The Saddleback Deformity in Teleost Fish: Identification of a Unique Global Hotspot in Eastern Australia

The saddleback deformity, an abnormality of the dorsal fin and profile, lacking one to all of the dorsal spines, accompanied by shape, number and position abnormalities of associated pterygiophores, has been reported in teleosts under culture conditions and in the wild in many locations throughout the world, including North and South America, Asia, Australia, Europe, India and the Middle East. A unique global hotspot for saddleback deformities in wild teleosts is the southeast Queensland Australia coastal region between 26° S and 28° S. At this location the incidence of saddleback has been relatively stable but very high at about 10% of individual teleosts taken in the associated fishery since 1997. Opinions on causation have focused on two possibilities, a developmental defect associated with water pollution or a physical injury. The range of skeletal deformities is vastly different in cultured teleosts compared with those occurring in the wild. There is now mounting evidence that physical injury is causing saddleback in teleosts in southeast Queensland Australia. Such injury could be caused by predatory behaviour of piscivorous fish or birds, parasites, or escapement or release from fishing nets and other fishing gear. Population mortality rates associated with saddleback in southeast Queensland are unknown, but expected to be high. The high level of occurrence of saddleback in teleosts in southeast Queensland Australia together with the good understanding of their fisheries biology (age and growth rates, reproductive biology, habitat dependence) and stock assessments of the associated fisheries provide excellent opportunities for further research which would add to the scientific understanding of the saddleback deformity in teleosts throughout the world. A recommendation from this review is that support should be sought by research providers (universities and Government research agencies) from routine annual funding offers from the Australian and Queensland Governments to achieve an increase in the scientific understanding of the saddleback deformity.