Goldfish

1 Species Overview

The goldfish, also called the golden crucian carp, has the Latin name Carassius auratus. Originating in China and well known to the Chinese people, the goldfish has been refined through continuous breeding into more than 125 varieties, and is the earliest species in the history of ornamental fish worldwide.

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Actinopterygii

Order: Cypriniformes

Family: Cyprinidae

Subfamily: Cyprininae

Genus: Carassius

2 Appearance

Through crossbreeding, goldfish now have more than 125 varieties, so their body color and head shape vary enormously. Here is a summary of common goldfish types and their traits, plus a classification of goldfish head shapes, for enthusiasts to get acquainted.

I. Common Varieties

1. Grass type (caoyu): also the ancestral golden crucian type. Mainly single-tailed grass goldfish and comet (swallowtail) grass goldfish; the body is laterally compressed and spindle-shaped, with a dorsal fin and long, pointed triangular pectoral fins. They are the primitive form of goldfish and the main variety in China’s large-scale aquaculture. The golden crucian (jinji) has a short, single-lobe, notched caudal fin and an all-over orange-red body — the most ancient goldfish variety.

2. Wen type: evolved from grass goldfish through domestication and continuous selective breeding; viewed from above, the body resembles the character ‘wen’, hence the name. Wen goldfish come in many colors and varieties, most of which are highly reputed best-sellers on the international market. Common Wen types include the gaotou (hooded/cap) group, the pearl (pearl-scale) group, and the wen group proper.

3. Dragon-eye type (longjing): long regarded as the authentic Chinese goldfish, famous for its pair of especially large eyes. After being introduced to Japan in 1895, it was consistently called the ‘Chinese goldfish.’

4. Egg type (dan): named for its short, rounded body shaped like a duck egg. It is hardier than the dragon-eye and wen types and grows faster. Egg-type goldfish are prestige items on the international market; their main traits are a short, plump, egg-shaped body and no dorsal fin, with paired caudal and anal fins. Fin length and shape vary greatly — for example, the velvet-ball, bubble-eye, and lionhead have short, small, rounded fins, while the danfeng, curled-gill, and red-cap have longer, larger fins.

II. Common Head Shapes

1. Flat-head type: the head skin is thin and smooth, divided into narrow flat-head and wide flat-head.

2. Goose-head type: a thick wen (fleshy growth) bulges on top of the head, while the cheek covers on both sides are thin and smooth.

3. Lion-head type: thick wen bulge on top of the head and on the cheek covers on both sides; when well developed they can even cover the eyes.

In addition, common names used to describe head types include:

1. Lionhead: thick wen on top of the head and on both cheek covers, which can cover the eyes when developed. Has a dorsal fin.

2. Gaotou (High-head / Hooded): a thick wen bulges on top of the head while the cheek covers are thin and smooth. Has a dorsal fin.

3. Tigerhead: thick wen on top of the head and both cheek covers, which can cover the eyes when developed. No dorsal fin.

4. Goosehead: a thick wen bulges on top of the head while the cheek covers are thin and smooth. No dorsal fin.

5. Shouxing head (Longevity / Old Man): a kind of tigerhead whose crown protrudes forward, resembling the head of the God of Longevity (Shouxing), hence the name.

6. Cat-lion head: a kind of tigerhead with very developed head wen, mainly chrysanthemum-petal shaped.

7. Ranchu head: a kind of tigerhead developed in Japan. Viewed from above, the front of the wen is square with two snout protrusions. But in side view its wen is not as large as in the Chinese tigerhead, lionhead, shouxing, or cat-lion, nor as pronounced as domestic head-wen types.

8. Crown head: the unique head wen of the crown pearl goldfish — a smooth, single wen.

3 Care Basics

The most important thing in keeping goldfish is water quality. For goldfish to grow healthily, the dissolved oxygen level, water depth, and water changes are all critical in husbandry. Only by getting these right can you prevent health problems during seasonal changes.

1. Dissolved oxygen: natural water (rivers, lakes, seas) has a relatively high dissolved oxygen level, up to 8–12 mg/L, but under artificial conditions ponds and tanks have a small open surface, limited light, and relatively high stocking density, so an air pump is needed to add oxygen. If stocking density is low, run the aerator about 8 hours a day; if density is high, run it 24 hours a day.

2. Light: light is important for water transformation and aquatic plant growth, and the ultraviolet in sunlight has a sterilizing effect. So for indoor tanks lacking light, supplement with artificial lighting — install a UV lamp for a few hours daily to make up for the lack of sunlight.

3. Water depth: goldfish that swim too vigorously tend to become elongated, flat-bellied, with shorter and thinner tails and pointed, degenerated head features. As noted by hobbyists, the best water for goldfish is a pale green water with a little planktonic algae — this keeps the goldfish’s color vivid. If this water is too deep (over 50 cm) the fish may not even be visible (still water over 50 cm develops a top-bottom temperature difference in summer). Therefore, keep goldfish in still water at a low depth (no more than 40 cm). A simple example: in parks you see only golden crucian carp in lakes, never high-quality goldfish.

4. Water changes: change and replenish water preferably after 4 p.m., when the goldfish have already fed. At water change, remove leftover food and all debris from the container, then add an appropriate amount of aged water. The method: first use a gauze net to skim floating dirt and foam from the surface, then gently swirl the water in the same direction 3–5 times with the net to concentrate debris in one spot, siphon out the debris, and slowly add aged (conditioned) water along the container edge in a suitable proportion.

4 Tank Environment

Goldfish originate from China and are kept by very many people there. To raise healthy goldfish, create a captive environment close to their wild habitat, so they stay beautiful and healthy companions.

1. Water temperature: goldfish are poikilothermic — their body temperature follows the water temperature. But summer and winter temperatures are also a test for them, so try to keep a stable-temperature environment.

2. Stocking density: a home rectangular aquarium is small in volume, so never overstock — fewer is better. In a container 40 cm long × 25 cm wide × 30 cm high, you can keep 6–8 small goldfish 5–7 cm long. In a round glass bowl 26 cm in diameter × 13 cm high, keep 4–6 small goldfish 4–6 cm long. Adult fish over 8 cm should not be kept in a small glass bowl but in a large glass tank or ceramic jar, with a small aerator on standby against oxygen shortage. These densities are only reference figures; adjust by water temperature, fish condition, and water quality — do not apply mechanically. Generally: larger fish, fewer of them; stock more in winter, fewer in summer; more when water is cool, fewer when warm.

5 Feeding

Like many animals, a single diet leads to nutritional imbalance in goldfish. Goldfish feed must be rich in protein, trace elements, and inorganic salts — what to feed and when is a headache for many hobbyists.

1. Animal feeds: for example, bloodworms, daphnia, cyclops, paramecium, mosquito larvae, midge larvae (chironomid), and tubifex. These live foods are rich in protein and other nutrients and are the goldfish’s favorite.

2. Plant feeds: for example, duckweed (Wolffia) and aquatic plants. The plant bodies are rootless and tiny like grains of sand and fairly nutritious, but animal feeds are ideal for goldfish. So when feeding plant matter, pair it with some animal feed to balance nutrition and keep the diet healthy.

3. Compound (synthetic) feed — the common dried fish food sold in markets. Professionally produced fish food has very good nutrient composition and ratios. It is rich in protein, carbohydrates, fats, vitamins, and inorganic salts, meeting the goldfish’s growth needs. It is also convenient to buy and easy to feed, so this dried compound feed is usually the keeper’s first choice.

If conditions allow, do not feed only one type of food for long periods. Vary the diet periodically and add some animal feed so the goldfish’s meals are more varied.