 ½ 11–10 4/11 3/10 .472 132–131 16–17 60 8 + 11–8 + 10 38
2 M 24 ½ 11–11 4/10 3/11 .535 115–127 15–15 60 10 + 13–9 + 11 38
3 M 14 ¼ 11–12 5/10 3/11 .471 132–132 16–17 62 8 + 12–9 + 12
4 M 23 12–13 4/11 3/10 .506 135–128 14–14 61 9 + 13–8 + 12 19
5 M 23 ¼ 12–12 4/10 4/10 .494 127–127 14–15 61 9 + 12–9 + 12 37
6 M 22 + 11–12 5/11 4/10 .193 127–130 16–17 60 9 + 12–8 + 12 3 +
7 M 22 ¼ 11–10 5/10 .314 131–133 17–17 62 8 + 10–9 + 11 45
8 M 21 11–12 4/10 3/11 .495 132–128 17–17 62 9 + 13–8 + 12
9 M 19 ½ 10–12 4/11 3/11 .490 126–128 17–17 60 8 + 12–9 + 12 58
10 M 21 ½ 11–12 5/11 4/10 .511 123–125 62 9 + 13–9 + 12 11
11 M 22 12–12 5/11 4/10 .512 128–120 14–15 62 8 + 9–8 + 11 50
12 M 23 ½ 11–11 5/11 4/11 .520 126–127 14–16 60 8 + 10–8 + 10 52
13 M 22 ¼ 11–12 5/10 4/10 .504 129–130 17- 61 8 + 11–9 + 11 55
14 F 23 ½ 11–12 4/11 3/10 .493 120–130 14–15 61 8 + 11–8 + 10 50
15 F 181 11–11 5/11 4/11 .486 125–125 15–16 61 7 + 11–7 + 11 49
16 M 22 ½ 10–11 5/10 1/11 .518 128–128 15–16 62 8 + 12–9 + 6 91

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Table 2. 14 Rainbow Trout from Lake Lyndon.
Sex. Total length (in inches). Branchiostegals. Dorsal fin rays. Anal fin rays. Dorsal fin insertion ratio. Scales in lateral line. Scales in adipose fin series. Vertebrae. Gill-rakers. Pyloric caeca.
1 M 13 10- 3/11 2/11 .469 119–120 16- 61 8 + 10–9 + 11 50
2 F 19 + 11- 5/12 3/11 .510 124–125 61 7 + 11–7 + 12
3 F 18 11- 5/11 3/11 128–120 60 8 + 13–8 + 14
4 F 19 ¾ 11–12 4/11 2/11 .474 132- 16- 62 47
5 F 17 12- 3/11 3/10 .483 130- 16- 61 8 + 13–8 + 13 54
6 F 17 11–11 3/11 2/11 .461 120–133 16- 61 9 + 12–8 + 12 53
7 M 15 ½ 11–12 4/11 2/11 .472 132–130 16- 61 9 + 10–9 + 11 48
8 M 19 3–10 4/12 3/10 .513 127–128 62 8 + 10–8 + 10
9 M 20 ½ 11–12 4/9 3/9 .518 131–132 62 9 + 12- 51
10 M 14 ½ 10–11 3/11 3/10 128–130 62
11 F 14 + 11–12 3/11 3/10 122–124 61
12 M 19 11- 3/11 3/11 134–130 61
13 M 17 11- 3/11 3/10 130–128 61
14 M 16 + 10–11 4/10 3/10 128–129 60
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[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Table 3. 23 Rainbow Trout from Lake Coleridge.
Sex. Total length (in inches). Branchiostegals. Dorsal fin rays. Anal fin rays. Dorsal fin insertion ratio. Scales in lateral line. Scales in adipose fin series. Vertebrae. Gill-rakers. Pyloric caeca.
1 F 21 9–11 4/11 3/11 .477 128–130 16- 62 8 + 11–8 + 12
2 F 25 ½ 9–11 4/12 4/10 128–132 14–15 61 9 + 11–9 + 12 53
3 M 23 11–11 4/12 3/10 131–132 17–16 63 9 + 12–8 + 11 51
4 F 27 ¼ 11–12 4/13 3/12 130–133 15–15 61 7 + 12–7 + 12 60
5 M 21 11–11 4/10 3/11 127–129 61 7 + 11–9 + 12 [ unclear: ]
6 F 25 ¾ 10–11 3/12 3/12 131–128 61 7 + 12–8 + 12 63
7 M 25 ¼ 11–12 5/11 4/11 126–126 61 10 + 11–9 + 12 31
8 M 26 ¼ 10–11 4/11 3/10 126- 15–15 62 9 + 10–9 + 12 44
9 F 25 10–11 4/10 4/10 128–131 15- 57 8 + 11–8 + 12
10 F 24 ½ 10–11 3/12 4/11 129–127 17- 61 9 + 11–9 + 12
11 F 25 ¼ 12–12 5/12 4/11 134- 17- 61 8 + 11–8 + 12 59
12 M 27 ½ 10–10 4/11 3/10 130–132 17- 60 9 + 12–10 + 12 53
13 M 25 11- 3/11 2/10 120- 60 8 + 12–8 + 12 50
14 F 27 ½ 10–11 3/12 3/12 130–131 16–16 61 9 + 10–8 + 10 50
15 F 22 ½ 11- 3/11 4/11 127–129 15- 60 9 + 10–9 + 10 56
16 M 26 11–11 4/11 3/11 131–131 62
17 M 24 12- 3/12 2/12 130- 61 8 + 12–10 + 13 64
18 M 26 11–11 4/11 3/11 128–130 61
19 M 17 ½ 10–11 3/11 3/11 127- 61 8 + 12–8 + 13 51
20 M 23 ½ 11–11 3/11 3/11 133–134 14–19 63 9 + 11–9 + 13 47
21 M 27 12–13 3/11 3/11 131–132 15–17 62 9 + 12–8 + 11 50
22 M 27 11–11 3/11 3/11 134- 15–17 62
23 M 20 11–11 4/11 3/11 .461 119–122 16–17 56 9 + 12–9 + 11 53

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Table 4. 8 Rainbow Trout from Lakes Pearson, Georgina and Rubicon.
Sex. Total length (in inches). Branchiostegals. Dorsal fin rays. Anal fin rays. Dorsal fin insertion ratio. Scales in lateral line. Scales in adipose fin series. Vertebrae. Gill-rakers. Pyloric caeca.
1 M 21 12–12 4/11 3/10 .497 132–132 18–19 62 7 + 11–9 + 8 43
2 F 22 ½ 12–12 4/10 3/10 .485 129–130 17–18 61 9 + 11–10 + 12 43
3 F 25 11–12 4/11 3/10 132–134 16- 62 8 + 11–8 + 11 45
4 M 22 ½ 12–12 3/10 3/11 126–126 15–16 62 8 + 11–8 + 12
5 F 22 11–11 4/10 3/10 131–132 16–17 62 8 + 12–9 + 12
6 23 ½ 12- 5/11 2/11 132- 63 9 + 11–9 + 12 57
7 M 23 ½ 11–11 4/11 4/10 129–130 15- 62 9 + 12–9 + 12
8 M 19 12–12 2/11 2/11 133- 15–17 61 8 + 10–8 + 11 57