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An improved method for isolating viruses from asymptomatic carrier fish

This paper describes a method using elevated levels of penicillin, streptomycin, and nystatin instead of filters to control bacteria and mold contaminants in specimens processed for virus isolation. Filters were shown to significantly reduce the virus concentration. Virus and tissue cultures were not affected by this procedure. In field tests nearly three times more specimens were positive for virus with this method than with the widely used filter technique. Moreover, the cost of materials was less. This method is recommended for inspection and certification purposes.

Transactions of the American Fisheries Society

Age, growth, reproduction, and food of the burbot, Lota lota (Linnaeus), in southwestern Lake Superior

This study was based on 1,285 burbot ( Lota lota ) collected in three areas in southwestern Lake Superior in 1966-69. Age was determined from otoliths, the marginal zones of which were opaque from December to May and translucent from June to November. Average lengths of the age groups and annual increments were measured from a curve fitted by inspection to point estimates of lengths at capture. Burbot grew 5.7 inches during the first year of life and 4.3 inches during the second. Later annual increments through the twelfth year ranged from 1.2 to 2.6 inches. Average total lengths and calculated weights were 16.1 inches and 1.1 pounds at age V and 23.4 inches and 3.2 pounds at age X. First maturity was at age I, at a total length of 9.7 inches for males and 10.7 inches for females; all fish were mature at age V and at lengths greater than 16.4 inches (males) and 15.9 inches (females). Most burbot collected near shore in the Apostle Islands area in late January and February were spent, but none collected in offshore areas during January and March had spawned. The estimated number of eggs in the ovaries of eight burbot 14.7-21.3 inches long ranged from about 268,800 to 1,154,000 and averaged about 812,300. Burbot of all sizes fed on fish and crustaceans. Fish heavily predominated in the food of large burbot taken during the winter (99.6% of the volume) but crustaceans ( Mysis and Pontoporeia ) became increasingly important during the summer and fall (when they contributed more than 73% of the volume). Due to the wide variety and large volume of food consumed, the burbot is probably a significant competitor of many other species.

Transactions of the American Fisheries Society

Fecundity of the sea lamprey (Petromyzon marinus) in Lake Superior

An infectious agent, which appears to be a virus (RJV) has been isolated from the liver of a wild raccoon which has led to a highly fatal type of disease characterized by conjunctivitis and an elevated serum bilirubin frequently accompanied by jaundice on inoculation of raccoons. Ferrets also appear to be susceptible to infections with this agent.

Transactions of the American Fisheries Society

Application of theory and research in fishery management of the Laurentian Great Lakes

The Great Lakes have a high potential for the conduct of research and useful application of research findings, but the history of the Great Lakes indicates that extensive research and intensive management have failed to prevent deterioration of the fisheries. At times the research was not done before a loss occurred, or did not provide the information needed to solve a problem, or was not interpreted to indicate a need for corrective action. Three examples are used to illustrate these problems: (1) Sea lamprey ( Petromyzon marinus ) research was not initiated until 50 years after the destructiveness of the sea lamprey was recognized, and control measures were not developed or applied until species most vulnerable to the lamprey had been greatly reduced or eliminated. (2) Most research on the alewife ( Alosa pseudoharengus ) has been directed toward determining why large numbers of alewives die during the spring and summer, but has not provided the information most urgently needed by management to use alewives to best advantage, or to reduce the biological or human problems that alewives cause. (3) After a study during 1926-30 to determine if pollution was affecting fish in Lake Erie, it was concluded that the detrimental effects of pollution in certain regions were offset by the benefits of enrichment in other areas, but managers were not warned that areas of pollution might expand, and eventually influence the entire lake. The Great Lakes ecosystem is complex and in a state of rapid change. Thus, the outcome from the application of theory is uncertain at best and there can be no assurance that the desired results will be attained. The programs for sea lamprey control and salmonid restoration are a current example of difficulty in application of theory in management. Superficially the sea lamprey appears to be under control and salmonids have been restored. The postcontrol abundance of sea lampreys, however, is equal to the abundance that caused the initial collapse of the lake trout ( Salvelinus namaycush ), and there is evidence that the damage lampreys are inflicting on lake trout is as heavy as it was in the precontrol period. Also, in the presence of an abundance of hatchery-reared salmonids, the lamprey is reproducing and thriving as well as or better than it did during its initial population explosion, and indications are that it will increase rather than decrease under the present method and level of control. Successful application of theory and research to fishery management has always been impeded by lack of continued and close coordination among some 30-40 state, provincial, and federal governmental units that have varying degrees of influence on fishery programs of the Great Lakes. Frequently agreements that have been reached among conservation agencies were not sustained by legislative units, or were nullified by organizational changes. As a result, conflicting approaches were sometimes taken by management agencies with jurisdiction in different areas of the same lake. Sustained and compatible management objectives and practices can, however, contribute to greater stability, and optimum usefulness and productivity.

Transactions of the American Fisheries Society

Disinfection of contaminated water by ultraviolet irradiation, with emphasis on whirling disease (Myxosoma cerebralis) and its effect on fish

Rainbow trout fry developed whirling disease upon exposure to water contaminated with Myxosoma cerebralis. When similarly contaminated water was irradiated with 2537 Angstrom units of ultraviolet light at dosages of 35,000, 43,000, and 112,000 microwatt sec/cm 2 , infection of fry was prevented. The minimum effective dosage was not determined in the present experiments. High mortality and a 61% growth inhibition of survivors occurred in the infected fry.

Transactions of the American Fisheries Society

Effects of TFM and Bayer 73 on in vivo oxygen consumption of the aquatic midge Chironomus tentans

Exposure of fourth instar larvae of Chironomus tentans to 2.0‐8.0 mg/liter of TFM (3‐trifluormethyl‐4‐nitrophenol) for 6 hr at 22 ± 0.5 C in soft water resulted in a significantly increased rate of larval oxygen consumption compared to that of control larvae, as measured with the Warburg respirometer. Maximum stimulation of oxygen consumption occurred with 8.0 mg/liter of TFM, and 1.0 mg/liter of TFM had no measurable effect on basal respiration. When hardness of exposure water was progressively increased, the effect of TFM on oxygen consumption was diminished. Bayer 73 (5,2′‐dichloro‐4′‐nitrosalicylanilide) stimulated oxygen consumption at 0.75 and 1.0 mg/liter, had no significant effect at concentrations less that 0.75 mg/liter, and inhibited oxygen consumption at concentrations of 1.20 mg/liter or greater. Mixtures of TFM and Bayer 73, in the ratio of 98:2, had no greater effect on oxygen consumption than TFM alone.

Transactions of the American Fisheries Society

Nitrogen and phosphorus balance of grass carp, Ctenopharyngodon idella, fed elodea, Egeria denea

The herbivorous grass carp fed winter elodea exhibited a negative nitrogen balance in metabolism, suggesting that food having a higher protein content would be required for normal growth. About a third of the phosphorus contained in food was retained; hence, a combination of aquatic plants and grass carp might afford an effective biological method for removing phosphorus from water. Water quality was altered by the excretion of ammonium and orthophosphate by grass carp. Even though the grass carp might be useful in removing some phosphorus from water, its principal impact was to increase the rate of recycling of nitrogen and phosphorus.

Transactions of the American Fisheries Society

The jumping ability and behavior of green sunfish (Lepomis cyanellus) at the outflow of a 1.6-ha pond

Effects of a plunging water flow on the behavior of green sunfish (Lepomis cyanellus) 7.1 to 9.7 cm in total length were studied at the outflow of a 1.6‐ha pond. Jumping ability and behavior were measured at 12‐hr intervals using a fishˈs position in a 0.9 m 2 ‐vertical grid or in the discharge pipe. Activity was influenced by flow rate, time of day, and time of year. Fish jumped up to 10 times their body length and traversed a horizontal distance of 0.6 m. Fish with the greatest mean length jumped the highest. The majority of the fish were captured during the 0600‐hr tending period: 79.9% pipe only study and 82.4% pipe and grid combined study.

Transactions of the American Fisheries Society

Comparative toxicity of two Iodophors to rainbow trout eggs

Toxicity of Wescodyne (R) and Betadine (R) to eyed eggs was not adversely affected by water hardness (as calcium and magnesium) or by exposure periods up to 60 min. Both iodophors were much more toxic below pH 6.0 than at pH 8.0. In general Wescodyne was slightly more toxic than Betadine. Significant egg loss occurred if freshly fertilized eggs were water-hardened in either iodophor at 100 ppm of iodine, but egg loss at 25 ppm of iodine or at 100 ppm if the eggs were disinfected 30 min after water hardening was comparable to the control. Also, there was no effect on the egg mortality or fry development following single or multiple exposures after eggs were water hardened. At pH 6.0 and above, Wescodyne and Betadine at 100 ppm iodine in a 15-min dip would be safe to use on rainbow trout eggs at any stage of development after water hardening. Recommendations and precautions for hatchery use are given.

Transactions of the American Fisheries Society

A respirometer with controllable oxygen levels

Construction details and operation of a respirometer with capabilities for controlling the oxygen level at preselected levels is described. The interaction of an oxygen sensor and electronic switch energizes an electrolysis cell which replenishes oxygen used by a test organism. Respiration rate of any aquatic or semiaquatic organism may be determined by this apparatus.

Transactions of the American Fisheries Society

Channel catfish virus experiments with different strains of channel catfish

Experimental infections of channel catfish virus were made by feeding virus to six strains of 1‐, 2‐, and 3‐month‐old channel catfish from different geographical areas and two hybrid strains. There was no significant difference in mortality between age groups. Mortality rates differed significantly between the various strains, with mean mortality ranging from 10% to 71% among infected fish. Mortality percentage of the Falcon group was significantly higher than all other groups. Hybrid strains had the lowest percentage of mortality.

Transactions of the American Fisheries Society

Effect of egg concentration in an incubation channel on survival of chinook salmon fry

Eyed eggs of chinook salmon (Oncorhynchus tshawytscha) were planted in the Abernathy (Washington) incubation channel at concentrations of 7,180, 10,764, and 14,349 eggs/m 2 of gravel. Numbers of eggs planted were 200,000, 240,000, and 200,800, and survivals to the downstream migrant stage were 78.5, 85.0, and 79.1%, respectively; the differences were not statistically significant. The concentration of 14,349 eggs/m 2 is near the capacity of the channel. This stocking rate is 10 times that commonly recommended for artificial spawning channels. Egg concentration was apparently limited only by the physical capacity of the gravel.

Transactions of the American Fisheries Society

Feeding behavior and temperature and light tolerance of Mysis relicta in the laboratory

Live specimens of Mysis relicta from Lake Michigan were held for one year in the laboratory to determine feeding behavior and tolerance to light and temperature. Mysids fed by moving with rapid, horizontal jerking motions toward food as it settled toward the bottom and by swimming slowly, upside down, to gather particles floating on the surface. Scavenging was common. Mysids tolerated considerably higher temperatures than previously reported. Temperature increases (from 5 C) of 1 C per day and 1 C per minute resulted in TL m values of 20.5 C and 20.4 C, respectively. Mortality increased rapidly at temperatures above 13 C. The upper lethal limit for mysids acclimated to 5 C was about 22 C. Survival under continuous, high light intensity (32 foot-candles) was considerably higher than previously reported. Low water temperature (5 C) may have increased light tolerance.

Transactions of the American Fisheries Society

Requirement of Atlantic salmon for dietary phosphorus

Triplicate lots of young Atlantic salnon (Salmo salar) were fed a diet containing graded levels of supplemental inorganic phosphorus. The basal diet, containing mainly dehulled soybean meal and other plant materials, provided 40% crude protein, 0.7% phosphorus, 1.5% calcium, and 4,000 IU of supplemental cholecalciferol per kg of diet. Supplements of inorganic phosphorus significantly improved growth, feed utilization, and bone ash content. Inorganic phosphorus supplementation up to 0.6% of the diet increased growth rate and bone ash content; additions beyond this level had little further effect. This study suggests that when young salmon are fed diets containing 0.7% phosphorus from plant sources, the minimum requirement for supplemental inorganic phosphorus is approximately 0.6% of the diet.

Transactions of the American Fisheries Society

Inhibition of salt water survival and Na-K-ATPase elevation in steelhead trout (Salmo gairdneri) by moderate water temperatures

The steelhead trout metamorphosis from a freshwater parr to a sea water-tolerant smolt possessing the migration tendency was evaluated at six different growth temperatures ranging from 6 to 15 C during January through July. The highest temperature where a transformation was indicated was 11.3 C. By April fish reared at 6 C had elevated ATPase levels typical of smolts or migratory animals and showed 92% survival in sea water. Ten and 11.3 C-reared fish showed a short-lived elevation in ATPase in mid-April alone concurrently with 100% sea water survival at that time. Only in 6 C-reared animals did the salt water survival ability continue into May. High ATPase levels likewise were prolonged into May and June only in the 6 C-reared group. The data indicate that metamorphosis (and therefore successful migration) of juvenile steelhead trout is directly controlled by water temperature.

Transactions of the American Fisheries Society

Effects of inbreeding on rainbow trout populations

An approach for measuring inbreeding depression on the basis of differences between inbred and outbred half‐sib family groups is described. Using this method, estimates of inbreeding depression in populations of rainbow trout (Salmo gairdneri) following one generation of brother‐sister mating was calculated for three production traits–percent egg hatchability, percent fry survival from swim‐up to 150 days, and weight at 150 days. The inbreeding depression estimates obtained from male and female half‐sib families were 1.7 and 4.4% for percent egg hatchability, 22.2 and 16.1% for percent fry survival, and 12.0 and 9.8% for weight at 150 days, respectively. Estimates for fry survival and weight at 150 days were significant at P < 0.01 while egg hatchability estimates were nonsignificant. Following one generation of full‐sib mating, the calculated effect of inbreeding on the number of live fish and total weight of fish at 150 days of age showed a reduction of 16.1 and 24.4% in female families and 22.1 and 31.4% in male families, respectively. The difference between inbreeding depression estimates derived from male and female half‐sib groups provide a measure of the maternal influence. Generalized trends of increasing depression with increasing levels of inbreeding from F = 0.125 to F = 0.50 were significant for weight at all ages from 77 to 150 days, but were nonsignificant for percent hatchability or percent fry survival. Inbreeding depression estimates for weight are considered to be minimum estimates because higher mortality rates in the inbred families resulted in lower fish density during the rearing period and, therefore, compensatory growth which reduced the weight difference between inbred and outbred families.

Transactions of the American Fisheries Society

Retention of mercury in the muscle of yellow perch (Perca flavescens) and rock bass (Ambloplites rupestris)

Mercury‐contaminated yellow perch (Perca flavescens) and rock bass (Ambloplites rupestris) were collected from Lake St. Clair and stocked in two earthern ponds in September 1970. Twenty‐six months later, concentrations of total mercury in the fillets had declined 53% in the yellow perch and 59% in the rock bass; however, the mean weight of the fish increased 88 and 183%, respectively, during the same period. All of the reduction in mercury concentrations was attributable to dilution by growth. Slight discrepancies between the theoretical and observed reduction of mercury concentrations suggest an initial redistribution of residues from other tissues to the muscle and a continued incorporation of background amounts of mercury during growth.

Transactions of the American Fisheries Society