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USGS1951

Tissue levels of various sulfonamides in trout

Studies were made on the tissue levels of sulfonamides in trout. The tissue concentrations of sulfamerazine were determined in brook trout given various doses of this drug. It has been found also that there exists a relationship between the rate of feeding, depending on the size of trout, and the tissue concentration of sulfamerazine. The level of sulfamerazine rose much faster and higher in blood and liver than in kidney and muscle. However, after the treatment was discontinued sulfamerazine level in all tissues dropped within 3 days to about 1 milligram percent. From the tested sulfonamides, sulfanilamide was absorbed fastest and produced highest tissue concentration. Sulfamerazine and sulfamethazine gave similar tissue levels, but the tissue concentration rose faster with sulfamerazine. Sulfadiazine and sulfaguanidine reached lower tissue levels. The tissue level of sulfathiazole was less than 1 milligram percent and sulfathalidine and sulfaquinoxaline were not absorbed from the intestine at all.

Transactions of the American Fisheries Society↗

USGS1951

Status of the lake trout fishery in Lake Superior

The production of lake trout in the United States waters of Lake Superior was low (only 1,465,000 pounds) in 1879, the first year for which there is a record. Expansion of the fishery must have started soon thereafter, for the take was 3,488,000 pounds in 1885, the next year for which we have statistics, and averaged 3,416,000 pounds in 1885–1892. The years after 1892 can be divided readily into three general periods with average yields as follows: 1893–1907–4,599,000 pounds; 1908–1925–2,168,000 pounds; 1926–1949–3,049,000 pounds. A take of 3 million pounds can be held as “normal” in the modern fishery. During the three periods just listed the percentage contributions of the individual states to the United States total (as computed from the averages for individual periods) ranged from 65.1 to 71.5 for Michigan, 17.5 to 25.6 for Wisconsin, and from 9.3 to 11.0 for Minnesota. In the Canadian (Province of Ontario) waters of Lake Superior the average annual output of lake trout rose from 309,000 pounds in 1871–1882 to 900,000 pounds in 1883–1893, 1,567,000 pounds in 1894–1903, and 2,189,000 pounds in 1904–1918. This last period of relatively high yield was followed by two intervals of successively lower average catches–1,691,000 pounds in 1919–1929 and 1,395,000 pounds in 1930–1949. For the combined United States and Canadian waters of Lake Superior the general trends in the production of lake trout can be described by the following averages: 1879–1,653,000 pounds: 1885–1892–4,325,000 pounds; 1893–1907–6,236,000 pounds; 1908–1949–4,403,000 pounds. The short‐term fluctuations of production during the more recent years give evidence of periodicity in the output of lake trout in Michigan, Ontario, and in the entire lake. Furthermore, these periodic fluctuations tended to be similar in Michigan and Ontario waters. The coefficient of correlation (r) between production in Michigan and Ontario in 1920–1949 (after elimination of trend in the statistics for both areas) had the significant value of 0.456. This correlation suggests that Michigan and Ontario fishermen exploit a common stock or stocks subject to similar fluctuations. Statistics on the production of lake trout in 5 of the 6 statistical districts of the State of Michigan waters of Lake Superior (see Fig. 2 for boundaries of the districts) in 1885 suggest that in most areas the fishery was then in the process of development. Even in 1891–1908 when the general level of production was high, there is evidence that during certain periods the catch in some areas was influenced strongly by factors (such as accessibility to market) other than the natural productivity of the waters. Comparisons of the average annual output of lake trout in the individual districts in 1891–1908 and 1929–1943 (the base period for our modern statistical analysis) reveal an enormous decrease in the Whitefish Bay region (S‐6) from 916,000 pounds in 1891–1908 to only 177,000 pounds in 1929–1943, a substantial drop (from 655,000 pounds to 385,000 pounds) in the Marquette‐Munising area (S‐4), and a small decrease (from 141,000 pounds to 138,000 pounds) in the Black River‐Ontonagon district (S‐2). Among the remaining districts the average yearly take increased from 322,000 pounds in 1891–1908 to 354,000 pounds in 1929–1943 at Isle Royal (S‐1), from 428,000 pounds to 501,000 pounds in the Grand Marais district (S‐5), and from 422,000 pounds to 506,000 pounds in the Keweenaw area (S‐3). These changes in the catch resulted in a westward shifting of production centers. Districts S‐1, S‐2, and S‐3 which together contributed only 30.7 percent of the 1891–1908 catch accounted for 48.4 percent of the take in 1929–1943. The 1929–1949 production in all districts exhibited periodic fluctuations that were characterized by peaks in the middle 1930ˈs and middle 1940ˈs. The indices of abundance or availability as computed from records of the catch of lake trout per unit of fishing effort showed periodic fluctuations in all districts of the State of Michigan waters similar to those of production (the peaks and the intervening minima fell a little earlier in the curves of abundance than in the production curves). For the combined districts the abundance of lake trout, expressed as a percentage of the 1929–1943 mean, stood at 108 in 1929, dropped to 100 in 1931, rose to a 21‐year high of 137 in 1934, decreased to 80 in 1940, increased again to 107 in 1944 and then fell to the 21‐year low of 65 in 1949 (this last decline was interrupted by a small increase in 1947). The 1929–1949 fluctuations in abundance were similar in the 5 mainland districts (S‐2 through S‐6). The coefficients of correlation (r) were significant for all 10 pairings and those for the 4 easterly districts (S‐3 through S‐6) were extremely high (p < 0.001 for all 6 values). Thus we have evidence that the fishermen along the mainland exploit common stocks or stocks in which the factors controlling availability are the same or subject to closely similar fluctuations. The fluctuations in abundance in S‐1 were correlated significantly (p < 0.05) with those in S‐2 but otherwise appeared to be independent of conditions along the mainland. The distinctly cyclic fluctuations that characterized the statistics on production and abundance were much less apparent in the 1929–1949 data on fishing intensity in the State of Michigan districts. In districts S‐3, S‐4, and S‐5 a possible tendency toward a cyclic fluctuation seems to have been obscured by a long‐term upward trend that was becoming stronger toward the end of the 21‐year period. For the combined districts the level of fishing pressure was consistently high after 1943. Over the 6‐year period, 1944–1949, fishing intensity expressed as a percentage of the 1929–1943 mean averaged 142; for the most recent 4 years, 1946–1949 the average intensity index was 151. On the whole, the 1929–1949 production of lake trout in the State of Michigan waters of Lake Superior was unreliable as an indicator of changes in abundance. The coefficient of correlation between the fluctuations of catch and abundance was, to be sure, positive and significant in S‐1 (p < 0.05) and S‐6 (p < 0.01), but in the remaining districts and for the combined districts the values of the coefficient were far below the level of significance. The failure of production to serve better as an indicator of changes in abundance can be attributed to the negative correlation that existed between abundance and fishing intensity (values of r highly significant in every district but S‐6 and for the combined districts). The relationship suggests that fishermen have increased their fishing pressure in order to maintain their production during the recent years of declining abundance. The condition of the lake trout fishery of the State of Michigan waters of Lake Superior must be termed unhealthy and the outlook for the future is not good. Production in 1949 stood at 106 percent of the 1929–1943 mean, but this level of yield was made possible only by fishing intensity that was 162 percent of average; the abundance index in 1949 was only 65. Certainly the stocks of lake trout are in a poor state to withstand the threatened inroads of sea lampreys which have been taken from all parts of Lake Superior and are known to have established spawning runs at least as far west as the Keweenaw Peninsula.

Michigan, Minnesota, Wisconsin↗

USGS1952

Further studies on factors determining tissue levels of sulfamerazine in trout

There is considerable variation in the tissue level of sulfamerazine among individual trout in a treated population. This fact may be the reason why prolonged sulfonamide therapy sometimes fails to free all trout from Bacterium salmonicida. The quantity of food given with a standard dosage of sulfamerazine has a pronounced effect on the tissue concentration of sulfamerazine; the concentration increased when the quantity of food decreased. It appears therefore, that trout should be fed at a rate very closely adjusted to their optimum feeding requirements for the best practical results. The start of treatment with high initial doses of sulfamerazine had no effect on the tissue concentration sustained by the maintenance dosage. The relative distribution of sulfamerazine in various organs and tissues of rainbow trout was about the same as in brown and brook trout. The only difference noticed was the lack of peak levels of short duration between the 8 and 10 days of treatment, which is characteristic for brook and brown trout.

Transactions of the American Fisheries Society↗

USGS1952

Movements of yellow perch marked in southern Green Bay, Lake Michigan, in 1950

To obtain information on the post-spawning movements of yellow perch that spawn in southern Green Bay, Lake Michigan, 4,172 fish caught in drop nets were marked by tagging with monel-metal strap tags attached to the right operculum and 24,799 were marked by clipping off the second or membranous dorsal fin. Marking was done during the period from May 3 to 17, 1950, at six main stations, all located in the southern end of Green Bay. The average length of the tagged perch was 7.3 inches and all fell within the range 5.5–14.4 inches. Most (90.9 percent) of the fish were below the minimum legal length of 8.0 inches. The follow-up procedure consisted of informing commercial and sports fishermen of the program and enlisting their cooperation in watching for marked fish; accounts of the investigation were released through newspapers and descriptive posters were distributed. The personnel connected with the investigation examined catches frequently. The large majority (101 or 79.5 percent) of the 127 tagged perch recaptured in the experimental nets during the marking operations were retaken at the tagging station at which they were released. Of the 108 tagged perch captured by commercial fishermen and anglers following the opening of the season on May 20, 96 were taken by drop nets, 6 by gill nets, and 6 by hook and line. The mean lengths for the three groups were 7.7, 7.1, and 9.25 inches, respectively. All recoveries were made in the Wisconsin waters of Green Bay. Most of the “open-season” recoveries (86 fish; 79.6 percent) were made during the period May 20-May 31. Recaptures during subsequent months were: June–14; July–7; August–none; September–1. Of the 86 perch recaptured May 20–31, 70 were retaken inside and 16 outside the tagging area. The majority (14 of 22) of those recovered after May 31 were retaken outside the tagging area. The average length of the 20 tagged yellow perch recaptured by drop nets (data restricted to fish from a single type of net to avoid bias from gear selectivity) outside the tagging area (8.42 inches) was 0.96 inch greater than the mean length (7.46 inches) of the 76 fish retaken inside the area. This statistically highly significant difference lends support to the belief of commercial fishermen that the larger of the yellow perch that spawn in southern Green Bay move out soon after spawning. The percentage of recapture of tagged perch increased sharply with increase in the size of the fish. Not one of 169 tagged fish less than 6.5 inches long was recovered. The rates of recapture at greater lengths were: 6.5 to 8.9 inches–2.5 percent; 9.0 to 9.9 inches–11.4 percent; 10.0 to 14.4 inches–16.7 percent. Among the several factors suggested in explanation of this relationship, the most important appear to be the lesser ability of the smaller fish to survive the rigors of handling and tagging, greater loss of tags from the smaller fish, and the greater likelihood of overlooking the smaller of the tagged fish in the sorting of the catch. The factors just mentioned and the lack of knowledge of the efficiency of measures taken to obtain records of recoveries preclude the 2.6-percent return of all tagged fish from being accepted as an approximation of the rate of recapture. Neither should the 6.6-percent return of tagged fish of legal size (8 inches and longer) be taken as an estimate of the rate of exploitation. Although 465 fin-clipped perch were recovered in the experimental nets during the marking operations, only 68 of 24,799 fish so marked were recovered after the fishing season opened. All but one of these 68 were retaken near the point of marking. The difficulty of detecting a perch with a missing membranous dorsal is believed to be a major cause of the poor returns from fin-clipped fish. These investigations have demonstrated that for studying migration of yellow perch, tagging is superior to fin-clipping as a method of marking. The technique of the tagging, however, needs to be improved, and better means must be found to trace tagged fish of small size. Furthermore certain small regions in the bay not at present open to commercial fishing must be explored in order to obtain more comprehensive information as to migration.

Transactions of the American Fisheries Society↗

USGS1951

Downstream movement of recently transformed sea lampreys, Petromyzon marinus, in Carp Lake River, Michigan

In order to obtain more precise information concerning the downstream movement of recently transformed sea lampreys, a trapping device was operated in the Carp Lake River, Emmet County, Michigan, from October, 1948, to July, 1951. The period of downstream migration typically extends from the latter part of October to the middle of April. It varies, however, from year to year with climatic conditions. A few migrants usually appear every day during this period but a sudden increase in water level is characteristically accompanied by a surge in downstream movement of newly transformed sea lampreys. This phenomenon is realized principally during the spring floods and often concurrently with autumn rains and mid-winter thaws. A total of 7,969 downstream migrants were taken in the 1948–49 season; 16,235 in 1949–50, and 15,103 in 1950–51. Measurements of representative samples from the total catch of sea lamprey migrants of the 1948–49 and 1949–50 seasons revealed a range in length of 95 to 190 millimeters and an average length of 145 millimeters (3.7 to 7.5 inches; mean –5.7 inches).

Transactions of the American Fisheries Society↗

USGS1952

Diseases and parasites of the sea lamprey, Petromyzon marinus, in the Lake Huron basin

Sea lampreys from the Lake Huron basin carried no external parasites and showed a fairly low degree of infection by internal parasites. The material examined represented three life-history stages of the sea lamprey. Recently transformed downstream migrants (215 specimens) harbored only nematodes belonging to the genus Camallanus. The percentage of infection was 2.3. Active feeders from the lake (29 lampreys) revealed the highest degree of parasitism (31.0 percent) with the following parasites present: Echinorhynchus coregoni Linkins; Triaenophorus crassus Forel; and Camallanus sp. Among the 257 sexually mature upstream migrants (14.8 percent infected) Echinorhynchus coregoni and E. leidyi Van Cleave were the most common. Only occasional nematodes and cestodes were found, which fact indicates a failure of the lamprey to carry these parasites to the end of its natural life. Of the parasites observed, only the nematodes gave evidence of serious damage to the host. The study suggests that the role played by parasites in the natural control of the sea lamprey in its new habitat in the upper Great Lakes is of minor importance.

Transactions of the American Fisheries Society↗

USGS1953

Movement of parasitic-phase sea lampreys in Lakes Huron and Michigan

A program of tagging was carrie dout in the waters of northern Lake Huron during the fall and winter of 1951-52 in order to supplement the small amount of information available on movement of sea lampreys during their parasitic phase. A total of 219 parasitic-phase sea lampreys were tagged and released at three localities. Of this number 38 or 17.2 percent were recovered. One tag was recovered near North Manitou Island, Lake Michigan. The remaining 37 were take in Lake Huron or in streams tributary to that lake. The dispersal of tagged lampreys throughout Lake Huron was wide. Five marked individuals were taken in the southern part of the lake over 150 miles from the point of tagging; 4 of these 5 were captured in Canadian waters. The marked lampreys exhibited no distinct pattern of migration other than a tendency toward a general southeasterly movement in Lake Huron.

Transactions of the American Fisheries Society↗

USGS1953

A more comprehensive description of Bacterium salmonicida

The purpose of this study was to establish a set of descriptive data which could be used as a reference or a standard in the identification of Bacterium salmonicida, the cause of furunculosis in fish. Since a complete description of B. salmonicida was not available, bacteriologists were not in a position to identify this microorganism in a manner which would meet the rigorous requirements of present‐day bacteriology. Ten strains of B. salmonicida were employed in these studies. A detailed description is presented which includes the morphological, cultural, and physiological characteristics of B. salmonicida. In addition, various factors such as oxygen, pH, temperature, and composition of media are discussed in terms of their influence on the formation of the melanin‐like pigment which is characteristically produced by this microorganism.

Transactions of the American Fisheries Society↗

USGS1953

Technique for the application of a streamer-type fish tag

Principal features of the technique are: attachment of the plastic tag by means of a nylon-thread loop prepared in advance of field work; use of a curved surgical needle with cutting edge and a split eye for application of the tag. The procedures for splitting the needle's eye and for applying the tag are described and illustrated by a series of photographs.

Transactions of the American Fisheries Society↗

USGS1953

The movement of tagged lake trout in Lake Superior, 1950-52

A total of 733 native lake trout was tagged at two widely separated localities in Lake Superior; subsequent recaptures numbered 155 fish (21.1 percent) during the year following marking. In October 1950, 116 large lake trout (average total length, 27.3 inches) were tagged near Keweenaw Point, Michigan. Fifteen (12.9 percent) were recovered during the first year at points as far west as the Gooseberry River, Minnesota (190 miles), north to the Slate Islands, Ontario (95 miles), and east to Grand Marais, Michigan (100 miles). Nine fish (7.8 percent) were recovered during the second year after marking. Returns from 617 tagged lake trout of smaller size (average length 18.2 inches) released in the Apostle Island region of Wisconsin during the period June 12 to August 6, 1951, numbered 140 (22.7 percent) during the first year. Of these fish, 90 percent were recaptured within a radius of 50 miles of the points of release. Seventy-six percent were caught in Wisconsin, 14 percent in Minnesota, and 9 percent in Michigan waters. The fish retaken in Michigan had moved 120 to 255 miles between the time of release and recapture, traveling as far west as Grand Marais. Lake trout recaptured at distances of more than 50 miles from the tagging locality were of larger average size than marked fish caught within this radius. The four types of tags used in the marking of lake trout in the Apostle Island region, together with the number tagged and percentage recovered during the first year were as follows: 103 aluminum lower-jaw tags (used only on fish less than 17 inches in length when marked)-10.7 percent; 200 monel upper-jaw tags-14 percent; 162 streamer tags-19.8 percent; and 152 Peterson tags-45.4 percent. Obviously lake trout marked with the Peterson tag, with the discs and ends of the pin projecting from each side near the point of maximum girth, were more vulnerable to the fishery than were fish marked with other tags. The recoveries of marked fish show that Lake Superior lake trout-particularly fish of large size-may move many miles and freely cross political boundaries; and that the rate of harvest is moderately high for a fish with a life history as long as that of the lake trout.

Michigan, Minnesota, Wisconsin↗

USGS1954

Fluctuations in production and abundance of commercial species in the Red Lakes, Minnesota, with special reference to changes in the walleye population

The Red Lakes in northwestern Minnesota comprise 275,000 acres of water which support a commercial fishery producing up to 1.5 million pounds of fish per year. Walleye, Stizostedion vitreum vitreum (Mitchill), and yellow perch, Perca flavescens (Mitchill), are the principal species. Statistics for the past 37 years have been analyzed and fluctuations in the abundance of the important species calculated for the 24-year period, 1930–1953. The fishing is carried on exclusively with 3 1/2-inch-mesh (extension measure) gill nets by Chippewa Indians and the catch is marketed through a cooperative fishery enterprise. There have been wide fluctuations in the abundance of principal species but, although fishing effort has increased greatly during the past few years no trends have developed. Changes in walleye abundance have been shown to be independent of changes or levels of fishing effort, and to be determined by strength of individual year classes. Gear competition has no effect on abundance estimates. Strength of year classes is not correlated with size of brood stock, abundance of competing species, or amount of hatchery fish planted. Weather conditions cannot be correlated with observed changes in strength of year classes. Implications for management include provision of adequate prediction of abundance, and annual adjustment of fishing practices to make greatest use of the available stock. Gear limitations should be designed to secure harvest at optimum size of fish and to provide a suitable economic status for the fisherman.

Transactions of the American Fisheries Society↗

USGS1954

The nature of bacteria pathogenic to fish

A review is made of the progress in research on bacteria which are pathogenic to fish, with particular emphasis on those investigations performed during the past decade. The report includes a critical review of material published; the comments and suggestions are designed to stimulate the initiation of new research projects.

Transactions of the American Fisheries Society↗

USGS1954

Infectious diseases of Pacific salmon

Investigations on infectious diseases of Pacific salmon due to micro-organisms other than viruses are reviewed. The etiological agents include trematodes, fungi, protozoa and bacteria. Bacteria have been found to be the most important agents of disease in the several species of Pacific salmon. Kidney disease, due to a small, unnamed Gram-positive diplobacillus, causes serious mortalities in young salmon reared in hatcheries. The disease has also been found in wild fish. Aquatic myxobacteria are important agents of disease both in the hatchery and in the natural habitat. One of the myxobacteria, Chondrococcus columnaris , causes disease at relatively high water temperatures. The problem of the taxonomy of this organism is discussed. Another myxobacterium, Cytophaga psychrophila , has been found responsible for epizootics in coho salmon at lower water temperatures, i.e., in the range of 40° to 55° F. In outbreaks of gill disease in young salmon, myxobacteria of several kinds have been implicated. A variety of bacteria has been found responsible for outbreaks of disease in salmon in sea water. The most important of these is a species of Vibrio . Tuberculosis has been found in adult chinook salmon and the evidence indicates that the disease was contracted at sea.

Transactions of the American Fisheries Society↗

USGS1953

Therapy of bacterial fish diseases

During the past decade considerable progress has been made in the therapy of bacterial fish diseases. This progress was possible largely because of the introduction of powerful chemotherapeutic agents such as sulfonamides and antibiotics. Fish furunculosis can be treated with very good results with sulfamerazine, sulfamethazine, and sulfaguanidine as well as by chloramphenicol and terramycin. Ulcer disease caused by Hemophilus piscium resists treatment with sulfonamides but responds well to the above mentioned antibiotics. Chemotherapy of fish diseases caused by pseudomonads is possible with chloramphenicol, but sanitary measures are preferred. External disinfections with Roccal and pyridylmercuric acetate (PMA) are satisfactory in treatment and prophylaxis of gill diseases which are probably caused by superficial infections with myxobacteria. Sulfonamides are helpful in systemic infections with myxobacteria and are also being used with some success for the control of a recently described kidney disease of salmonold fishes. Also described are methods of control of other fish diseases and of immunity in cold‐blooded animals and fishes. Most of the drugs in the described treatments may be toxic to fishes, and therefore should be used with caution.

Transactions of the American Fisheries Society↗

USGS1954

Virus diseases of fish

Viruses are probably the cause of a wide spectrum of fish diseases. Although relatively few virus diseases of fish are known today, some of the diseases of unknown etiology, as well as some diseases presently accepted as due to bacteria, protozoa, fungi or nutritional deficiencies, possibly will be recognized eventually as virus diseases. Some viruses may induce proliferative tissue changes whereas others may cause degenerative change. Although several diseases of a proliferative nature have been reported to be of virus origin, positive experimental evidence for the transmission of a virus from one fish to another, has been presented for only lymphocystis. The degenerative or non-neoplastic diseases of possible virus origin give the fish-culturist the most concern because of the severe mortalities resulting from infection. Epizootics of this nature have been reported in carp (Cyprinus carpio) and rainbow trout (Salmo gairdneri) in Europe, in acara (Geophagus brasiliensis) in South America, in kokanee, (Oncorhynchus nerka kennerlyi) and in sockeye salmon (Oncorhynchus nerka nerka) in the State of Washington. It has been demonstrated that each epizootic was caused by an infectious filterable agent, probably a virus.

Transactions of the American Fisheries Society↗

USGS1954

Sulfonamide toxicity in brook trout

Sterility was observed in female brook trout that were treated with sulfamerazine at frequent intervals for 2 years to control endemic furunculosis. Feeding sulfamerazine for a period of 8 months caused massive kidney damage similar to that observed in humans who develop allergies to “sulfa” drugs. Kidney damage of the type observed would probably cause renal insufficiency which would handicap any physiological function including reproduction. Feeding sulfonamides for periods up to 13 weeks did not produce kidney damage.

Transactions of the American Fisheries Society↗

USGS1955

The pygmy whitefish, Coregonus coulteri, in Lake Superior

Bottom trawling by the U. S. Fish and Wildlife Service motor vessel Cisco in Lake Superior in 1952–1953 revealed a large population of a tiny whitefish, Coregonus (Prosopium) coulteri, which has been reported previously only from northwestern North America. The hiatus in range, from Lake Superior to the Columbia River basin, is the greatest known for a North American freshwater fish. Although minor structural differences characterize the disjunct populations of the pygmy whitefish, these are not deemed worthy of nomenclatorial recognition. Comparisons with related species indicate that the pygmy whitefish is distinctive in the small size, large scales, few vertebrae, few pyloric caeca, and in other characters. The pygmy whitefish is widely distributed in Lake Superior, especially in semi-protected bays, such as Keweenaw Bay which yielded about 68 percent of the 1,623 specimens caught. The bathymetric range was 10 to 49 fathoms, with maximum abundance at the 25- to 39-fathom interval. Average length of fish increased progressively with water depth, chiefly because the number of yearlings declined from 100 percent at 10–14 fathoms to none at 45–49 fathoms. The average total length of pygmy whitefish caught by trawling was 3.4 inches (range 1.2 to 5.7). Extraordinarily slow growth was revealed by the examination of scales. Two fish from Keweenaw Bay, both nearing the end of their eighth growing season, were only 5.4 inches long. Compared to Keweenaw Bay, growth rate was about the same near Laughing Fish Point, faster in the Apostle Islands (and in Bull and McDonald Lakes, Montana), and slower in Siskiwit Bay, Isle Royale. Females grew more rapidly than males after the second year and had a longer life span. All male pygmy whitefish were mature at the age of 2 years and a total length of 3.6 or more inches. Most females were mature at 3 years and 4.2 inches; all older females were mature. Mean egg production was 362 (range, 93 to 597) per fish and 26 per gram of total weight for fish from 3.4 to 5.9 inches long. Spawning in 1953 occurred sometime in November or December. Crustacea (principally ostracods and amphipods–copepods in the young) occurred in 106 of 112 pygmy whitefish stomachs and made up 77 percent of the total food volume. When available, fish eggs appear to be important in the diet. Other cold-water fishes–cottids, ninespine sticklebacks, smelt, and four species of coregonines–were the most frequent associates of the pygmy whitefish. Lake trout and trout-perch were also taken with it at the same stations or in the same trawl hauls. Its closest relative in Lake Superior, the round whitefish, was not an ecological associate.

Transactions of the American Fisheries Society↗

USGS1955

Early life history of the yellow perch, Perca flavescens (Mitchill), in the Red Lakes, Minnesota

The early life history of the yellow perch, an important commercial species in the Red Lakes, Minnesota, has been studied with special reference to length at scale formation, growth rate during first season of life, and food habits as they relate to growth and survival. Scales are fully imbricated in the area of 12th to 14th lateral line scales at 24 millimeters total length. There is a wide annual varition in first season's growth which is not correlated with growth in older fish. Body-scale relationship is rectilinear from 24 to 280 millimeters. Length-weight relationship during the first year is expressed by the equation W = 0.6198 × 10 −5 L 3.1251 which is very similar to that describing the relationship in later years. Stomach analysis indicates food is primarily plankton but in some seasons fish may be strongly dependent on bottom forms. Variations in food availability appear to be associated with changes in growth and may have a major influence on survival.

Transactions of the American Fisheries Society↗