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Forty-three adult sockeye salmon (Oncorhynchus nerka) fitted with ultrasonic transmitters were tracked in coastal waters near the Fraser River in July and August, 1967 and 1968. Movement patterns of individual fish were unpredictable. Some moved actively in appropriate directions, some drifted passively, still others travelled southward away from their presnmed destination. Fish released in pairs did not travel along similar paths. Active fish moved generally northward toward the Fraser River, keeping away from shore and following axes of tidal currents. There was little straying into bays and channnels with slow currents. Some fish remained active both during the day and at night, while others became inactive after sunset or when the sun was not visible behind clouds. Average ground speed was about 1 body length/s (61 cm/s). Orientation to geoelectric fields is postulated, along with a compass-related orientation northward.

We compared the homing ability of three groups of rainbow trout (Salmo gairdneri) stocked in Lake Michigan by different procedures. One group of juvenile rainbow trout was imprinted to a synthetic chemical, morpholine, during the presmolt and smolt stages, and a second group was not imprinted. Both groups were stocked directly into Lake Michigan, 1 km north of the Little Manitowoc River. A third group of trout was retained in a pond on the Little Manitowoc River during the presmolt and smolt stages and then released into Lake Michigan at the same location as the other two groups. During the adult spawning migration, morpholine was metered into the Little Manitowoc River. This river and 16 other locations were monitored for returning fish. The morpholine-imprinted fish returned to the Little Manitowoc River in greater numbers and strayed less than did fish from the other two treatment groups. This result is a consequence of exposure to a unique odor cue at the critical period for imprinting.

The migratory behaviour of coho salmon was studied in the field. Coho salmon, Oncorhynchus kisutch, exposed to synthetic odours in a hatchery and released into Lake Michigan as juveniles, were recaptured as migrating adults 18 months later. The movements of 43 individuals were followed in experiments examining the role of imprinted chemical cues in the homing migration. Movements in relation to controlled distributions of the imprinting odours revealed that chemical cues are used by the salmon in their upstream migration. Acting with the rheotactic response, fish were guided upstream by imprinting odours simulating their home stream. Coho salmon, in the absence of their imprinting odour, respond negatively to the current. Differential responses to current appear to serve in segregating fish imprinted to odours of different home streams.

Daily movements of 17 carp bearing ultrasonic transmitters were monitored during autumn and winter of 1974-1975 and 1975-1976. In each year these fish joined concentrations of carp in two areas of Lake Mendota in late autumn before freeze-up. Instrumented carp arrived at these two areas with relative synchrony from different parts of the lake. Commercial fishermen, advised of these locations, harvested 46,400 kg of fish. The use of carp bearing ultrasonic transmitters to locate large concentrations could be useful as both a commercial fishing and management technique.

Phenol, a common pollutant in municipal water supplies, cannot be readily detected in low concentrations until it has reacted with chlorine forming odorous chlorophenols. A method is here presented whereby bluntnose minnows (Hyborhynchus notatus) are used to detect the presence of phenols below the threshold for man (0.01 p.p.m.). Fishes of two aquaria were trained to associate the odor of phenol with food; the odor of a p-chlorophenol with punishment. The minnows of two other aquaria were trained to the same two odors, but with reverse meanings. Upon completion of the training period, the minnows were discriminating successfully between these two substances at concentrations of at most 0.0005 p.p.m. A generalization test, using p-chlorophenol as the third odor, indicated that the fishes were able to distinguish it from the two training odors. The biological assay of phenolic compounds by this method is primarily one of detection and not of quantitative analysis.

Effect of hypophysectomy, isletectomy and ACTH on glycemia and hematocrit in Ictalurus melas were studied. The mean blood glucose (BG) and hematocrit in intact untreated fish were found to be 69.65 mg/100 ml and 33.7% respectively. Following hypophysectomy there was a 73.1% decrease in BG and a 50% decrease in the hematocrit. Changes in sham-operated controls were insignificant. Eight IU of porcine ACTH administered in two injections on days 6 and 8 post-hypophysectomy increased the BG to pre-hypophysectomy level and the hematocrit to 70% of its initial value on day 9, whereas in vehicle injected controls BG and hematocrit values remained at their post-hypophysectomy level. Isletectomy caused hyperglycemia in all the experimental animals. It induced a net increase of 142.3% over the pretreatment BG compared to 5.2% increase in sham-operated controls. Isletectomy unlike hypophysectomy did not produce any significant change in the hematocrit.

The object of this paper is to examine the consequences of inadvertent lake fertilization in an effort to forecast the outcome of deliberate fertilization projects. Enrichment of water, be it intentional or -unintentional, is called eutrophication. Naumann ('31) defined it as the increase -of nutritive substances, especially P and N, in a lake. In this paper eutrophication will be interpreted in the broadest sense; namely, lake enrichment owing to any and all nutritive substances. A survey of the limnological literature reveals a number of lakes in which entrance of domestic (cultural) drainage, over and above normal edaphic influence, was followed by marked biological changes. Countries from which these are reported are Austria, England, Finland, Germany, Italy, Sweden, Switzerland, and the United States. A list of the lakes is given in table I. It goes without saying that domestic fertilization poses a serious problem in applied limnology. In many cases pollution, though unintentional, has led to esthetic deterioration of a lake-obnoxious scums of algae discolor the water and the shore, and upon decomposition produce foul odors. Boating and swimming become uninviting owing to scums and excessive growths of large aquatic plants. Riparian property values depreciate and the economy of the whole community may suffer. In addition, municipal water costs increase because of difficulties in filtration and deodorization of the water. Experiments on the artificial enrichment of lakes are few in number and often difficult to interpret. One would like to see further tests made, but in the meantime a clearer view of the problem may be obtained by examining the case histories of domestically eutrophied lakes where biologists have accumulated observations of the succession of limnological events. True, most of these cases offer only circumstantial evidence, as controls are lacking. Nevertheless this historical approach is intended to aid in assessing proposed lake fertilization programs.

Sonar equipment was used during 1966 to study the relation between seasonally changing temperatures and swimming speeds of yellow perch, Perca flavescens (Mitchill), in Lake Mendota and the movements of the fish with respect to water currents in the lake. From its lowest point during winter (0–5 C) the rate of movement increased with increasing water temperatures until the maximum rate was reached during mid-summer when water temperatures were 20–25 C. As the lake cooled in autumn, the swimming speeds declined. The range of speeds in the frequency distribution during winter was less than that during summer when the distribution was spread out and encompassed a wide range of speeds. The swimming rate increased linearly with increasing temperature. The swimming speeds of individual perch were commonly only one-half those of schools at a given temperature interval suggesting that a “group effect” was correlated with the behavior of the perch schools. No consistent orientation of fishes to the curren...

Rather suddenly, in the early 1940's, the cisco in Lake Mendota became scarce. The evidence suggested that the decline was caused by heavy summer mortalities in 1940 and 1941, but further study indicated that the summer mortalities had involved mainly older fish and that the primary cause for the decline was a scarcity of young fish in the population at the time of mortalities. Accordingly, our efforts were turned toward a search for the cause of weak year-classes, or year-class fluctuations in general. It was postulated that year-class failures might arise if the eggs hatched under the ice because then the illumination would be insufficient to enable the larval cisco to feed. Experiments were conducted in the laboratory to determine the effects of illumination and of various patterns of incubation temperatures on the date of hatching of the eggs. Eggs exposed continuously to room illumination for 135 to 140 days hatched 7 to 8 days earlier than eggs incubated continuously in darkness. Different values of incubation temperatures acting on the eggs for about one month from the time of fertilization induced the expected proportional rates of development of eggs, but when the eggs were refrigerated at a common temperature after this first month, the rate of development of advanced embryos was retarded while the less developed embryos gained. Under such treatment, eggs incubated at temperatures differing by 1°C in the range 1°–6°C, and then incubated for the remainder of the period at a common temperature below 4°C, hatched about one day apart. Eggs incubated from the time of fertilization at a common temperature below 3°C, and then incubated for the last month at higher temperatures differing by 1°C in the range 1°-6°C, hatched 7 days apart. Eggs which had developed rapidly toward the hatching stage lay dormant for about 3 months at temperatures below 3°C. They hatched about 4 days earlier than eggs incubated continuously at temperatures below 3°C, having accumulated about 150 degree-days greater exposure. The evidence clearly indicated that the eggs of the cisco in Lake Mendota never hatch under the ice regardless of natural seasonal variations in temperatures and illumination incurred during the incubation period. Moreover, the dates of hatching are probably not affected significantly by any factor except possibly different temperatures incurred after the departure of the ice from year to year. Experiments conducted on larval cisco indicated that they require illumination for feeding. They starve if held in darkness with natural densities of food. They begin to swallow water on the first day after hatching as indicated by keeping them in a solution of 2,3,5-triphenyltetrazolium chloride. They also begin to swallow particulate materials within the first day. By the third day they began to consume adult Cyclops sp. and by the fifth day better than 90% of the larval fish fed on adult Cyclops sp. During the first week, the swimming ability of the food organisms was a decisive factor in the degree of feeding success shown by the larval fish. The test consisted of offering living Cyclops sp. to one group of fish and freshly killed Cyclops sp. tothe other group. After the first week, the fish fed equally well on both types of food. The larval fish tolerated about 108–120 degree-days of starvation without harm. Yet, when provided with food they began to feed before the yolk sac was absorbed. The initial postulated cause for year-class failures has been disproved. It is estimated that the eggs never hatch prior to April 25, and since 1880 the ice has not remained on Lake Mendota later than April 21.

The white bass, Roccus chrysops, has two principal spawning grounds 1.6 km apart on the northern shore of Lake Mendota. Fish displaced from these spawning grounds return faithfully to their respective spawning sites, and of 1366 fish marked and displaced to midlake, a distance of 2.4 km, 181 were recaptured in fyke nets and less than 9% erred by being recaptured at the net on the other spawning ground. Fish released at the spawning ground were not recaptured in greater percentage than those displaced and released in mid-lake. Fish to which floats were attached for direct tracing moved generally north from the center of the lake when released on clear days. Moreover, fish released between the two spawning grounds also moved north on clear days. On cloudy days, however, or if blinded witheyecaps, they moved at random. Unexplained is how they differentiate between the two spawning areas; apparently it is by means other than with the aid of the sun. A laboratory analysis of the sun-compass mechanism was made. An immature specimen of Lepomis macrochirus was trained, at a specific time of day, to find cover in one of sixteen boxes of a circular tank. When trained, the fish entered the training box in a consistent compass-direction at any time of day. Under an overcast sky the choices were completely unoriented. When tested under an artificial sun, (light bulb), this fish responded as though it were the real sun, at that time of day and sought cover in the “artificial” diiection, reaffirming the presence of a biological clock. White bass were also successfully trained to a compass-direction under the natural sun. Lepomis gibbosus was tested with another method. It too has a sun-compass mechanism. These field and laboratory experiments suggest strongly that the sun serves as the point of reference, and that the animal compensates for its movement by a biological chronometer.

Rates of oxygen consumption were determined for: 1) single young-of-the-year white bass, Morone chrysops (Rafinesque), forced to swim in a rotating annular respirometer, and 2) groups of young-of-the-year fish fed meals of live zooplankton. Sustained swimming activity and maximum metabolic rates generally occurred at a rotation velocity of 15 rpm. The decline in oxygen consumption with time and increased velocities in six experiments suggested decreases in excitement and swimming activity. Post-feeding increases in oxygen consumption were observed in six groups. After this initial elevation, metabolic rates continued to increase slightly or declined. The importance of measuring the components of total respiration and their caloric equivalents is stated and will be discussed in a subsequent paper.

The seasonal fluctuations in the quantities and kinds of phytoplankton in lakes has received the attention of limnologists for many years. For southern Wisconsin lakes, a good general description of the annual phytoplankton cycles of pelagic waters has been presented by Birge and Juday (1922). Causes of these fluctuations have sometimes been explained on the basis of the levels of chemical nutrients, especially phosphorus and nitrogen compounds, which are present in natural waters, though few generalizations of real or supposed biological and chemical relationships have thus far had wide application. At the present only a limited amount of information has been gained from experimental algal cultures which can be applied directly toward an understanding of the usually different conditions existing in various natural waters. The experiments of Chu (1942), Rodhe (1948), and Gerloff, Fitzgerald, and Skoog

A small ultrasonic fish tag is described, which is useful in studies of the game and pan fishes of freshwater lakes. The device emits a continuous signal of from 14 to 20 hr duration, at a frequency of 65 kilohertz. With the receiving equipment described, 37 white bass, Roccus chrysops (Raf.), have been successfully tracked in Lake Mendota for periods up to 13 hr. A study of the frequency of recapture of spawning white bass, marked with “dummy” transmitters in various ways, suggested that implantation in the stomach provided the more satisfactory tagging procedure. Of 672 fish tagged in various ways, 8.1% of those tagged externally, 6.2% of those with the tag implanted in the body cavity, and 18.8% of those with the tag placed in the stomach were recovered. In comparison, 17.5% of those marked with a hole punched in the soft dorsal fin were recaptured.

Gonadal maturation normally occurs in green sunfish during spring, under long daylengths and elevated water temperatures. Experiments on fish with regressed gonads during winter indicate that gonadal recrudescence is stimulated in both sexes of this species only by a combination of both elevated water temperatures (> 15C) and long (artificial) photoperiod (15 hr). This suggests that the natural appearance of this combination of stimuli during spring is essential for stimulating the maturation of green sunfish gonads at this time of the year.

Intraseasonal changes in caloric contents of planktonic cladocerans (Daphnia spp. and Leptodora kindtii), amphipods (Hyalella azteca), and chironomid larvae (primarily Glyptotendipes sp.) were studied in 1968. Mid—summer decreases of 823, 2117, and 422 g—cal/g dry weight were observed in the Daphnia, L. kindtii, and H. azteca, respectively. Calorica content of Daphnia increased again during August and early September. The energy content of chironomid larvae increased steadily during June and July and then declined. The low value (4899 g—cal/g dry weight) occurred on 9 September. Variation in energy content of the Daphnia appeared to be related to known changes in population numbers. The influence of significant changes in caloric contents of food organisms on the daily ration of predator fish species is discussed.