Farming goldfish

Modern goldfish have been selectively bred over several centuries to provide the wide range of varieties that we now have available, including single and fantails (double tails). The wild form of Carassius auratus is a bronze coloured fish that occurs in parts of Asia and eastern Europe, and from which a range of colours from white to black via yellow, orange, red and mixtures of these colours has been cultivated.  Some varieties lack certain fins and others are characterised by warty growths on their heads.
 
Goldfish live in slow moving water bodies and this is therefore the environment they prefer.  A wide range of water temperatures is tolerated from near freezing to over 30°C, with the optimal being around 24-26°C.  They are equally tolerant of a wide range of the other water quality parameters, and this hardiness is part of why they have become so widely kept as pets.
They are omnivores and feed on aquatic insect larvae and other invertebrates along with some plant material.  Small vertebrates, including goldfish fry, are also eaten when the opportunity presents itself.  Farmed goldfish are fed artificial feed as this is far easier to transport, store and feed in large quantities.
 
Goldfish are spring breeders and in nature the adult males and ripe females will rush through submerged vegetation at dawn to lay and fertilise their eggs.  Those females that are not currently involved in spawning, and the sub-adults, feast on the recently spawned eggs.  At the appropriate water temperature, the eggs hatch in about 3 days and the larvae utilise their yolk sac for a further 3 days until they become free-swimming.
 
Goldfish farmers carefully select breeders that are excellent examples of the variety they represent, and that are vibrant, healthy individuals.  Males and females are conditioned separately to optimise their supply of eggs and prevent premature spawning.  Every week females are checked to identify those that are ready to spawn and these are placed into a spawning tank with one or two prize males per female.  Artificial spawning material, such as shadecloth or cabbage bags, is provided for the females to deposit their eggs onto.  The males will then fertilise these eggs as they are laid.  Once the egg laying slows and the breeders switch their attention to egg eating, they are removed and returning to their respective, gender-based tanks.
 
Male goldfish are ready to spawn throughout the spring and summer months whilst individual females move through cycles of being ready to spawn and then replenishing their egg supply.  These cycles are typically a few weeks long.
 
The shadecloth containing the eggs is moved to a clean tank for the incubation period and the spawning tank is cleared and readied for the next breeding event.  Once the larvae are free-swimming feeding commences; the first feed is usually brine shrimp larvae or some other highly nutritious live feed and as the larvae grow artificial feed is incorporated into the diet.
 
Goldfish are typically farmed in tanks or earth ponds, with the latter offering the dual advantages of being inexpensive infrastructure and because ponds contain natural feed items which boost the health and growth of the fish.  The counterbalance is that predators need to be managed to ensure that they do not eat all the young fish.
 
Growth is rapid and goldfish reach a marketable size by about 3 months of age.  However, most are retained and sold at a larger size where they command a higher price.  Also, goldfish start out life as bronze coloured fish irrespective of their genetic linage.  After a few weeks or months they switch to their final colouration.  Bronze fish have no commercial value, and early colouration is one of the genetic factors to consider where selecting future breeders.  Careful sorting and selection of the fish is performed when the fish are small; potential breeders are identified, and the balance of fish that can be sold are kept and raised separately.
 
When held under optimal conditions goldfish are fairly resistant to most health related challenges.  Ensure that the water quality is always good, feed a quality diet inclusive of live feeds and do not crowd the fish.  If poor health is suspected identify the cause immediately and commence with appropriate remedial action or treatment.
 
Once goldfish attain market size they are starved for 24 hours prior to being marketed.  The fish are packed in clear plastic bags half-filled with water of the same quality as the fish were held in.  Once the correct number of fish is placed into the bag the air is squeezed out, and it is filled instead with oxygen and sealed with an elastic band.  The oxygen in the bag enables the fish to travel for several hours to reach their destination without suffering decreased oxygen levels in the transport water.  On arrival the unopened bag is drifted in the new tank for 10 minutes to equalise the temperature, the bag is opened and the fish are gently released into the new tank.
 
Within Southern Africa goldfish are typically sold to pet shops or nurseries which in turn retail them to the public.  Smaller fish, and the more common varieties, trade for a few Rand each, but large specimens and fancy varieties can sell for hundreds of Rand per individual.  There is a strong local demand for goldfish with the market price largely dictated by the cost of importing them.  Before venturing into the potentially appealing business of farming goldfish, be very sure who you will sell your fish to and the price that you will obtain.