Dictionary of Ichthyology
Brian W. Coad and Don E. McAllister†
X
x = indicates a hybrid between two species with the female parent's scientific name first, e.g. Rutilus rutilus x Abramis brama.
X diameter = a measure of the diameter of leader and tippet material in angling. 0X is the largest at 0.011 inches and 8X is a small diameter at 0.003 inches. Strength varies with the type of material used, not necessarily the diameter. The diameter in thousandths of an inch is calculated by subtracting the number before the X from 11. Originally a leader was made of cat gut extruded from a machine at 0.011 inches; successive extrusions tapered it down so one additional extrusion gave the 1X or 0.010 inch diameter, and so on.
X-Y bone = an accessory bone in the caudal fin of such fishes as Phycidae. Found anterior to the neural and haemal spines of the first preural centrum, helping support secondary caudal fin rays.
xanthic = having a yellow pigmentation.
xanthin = a yellow pigmentation occurring in nature and aquarium bred fish often giving a gold colour, e.g. the midas cichlid or yellow devil (Amphilophus citrinellus) and the aquarium variant of the severum cichlid (Heros severus).
xanthism = having a yellow pigmentation.
xanthochromic = of a yellow or golden colour, a common mutation in aquarium fishes.
xanthophore = a yellow chromatophore. The pigment involved is a carotenoid and the cell is neural-crest derived.
XBT = abbreviation for an expendable bathy-thermograph, an instrument that records water temperature with depth.
xebec = a small, three-masted vessel used by Mediterranean pirates and still used in commerce to a limited extent. From the Arabic shabbak. Also spelled zebec or chebec.
xerophil = a reproductive guild (q.v.) found in annual fishes, where embryos survive without water for months in intermittent pools, hatching when the pool floods. In the cleavage phase blastomeres disperse and rest in a facultative diapause followed by two more obligate resting intervals, e.g. Nothobranchius guentheri.
xerotype = in taxonomy, presumably an unofficial term for a type normally stored in fluid that has dried up. Deliberately dried skins of fishes and stuffed skins might be called this.
xiphi- (prefix) = shaped like a sword.
xylophagy = wood-eating, found in environments containing little in the way of alternative food sources, e.g. in such loricariid catfishes as Panaque and Cochliodon.
xyphosis = dorso-ventral curvature of the vertebral column.
© Brian W. Coad (www.briancoad.com)