Sunfish Lepomis Research Articles

Further Observations on the use of Hybrid Sunfish in Stocking Small Ponds

Abstract A total of 16,075 hybrid sunfish (Lepomis microlophus, female x L. macrochirus, male) were placed in 78 small ponds in southwestern Indiana in November, 1947. During the summer of 1949 each pond was seined. All together 722 hybrid sunfish were taken from 62 ponds. Of that total, 317 individuals were caught from 29 ponds in which no other fish were present and the remaining 405 were taken from 33 ponds that contained other kinds of fish. The remaining 16 ponds yielded no hybrids during seining operations. In general, the hybrid sunfish from those 29 ponds in which they had no competition from other species grew faster and were relatively heavier for their length, especially in the larger size groups, than those taken from the other ponds. The hybrids were relatively larger and heavier for their length than individuals of the same age groups in either of the parent species taken from similar ponds. Data on the fork lengths and total lengths of hybrid sunfish and on respective average weights are gi...

THE CULTURE OF VOLVOX AUREUS EHRENBERG

1. Volvox aureus Ehrenberg has been maintained in rich clone cultures for eighteen months without observable decrease in vitality on a medium prepared from spring water, commercial fishmeal, and ferric chloride.2. The presence of iron in the medium was found to be essential to the continuous culture of Volvox. This was added as ferric chloride. Cultures lacking iron died out in about six weeks.3. Either local spring water or Huckleberry spring water served satisfactorily in the preparation of fishmeal extract medium, but tap water and distilled water could not be substituted for these.4. Spring water media containing peptone, beef extract, milk, or urine in various concentrations would not support continuous growth and reproduction of Volvox.5. Uspenski's medium and modified Knop's solution were found to be of little value in the culture of Volvox.6. Powdered muscle of the marine butterfish (Poronotus triacanthus Peck) or the fresh-water sunfish (Lepomis gibbosus Linnaeus), with lipoids extracted, could b...

TEMPERATURE AND CRITICAL ILLUMINATION FOR REACTION TO FLICKERING LIGHT

The curve connecting mean critical illumination (I(m)) and flicker frequency (F) for response of the sunfish Lepomis (Enneacanthus gloriosus) to flicker is systematically displaced toward lower intensities by raising the temperature. The rod and cone portions of the curve are affected in a similar way, so that (until maximum F is approached) the shift is a nearly constant fraction of I(m) for a given change of temperature. These relationships are precisely similar to those found in the larvae of the dragonfly Anax. The modifications of the variability functions are also completely analogous. The effects found are consistent with the view that response to flicker is basically a matter of discrimination between effect of flashes of light and their after effects,-a form of intensity discrimination. They are not consistent with the stationary state formulation of the shape of the flicker curve. An examination of the relationships between the cone portion and the rod portion of the curves for the sunfish suggests a basis for their separation, and provides an explanation for certain "anomalous" features of human flicker curves. It is pointed out how tests of this matter will be made.

ON CRITICAL FREQUENCY AND CRITICAL ILLUMINATION FOR RESPONSE TO FLICKERED LIGHT

The curve of mean critical flicker frequency as a function of illumination has been determined for the reaction of the sunfish Lepomis to flicker. It exhibits expected quantitative disagreements with the curve of mean critical illumination as a function of flicker frequency in the same organism. The form of the dependence of the variation of critical frequency of flicker upon illumination can be predicted from a knowledge of the way in which variation of critical illumination depends upon flicker frequency. It is pointed out that these findings have an important bearing upon the interpretation of the data of intensity discrimination.

THRESHOLD INTENSITY OF ILLUMINATION AND FLICKER FREQUENCY FOR THE EYE OF THE SUN-FISH

The sun-fish Lepomis responds to a moving system of stripes by a motion of its body. By changing the velocity of motion of the stripe system different flicker frequencies can be produced and thus the relation of flicker frequency to critical intensity of illumination can be studied. Threshold illumination varies with flicker frequency in such a way that with increasing flicker frequency the intensity of illumination must be increased to produce a threshold response in the fish. The curve of critical illumination as a function of frequency is made up of two distinct parts. For an intensity range below 0.04 millilambert and flicker frequencies below 10 per second, the rods are in function. For higher intensities and flicker frequencies above 10, the cones come into play. The maximum frequency of flicker which can be perceived by the fish's eye is slightly above 50 per second. The flicker curve for the eye of Lepomis can easily be compared with that for the human eye. The extent of the curve for the fish is greater at low illuminations, the fish being capable of distinguishing flicker at illuminations lower than can the human eye. The transition of rod vision to cone vision occurs for the fish and for the human eye at the same intensity and flicker frequency. The maximum frequency of flicker which can be perceived is for both about the same.

ON THE VARIABILITY OF CRITICAL ILLUMINATION FOR FLICKER FUSION AND INTENSITY DISCRIMINATION

From the data of experiments with bees in which threshold response is employed as a means of recognizing visual discrimination between stripes of equal width alternately illuminated by intensities I(1) and I(2), it is shown that the detectable increment of intensity DeltaI, where DeltaI = I(2) - I(1), is directly proportional to sigma(I2) (I(1) being fixed). From tests of visual acuity, where I(1) = 0 and the width of the stripes is varied, sigma(I2) = kI(2) + const.; here I(2) = DeltaI, and DeltaI/I(2) = 1. When the visual excitability of the bee is changed by dark adaptation, lambdaI identical with kDeltaI (= k' sigma(DeltaI)) = k'' I + const. For the measurements of critical illumination at threshold response to flicker, sigma(I2) (= sigma(DeltaI)) = k I(2) = k' DeltaI + const. The data for critical illumination producing threshold response to flicker in the sun-fish Lepomis show for the rods sigma(I2) = K I(2) for the cones sigma(I2) = K'(I(2) + const.). The data thus indicate that in all these experiments essentially the same visual function is being examined, and that the recognition of the production of a difference in effect by alternately illuminated stripes takes place in such a way that d (DeltaI)/d (sigma(I2)) = const., and that DeltaI is directly proportional to I (or "I(2)," depending on the nature of the experiment). It is pointed out that the curve for each of the cases considered can be gotten equally well if mean I or sigma(I) is plotted as a function of the independent variable involved in the experiment. Certain consequences of these and related facts are important for the treatment of the general problem of intensity discrimination.