1Hubei province Fisheries Institute, 96 Donghu Road, Wuchang, 430071, Hubei, PRC (E-mail: hinafish1@263.net)

2Kentucky State University (wang1@mis.net)

3Asia and Pacific Aquaculture Ltd (Wuhan). 96 Dong Road, Wuchang, 430071, Hubei, PRC (E-mail: chinafishery@263.net)

4Dept. Evolution, Ecology, and Organismal Biology, the Ohio State University, Columbus, Ohio, 43210, USA. (E-mail: culver.edu)

5Biology Department, Mount Union College, Alliance, Ohio, 44601, USA. <e-mail:wuli@muc.edu>

6Hubei Province Foreign Experts Bureau

Abstract

Yellow perch(Perca flavescens) have been propagated in China for the first time. From 14 March 14 to 3 May 2000, 93 pairs of yellow perch were held in 8 groups for propagation at the Hubei Province Fisheries Institute fish farm. A total of 681,400 eggs were produced, of which 306,400 eggs were from natural reproduction and 375,000 eggs after hormone induction. Upon fertilization, we obtained a total 403,000 fry.

(1). Mono- and poly-culture are two ways for brood fish rearing in central China whether by feeding on pellet feeds or live food. When the water temperature reached 14℃, the induction of ovulation of yellow perch was 100 per cent. (2) Ovulation-inducing hormones: CPG, HCG, LH-RH-a could all be used as ovulation inducing agents, but when we used the three spawn-inducing agents at the same time, the effect was the best, using a doses of CPG (3mg/kg) + HCG (1500IU/kg) + LH-RH-a (5μg/kg). (3) The best induction of ovulation occurred (on March 14, 20, 24, and 27), at a water temperature of 14-25℃). The fertilization rate averaged 93%, on April 6 and 12, (at a water temperature of 22-28℃) , whereas the fertilization rate fell to 78%, on April 25 and as low as 33% on May 3 at a temperature of 25-32℃. (4). Cement pools filled with water from East Lake Fish Farm, Hubei Province Fisheries Institute, were used to hold eggs to hatching and the highest hatching rate (76%) with the shortest development time (115 h) was obtained at a water temperature of 22-27℃. (5). The newly hatched fry were 3.1-4.0 mm TL, and yolk sac absorption required an additional 78 h. At this time, fry began to feed and develop to the mixed nutrition stage.

Key words: yellow perch artificial propagation

Yellow perch Perca flavescens, considered a “cool-water fish,” was originally distributed in the central and north of North of America, at the water temperatures of from 0-42℃. The fish is brightly coloured, beautiful, and its flesh tastes fresh and good. It is one of the favorite sports fish in North America. The fish is distributed in the lakes and slow flowing rivers in the Eastern and Northern portions of North America.

The fish was initially introduced as juveniles into China from America by the Quality Fresh-water Fish Farm of the Southern Demonstration of China under the help of the Hubei Province Foreign Experts Bureau, in 1997. After three years’ culture and research, many of the yellow perch had reached sexual maturity. In 2000, our fish farm obtained 400,000 fishes successfully firstly in artificially induced ovulation. In this paper, we discuss the methods we used for propagation of yellow perch in China, and describe the results of these experiments.

Materials and Methods
Brood stock was introduced from America in 1997, held in ponds for three years, the fish grew up to sexual maturity with 28-32cm in body length, with 200-280g in weight.

The culturing of brood stock

1. Culture ponds: Experiments were performed in three culture ponds, 2 mu, 3.5 mu, 5 mu in area, respectively (1 mu = 666.7 m2). The bottoms of culture ponds consisted of clay, covered with a 20-30 cm-thick layer of silt, every culture pond had inlet and outlet, the depth of the water averaged 1.2m, whereas in the 3.5 mu pond the depth was 2.2 m. The major culture pond was adopted in the pond of 2 mu, the mixed culture was adopted in the pond of 5 mu.

2. Stocking density: 200 fish of yellow perch per mu with a total biomass of about 52.4 kg, were stocked in each pond and smaller amount of bighead carp (about 50 fish) was also stocked. Hence 70-75% of the total fish stocked in each was a yellow perch. Grass carp (with 5cm total length) 50 fish per mu with a total biomass of about 112 kg and less amount of common carp were stocked as well.

3. Feed culture: two feeds were used to culture the brood fish:

(1). Artificial formula feed, for fish consisted of fish meal, bean cake, rapeseed cake containing 32-36% of protein. (2), Limnodrilus and sundry fishes, the artificial formula feeds were fed for major culture of 2 mu, the fresh Limnodrilus and sundry fishes were fed for major culture of the 3.5 mu pond. Fertilizers were used for mixed culture, and some fresh fish meal was also added. Brood fish were fed twice per day (morning and afternoon). Feeding rate was about 5.5% of total biomass in spring and fall, 7% in summer, 3% in the winter. Pond fertilizer consisted of grass (500 kg) and chemical fertilizer (20 kg, about 18 kg from July to August). Fertilization was kept to a minimum to maintain water quality.

Fresh water was poured into culture ponds and the concrete pools biweekly, providing a 20% replacement of water every two weeks. Quick lime was used for sterilization (30kg/mu) in order to prevent fish diseases.

Induction of Ovulation and Spermiogenesis

In mid-March, at a water temperature of 14℃, sexually mature yellow perch began to spawn. From March 14 to May 3, ovulation and spermiogenesis induction by hormone injection was conducted with eight batches, using a total of 93 pairs of yellow perch.

Adult perch were netted 2 hours before being induced and were held in a 3.6m2 square cage. The brood stock was stimulated by slow flowing water. Identification of sexes: the male brood stock looked narrow, with nuptial colours. Nuptial tubercles appeared on its head and the body was harsh to the touch. When we pressed the fish abdomen, milky sperm flowed out. The female brood stock looked fat, with little nuptial colour or nuptial tubercles. Its abdomen was soft and enlarged.

The ovulation-inducing agents and injection: Carp Pituitary Gonadotrophin, Human Chorionic Gonadotrophin, Luteinizing Hormone-Releasing Hormone-analog were used at dosages of 5mg/kg for CPG, 2500IU/kg for HCG, 80g/kg for LRH-A, 3 mg/kg for PG+HCG+LRH- 5μg/kg for 1500IU/kg. For females, two injections were applied, 1/9 of the total dose were for the first injection; the rest was for the second. For males, a single injection of one-half the female dose was given when the females received the second injection. The first injection was carried out at 18:00, the second, at 23:00 so as to induce the female to spawn at about 8:00 on next morning.

For “natural” breeding, the brood stock was brought to three cement pools with an area of 120m2 and a depth of over 0.8m. Water quality was kept very clear by a filtration system in order to more easily collect the eggs.

For both the “natural” and induced groups, the ratio of females to males was 1:1. Both groups of brood fish were brought into 1 m2 square pools at 0900-1200 h.

Artificial induction of ovulation and spermiogenesis

After injection, the brood stock was taken into a net cage, keeping the water flowing so as to induce females to spawn the next morning at about 0800h. After ovulation, we pressed the abdomens of the females, and the eggs flowed into a basin of (6.5%) physiological saline.

At the same time, a male was pressed to cause the sperm to flow into the basin. We shook the basin gently for 3 minutes until the eggs were well-distributed throughout the basin, being careful to keep them in a natural state in order not to press or tear the eggs, until we could place the eggs into a pool to be hatched.

Hatching

The area of the cement hatching pools was 4m2, the water depth was 0.8m, and we used adjustment of the inflow and outflow to carefully control temperature. The eggs were kept at a depth of 0.5m. Malachite green (15 ppm) was used to disinfect for 20 minutes before the eggs were put in the water, which was kept flowing slowly.

The inlet and outlet were covered with three nylon silk sieves to protect the eggs against Daphnia. The mesh size of the sieve was 60μm in order to keep Cyclopoida from destroying eggs in hatching pools.

Attention was paid to the flowing speed to avoid injuring the eggs. The sieves in the outlet were washed regularly to keep them flowing freely. The eggs were kept in the middle or upper level of the water, at 0.5m depth.

Malachite green (8ppm) was used to disinfect the eggs every day. The eggs were inspected every day, and moldy or dead eggs were removed to avoid infection of other eggs. The eggs were sheltered from the sunshine by colourful clothing suspended above the hatching pool. With an incubation temperature range of 20-27℃, the eggs hatched after 115 hours.

Results and Discussion

1. Age of sexual maturity and the distinguishing characters of male and female yellow perch;

Under artificial culture, most yellow perch males matured at the age of 1 year, whereas females matured at the age of 2-3 years. The appearance of males and females were similar except that nuptial tubercles appear on the head and body of the male yellow perch. The body was harsh to touch, and the anus had a single noticeable aperture. The female was a little bigger than the male, had little nuptial colour and no nuptial tubercles, and the anus had two obvious apertures.

2. Induction success under various conditions

The induction rate of yellow perch was 100% when the brood stock was stocked as a polyculture with silver carp, bighead carp, grass carp, and common carp, and fed on formula pellet and live food. All hormone successfully induced ovulation and spermiogenesis, but success was best when all three hormones were used together. Using this method, the induction rate was 100% in five replicate experiments. Effect of time on fertilization success: the best results were obtained on March 14, 20, 24 and 27 (water temperature of 14-27℃)when the fertilization rate was 93%, whereas on April 6 and 12 (at water temperature of 22-28℃) it was only 78%; it dropped to 33% on April 25, May 3 (at the water temperature of 27-32℃). Optimum temperature for fertilization thus ranges from 14-27℃; above 27℃, success was poor.

3 From 14 March to 3 May 2000, we performed eight ovulation/spermiogenesis and egg fertilization experiments involving 93 male/female pairs. Five experiments involved artificial induction with hormone injection and three with natural ovulation/spermiogenesis.

Fecundity of 200 g females was 8,000 to 10,000 eggs/female, whereas those weighing 150g produced 6,000 to 8,000 eggs/female. Fertilization rates on March 14, 20, 24 and 27 were 91%, 92%, 97%, and 95%, respectively. On April 6 and 12, the fertilization rates for eggs from induced spawnings were 80% and 76%, whereas on April 25 and Ｍay 3, the fertilization rates from induced spawnings were 34% and 31%, respectively.

4. Hatching

In order to know the best temperature of hatching and heighten the hatching rate and get good fry we did the experiment in different.

Water temperature

Hence when water temperature ranged from 22-27℃, hatching rate was best with (75.8%), and the hatching time was shortest (4 days). The survival rates in eight tests were (on March 14 –27) 62%, 65%, 76%, 73%, respectively, whereas on April 6, 12, 25 and May 3, they were 46%, 35%, 7%, and 9%, respectively. Embryonic development: the eggs of yellow perch were round and orange, and were 1.2-1.4 mm after absorbing water. The egg membrane was radiate in shape, and about 2.5-3 um in thickness. The membrane remained adherent from fertilization through embryonic development, so that even 47 hours after fertilization, the eggs were still about 3.0-3.5 mm. Developmental events included: blastoderm protrusion at 72 min after fertilization; first eleavage-2 cell stage at 5 h and 57 min; morula stage at 8 h and 22 min; blastula stage at 14 h and 26 min; early gastrula stage at 21 h and 42 min; middle gastrula at 24 h and 5 min; late gastrula stage at 29 h and 40 min; neuroembryonic stage at 37 h and 20 min; myomere development at 64 h and 36 min; intestines and anus formed 115 h; thereafter, the eggs hatched out continuously.

Throughout the procedure we were careful to: ( 1) filter the water used in hatching to remove particulate impurities and Cyclopoida; (2) maintain a constant water flow rate or use a pump could to supply oxygen if installed a suitable distance from the eggs to avoid injuring the fry; and (3) disinfect eggs twice daily, morning and night, clearing away moldy eggs to avoid infection of other eggs. Newly hatched fry were 3.1-4.0 mm in total length with a large yolk sac. The body is green, with a pectoral fin. Yolk sac and blood vessels in abdomen could be seen clearly. 14 hours after hatching, the caudal fin began to calcify, 21 hours later, the pigment increased on the head and the tail, with a body length of 5.1-5.7 mm, 40 hours later one could observe the clear contours of the swim bladder, with winding intestines under the swim bladder. 90 hours later the yolk sac disappeared. The body was yellow, black and grey with slim body, and the ability to swim became stronger and the fry more agile, as they began the transit from endogenous to exogenous feeding on natural live feed.

The fry should be fed with the foods they prefer. We fed them yolk twice per day after filtering it through gauze. The dose was about 1/3 of yolk for 50000 of fry. The soya-been milk and miniplankton also can be used. The miniplankton should be filtered by gauze with the size of 40 mu before feeding.

Conclusions:

1. The brood stock of yellow perch could be mono- or polycultured with Chinese local fishes, including silver carp, bighead carp, grass carp, and common carp. Artificial feed and fish meal were used to feed the brood fish and we achieved a spawn-inducing rate of 100%.

2. Carp Pituitary Gonadotrophin, Human Chorionic Gonadotrophin and Lutein Releasing Hormone-analog of common carp all can be used as spawn-inducing agents of yellow perch. The best results were obtained when the three agents were adopted. (the dose of spawn-inducing: CPG: 3mg/kg, HCG: 1500IU/kg, and LH-RH-a 5μg/kg).

3. Natural spawn and artificial insemination of yellow perch spawn-inducing can be done successfully.

4. The eggs can be hatched in cement pools kept rich in oxygen by maintaining a slow flow of clean water or by aerator or air pump. Every fish farm should choose optimal way of breeding according to its specific circumstances.

5. The yolk mini-plankton and soya-bean milk can be used to feed juvenile fish.

The Brood Stocks of 22 groups came from 5 mu polyculture ponds on March 14 and April 6, the others came from a perch monoculture pond.