ALBINISM, AMBICOLOKATION, REVERSAL 



^3 



As in other groups of fishes, albinism is by no means uncommon, and examples 

 lacking pigment on a part or on the whole of the ocular side have been described in 

 such diverse genera as Scophthalnms, Limanda, Platichthys, Pleitronectes and Solea. 

 As a rule the albinism is of a partial character, and may be of a patchy nature, 

 jiroducing an effect which is sometimes referred to as piebald.* Even in the more 

 completely albino examples there is nearly always some pigment on the head on the 

 ocular side, generally extending from the tip of the snout backwards to about the 

 region of the prsoperculum, and complete absence of pigment on this surface is very 

 rare indeed (Fig. i6). Often the pigment extends further back, and examples with 

 the hinder part of the ocular side white and the anterior part normally coloured are 

 not imcommon. Xanthochroism, a condition in which only the orange and red 

 pigment is developed and the fish assumes a bright golden colour, does not appear to 



-Dab (l.imandii limanda). .Albino specii 



(x- J.) 



ha\e been recorded in many Flatfishes, but 1 have seen a small Dab (Limanda) from 

 Dymchurch, Kent, which exhibited this abnormality. 



Of greater interest is the occurrence among Flatfishes of examples in which pigment 

 is developed on the blind side as well as on the ocular side, a condition for which 

 Cunningham has suggested the term " ambicoloration ".- A great deal has been written 

 concerning this phenomenon, and s'arious theories advanced as to its causation, but 

 few of the authors concerned seem to have appreciated the fact that there is more 

 than one type of pigmentation of the blind side in Flatfishes, and some confusion of 

 thought has consequently resulted. After examining a large .series of abnormally 

 coloured Flatfishes, 1 have been led to conclude that pigmentation of the lower side 

 may be divided into three categories ; for convenience these may be referred to as 

 " staining ", " spotting " and " true ambicoloration ". 



' Areas on the head or body devoid of pigment frequently folio 

 especially one which affects any part of the vertebral column. 



to the fish, and 



■ be observed that in the Witch {Glypiocephalus) the blind side is normally grey instead 

 vhite, a number of chromatophores being developed. Other Flatfishes have been described in 

 ch the blind side is normally pigmented to some extent (c. «. Taninpsdla, Eiigyophrys). 



