When goldfish are newly hatched from eggs, they do not eat food and rely on absorbing the yolk sac in their abdomen to survive. However, after 2 – 3 days, when the nutrients in the yolk sac are completely consumed, goldfish have to obtain food from the external environment. All the life – activities of goldfish throughout their lives, such as growth, development, and reproduction, are based on obtaining food nutrients from the outside world.
Fish are the most numerous group among vertebrates, with a large number of existing species. Classified by food types, they can be divided into herbivores, carnivores, omnivores, and detritivores. Goldfish are omnivores and can feed on various plant – based baits such as algae, waterweeds, duckweeds, plant seeds, rice grains, bread crumbs, etc., as well as animal – based baits such as zooplankton, tubifex worms, minced fish and shrimp, shrimp and crab eggs, fish meal, and animal offal. Goldfish do not have teeth in their upper and lower jaws, but they have pharyngeal teeth on the pharyngeal bone in the throat. These pharyngeal teeth can cooperate with the pharyngeal mill below the basioccipital bone to crush, cut, or grind relatively hard foods, such as the shells of plant seeds and large zooplankton.
The gill rakers of goldfish are large and wide. When goldfish ingest food from the outside, the water that enters the oral cavity together with the food can be discharged out of the body through the gill slits via the gill rakers, while the food is filtered by the gill rakers, ground by the pharyngeal teeth, and then sent to the intestinal tract for digestion and absorption. Plant – based foods are rich in fiber and need to stay in the intestinal tract for a relatively long time to be digested, so the intestinal tract of goldfish is relatively long.
Fry and adult goldfish have different feeding habits. Fry, whose yolk sac has just disappeared and start to ingest food from the outside, are only over 1 centimeter in total length. Not only are their bodies and mouths small, but their newly – formed digestive systems are also very delicate. They can only feed on small and relatively soft zooplankton such as rotifers and paramecia. This kind of small zooplankton can be artificially cultured or obtained when rinsing bloodworms fished from natural ponds, because these small zooplankton exist in natural ponds and are often fished back together with bloodworms. The water used to rinse bloodworms can be easily filtered with a fine white cloth to obtain them. If it is impossible to obtain this kind of small zooplankton, finely – ground cooked egg yolks or duck egg yolks can be used as substitutes.
During the period of dietary transition from relying on yolk – sac nutrients, then to small zooplankton nutrients, and finally to omnivorous nutrients, the quality of the bait and the proper feeding method are closely related to the survival rate of goldfish and the success of cultivating high – quality goldfish. Adult goldfish mainly feed on larger – sized baits, and their diet range is very wide. In recent years, the emergence of various artificial synthetic baits has provided an abundant source of food for goldfish, bringing great convenience to home fish – keeping.
