Plaice
Plaice denotes a group of right-eyed flatfish species in the family Pleuronectidae, principally the European plaice (Pleuronectes platessa) and American plaice (Hippoglossoides platessoides), distinguished by their compressed, asymmetrical bodies with both eyes positioned on the upper (ocular) side and adapted for demersal existence on soft sediments.[1][2] These species exhibit camouflage through mottled pigmentation on the dorsal surface, typically brownish with distinctive orange spots in P. platessa, enabling blending into sandy or muddy substrates where they forage nocturnally on benthic invertebrates such as polychaetes, bivalves, and crustaceans.[3][4] European plaice inhabit coastal shelf waters of the northeast Atlantic from the North Sea to the Bay of Biscay, preferring depths of 10 to 200 meters on sand or mud bottoms, with juveniles settling in shallower nurseries and adults migrating seasonally influenced by temperature.[1] American plaice occupy deeper continental slopes in the northwest Atlantic, from Labrador to Rhode Island, at depths often exceeding 100 meters, reflecting adaptations to colder, more stable environments.[5] Both undergo metamorphosis from bilateral larvae to benthic juveniles, with growth rates varying by region and exhibiting Heincke's law, wherein older individuals shift to deeper waters. Commercially vital, plaice fisheries yield substantial harvests, with European plaice supporting demersal trawls in European waters and American plaice contributing to North American landings, such as 1.5 million pounds valued at $2.5 million in 2022, though sustainability concerns arise from historical overexploitation and bycatch in mixed fisheries.[2] Prized for firm, white flesh in culinary applications like grilling or frying, these species underscore the interplay of ecological dynamics and human harvest pressures in marine resource management.[6]Taxonomy and Classification
Etymology and Nomenclature
The English word plaice derives from Middle English plaice or plais (attested around 1300), borrowed from Old French plaiz or plaïs, which in turn originates from Late Latin platessa, a term for flatfish linked to Ancient Greek platús ("broad" or "flat").[7][8] This linguistic root underscores the fish's dorsoventrally flattened body, evoking a broad, plate-like form akin to a dish.[9] In binomial nomenclature under the Linnaean system, the European plaice—Pleuronectes platessa—serves as the type species for its genus, formally described by Carl Linnaeus in the 10th edition of Systema Naturae published on January 1, 1758.[10][11] The generic name Pleuronectes combines Greek elements pleurá ("side") and néktes ("swimmer"), alluding to the asymmetrical, side-swimming locomotion of flatfishes, while the specific epithet platessa directly echoes the vernacular etymology for flatness.[12] Vernacular nomenclature varies regionally, with "plaice" primarily denoting P. platessa in European fisheries from the North Atlantic to the Baltic Sea, though it has historically been conflated with similar flatfishes like the dab (Limanda limanda) in early texts due to overlapping common names.[13] In North American contexts, the term applies to the American plaice (Hippoglossoides platessoides), reflecting adaptive usage in transatlantic fisheries rather than strict taxonomic equivalence, as distinguished by morphological and genetic criteria established post-Linnaeus.[14] Such distinctions emphasize the need for precise scientific naming to avoid ambiguities in historical records and commercial trade, where P. platessa accounted for over 80% of global plaice landings in recent assessments.Phylogenetic Position
Plaice species occupy a position within the order Pleuronectiformes, which encompasses flatfishes distinguished by the metamorphic migration of one eye to the ipsilateral side, enabling a benthic lifestyle with both eyes oriented dorsally. This order includes approximately 800 species across 14 families, with Pleuronectiformes exhibiting monophyly supported by molecular data from mitochondrial and nuclear genes, despite historical debates on basal divergences such as the placement of Psettodidae.[15][16] European plaice (Pleuronectes platessa) is classified in the family Pleuronectidae (righteye flounders), where adults display dextral eye positioning, and represents the sole extant species in its genus. American plaice (Hippoglossoides platessoides) also belongs to Pleuronectidae but in the distinct genus Hippoglossoides, reflecting phylogenetic divergence within the family as resolved by multilocus analyses incorporating four nuclear and three mitochondrial markers. These studies, conducted post-2010, confirm genus-level separations through coalescent-based phylogenies, attributing distinctions to accumulated genetic variation in coding and non-coding regions without evidence of recent hybridization.[17][18] The family's evolutionary history traces to stem-group Pleuronectiformes in the early Eocene (approximately 53–57 million years ago), evidenced by otolith fossils from Paleocene-Eocene boundary strata that exhibit early asymmetric morphology akin to modern forms, predating skeletal remains of crown-group taxa. This timeline aligns with post-Cretaceous diversification of percomorph fishes, where selective pressures for crypsis on substrates drove ocular asymmetry as a derived trait, corroborated by comparative anatomy of Eocene fossils like Heteronectes chaneti.[19][20]Physical Description
Morphology and Anatomy
Plaice species, including Pleuronectes platessa and Hippoglossoides platessoides, are dextral flatfish exhibiting pronounced bilateral asymmetry due to post-larval metamorphosis, during which the left eye migrates to the right side, positioning both eyes dorsally while the body compresses vertically for a benthic lifestyle.[1][21] The eyed side faces upward for visual orientation on the substrate, with the blind side pigmented minimally and lacking ocular development. This asymmetry extends to the skull and viscera, which shift rightward, supported by a reinforced axial skeleton adapted for weight-bearing on soft sediments.[22] Body dimensions vary by species but generally feature an ovate to oblong shape, with total lengths averaging 30-75 cm and maxima approaching 90 cm in P. platessa. The mouth is large, extending past the lower eye margin, facilitating opportunistic predation on bottom-dwelling prey. The caudal fin is rounded, aiding maneuverability over uneven seabeds, while the lateral line runs straight along the body midline, enhanced by cycloid scales that are smooth in P. platessa but rougher in H. platessoides.[1][21] Fin ray counts provide diagnostic traits: P. platessa typically has 62-72 dorsal rays, 3-4 pectoral rays, and 46-59 anal rays, with the dorsal fin originating anterior to the snout.[23] Internally, the skeletal framework includes a flattened cranium with a bony ridge posterior to the eyes in P. platessa, and vertebrae numbering around 45-47, optimized for flexibility and stability in undulating propulsion via undulatory fin motions. Sensory structures emphasize chemoreception and mechanoreception: enlarged olfactory rosettes detect chemical cues in turbid waters, while the lateral line system, comprising neuromasts along the body and head canals, enables vibration and pressure gradient sensing for prey localization and predator avoidance in low-light conditions, as confirmed by neuroanatomical examinations.[24]