Carassius auratus grandoculis

Carassius auratus grandoculis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cypriniformes
Family:	Cyprinidae
Genus:	Carassius
Species:	C. auratus
Subspecies:	C. a. grandoculis
Trinomial name
Carassius auratus grandoculis Temminck & Schlegel, 1846[1]

Carassius auratus grandoculis (Japanese: nigoro-buna), a fresh-water ray-finned fish, is a wild subspecies of goldfish endemic to Japan, its habitat limited to Lake Biwa, its tributaries and distributaries, irrigation canals.

In some literature, it is misleadingly referred to as a "crucian carp," which is not strictly incorrect since this common name is popularly applied to the whole genus Carassius. However it does not belong to the crucian carp species, C. carassius.

Etymology

Its Japanese name nigorobuna (ニゴロブナ) is ascribed various etymologies. One theory has it that it earned the name "ni-gorō-buna" (似五郎鮒) meaning "resembling (gen)gorō-buna", because once it reaches sizes of 1 foot or over, it begins to look confusingly similar to the gengorō-buna (源五郎鮒), C. cuvieri, the wild form of the Japanese crucian carp, a closely related species also endemic to the lake.^[2] It is alternatively styled 煮頃鮒, which crudely translates to "braising-timely-carp."

Morphology

The fish attains 35 cm (13¾ inches)^[3][4] total length at maturity. Its shape resembles the nagabuna or Carassius auratus ssp.1 ^[5] that populate Lake Suwa; body depth is short, breadth is wide.^[6] The head is large, with a ventricular contour that is characteristically ridged.^[6] The mouth slit is slanted upwards.^[6] Around 61 (or 52–72) gill rakers can be counted, and the dorsal fin rays consist of 1 spine and 17 (or 15~18) soft rays. The anal fin has 1 spine and 5 soft rays.^[6] The basal length of the dorsal fin is rather long.^[6] The total length is 2.7x^[6] the body depth.

Behavior

Young larvae and juveniles are found on the surface and medium depths entrenched within the reed growths^[6] around the lake, in other words, inlets rich in aquatic plants.^[7] Adults occupy shallower waters in summer, and move to deeper waters during the cold winter months.

One study (Hirai 1969) showed that when larvae of about 1 cm length were compared, nigorbuna was "scarce(ly)" feeding on algae, compared with local "genogoro-buna", which had 25–50% algal digestive tract conten by bulk. The fish also showed a preference for certain water fleas over another, relying heavily on Chydorus spp. ( Data related to Chydorus at Wikispecies) and to a lesser extent on Mesocyclops. By contrast, the gengoro-buna kept in the same enclosure preferred wheel animals (rotifer spp.). The fry (larvae) of both species largely ignored other types of zooplankton (such as Alona, Scapholeberis, and copepodid larvae) which were plentiful.^[8] As they grow into juveniles exceeding 1 cm the nigorobuna begin exhibiting behavior of pecking at aquatic plants to feed on attached algae, so by the time they attain 2 cm lengths,^[6] algae (and rotifers, small percentage) account for half their diet.^[9] When they grow larger they capture semi-bottom dwelling zooplanktons.^[6]

They adults spawn from April to June, laying eggs upon aquatic plants when water levels rise due to rainy season.^[6] The hatchlings live by the reedy shore, move offshore as they grow, reaching full size in 2~3 years.^[10]

Uses

funa-zushi made from "nigoro crucian carp". Females carrying roe (pictured) are especially prized.

This is a highly prized fish commercially, made into authentic funazushi, salted and fermented in rice. It is a local delicacy of Shiga Prefecture. The dish is one of the surviving relics of traditional fermented sushi known as narezushi.

This species is said to make superior funazushi that is tender down to the bones, in contrast to imitations now being made by substituting the aforementioned gengoro-buna, Carassius cuvieri.^[11] The ginbuna (Carassius auratus langsdorfii is also said to be used as a substitute.

Fishing regulations

Annual catch estimated to be 500 tons in 1965 fell to 178 tons by 1989, and drastically down to 18 tons by 1997,^[10] so that efforts were begun to release fisheries raised spawn into nearby rice paddies connected with the water system.^[10] Nowadays, the species is also farmed in Saitama Prefecture.^[12]

Shiga Prefecture, in its announced project to recover the fish stock, promulgated regulatory rules through its Lake Biwa Fisheries Management Commission, effective April 1, 2007, prohibiting the capture of fish measuring 22 cm or less.^[13]

The devastation of numbers is blamed on habitat loss as well as introduction of nuisance alien species such as black bass and bluegill into the Lake Biwa system.

References