Fish Anatomy and Classification

• Fish is a cold-blooded lower vertebrate with fins and gills, typically living in water with or without scales.
• Fish can also refer to molluscs, crustaceans, and aquatic animals harvested from water.

Fish Groups

• Bony fishes (Osteichthyes) make up over 90% of living fish species, found in both marine and fresh water, including tilapia, catfish, cod, mackerel and flat fishes.
• Cartilaginous fishes (Teleosts) have skeletons of cartilage and sharp, tooth-like scales pointing backwards, primarily inhabiting marine environments like sharks, skaters, and rays.

Fish Identification Features

• The fish body is divided into the head, trunk, and tail regions.
• The head includes the mouth, eyes, nostrils, and operculum.
• The trunk comprises lateral lines, dorsal, pelvic, pectoral, and anal fins.
• The tail consists of the caudal fin.

Fish Skin

• Fish skin contains an outer Epidermis layer overlaid by a cuticle, a middle Dermis layer and an inner Hypodermis layer.
• Fish skin serves as the main protector against the environment.
• It acts as an osmotic barrier, the first line of defense against disease, and contains sensory receptors and performs excretory, respiratory, and osmo-regulatory functions.
• Pelagic fish species often have scales, like tilapia, which are protective outgrowths.
• Bottom dwellers, such as catfish, possess tough, leathery skin with mucus.
• Mucus protects the epidermal layer.

Fish Shapes

• Fusiform: Streamlined shape with pointed ends reduces frictional resistance, seen in mackerel, tuna, and sharks.
• Compressiform: Laterally compressed with tall, thin bodies, allowing entry into vertical crevices, as seen in tilapia.
• Depressiform: Flattened from top to bottom, slow-moving bottom dwellers.
• Anguilliform: Long, skinny, snake-like fish, such as Clarias sp, eel fish, and hagfish.
• Taeniform: Thin, ribbon-like shape with hiding abilities, rare in fresh water, like ribbon fish.
• Sagittiform: Elongated, arrow-shaped body for quick strikes, seen in barracuda, pikes, killifish, and gars.
• Globiform: Globe-like or ball-like, slow-swimming bottom dwellers.

Mouth Types

• Inferior Mouth: Upper jaw is longer than the lower jaw, seen in Mochokidae and Cyprinidae.
• Superior Mouth: Lower jaw is longer than the upper jaw, mouth upturned, found in Marcusenius.
• Terminal Mouth: Upper and lower jaws are the same length, as in Cichlidae.
• Sub-Terminal: Similar to inferior, but the lower jaw is slightly longer.
• Protracted: Lower and upper jaws are protractile, pointing forward.
• Retracted: Lower and upper jaws are withdrawn.

Fish Fins

• Fins are named by their position on the body.
• Dorsal Fins: Located on the back, can be single or double.
• Ventral Fins: Found on the ventral side, including pectoral, pelvic (sometimes absent), and anal fins.
• Tail or Caudal Fin: Can be rounded (Clarias), truncate (cichlids), emarginate (Cromeria), lunate (some spp of Labeo), forked (Clupeids), or pointed.

Fish Scales

• Scales are exoskeletons of dermal origin.
• The presence or absence of scales differentiates non-scaled (catfish) from scaled (tilapia) fish.
• Scale types include:
  • Cycloid: Smooth posterior margin (e.g., Citharinus species)
  • Ctenoid: Spiny/serrated posterior margin (e.g., Ctenopoma species)
  • Rhomboid or Ganoid: Rhombus shape (e.g., Polypterus)

Fish Nostrils

• Cichlids are distinguished by their nostril number and position.
• Some fishes may have two pairs of nostrils, while cichlids have one on each side of the head.
• Nostrils can be widely separated or close to the eye, as in Notopteridae.

Fish Lateral Line

• Most fish species have lateral lines which vary in length, position and conspicuousness.
• Many fish have a single, continuous lateral line from the caudal peduncle to the opercular bone.
• Lateral lines may be broken (discontinuous) or consist of two overlapping lines.

Fish Barbels

• These whisker-like structures arise from the mouth region.
• Catfish are named for their whisk-like structures, consisting of Mandibular, maxillary, and nasal barbels.
• Mandibular barbels: Arise from the lower jaw.
• Nasal barbels: Arise from the nostrils.
• Maxillary barbels: Arise from the upper jaw.
• Serrated barbels: Ciliated or have hair-like features.

Fish Classification (Nigeria)

• Centropomidae: Lates niloticus (Nile perch) (Igbo / apale) - Present (scales)
• Gymnarchidae: Gymnarchus niloticus (Trunk fish) (Osan) - Present
• Bagridae: Bagrus domac (Silver catfish) (Iko) - Absent
• Malapteruridae: Malapterurus electricus (Electric catfish) (Ojiji) - Absent
• Clariidae: Clarias gariepinus (Catfish) (Aso) - Absent
• Mormyridae: Mormyrops deliciosus (Mormyrid / Elephant fish) - Present
• Osteoglossidae: Heterotis niloticus (Slap water fish) (Aika/Afo) - Present
• Mugilidae: Mugil cephalus (Flat head or bully mullet) - Present
• Cichlidae: Oreochromis niloticus (Nile tilapia) (Epia) - Present
• Cyprinidae: Cyprinus carpio (Grass carp) - Present
• Channidae: Channa obscura (Snake head fish) - Present
• Mochokidae: Synodontis nigrita (Catfish) (Okoko niko) - Absent
• Characidae: Alestes dentex (Silver side fish) (Arefe) - Present
• Clupeidae: Ethmalosa fimbriata (Bonga fish) (Agbodo) - Present
• Schilbeidae: Schilbe mystus (African glass catfish) (Asan) - Absent