Central Mudminnows Research Articles

Seasonal variation in baseline and maximum whole-body glucocorticoid concentrations in a small-bodied stream fish independent of habitat quality

Alterations to natural habitats are becoming more common due to changes in anthropogenic land use. As such, there is increasing interest in determining how wild animals adapt and respond to environmental stressors. The glucocorticoid (GC) stress response enables animals to react appropriately to environmental challenges but can be affected by many factors, two of which are habitat quality and time of year (i.e., season). This study tested whether baseline and maximum (stress-induced) whole-body cortisol concentrations varied in relation to habitat quality and season using wild central mudminnows (Umbra limi) collected from two connected streams differing in habitat quality in each of four seasons. Overall, baseline and maximum cortisol levels did not differ significantly between the two systems but there was evidence of a seasonal effect. Baseline cortisol levels in the fall and summer were significantly (P<0.01) lower than those in winter and spring and maximum cortisol levels in the summer were significantly lower (P<0.01) than those in the spring. Inconsistent with the prevailing paradigm, our results indicate that habitat quality does not always influence baseline GCs or the stress response. In contrast, baseline and maximum GCs in this species do vary seasonally. As such, seasonality should be considered in the interpretation of stress response data especially when using small-bodied stream fish as biological indicators.

Anti-predator behaviour in response to conspecific chemical alarm cues in an esociform fish, Umbra limi (Kirtland 1840)

When a predators attack prey, damaged prey tissue releases chemical information that reli- ably indicates an actively foraging predator. Prey use these semiochemicals to cue anti-predator behaviour and reduce their probability of predation. Here, we test central mudminnows, Umbra limi (Kirtland 1840), for anti-predator behavioural responses to chemical cues in conspecific skin extract. In a field experiment, traps scented with mudminnow skin extract (alarm cue) caught fewer mudminnows than traps scented with water (control). Under controlled laboratory conditions, mudminnows showed a signif- icant reduction in activity and movement to the bottom in response to alarm cues relative to water controls. Reduced activity and increased time on the bottom of the tank are both known components of an anti-predator response. Thus, based on field and lab data, mudminnows exhibited anti-predator behavio- ural responses to chemical alarm cues released by damaged epidermal tissue. Histological preparations of epidermal tissue did not reveal the presence of specialised ''alarm substance'' cells for the produc- tion of chemical alarm cues. This is the first report of an alarm reaction in an esociform, an order with a long evolutionary history of piscivory.

Tylodelphys scheuringi (Diplostomidae) Infecting the Brain of the Central Mudminnow, Umbra limi, in Silver Creek, Michigan, U.S.A

Abstract Tylodelphys scheuringi (Hughes, 1929) Dubois, 1938 (Trematoda) infected the brain of 22 (42%) of 52 central mudminnows, Umbra limi, collected in May through August 2005 from Silver Creek in Lower Michigan. This larval diplostomid was found unencysted under the dura mater of the optic lobes and cerebrum of the dorsal portion of the brain. The mean intensity and mean abundance of T. scheuringi were 8.5 ± 6.6 and 3.6 ± 5.9, respectively. The Spearman's rank correlation coefficient between intensity of T. scheuringi and mudminnow length was nonsignificant (rs = 0.11, P > 0.05). The ventricles of the brain, the eyes, and the coelom were negative for T. scheuringi. This is the second report of T. scheuringi in the brain of fish from North America.

Foraging in a Lethal Environment: Fish Predation in Hypoxic Waters of a Stratified Lake

Development of low oxygen conditions (hypoxia) in bottom waters of stratified lakes has a profound effect on the distribution of aquatic organisms. Fish avoid hypoxic waters by moving into oxygenated water and suffer massive die—offs when migration is not possible. However, central mudminnows (Umbridae: Umbra limi) were captured regularly in severely hypoxic bottom waters of a lake in northern Wisconsin, USA. Caging experiments confirmed the lethality of this environment to mudminnows. The presence of freshly ingested phantom midge larvae (Diptera: Chaoborus) in the stomachs of mudminnows during the day coupled with the observation that Chaoborus are restricted to hypoxic waters during the day indicate that mudminnows routinely ventured into a lethal environment to forage. This conclusion was supported by caging experiments whereby mudminnows denied access to hypoxic water during the day did not contain Chaoborus in their stomachs. In laboratory experiments, ingestion of air bubbles enhanced the ability of mudminnows to forage in hypoxic water, but even in the absence of surface access, mudminnows readily foraged in hypoxic waters. These data help explain reports of other fish venturing into hypoxic waters and suggest that foraging in hypoxic waters may be common among some fishes when food abundance is low in surface waters.

An experimental study of factors affecting the distribution of yellow perch and central mudminnows along a species richness gradient

Effects of environmental factors on the distribution and abundance of yellow perch and central mudminnows in northern Wisconsin were examined by holding populations of these fishes within single-species enclosures in a series of three small forest lakes having a species-richness gradient of one to four species. These enclosures allowed each species to experience environmental conditions within each lake without directly interacting with each other. In the four-species lake, two other sets of enclosures addressed the effects of intra- and interspecific competition. Changes in total biomass of enclosure stocks (from growth and mortality) indicated that in the absence of other species, perch did best in the lake containing the richest fish assemblage, intermediate in the two-species lake, and worst in the mudminnow-only lake. Mudminnow stocks similarly performed significantly better in the four-species lake than the mudminnow-only lake. These results suggest that the lakes' environmental conditions contribute to the patterns of presence and abundance of perch, but that interspecific interactions override a similar contribution for the mudminnow, which is regarded as a fugitive species. Perch performances were also sensitive to fish densities within enclosures, declining significantly when stocks were doubled, either by adding more perch or equal numbers of mudminnows.

Induction of micronuclei and nuclear abnormalities in the erythrocytes of mudminnows (Umbra limi) and brown bullheads (Ictalurus nebulosus).

The authors are interested in determining whether the MN technique can be developed as an in situ assay for genotoxicity in fish species; and in particular, the brown bullhead (Ictalurus nebulosus). In this study, central mudminnows (Umbra limi) and brown bullheads were exposed to EMS and benzo(a)pyrene (BaP) by intraperitoneal injection. The various experiments were designed to: i) compare the sensitivity of the MN and SCE assays using the mudminnow model; ii) determine whether MN are induced in the erythrocytes of the brown bullhead by exposure to genotoxic chemicals (EMS and BaP); iii) determine whether erythrocytes harvested from the erythropoietic tissues of fish (pronephros) have a greater incidence of MN than peripheral erythrocytes; iv) examine the association between the induction of MN and the induction of nuclear abnormalities in erythrocytes after exposure of genotoxic agents.

Habitat use of the central mudminnow (Umbra limi) and yellow perch (Perca flavescens) in Umbra-Perca assemblages: the roles of competition, predation, and the abiotic environment

We compared spatial distributions and diel activity patterns of three fish populations (co-occurring central mudminnows and yellow perch, and a mudminnow population in a single-species assemblage) throughout the year in two small, northern Wisconsin dystrophic lakes. In winter, all three populations were more active offshore and during the day. During spring and summer–fall all were concentrated inshore, near the bottom, and were more active around dawn and dusk. Winter distributions appeared to be responses to abiotic conditions (ice cover and low oxygen availability); overall patterns during open-water periods appeared to be linked to prey availability (e.g., chironomid emergences). Although the three populations were generally similar, some aspects of habitat use differed between species, between lakes, or between dominant and subdominant populations, with the direction of differences varying seasonally. The yellow perch population was recovering from a size-selective winterkill and between spring and summer underwent an ontogenetic niche shift, first being competitors with mudminnows, then becoming predators on mudminnows. Mudminnows did not alter their vertical or diel activity patterns in the presence of these predatory perch. They did become more concentrated inshore in summer–fall, near structural refuge provided by the bog mat, and, unlike the other two populations, failed to shift their activities offshore at twilight. Our study suggested that a simple habitat in the study lakes contributed both to overall similarities in habitat use and strong interactions between co-occurring populations. However, the ecological flexibility demonstrated by mudminnows may prevent their total exclusion from lakes inhabited by perch and allow them to respond to changing biotic environments.

Competition in Umbra-Perca fish assemblages: experimental and field evidence.

One potentially important effect of interspecific competition in freshwater fish communities is to increase predation intensity from gape-limited piscivores by lowering growth rates of prey species. We investigated the operation and consequences of competition between central mudminnows (Umbra limi) and yearling yellow perch (Perca flavescens) in a system where size-limited predation on mudminnows by larger perch is a principle structuring mechanism. During laboratory experiments in which mudminnows foraged for patchily-presented food in the presence and absence of yearling perch, the food intake of mudminnows decreased at both the population and individual-fish levels when perch were present. Mudminnows were neither less active nor did they occupy lower-quality food patches in the presence of perch; exploitation competition, rather than interference or predator avoidance, appeared responsible for reduced feeding success. To assess effects of competition in the field, we examined size distributions and condition factors of yearling mudminnows and perch in small Wisconsin lakes having mudminnow-only and mudminnow-perch assemblages. Yearling mudminnows were smaller and in poorer condition in an assemblage composed (by mass) of 45% yearling perch than in two mudminnow-only assemblages. Conversely, yearling perch were larger and in better condition when the mudminnow-perch assemblage contained only 45% perch then when it contained 92% perch. Our experimental and field results indicated that an asymmetrical competitive relationship could contribute directly to the interspecific population dominance of perch over mudminnows in Umbra-Perca assemblages through reduced food intake, growth, and condition of mudminnows, and indirectly through increased vulnerability of mudminnows to size-limited predation.

Size-Limited Predation, Winterkill, and the Organization of Umbra–Perca Fish Assemblages

We compared population densities and size structures of central mudminnows (Umbra limi) occurring with and without yellow perch (Perca flavescens) in six small lakes in northern Wisconsin over a 6-yr period. Our observations suggested that a size-dependent predator–prey interaction was a major mechanism organizing these assemblages. Densities of mudminnows cooccurring with perch averaged 12% of populations in mudminnow-only lakes. Large mudminnows (≥76 mm total length) predominated in populations with perch whereas smaller fish predominated in single-species assemblages. Following severe winterkills of adult perch in two lakes, mudminnow densities increased significantly due to high survival and recruitment of yearlings. Increases in small mudminnows lasted only a year: densities and size distributions returned to prewinterkill patterns when perch that had survived winterkill attained lengths &gt;13 cm. To examine the role of size-limited predation, we performed an experiment in 2000-L tanks, varying the initial size distributions of mudminnows and perch and measuring size-specific survival among mudminnows. Predation in the experimental populations was greatest when large perch (121–180 mm) were with populations of predominantly small mudminnows (&lt;76 mm); smaller perch (114–132 mm) were significantly less successful as predators whereas large mudminnows were significantly less vulnerable to predation by even large perch. Despite this interaction, central mudminnows coexist at low densities with yellow perch; possible factors permitting coexistence are fish sizes and spatial and structural refuges.

Surviving winter hypoxia: behavioral adaptations of fishes in a northern Wisconsin winterkill lake

Winterkill lakes often have a characteristic fish community, presumably composed of species able to survive winter hypoxia. Our research on a small winterkill lake in northern Wisconsin indicates that fishes common in winterkill lakes have behavioral adaptations for tolerating or avoiding winter hypoxia. We examined the distribution of fishes within the lake during one winter (December through May), and fish migrations into and out of the lake for two consecutive years. As DO within the lake declined in late fall, adult-sized fishes of four species, brook stickleback, finescale dace, redbelly dace, and fathead minnow, moved to the ice-water interface where DO levels were highest. Stickleback, and to a lesser extent, fathead minnows, also moved toward the more highly oxygenated water near the inlet. During the first year, young-of-the-year fishes of blacknose shiner, Iowa darter, redbelly dace, and fathead minnow, avoided hypoxic conditions by emigrating from the lake via the outlet stream in late fall and early winter while DO within the lake was still relatively high. Blacknose shiner, redbelly dace, and fathead minnow returned to the lake in spring. Almost no fishes were trapped leaving the lake in the second fall-winter season. Central mudminnows neither moved to the ice-water interface nor emigrated from the lake as DO dropped. Mudminnows survive winter hypoxia by breathing oxygen-containing bubbles trapped beneath the ice. These relatively simple behavioral adaptations allow fishes to survive or avoid hypoxic conditions lethal to other species and may help explain the consistency in fish communities of winterkill lakes.

Density Compensation in Umbra‐Perca Fish Assemblages of Northern Wisconsin Lakes

Small, shallow seepage lakes in northern Wisconsin that have both low winter oxygen concentrations and low pH possess depauperate fish assemblages containing primarily or exclusively central mudminnows, Umbra limi, and yellow perch, perca flavescens. Six times during three years I determined the total densities of fish in five lakes by mark—recapture and catch—per—effort methods. The richness of the fish assemblages in these lakes varied from one to three species in a nested pattern. While seasonal variations in density occurred within and among lakes due to variations of growth, mortality, and recruitment, total densities overall were independent of species richness. the pattern, called complete density compensation, suggests that total densities are expressions of the lakes' similar abilities to support fish and that the species interact rather than being independent. An intense negative correlation between perch and mudminnow densities was found, suggesting a strong interspecific population dominance of perch over mudminnows. There was also indirect evidence that both competition (exploitation and interference) and predation by perch regulate mudminnow populations when the species co—occur. Because these assemblages were unpredictably variable in time and space, conclusions from single censuses would have been unreliable. An exercise simulating single seasonal censuses from each richness class showed that less than one—half of such single censuses would have produced the pattern of complete compensation that was observed in the field study. In general, my results support the idea that the relative importance of the factors that determine community structure, or even the factors themselves, can differ not only from assemblage to assemblage at any one time, but even from season to season or year to year within a single assemblage.

Factors Structuring Fish Assemblages Along a Bog Lake Successional Gradient

Three alternate and distinct fish assemblages were identified in 43 northern Wisconsin lakes encompassing a gradient from bog ponds to small, oligotrophic lakes having little bog character. Multivariate analysis of physical/chemical variables identified three general environmental factors that influence community type and species richness. These factors are: (1) habitat size and heterogeneity; (2) lake productivity— pH; and (3) winter oxygen concentrations. Ordination of lake fish assemblages along these environmental gradients revealed that two factors, lake pH and winter anoxia, were especially crucial in determining assemblage type. Maintenance of these discrete assemblages is also the result of biotic interactions (exclusion of cyprinids due to predation or competition from centrarchids). A centrarchid assemblage dominated lakes across a wide range of habitat types and pH, providing winter anoxia does not occur. Lakes with low winter oxygen concentrations harbor a cyprinid assemblage if the pH is above 5.2—5.4. Lakes that are acidic and also have low winter oxygen contain only two physiologically hardy species comprising the Umbra—Perca assemblage: central mudminnow (Umbra limi) and yellow perch (Perca flavescens). Five fishless lakes had physical and chemical characteristics similar to lakes with an Umbra—Perca assemblage. Within the fish assemblages, no subgroups of closely associated species were evident. For Umbra—Perca lakes, few environmental differences were evident between lakes having (1) no fish, (2) central mudminnows only or, (3) yellow perch and central mudminnows. The sequential loss of species along a gradient from oligotrophic seepage lakes to bog ponds reflected the increased harshness of the chemical environment and the loss of near—shore habitat zones. Species that are specialized zooplanktivores, that utilize hard—bottom substrates for spawning for feeding activities, or that are intolerant of low pH were limited to lakes with little bog character. Lakes in intermediate stages of succession contain acid—tolerant species that are food and habitat generalists. Lakes near the final stages of senescence contained only yellow perch and central mudminnows. The location of bog lakes at the lower end of several environmental gradients makes them valuable sites for studying the influence of environmental factors and biotic interactions on the structure of aquatic communities.

In vivo induction of sister-chromatid exchange in Umbra limi by the insecticides endrin, chlordane, diazinon and guthion

Central mudminnows, Umbra limi, were exposed to the insecticides endrin, chlordane, diazinon and guthion at concentrations of 5.4 × 10 −12 M to 5.4 × 10 −9 M in the aquaria water. Endrin, chlordane and diazinon caused significant increase in the frequencies of SCE. The results of these tests in part are in contrast to previous work which did not find endrin to be mutagenic. Our results suggest that the in vivo SCE test is an efficacious method of detecting mutagenic pesticides in water.

Breathing Gas Mixtures Different from Air: An Adaptation for Survival Under the Ice of a Facultative Air-Breathing Fish

Gaseous respiration by central mudminnows (Umbra limi), particularly their use of bubbles composed of gas mixtures other than air, may have evolved as an adaptation to the oxygen-depleted, carbon dioxide-rich water of winterkill lakes. Under simulated winterkill conditions, mudminnows frequently engulfed gaseous bubbles. Use of bubbles was not related to varying methane or nitrogen content (0 to 80 percent) when all bubbles contained 20 percent oxygen. When the oxygen content of bubbles varied (0 to 20 percent), fish visited bubbles randomly but remained longer and took fewer "breaths" at bubbles with high oxygen content. High temperature (16 degrees to 34 degrees C) and low pH (6.8 to 4.5) did not stimulate increased air-breathing when dissolved oxygen was sufficient.

Survival mechanisms of the central mudminnow (Umbra limi), fathead minnow (Pimephales promelas) and brook stickleback (Culaea inconstans) for low oxygen in winter

Three species (central mudminnow, fathead minnow and brook stickleback) survive when a northern Wisconsin lake becomes anoxic in winter. Some gas bubbles beneath the ice contained as much as 11° oxygen when the lake water contained <0.30 mg 1−1 dissolved oxygen. Experiments conducted in the field determined that gas bubbles prolonged survival of all species, especially the mudminnow and stickleback. In the laboratory, brook sticklebacks exhibited the lowest and fathead minnows the highest routine metabolic rate corrected for weight. Rate of gill ventilation of all three increased from 20 to 70 beats per minute as oxygen levels declined from 4.0 to 0.25 mg 1−1. At low oxygen levels they moved to the upper one-third of the test tanks. Small size, low metabolic rate, tolerance of low oxygen conditions and reduced activity resulted in reduced demand for dissolved oxygen. Head shape, ventilation rate, vertical movement and utilization of high oxygen microzones also enhanced exploitation of low levels of dissolved oxygen. Central mudminnows used oxygen directly from gas bubbles found under the ice.