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For fancy goldfish, the body shape is much shorter and deeper than the typical torpedo shape seen in most fish.
The peduncle is the area of the fish that joins the body and the caudal fin together. In Japanese ranchus especially, a thick peduncle when viewed from above is a very desirable trait.
The lateral line looks like a series of small dots running from the head to the tail of the fish, and it consists of sensory organs that detect vibrations and water current direction.
The scales overlap in a regular pattern, and a high quality goldfish has very uniform scales in both size and shape. The pearlscale goldfish has thick, domed scales that have a pearl-like appearance.
The vent is the site of waste elimination. The female vent protrudes slightly and is almost circular in shape, while the male vent is indented and more narrow.
Differing varieties of goldfish have different head shapes; for example, the ryukin has a pointed triangular head, while the ranchu has a broad, squared head that’s covered in raspberry-like head growth.
Opercula (Gill Covers)
The operculum is a hard bony flap that covers and protects the gills. It’s open in the back for the release of water.
Goldfish lack eyelids, so they sleep with their eyes open. Differing varieties of goldfish have different eye shapes; for example, the telescope has protruding eyes, and the bubble eye has large fluid-filled sacs under each eye.
The nostrils are connected by a U-shaped passage lined with cells that detect odors, and each nostril has a fleshy narial flap on the outside of it. In the pompon goldfish, the narial flaps are exaggerated and form multiple folds of fleshy material; which are called narial bouquets.
Goldfish are suction-feeders. To ingest food, they quickly expand the mouth cavity which results in a pressure difference between the inside of the mouth and the outside environment. This pressure difference causes water, along with the food item, to flow into the fish’s mouth.
The dorsal fin is used for steering and maintaining an upright position in the water. There are many varieties of goldfish that lack a dorsal fin, like the ranchu, lionhead, and celestial.
The dorsal spine is the leading ray of the dorsal fin. It is rigid and helps the dorsal fin remain upright. Sometimes the dorsal spine can become broken if the fish suffers an injury, and in that case the dorsal fin will normally be bent over.
The pectoral fins are used for steering, braking, and maintaining an upright position in the water.
Breeding Tubercles (Breeding Stars)
Breeding tubercles can be found on the leading ray of the pectoral fins and on the gill covers of male goldfish in breeding season.
The pelvic fins are used for steering.
The anal fins are also used for steering. In double-tailed goldfish, the anal fins should be paired and should be the same size and shape. Anal fin deformities are fairly common in fancy goldfish.
The caudal fins provide thrust for swimming and act as a rudder. Most fancy goldfish have two caudal fins that are split apart from one-another.
Fancy goldfish with properly-split caudal fins have four caudal lobes. Some goldfish have what’s called a tripod tail, and this means there is only one upper caudal fin lobe which separates into two lower lobes.
The caudal fork is the indentation between the lobes of caudal fin. In some goldfish varieties, like the veiltail and the butterfly tail, there should be no caudal fork present. Instead, the end of the tail should be squared-off and straight.
The fin rays are bony projections that give the fins structural support.