Relative weight as a condition index for muskellunge

Weight-length data were obtained for 45 muskellunge (Esox masquinongy) populations (N=4,343) from 16 states to develop a standard weight (Ws) equation that would allow calculation of relative weight (Wr) values. We developed a 75-percentile equation using the regression-line-percentile method. The proposed equation, based on all fish combined, is log10 Ws(g) = −6.066 + 3.325 log10TL(mm). The English equivalent for this equation is log10Ws(lb) = −4.052 + 3.325 log10TL(in). This equation is useful for 38 cm and longer muskellunge, and there was no evidence of consistent trends in increasing or decreasing Wr with increasing fish length. Because muskellunge can be sexed based on external characteristics, we also developed separate Ws equations for male and female muskellunge. However, Wr values calculated with the combined equation were quite similar (Wr values within 1–2) to those for values calculated from the female-only Ws equation. Values calculated with the male-only Ws equation were slightly more variable.

Physiological responses of hatchery-reared muskellunge to handling

Increases in plasma lactate and glucose concentrations, along with decreases in plasma chloride and liver glycogen concentrations, were observed in muskellunge in response to capture and handling. Holding muskellunge in 0.3% NaCl alleviated some of the physiological symptoms of stress, but holding the fish in the lake for 48 hr before release had no effect. Physiological responses to fin-clipping and transport by truck were slight in comparison to that of original capture. Salt treatment and reduction in duration and frequency of handling is recommended.

Early gonadal development and sexual differentiation in muskellunge

Primordial germ cells (PGCs) were first identified in muskellunge (Esox masquinongymm TL were at the early stage of perinucleolus (early diplotene). Our observations indicate that in muskellunge ( mm TL. Female gonads contained lobes with germ cells, including oogonia, early-prophase oocytes, and large oocytes. Spermatogonia and cells undergoing mitosis were observed in the testis. Ovaries in a fish of 250 mm TL, female gonads could be clearly identified from the ovarian sac and groups of oogonia, whereas in another type of gonad, the morphology of undifferentiated gonads was maintained. Germ cells became numerous in both sexes at 211 mm TL, while the germ cells were still considered to be undifferentiated. In a fish of 138 mm TL. Some of the PGCs underwent mitotic division at this stage. The ovarian sac started to develop in a fish of 82 mm TL, gonad strings were complete and formed a typical gonad shape in cross section. Blood vessels were first found in the gonads with Crossmon staining at 46 mm total length (TL) 3 weeks post fertilization. At 32 ) of 14i) the PGCs remained in a resting state for up to 8 weeks post fertilization, (ii) gametogenesis occurred earlier in females than in males, (iii) the gonads developed from an undifferentiated stage directly into an ovary or testis, and (iv) the somatic elements in the gonads differentiated prior to the germ cells.

Assessment of seasonal changes in energy density and condition in age-0 and age-1 muskellunge

The objectives of this study were to evaluate seasonal changes in the energy density of age-0 and age-1 muskellunge Esox masquinongy and to compare energy density to various estimates of condition. Three treatment groups of muskellunge were evaluated to determine temporal changes in energy density (J/g wet weight [ww]), water content, condition factor (K TL; K = W/L 3, where W = weight and L = total length in centimeters), and relative weight (Wr .; ratio of actual to “standard” weight) through the first year following hatching. Treatment groups were (1) hatchery (muskellunge reared and maintained in hatchery ponds), (2) stocked (hatchery-reared muskellunge stocked in lakes), and (3) natural (muskellunge naturally produced in lakes). Energy levels and relative condition were compared for fish 4 and 11 months old. Differences in energy density were observed between all three treatment groups. An average overwinter reduction of 494 ± 192 J/g ww in energy density was observed over all treatment groups combined. Natural fish lost less energy (8%) over winter than either hatchery (12%) or stocked fish (15%). A simple linear model effectively relates energy to indices of condition for muskellunge. A weak positive relation (P < 0.0001, r 2 = 0.39, 0.40, and 0.43) was observed between dry weight energy density and three indicators of fish condition (percent water, K, and Wr ). Our results show that condition indices may not be the best indicators of seasonal fluctuations in total energy within and between fish populations. Seasonal fluctuations in energetic values for a population can be more accurately determined through assessment of percent water in individual fish.