How to Identify Flatfish

To identify Flatfish (Pleuronectiformes), look at these key features.

Physical Characteristics

Body shape

flat

Coloration

Highly variable, typically cryptic. The eyed side is pigmented with shades of brown, grey, green, or mottled patterns to blend with the seabed. The blind side is usually white or pale.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Asymmetrical body with both eyes on one side of the head in adults., Highly compressed body, adapted for benthic life., Dorsal and anal fins extend along much of the body length., Ability to change coloration to match substrate (chromatophores).

Dorsal fin

Long, continuous fin extending from the head to the caudal peduncle.

Tail fin

Typically rounded, truncate, or slightly emarginate, varying by family and species.

Pectoral fin

Small to moderately sized, often present on both sides, though sometimes reduced or absent on the blind side.

Distinctive fins

Pelvic fins are typically small and thoracic or jugular in position.

Identification Tips

1. 1

   Eye Migration

   Observe the position of the eyes. In adults, both eyes are on one side of the head. The direction of eye migration (left or right side) is a key taxonomic feature for distinguishing families (e.g., Pleuronectidae are typically right-eyed, Bothidae are typically left-eyed).

2. 2

   Lateral Line

   Examine the lateral line. Its shape (straight, arched over the pectoral fin) and presence of accessory branches can be diagnostic.

3. 3

   Fin Ray Counts

   Counting the number of rays in the dorsal, anal, and pectoral fins is often necessary for species-level identification, especially for closely related species.

4. 4

   Mouth Size and Dentition

   The size of the mouth and the type of teeth (e.g., small, conical, or strong canines) can indicate feeding habits and aid in identification.

5. 5

   Coloration and Pattern

   While variable, specific patterns, spots, or ocelli can be characteristic of certain species, especially when observed in their natural habitat or shortly after capture.

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