At what size do loaches start spawning, and how many eggs do they lay at one time?

The loach is called the “ginseng of the water” and has high farming value. Natural breeding means imitating natural environmental conditions under artificial control so that loaches spawn and hatch on their own. So at what size can loaches spawn? How many eggs can they lay at one time? Next, let us learn about it together.

At what size do loaches spawn?

Loaches reach sexual maturity at two years of age and begin to spawn. Mature female loaches have a large, round belly and smooth pectoral fins, and are larger than male loaches. The reproductive period of loaches is generally from April to August. From late May to late June, when the water temperature is around 25°C, is the peak spawning period.

The loach is a fish that spawns multiple times. Under natural conditions, breeding begins in early April, the peak spawning period is May to June, and spawning can continue until September. The breeding water temperature is 18-30°C, and the optimum water temperature is 22-28°C. Female loaches mature sexually later than male loaches. At a body length of 5 cm, a female loach has a pair of ovaries in its body; at a body length of 8 cm, the two ovaries merge together into one ovary, extending from the front end to the back end, and at this point the entire ovary begins to mature. The number of eggs carried by a female loach varies greatly depending on the size of the individual. The smallest sexually mature individual has a body length of 8 cm and carries about 2,000 eggs; at 10 cm the number of eggs carried is 7,000-10,000; at a body length of 12 cm the number of eggs carried is 12,000-14,000; at a body length of 15 cm the number of eggs carried is 15,000-18,000; at a body length of 20 cm the number of eggs carried is about 24,000. The largest number of eggs carried can exceed 65,000. The eggs are round, about 0.8-1.0 mm in diameter, swelling to 1.3-1.5 mm after absorbing water; they are yellow and semi-adhesive, with weak adhesive force. Because the eggs mature at different rates within the ovary, the number of eggs released each time is about 50%-60% of the number of eggs carried. The smallest sexually mature male loach has a body length of more than 6 cm and matures sexually earlier than the female loach. The male loach has a pair of testes located on both sides of the abdominal cavity, band-shaped and asymmetrical; the right testis is longer and narrower than the left and slightly lighter in weight. When the male loach reaches a body length of 9-11 cm, the sperm in the testes number about 100 million.

Loaches prefer to spawn on the morning of a sunny day after rain. Before spawning, the female loach swims in front, with several male loaches chasing closely behind. During estrus, the male and female loaches are mostly active at the water surface and around the fish nest. When estrus reaches its peak, the heads and bodies of the male and female loaches rub against each other and they successively swim out of the water. The male loach chases and entangles the female loach and curls around the female's belly to stimulate the female to spawn, while the male also releases sperm for external fertilization. The number of such actions varies with the size of the individual; large individuals may do it more than 10 times. The fertilized eggs first adhere to aquatic plants or other attachments, and with the fluctuation of the water they easily fall off the attachments and sink to the bottom.

How many eggs can they lay at one time?

1. Relationship between egg output and age and body length: The egg output of loaches of different ages and different body lengths is different. The relative egg output of female loaches with a body length of 15.1-20 cm and over 20 cm is twice that of those with a body length of 10-15 cm. After hormone injection, the difference in the number of eggs laid at one time by loaches of different ages is very obvious; those aged 4-5 years show a significant increase over those aged 1-3 years, about 2.2 times. The relative egg output varies at 22 eggs per gram.

2. Relationship between breeding results and water quality:

(1) pH: Fish are very sensitive to changes in water pH. In water with a pH of 5.6-9.0, loaches can all spawn, and the number of eggs laid is basically unaffected. However, below pH 6.5 and above 8.5, there is a clear effect on the fertilization rate of loach eggs and the hatching rate of loach fry, especially a greater effect on the hatching rate. The pH of the breeding water environment is best at 7-8, that is, neutral or slightly alkaline.

(2) Light: Loaches like to burrow into mud and live at the bottom, and are less sensitive to light. Tests have shown that no matter what color of light is used, there is no obvious difference in the breeding results for loaches.

(3) Water temperature: Loaches have better breeding results within a water temperature range of 18-26°C, especially best at a water temperature of 20-26°C. Below or above this water temperature range, the breeding results are greatly affected. For example, when the water temperature is 16-18°C, the spawning rate is only 25%, the fertilization rate is 30%, and the hatching rate is 20%; while when the water temperature is 20-26°C, the spawning rate reaches 100%, the fertilization rate is 89%-92%, and the hatching rate is 72%-77.4%.

(4) Relationship between the adhesiveness of fish eggs and the material of the fish nest: Loaches lay slightly adhesive eggs. Two kinds of fish nests were made with palm fiber sheets and aquatic plants, and the situation of adhering eggs and the fertilization rate and hatching rate of loach eggs were observed, to explore the requirements of loach spawning for artificial fish nest materials. Tests proved that the two fish nest materials showed no obvious difference in fertilization rate and hatching rate. However, the number of adhered loach eggs differed greatly; the number of fish eggs adhered to the palm fiber sheet fish nest was 4 times that of the aquatic plant fish nest.

Three methods of loach breeding

1. Natural spawning and breeding

Place parent loaches in a spawning pond. When the water temperature rises above 18°C, place disinfected palm fiber sheets, willow roots, aquatic plants, etc. in the pond as fish nests. After discovering that the loaches have spawned, transfer the fish nests with attached eggs to a hatching pond, and at the same time place new fish nests to let them spawn again. The hatching of fertilized eggs does not have high requirements for water quality and water temperature; generally, aquaculture water bodies can all be used for hatching, and the optimum water temperature is 20°C-28°C. After about 2 days, the fry can emerge from the membrane.

2. Artificial induced spawning and breeding

When the temperature is suitable in April-May, catch the parent loaches and select parent fish with a soft belly, a slightly pinkish color, and signs of imminent spawning, with a body length of 12 cm and a body weight of more than 20 g, preferably individuals of about 40 g, for drug-induced spawning. For the dosage, each female loach can use 1 carp PG or 5-10 micrograms of LRH-A, and the dosage for male loaches is halved. Then place the induced parent loaches in a spawning pond and let them spawn and fertilize on their own or carry out artificial fertilization. Finally, place the fertilized eggs on nests into a hatching pond for hatching. This method can obtain loach fry on time and in large quantities in a planned way.

3. Stocking for supplementary breeding

This is the simplest breeding method. That is, put an appropriate amount of mature loaches into the loach culture water body, but do not stock other fish first. During the reproductive season, place some artificial fish nests, and the loaches spawn in the culture pond and hatch in the original pond. The fry can be cultivated in small boxes and then still raised in the original pond.