Buoyancy Range, Gas Bladder Volume, and Lipid Content of Adult Bloater, Coregonus hoyi Gill, in the Laurentian Great Lakes

We analyzed buoyancy characteristics (buoyancy range, gas bladder volume, and lipid content) of adult bloater, Coregonus hoyi Gill, in the Laurentian Great Lakes. Buoyancy was measured directly in individual bloater and compared with the hydrostatic pressures at the depths of capture. The results of the buoyancy comparisons suggest that C. hoyi has a buoyancy range comparable to the 'free vertical range' of movement that has been described for other fishes. The buoyancy range of bloater does not support the argument that they undergo diel vertical migrations, as suggested in earlier studies. Rather, the buoyancy range for bloater reflects the depths of neutral buoyancy and the distance above these depths at which they can maintain vertical position in the water column. The available data suggest that adult bloater are neutrally buoyant near the lake bottom, and C. hoyi with 50% positive buoyancy are at the top of their depth range. Large bloater have relatively small gas bladder volumes and a high lipid content. Based on the observed vertical distribution of large and small C. hoyi and our results, we deduced that large fish are more adept than small fish at regulating their buoyancy for prolonged stays at higher hydrostatic pressures. Lipid content for bloater was not significantly different with respect to sex or origin (wild vs. captive-raised).