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SUMMARYLake Malawi boasts the highest diversity of freshwater fishes in the world. Nearshore sites are categorized according to their bottom substrate, rock or sand, and these habitats host divergent assemblages of cichlid fishes. Sexual selection driven by mate choice in cichlids led to spectacular diversification in male nuptial coloration. This suggests that the spectral radiance contrast of fish, the main determinant of visibility under water, plays a crucial role in cichlid visual communication. This study provides the first detailed description of underwater irradiance, radiance and beam attenuation at selected sites representing two major habitats in Lake Malawi. These quantities are essential for estimating radiance contrast and, thus, the constraints imposed on fish body coloration. Irradiance spectra in the sand habitat were shifted to longer wavelengths compared with those in the rock habitat. Beam attenuation in the sand habitat was higher than in the rock habitat. The effects of water depth, bottom depth and proximity to the lake bottom on radiometric quantities are discussed. The radiance contrast of targets exhibiting diffused and spectrally uniform reflectance depended on habitat type in deep water but not in shallow water. In deep water, radiance contrast of such targets was maximal at long wavelengths in the sand habitat and at short wavelengths in the rock habitat. Thus, to achieve conspicuousness, color patterns of rock-and sand-dwelling cichlids would be restricted to short and long wavelengths, respectively. This study provides a useful platform for the examination of cichlid visual communication. Supplementary material available online at

Matched plantings of domestic strain and interstrain hybrid (or wild strain) brook trout (Salvelinus fontinalis) were made annually in nine small Precambrian Shield lakes during 1973–77. Recoveries of planted fish were made by gillnetting and/or angling during 1974–80. In six study lakes, hybrids (and wild strains) were recovered at rates two to four times greater than the domestic strain; in three lakes recoveries were similar. Most domestic strain trout were caught in the year following planting whereas recoveries of hybrids and wild strains were spread over 3–4 yr. Each kilogram of hybrid (or wild) planted yielded 5.6 kg (1.2–12.3); each kilogram of domestic strain planted yielded 0.8 kg (0.2–2.1). Lakes containing only minnows and sticklebacks yielded the highest returns of brook trout; lakes containing competitive species yielded low returns. Rapid growth of brook trout occurred in lakes containing only minnows and sticklebacks; slowest growth was noted in lakes supporting white suckers (Catostomus commersoni). Domestic strain brook trout and the matched hybrid grew at approximately the same rate within a lake and in seven of the nine lakes ate the same food. The performance of the Nipigon × domestic hybrid qualifies it for consideration as a replacement for the domestic brook trout presently planted in Ontario lakes.Key words: planting, brook trout, trout strain, hybrid, Precambrian Shield, survival, stock

The dimerization of anti-apoptotic BCL-xL by three-dimensional domain swapping has recently been discovered at alkaline pH; however, the high energetic barrier between the dimer and monomer forms of BCL-xL prevents them from interconverting at room temperature and neutral pH. Here, we demonstrate that BCL-xL dimers can be easily prepared by heating concentrated protein above 50 degrees C. The 38 kDa BCL-xL dimer was fully characterized by multi-resonance nuclear magnetic resonance (NMR) spectroscopy, and the mechanism of dimerization by alpha-helix swapping was confirmed. Dimerization strongly affects the NMR signals from the turn between helices alpha5 and alpha6 of BCL-xL and a portion of the long loop between helices alpha1 and alpha2. Measurements of residual dipolar couplings demonstrate that the solution structure of the BCL-xL dimer is very close to the crystal structure. Dimer formation does not prevent tight binding of ligands to the hydrophobic cleft of BCL-xL; however, binding of a BID BH3-peptide or a polyphenol drug, gossypol, to BCL-xL significantly slowed monomer-dimer interconversion and is an example of the control of BCL protein oligomerization by ligand binding.

Matched plantings of hatchery‐reared yearling brook trout (Salvelinus fontinalis) and splake (Salvelinus namaycush × S. fontinalis) or brook trout and rainbow trout (Salmo gairdneri) were made in Little Minnow Lake for 6 yr prior to and 6 yr following the introduction of yellow perch (Perca flavescens). The mean return for each kilogram of fish planted was 3.3, 6.8, and 6.1 kg, respectively, for brook trout, splake, and rainbow trout in pre‐perch years but after yellow perch became established the mean returns were 0.4, 0.9, and 0.8 kg, respectively, all less than the weight planted. The 1967, 1969, and 1972 year classes of yellow perch successively dominated the fish community and yellow perch biomass fluctuated between 20 and 30 kg/hectare. The establishment of yellow perch resulted in a drastic change in the food habits of the planted salmonids and a reduction in their growth rates in excess of 50%. The evidence strongly indicates that planted salmonids could not compete successfully with yellow perch for the available food supply.