Philip A. Cochran

Lack of Host Species Selection by the Exotic Parasitic Crustacean, Argulus japonicus

Abstract We tested the hypothesis that Argulus japonicus, an external parasite of fishes, would prefer goldfish (Carassius auratus), a cyprinid with which it evolved, to the fathead minnow (Pimephales promelas), a common cyprinid native to North America. In each of two experiments, parasites were confined individually with goldfish and fathead minnows, and attachments to each fish were recorded. The frequencies of attachment were not significantly different from random, regardless of whether expected frequencies were adjusted to reflect the relative surface areas of the two host species. Moreover, once attached to a host, an Argulus was not more likely to detach from either host species within the first thirty seconds of attachment.

Aggregation and spawning by lampreys (genus Ichthyomyzon) beneath cover

SynopsisLampreys are generally reported to spawn in shallow water on open, gravel bottoms. During surveys in Wisconsin and Minnesota, we regularly observed aggregations of adult Ichthyomyzon c.f. gagei, I. castaneus, and I. fossor beneath such cover objects as boulders, woody debris, and, at one site, vegetation. In some cases, observations of eggs or rapid quivering by individual lampreys indicated that spawning was occurring. The literature includes scattered anecdotal reports of similar behavior in other populations of Ichthyomyzon. Our data for I. c.f. gagei suggest that aggregations beneath cover objects occur at a greater range of depths than those in the open, but that aggregations in the open can contain greater numbers of individuals. Facultative spawning beneath cover objects may permit lampreys to spawn in deep waters with swift current where spawning could not otherwise occur. Moreover, this behavior may reduce the vulnerability of spawning lampreys to some types of predators.

Diets of syntopic finescale dace, Phoxinus neogaeus, and northern redbelly dace, Phoxinus eos: a reflection of trophic morphology

SynopsisWe examined relative abundance, distribution, and gut contents of Phoxinus eos and P. neogaeus in a small northern Michigan bog lake. P. eos were usually 5–100 x more abundant than P. neogaeus, but both species were more abundant near the lake margin than offshore. Both species fed primarily on algae and invertebrates associated with the bog mat, but differences in diet were associated with differences in trophic morphology. As expected, because of its relatively longer intestine and smaller mouth, P. eos consumed relatively more plant matter, especially green algae, and fewer macroinvertebrates than P. neogaeus. These dietary conclusions were supported by analysis of two independent data sets. Further work is needed to discriminate between the effects of body size and trophic morphology on diet.

Change in Energy Density of the Sea Lamprey (Petromyzon marinus) during its Parasitic Phase: Implications for Modeling Food Consumption and Growth

Previous energetics-based models of feeding and growth by sea lampreys (Petromyzon marinus) have included the assumption that the wet energy density of sea lamprey tissue is constant. It was hypothesized that a seasonal or body-size related increase in wet energy density of sea lamprey tissue contributed to a tendency for model predictions to overestimate growth in wet mass by large sea lampreys late in the year. Bomb calorimetry of parasitic-phase sea lampreys collected in northern Lake Huron during 1996 and 1997 revealed that wet energy density increased with wet body mass. Seasonal effects were not significant once the effects of body mass were taken into account. Increased wet energy density resulted both from a decrease in percentage water content and an increase in energy density of dry tissue with increased body mass. Statistical comparisons failed to reveal significant differences between sexes or years. Although the overall mean wet energy density for sea lampreys sampled in the present study was similar to the empirically-derived constant value used in previous models, incorporating a relationship between wet energy density and wet body mass into our sea lamprey feeding model improved its ability to predict instantaneous growth.

Predation on Horsehair Worms (Phylum Nematomorpha)

ABSTRACT Field observations revealed cases of predation on horsehair worms by brown trout (Salmo trutta) in Maryland and Minnesota, a rock bass (Ambloplites rupestris) in Kentucky, and a crayfish in Wisconsin. Some fish contained more than one worm and may have consumed reproductive aggregations. In laboratory feeding trials with Gordius robustus, most individuals of several fish species either ignored the horsehair worms or rejected them after taking them into their mouths briefly, but a green sunfish (Lepomis cyanellus) consumed both individual worms and a compact ball of 18 worms. A literature review yielded cases of predation on horsehair worms by at least 12 fish species. Horsehair worms usually were only a trace component of the diet, but some individual fish had eaten multiple worms.

Horsehair Worms (Phylum Nematomorpha) in Lake Michigan

Horsehair worms, Gordius robustus, were collected on four occasions during 3 years along the shore of Lake Michigan in Door County, Wisconsin. These apparently represent the first published records from a Great Lakes environment. Although they are a predictable component of the benthic fauna at the study site, horsehair worms probably do not successfully complete the adult phase of their life cycle in Lake Michigan. Rather, animals found in Lake Michigan probably originate from a population in a more suitable aquatic habitat inland and are transported to the lake during their terrestrial parasitic stage. Within the study area, there are several likely sources for strays that reach Lake Michigan.

Testing and Extension of a Sea Lamprey Feeding Model

Abstract A previous model of feeding by sea lamprey Petromyzon marinus predicted energy intake and growth by lampreys as a function of lamprey size, host size, and duration of feeding attachments, but it was applicable only to lampreys feeding at 10°C and it was tested against only a single small data set of limited scope. We extended the model to other temperatures and tested it against an extensive data set (more than 700 feeding bouts) accumulated during experiments with captive sea lampreys. Model predictions of instantaneous growth were highly correlated with observed growth, and a partitioning of mean squared error between model predictions and observed results showed that 88.5% of the variance was due to random variation rather than to systematic errors. However, deviations between observed and predicted values varied substantially, especially for short feeding bouts. Predicted and observed growth trajectories of individual lampreys during multiple feeding bouts during the summer tended to correspo...

Cavity Enhancement by Madtoms (Genus Noturus)

ABSTRACT Three species of madtoms (Noturus flavus, N. funebris, and N. gyrinus) were observed enlarging cavities beneath rocks by moving gravel in their mouths. This behavioral trait is probably widespread within the genus Noturus and occurs in other ictalurids. An experiment with N. gyrinus failed to demonstrate creation of new cavities beneath tiles laid flat on the bottom.

The Effect of a Fish Medication on Argulus japonicus, a Crustacean Parasite of Fish

ABSTRACT The effect on Argulus japonicus of Furan-2, a medication for fish, was tested in three trials. In each trial, survival of A. japonicus treated with Furan-2 was as high or higher than that of the controls. It is possible that Furan-2 inhibits microorganisms that otherwise would attack A. japonicus stressed by handling and held without food. When fish and Argulus must be confined together in the laboratory, it may be possible to use Furan-2 to treat the fish for pathogens without harm to the Argulus.

Notes on the Distribution and Biology of the Horsehair Worm Paragordius varius (Phylum Nematomorpha) in Wisconsin

ABSTRACT Female Paragordius varius were collected in a slough of the Mississippi River in Grant County and a small trout stream in Kewaunee County. The Kewaunee County specimen was laying eggs on July 25, later than reported for the species elsewhere in its range. Paragordius varius is much less common than Gordius robustus in Wisconsin, at least in small cold springs or springfed streams.