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Home , Arnoglossus imperialis, Bothidae, Brill (fish), Flatfish, Lemon sole, Megrim

Sherkin Comment 2003 - Issue No. 35...... Page 11 Two Sides to Every

are placed (ocular side) is usually of abnormalities from a significant Photos: © Declan Quigley By Declan T. Quigley Figure 1: Partial in Black coloured, while the opposite side area of Irish coastal waters. (ocular side) MORE than 600 of flatfish (blind side) is usually unpigmented. Albinism, which appears to be (Order: Pleuronectiformes) have In general, the percentage of con- relatively uncommon, is usually been described. The group has been genital abnormalities occurring in incomplete (partial albinism); part remarkably successful in colonising a is considered to be highest of the ocular side retaining its nor- wide range of , from among the Pleuronectiformes, possi- mal colour. The condition appears to seas to the tropics, and from shallow bly due to the complex occur most frequently in black sole estuarine waters (including freshwa- morphological changes which occur (Figure 1) in Irish waters. Albinism, ter) down to considerable during larval . How- and particularly partial albinism depths (≥1830m). However, they ever, it should be noted that several (13.6%), has accounted for about appear to be absent from the deeper other factors can give rise to abnor- 16% of all the anomalous flatfish abyssal and hadal zones. malities e.g. disease, nutritional known to have been recorded in Figure 4: Partially ambicoloured , Only 22 species of flatfish have deficiencies, injury and pollution. Irish waters to date (44). blind side above and ocular side below been recorded from Irish waters Some species of flatfish appear to More commonly, the blind side (Table 1). The Irish group includes exhibit a greater frequency of abnor- (which is normally white or unpig- several species which are exploited malities than others (Table 2). mented) may be completely by both the sea (10) However, this may only be a reflec- coloured or bear patches of colour. and anglers (8) e.g. , turbot, tion of recording effort. All of the This abnormality, which is termed , , , dab, , species exhibiting abnormalities in ambicolouration, is more common Figure 2: Ambicoloured Turbot , and black sole. Irish waters were commercially in some species than in others; it However, very little is known about important and therefore the chances appears to occur more frequently in the biology and distribution of the of abnormalities being observed are brill, turbot (Figure 2) and flounder remaining (12) species in Irish greater in these species. It seems (Figure 3) in Irish waters. In the waters. Indeed, most of them are reasonable to assume that abnormal- turbot ambicolouration is usually considered rare or uncommon, prob- ities would also be discovered in accompanied by other abnormali- ably because they have (as yet) no non-commercial species if greater ties, the most noticeable being the commercial or recreational value. numbers were examined. Some development of a ‘hook’ or ‘notch’ Figure 5: Brill with unusual black spots on In most respects the early pelagic international studies have found that at the origin of the , ventral side larvae of flatfish are similar to those the frequency of abnormalities in which does not join the head in the of symmetrical . However, specific species varied geographi- usual way. ‘Notched’ turbot were during metamorphosis in the later cally and this has sometimes been noted by naturalists during the stages of larval life the typical asym- linked to variations in water quality l800’s and some were of the opin- metry becomes obvious. The on due to pollution. However, it may ion that they constituted a separate Figure 6: Reversed Megrim Figure 3: Ambicoloured flounder, blind side one side of the migrates over also be simply a reflection of record- species: Platessa melanogaster. above and ocular side below the head and comes to rest close to ing effort. For example, more than Ambicoloured turbot may also its opposite number. At this stage the 75% of the Irish records were exhibit bony excrescences or nod- teristic spotting pattern for the pelagic life ceases and the young reported from Co Kerry where ules on both the ocular and blind species (e.g. red spots on the ocular fish assume a primarily bottom-liv- recording effort is known to have side; these nodules are only found side of plaice); while other speci- ing (benthic) existence. been consistently high since the on the ocular side of normal turbot. mens have exhibited spots which are The most noticeable feature of early 1960’s. Indeed, the first Ambicolouration (50%), including normally absent on these species adult is the asymmetry of recorded abnormalities were partial ambicolouration (Figure 4), e.g. brill (Figure 5). The condition the head, in which, depending on the reported from this area as far back as has accounted for nearly 60% of all where spots were either present or species, both are sited on either 1850. The remaining records came the anomalous flatfish recorded in absent, has accounted for 13.6% of the left (sinistral = left-sided) or from Co’s Waterford (1); Wexford Irish waters to date. all the anomalous flatfish recorded right (dextral = right-sided) side of (3); Dublin (2) and Antrim (1). It is Some specimens of flatfish have in Irish waters to date. the body. The side on which the eyes clear that there have been no records also been found lacking the charac- Finally, an even more interesting abnormality is the phenomenon of Figure 7: Reversed Flounder (above) and normal (below) Left-Eyed Flatfish Species Distribution *ISFC **BRFC ***Catch Figures (2001) reversal. Occasionally in flatfishes (Sinistral) Record Weight Record Weight Live Weight Value € individuals occur with the eyes and notice unless normal specimens are (kg) (kg) (tonnes) (x 1000) colour on the side which is usually available for comparison. Reversal Megrim wiffiagonis (Walbaum, 1792) offshore waters common 1.850 1.715 3705 8783 eyeless (blind side) and unpig- is more common in some species Four-spot Megrim L. boscii (Risso, 1810) deep water ? mented. During metamorphosis the Phrynorhombus norvegicus ( Gunther, 1862) inshore-offshore rare ? than others; studies have shown it to Eckstrom's Topknot P. regius (Bonnaterre, 1788) offshore waters moderately common ? eye from the ‘wrong’ side of the be extremely rare in dabs and four- Turbot maximus (L.) inshore common 15.436 15.308 186 1724 head (for the species concerned) Brill S. rhombus (L.) inshore common 4.313 7.257 96 712 spot megrim. It has only been Topknot punctatus (Bloch, 1787) inshore uncommon/local ? 0.382 migrates and the fish ends up having recorded in megrim (Figure 6),

Bothidae both eyes on what would be the flounder (Figure 7) and black sole in blind side in a normal fish. In sinis- Irish waters, representing 13.6% of Imperial (Rafinesque, 1810) inshore/offshore scarce ? Scaldfish A. laterna (Walbaum, 1782) inshore common ? tral forms, the right eye migrates to all abnormalities. Thor's Scaldfish A. thori Kyle, 1913 inshore rare ? the left side; in dextral forms, the

Right-Eyed Flatfish left eye migrates to the right side. Declan T. Quigley, Carrigadrohid (Dextral) Colouration follows the position of Smolts Ltd., Macroom, Co Cork, the eyes with the result that the fish Mobile: 087-9080521; Email: is the ‘wrong way around’. This Witch (L.) moderately deep water common 0.533 865 1469 [email protected] Long Rough Dab platessoides (Fabricus, 1780) moderately deep water common 0.155 phenomenon is very difficult to Halibut hippoglossus (L.) deep water uncommon 70.824 106.136 Dab limanda (L.) inshore common 1.064 1.254 Ambicolouration Albinism Spots Reversal Total % Lemon Sole kitt (Walbaum, 1792) inshore/offshore locally common 443 1070 Full Partial Full Partial Present Absent Sinistral Dextral Flounder flesus L. inshore common 2.229 2.593 Plaice P. platessa L. inshore common 3.736 4.635 824 2074 Megrim 336.8 Reinhardtius hippoglossoides (Walbaum, 1792) deep water rare Turbot 51 1 715.9 Brill 911022.7 Dab 1 1 2.3 Lemon Sole 1 1 2.3 Buglossidium luteum (Risso, 1810) inshore/offshore common Flounder 611818.2 variegatus (Donovan, 1808) offshore/deep water rare ? Plaice 1 114 715.9 lascaris (Risso, 1810) inshore/offshore rare ? Black Sole 1132715.9 Black Sole S. solea (L.) inshore common 2.869 2.966 356 3678 Total22316243344 Data Sources: * Annual Report of the Irish Specimen Fish Committee (2002) ** British Record (Rod Caught) Fish Committee (1995-2003) *** Central Statistics Office: Statistics (2001) % 50.0 6.8 2.3 13.6 4.5 9.1 6.8 6.8 Table 1. Flatfish species in Irish waters, with notes on habitat, distribution, angling records and commercial catches Table 2. Frequency of abnormalities in Irish flatfish species