Bibliography of the Maurice Lamontagne Institute

Louis A. GIGUÈRE

GIGUÈRE, L.A., R.L. DUNBRACK, 1990. Thin layer interference may reduce the visibility of transparent phantom midge larvae (Chaoborus trivittatus) to predators. Can. J. Fish. Aquat. Sci., 47: 1043-1046 .

The body wall of transparent aquatic animals is constructed of materials which have a higher refractive index than water. Because of this, light will reflect from their surface, making their body contours visible to predators. Electron micrographs of cuticle from the transparent pelagic state of the phantom midge Chaoborus trivittatus reveal thin layers less than a wavelength of light thick which could alter the spectral composition of this surface reflection by acting as an interference filter. This hypothesis is supported by measurements of the reflectance of the body surface of C. trivittatus. Reflectance was lower than expected at the wavelengths which maximize contrast in aquatic environments and higher than expected at ambient background wavelengths, suggesting that interference may reduce the visibility of Chaoborus to its predators by improving the spectral matching of its body reflection to the visual background.

GIGUÈRE, L.A., J.-F. ST-PIERRE, B. BERNIER, A. VÉZINA, J.-G. RONDEAU, 1989. Can we estimate the true weight of zooplankton samples after chemical preservation?. Can. J. Fish. Aquat. Sci., 46: 522-527 .

GIGUÈRE, L.A., B. CÔTÉ, J.-F. ST-PIERRE, 1988. Metabolic rates scale isometrically in larval fishes. Mar. Ecol. Prog. Ser., 50: 13-19 .

We estimated the rate of oxygen consumption of larval Atlantic mackerel Scomber scombrus at 3 temperatures (13, 16, 19 °C while controlling rigorously for methodological biases. Routine metabolic rates (µl O ₂h^-1ind.^-1) increase with body weight (W, in mg) and temperature (T, in °C) as : RMR=2.168•W^1.000•e^0.058•T(r²=0.96). Thus metabolic rates scale isometrically with respect to body weight in larval Atlantic mackerel. This finding is at variance with results obtained for juvenile and adult fishes which follow an allometric relationship (W^0.8).©1988 Inter-Research

GIGUERE, L.A., T.G. NORTHCOTE, 1987. Ingested prey increase risks of visual predation in transparent Chaoborus larvae. Oecologia, 73: 48-52 .

Transparency reduces the chances of detection of large planktonic animals by visual predators. An important constraint on the transparency of planktonic animals may be ingested food which could be seen through the body, thereby increasing the vulnerability of transparent zooplankton to visual predators. To test this hypothesis, we presented fed and un-fed Chaoborus larvae to juvenile coho salmon (Oncorhynchus kisutch). Overall, the presence of prey in the gut of Chaoborus increased their probability of capture by 68 %. Predation risks due to the visibility of ingested food increased in proportion to meal size : larvae with nearly full gut were captured about three times faster on the average than larvae which had little food in their gut. Although Chaoborus larvae may be able to reduce this increased predation risk by migrating downward to low light levels, this behavior would reduce feeding opportunities by removing the larvae from surface waters where prey density is generally high. In this way, visual predators may limit the growth and the maximum size that can be achieved by transparent animals.©1987 Springer-Verlag