Abstract— Anchovy and mackerel eggs and yolk-sac larvae were exposed to UV radiation in the bioactive band of wavelengths between 280 and 320 nm. the UV-B region of the spectrum. Irradiation levels were based upon predicted UV-B increases that would result from anthropogenic diminution of Earth's protective ozone shell. Dose-response relationships for mortality and histological and morphological effects were determined for two different spectral energy compositions, using FS-40 sunlamps and two filter combinations. Anchovy were more sensitive than mackerel to UV-B. Data for anchovy were analyzed in terms of DNA-effective doses, i.e. the integrated spectral thence (in J/m2/nm) with the energy at each nm weighted by its effectiveness relative to the Setlow generalized DNA action spectrum. Fifty per cent of anchovy survived a cumulative DNA effective dose of 1150J'm-2 over a 4-day period. In the surviving larvae. irradiation induced lesions in the brain and eye. caused marked dispersion of pigment within melanophores and retarded growth and development. At the lowest dosage used. 760 (J. m-2)DNA, growth was retarded and brain lesions occurred in anchovy. Calculations of Smith and Baker (in this issue) indicate that in clear ocean water a significant incidence of lesions and retardation of growth in anchovy could occur at the surface at a 25%, reduction in ozone and down to 3.5 m at a 50% reduction. Eggs and larvae of anchovy occur at these depths.