Evaluation of temperature selection differences among juvenile muskellunge originating from different latitudes

Genetic differences among muskellunge Esox masquinongy populations are related to residence in major river drainages, suggesting the existence of divergent stocks. By use of radio-telemetry we compared different seasonal and diel temperature selection in a southern Illinois reservoir for three geographically and genetically distinct stocks of age-2 muskellunge from throughout the latitudinal range of the species. Muskellunge from the Upper Mississippi River drainage were represented by the Leech Lake, Minnesota, population and the Ohio River drainage was represented by the Cave Run Lake, Kentucky, population. Progeny from North Spring Lake, Illinois, an interstock, or mixed-origin stock, were also evaluated. No differences in temperature selection were observed among stocks of juvenile muskellunge across seasons or diel periods. The seasonal mean temperatures of the water varied significantly—spring 21.7°C, summer 28.4°C, and fall 14.8°C, with an overall average temperature of 24.1°C, in agreement with previously published values obtained in laboratory trials. This lack of different temperature-selection patterns among stocks is in contrast with other life-history characteristics, for example growth, metabolism, and conversion efficiency, which have been shown to differ among populations and stocks.

Thermal resistance of pike (Esox lucius), muskellunge (E. masquinongy) and their F1 hybrid

Comparison of thermal resistances of pike, muskellunge, and their F1 hybrid indicates close similarity between the two species. There appears to be some hybrid vigour in that the hybrids tend to be more resistant to thermal stress at the average acclimation and test temperatures encountered in the experiments. The greatest difference between the hybrids and parents occurred at the lowest test temperatures. Differences between the parent species were apparent only in their response to acclimation temperature, the slope of the curve of resistance time on acclimation temperature being much steeper for muskellunge than that for pike.

The preferred temperature of fish and their midsummer distribution in temperate lakes and streams

Laboratory studies of preferred temperature with yellow perch (Perca flavescens) are compared with results from 21 other species. These show that temperature, if acting alone, can determine the distribution of fish in laboratory apparatus. Factors such as light, conditioned responses related to feeding routines, and social behaviour can interfere with the expression of the response to temperature. Subdued lighting conditions were necessary in the experiments with Oncorhynchus, Salvelinus and Coregonus, whereas full daylight was required in experiments with Perca flavescens.The level of thermal acclimation influences the range of temperature preferred. In general the preferred temperature is considerably higher than the acclimation temperature at low thermal acclimations, but this difference decreases up to the final preferendum, where both coincide. The final preferendum and the relation between acclimation and preferred temperature is characteristic for the species. The shape of the resulting curve may have some value in interpreting observations of fish mortalities and distribution in nature. The final preferendum of the yellow perch from the present work was 24.2 °C., from other work using older fish it was 21.0 °C.Summer field observations of yellow perch in Lake Nipissing, Costello Lake and Opeongo Lake in Ontario, showed average thermal distribution of 19.7 °C., 21.0 °C. and 21.2 °C. respectively. This agrees well with 20.8 °C. observed for four Wisconsin lakes. Oxygen depletion reported for Tennessee Valley reservoirs, distribution of primary prey species of lake trout in New York waters, and other factors, have been shown to modify the thermal distribution in nature. Differential sex response to temperature may be important in the perch. Field observations of thermal distributions for other species are also presented.A comparison of the laboratory and field data shows good agreement with fish having colder final preferenda: Salvelinus fontinalis, Salvelinus namaycush, Salvelinus hybrid and Coregonus clupeaformis. Fish with warmer final preferenda, such as Micropterus salmoides, Micropterus dolomieu and Lota lota lacustris, showed higher temperatures in the laboratory than was shown by field observations. Young Perca flavescens showed similar results, but experiments with older perch showed excellent agreement between laboratory results and held observations. The lack of agreement between laboratory results and field observations is attributed to age differences; laboratory experiments being performed with young fish and held observations being made on older fish.

Thermal ecology of subadult and adult muskellunge in a thermally enriched reservoir

The movement of adult muskellunge, Esox masquinongy Mitchill, has been investigated in a variety of systems, but temperature selection by muskellunge has not been examined where well‐oxygenated waters were available over a range of temperatures for much of the year. Thirty subadult and adult muskellunge tagged internally with temperature‐sensing radio tags were tracked from March 2010 to March 2011 in a Tennessee reservoir. Mean tag temperatures were 18.9 °C in spring (March to May), 22.1 °C in summer (June to August), 16.5 °C in autumn and 9.8 °C in winter (December to February). When the greatest range in water temperatures was available (7.1–33.3 °C; May to early August 2010), their realised thermal niche (mean ± 1 SD ) was 22.3 °C ± 1.8; the realised thermal niche was affected by fish size (smaller fish selected slightly warmer temperatures) but not sex. An electric generating steam plant discharging warm water resumed operation in January 2011, and most (86%) tagged fish occupied the plume where temperatures were ≈10 °C warmer than ambient water temperatures. No mortalities were observed 15 days later when plant operations ceased. Their affinity for the heated plume prompted concerns that muskellunge will be too easily exploited when the plant operates during winter.

Temperature tolerance of larval muskellunge (Esox masquinongy) F1 hybrids reared under hatchery conditions

Critical thermal maxima (CTM) of larval muskellunge (Esox masquinongy) and norlunge (Esox masquinongy females × E. lucuis males) were determined under hatchery conditions. Norlunge had higher temperature tolerance and developed faster. CTM of larval norlunge (30.9–36.0°C,X= 34.0°C) were significantly higher (P ≤ 0.01) than those of muskellunge (29.9–35.6°C,X= 32.8°C). Both fish exhibited a sharp decrease in CTM during swim-up, followed by a slow recovery period characterized by a general increase in CTM values. Both age and past thermal history had important effects on temperature tolerance of fry. Norlunge fry were better able to physiologically adjust to changing environmental conditions than were muskelunge.