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Compared to a control gas bladder inflation rate of 95·1 1·9%, zebrafish Danio rerio larvae 72 h post-fertilization maintained in closed chambers had an inflation rate of just 19·1 7.7%. Larval survivorship through 10 days in closed chambers (32%) was significantly less than that in open chambers (76%), and the extent of spinal curvature was significantly higher among larvae maintained in closed chambers. Larvae which failed to inflate their gas bladder showed very little change in body length, and had a final dry weight c. 14% of that for control larvae. The small number of larvae with inflated gas bladders found in closed chambers might be attributed to the inadvertent introduction of small bubbles into two replicates. These results indicate that access to an air-water interface is critical for the normal development of zebrafish larvae, but also that a small, submerged, spherical gas volume may to a limited extent be used for initial gas bladder inflation. 1999 The Fisheries Society of the British Isles

RNA concentration in carp (Cyprinus carpio) white muscle tissue increased with higher growth rate for all acclimation temperatures, while DNA, protein content, and tissue hydration were unaffected. For a given growth rate, RNA concentration per unit tissue weight and per unit DNA (RNA per cell) was higher in colder acclimated fish as a probable compensation for decreased RNA activity. Maximum growth resulted in an approximate doubling of the RNA/DNA ratio while, over the range of 12–30 °C, cold acclimation caused an increase of approximately 50%. Changes in DNA concentration and protein/DNA ratios at different acclimation temperatures indicated an increase in cell mass with warmer acclimation temperatures. Muscle RNA/DNA ratios and the rate of glycine uptake by scales were highly correlated. Regression equations describing this relationship for each acclimation temperature were not significantly different when scales were incubated at each fish's acclimation temperature, but were significantly different when glycine uptake was expressed for incubation at the temperature of maximum uptake. These results suggest a whole-body integration between thermoacclimatory changes in the RNA component of muscle protein synthesis and in the rate of amino acid transport by scales.

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