The trophic level mean and variance, and the degree of omnivory for five Celtic Sea fish predators were estimated using a database of stomach content records characterized by a high level of taxonomic resolution. The predators occupied a high position in the food web, i.e. 4.75 for Atlantic cod Gadus morhua, 444 for haddock Melanogrammus aeglefinus, 4.88 for European hake Merluccius merluccius, 5.00 for megrim Lepidorhombus whiffiagonis and 5.27 for whiting Merlangius merlangus. The level of taxonomic resolution of the prey did not greatly affect mean T-L predator values; an effect on variance was evident, low resolution masking intra-population variability in T-L. Generalized additive models (GAM) were used to explain the variability of predator T-L caused by environmental variables (international Council for the Exploration of the Sea, ICES, division and season) and predator characteristics (total length, L-T). Significant year, location season and interaction effects were found for some species and with L-T, at the scale of ICES subdivision. The species-specific variability of T-L could be due to spatio-temporal variations in prey availability and in predator selectivity following ontogenetic changes. Omnivorous fish T-L. was less affected by spatio-temporal variations. In addition, results showed that the omnivory index and T-L variability provide dissimilar information on predator feeding strategy. Combining information on T-L. variability and omnivory allowed between within individual and between-individual components contributing to trophic niche width to be separated and the type of generalization of fish predators to be identified. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.