Polychlorinated biphenyl concentrations of burbot Lota lota from Great Slave Lake are very low but vary by sex.

Total polychlorinated biphenyl concentrations (ΣPCBs) in whole fish were determined for 18 ripe female burbot Lota lota and 14 ripe male burbot from Great Slave Lake, a lake with no known point sources of PCBs. In addition, ΣPCBs were determined in both somatic tissue and gonads for a randomly selected subset of 5 females and 5 males. Mean ΣPCBs for females and males were 2.89 and 3.76 ng/g, respectively. Thus, males had 30 % greater ΣPCBs than females. Based on ΣPCB determinations for somatic tissue and gonads, ΣPCBs of females and males would be expected to decrease by 18 % and increase by 6 %, respectively, immediately after spawning due to the release of gametes. Results from a previous study in eastern Lake Erie indicated that males had 28 and 71 % greater ΣPCBs than females from populations of younger (ages 6-13 years) and older (ages 14-17 years) burbot, respectively. Thus, although younger burbot from Lake Erie had approximately 50 times greater ΣPCBs than Great Slave Lake burbot, the relative difference in ΣPCBs between the sexes was remarkably similar across both populations. Our results supported the contention that the widening of the difference in ΣPCBs between the sexes in older burbot from Lake Erie was attributable to a "hot spot" effect operating on older burbot because Lake Erie has received PCB point source loadings. Our results also supported the contention that male fish expend energy at a rate between 15 and 30 % greater than females. Eventually, these results will be useful in developing sex-specific bioenergetics models for fish.

Sex difference in polychlorinated biphenyl concentrations of burbot Lota lota from Lake Erie.

Whole-fish polychlorinated biphenyl (PCB) concentrations were determined for 25 female and 25 male burbot Lota lota from Lake Erie. Bioenergetics modeling was used to investigate whether the sex difference in growth rate resulted in a difference in gross growth efficiency (GGE) between the sexes. For ages 6-13 years, male burbot averaged 28 % greater PCB concentrations than female burbot. The sex difference in PCB concentrations widened for ages 14-17 years, with male burbot having, on average, 71 % greater PCB concentrations than female burbot. Bioenergetics modeling results showed that the faster growth rate exhibited by female burbot did not lead to greater GGE in female individuals of the younger burbot and that the faster growth by female fish led to female GGE being only 2 % greater than male GGE in older burbot. Although our bioenergetics modeling could not explain the observed sex difference in PCB concentrations, we concluded that a sex difference in GGE was the most plausible explanation for the sex difference in PCB concentrations of burbot ages 6-13 years. Not only are male fish likely to be more active than female fish, but the resting metabolic rate of male fish may be greater than that of female fish. We also concluded that the widening of the sex difference in PCB concentrations for the older burbot may be due to many of the older male burbot spending a substantial amount of time in the vicinity of mouths of rivers contaminated with PCBs.