Global warming effects on skeletal anomalies in fish

In a scenario of global warming, the direct and indirect effects of the rising temperatures on the onset of skeletal anomalies in fish are discussed. The teleost skeleton is a plastic organ system whose anatomy, histology, mechanical properties and number of elements is influenced by environmental (in addition to genetic) factors. It is fundamental for the fish’s existence as the many functions it plays, i.e. mechanical (protection, locomotion, feeding); signaling (i.e. notochord during the ontogenesis); regulatory (mineral metabolism; production of several hormones); storage (i.e., lipid, phosphorus); communication (sound production and reception); generation of secondary sexual characters. Global warming determines abiotic changes inducing indirect biotic modifications (physiological, ecological and behavioral), each possibly interfering with pattern and sequence of skeletal processes. Some effects of the rising temperature on fish skeleton are determined by changes in water viscosity and salinity, augmented pH, oxygen levels, impairment of the functionality of certain hormones, modification of aerobic/anaerobic metabolism, accelerated metabolic (and growth) rate, reduced living space availability, changes in food items availability and location, changes in toxicant mobility and bioavailability. Understanding the entire picture of the effects of the climate changes on fish is a complex matter, because of non-linear synergistic effects between biotic and abiotic factors and fish autoecology, ecophysiology, evolutionary history, life history and stage, still largely unexplored. This determines that the future projections of changes on water ecosystems have produced mixed results and are currently under debate. This review will focus on the extent to which aquatic warming temperatures will affect the skeleton modelling and remodelling processes that, in turn, affects phenotypic variability, autoecology and selective pressures. Whole-organism, environment and evolutionary scales are interconnected in a framework (eco-evo-devo) where the environment scale represents the challenges that developmental mechanisms have evolved to cope. The recent experience acquired on aquaculture-reared species showed that extreme environmental conditions will elicit epigenetic changes in phenotype; even without selection, this ‘artificial’ phenotype may be stabilized (genetically) through genetic assimilation sensu Waddington. Consequently, fundamental questions will include the effects of sublethal deformations on fish biodiversity, and if these responses will lead to permanent evolutionary change in some species.