Induced spawning and artificial incubation of Tilapia

Aquaculture, 5 (1975) 315-321 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

INDUCED

SPAWNING AND ARTIFICIAL

SHMUEL ROTHBARD*

INCUBATION

OF TILAPIA

and YOEL PRUGININ

Fish Breeding Farm, Gun Shmuel (Israel) Fisheries Diuision, Extension Service, Ministry

of Agriculture,

Tel Aviv (Israel)

* Present address: 5900-5 Chikko, Tamano City, Okayama, Setonaikai Saibai Gyogyo Center (Japan) (Received October 14th, 1974)

ABSTRACT Rothbard, S. and Pruginin, Y., 1975. Induced spawning and artificial incubation of Tilapia. Aquaculture, 5: 315-321. Methods for induced spaw.ning and artificial incubation of Tilapia nilotica and T, aurea are described. These methods were required for the production, in aquaria, of F, hybrids between the two species. Spawning families were established in long aquaria from which sexually ripe individuals were selected for stripping by their ‘
INTRODUCTION Spawning of Tilapia nilotica and T. aurea in earthen ponds for production of pure and crossbred fry is an established practice in the fish farms of Israel. As a rule, spawning takes place during April and May in shallow ponds stocked with one male to every five females. Three weeks after introduction of the breeding stocks into the spawning ponds the first fry are expected to be seen. Under these conditions a single female may spawn three to four times during one summer. In aquaria, kept at optimal conditions, intra-specific spawning may take place throughout the whole year. This is not the case for inter-specific spawning of T. nilotica and T. aurea. In our laboratory the two species did not interbreed in aquaria, but they appear to have done so on rare occasions (Fishelson, 1966). Establishment of all-male hybrid broods of Tilapia (Rothbard and Pruginin, 1972) requires single pair matings of T. aurea males with T. nilotica females Reprint request please address to: Professor R. Moav, Department University of Jerusalem, Jerusalem (Israel).

of Genetics, The Hebrew

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under controlled conditions. Since this could not be accomplished in aquaria in the natural way, we decided to adapt a method of induced spawning, which succeeded in several fish species (Shehadeh, 1973). Since 2’. nilotica and T. aurea are both mouth breeders (Fishelson, 1966) we also had to devise a method for artificial incubation of the eggs (Nussbaum and Chervinsky, 1968; Dadzie, 1970 a and b). The procedures of induced spawning and artificial incubation that lead to successful production, in aquaria, of F1 hybrids of the two species, are described in this paper. CONDITIONS REQUIRED FOR INTRA-SPECIFIC SPAWNING IN AQUARIA

Previous experience had shown that the following conditions may lead to satisfactory natural intra-specific spawning of T. aurea and T. nilotica in aquaria: (i) Temperature. Reproduction activity of Tilupiu begins at 22 “C, and the optimal temperature range is 25-29 “C. In this temperature range, spawning can be easily accomplished throughout the whole year. (ii) Food. Breeding stocks need to be fed with a fodder rich in proteins and vitamins since aquarium water is poor in plankton, algae, etc. - the natural food of Tifapia. (iii) Light. Daily illumination of 12-14 h with a 100-W fluorescent bulb suspended 50 cm above the water surface of the aquaria yields satisfactory results. (iv) Water. Since Tilapia require clear water for spawning, excretions and food remnants have to be removed by emptying and cleaning the spawning aquaria every 2-3 weeks. For the duration of the cleaning operation the fish may be kept in temporary containers. After cleaning, the aquaria should be refilled with water of the same temperature. The change of water often triggers sexual activity. The aquaria should also be aerated. (v) Aquaria. The spawning aquaria should be long. The ones we used had the following dimensions: length 200 cm, width 50 cm, and height 40 cm. The greater length permits the territorially protective male to “stake out” a territory for his nest, and it minimizes interference by non-participating females. (vi) Spcrwning families. Spawning families should be established prior to sexual maturity, i.e., when the fish are 4-5 months old, and reach a body weight not exceeding 50-100 g. When larger fish, taken from ponds, are introduced into aquaria they are very agressive - the male towards the females and even the females among themselves, and their mutual attacks frequently result in mortality (Mires, 1974). We established “spawning families” by stocking the aquaria with 50 small (2-5 g) fry of a single species. As they grew, the less developed ones were culled till only one selected and well developed male plus seven to ten selected females were left. These selected groups we defined as “spawning families”.

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MATING IN AQUARIA

The mating process begins when the male chooses the most developed female and drives off the rest of the females to the furthest corner of the aquarium. The whole process of spawning and fertilization lasts up to 2 h, and smaller females complete it more quickly than bigger ones. However, the mating is preceeded by a period of courtship that may sometimes last several days. Immediately after spawning, the female leaves the “nest” area of the aquarium with the already fertilized eggs in her mouth. Throughout the incubation period and until the hatched fry complete the absorption of the yolk sac, the females do not eat because their mouths are full - first with eggs and afterwards with fry. Soon after departure of the female from the “nest”, the male is ready to choose and mate with another female. The relatively small volume of water in the aquarium, the maintenance of optimal conditions and the presence of several females continuously excited by the sexual activity of the mated pair keep the male in a permanent state of sexual excitement so that it may mate throughout the whole year. Similarly, soon after the females complete the incubation and nursing of the young fry they are ready for a new round of mating. During the period of courtship and display the body pigmentation is highly intensified. The type and shades of pigmentation of T. nilotica and T. aurea are different in several respects as is summarized in Table I. The males’ pigments are much stronger and more typical of the species. Pigmentation of a courted or mated female is the next most intense, while other females have variable shades of dark-dull coloration without the bright and reddish colors. TABLE I Sexual display pigmentation

of T. aurea and T. nilotica

Area of pigmentation

T. aurea

T. nilotica

Whole body Edges of the dorsal fin Head Belly Caudal fin

metallic blue-green red metallic green light with red spots red-purple

light orange to purple black red-purple red black strips

PRODUCTION

OF INTER-SPECIFIC

HYBRIDS

IN AQUARIA

Choice of fish for stripping and artificial fertilization requires both males and females that are just about ready for natural spawning. They may be identified by the following external characteristics: (i) Intense display pigmentation. (Table I). This characteristic is particularly conspicuous and easy to identify in males. (ii) Swollen genital papilla (Fig. 1A and B).

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(iii) Erected scales caused by the stretching and swelling of the body during courting. The above indicators of sexual ripeness and readiness to spawn are of particular importance in females because only females that show all the three “on heat” signs simultaneously, can be stripped. When a 12-h daylight schedule is maintained the females are ready to be stripped after lo-12 h of light. Thus, by manipulating artificial lighting the experimenter can direct the time of stripping to suit his own convenience.

319

F bllen genital papilla Fig. 1. A: Swollen genital papilla of an “on heat” male Tilapia. B: Swc ripping of a male of an “on heat” female Tilapia. C: Stripping of a female Tilapia. D: St] arm to a % h.p. !f’ilapia. 33: Plastic incubators placed on a shelf attached by an acentric :y. low speed electric motor. F: Wire cages in a pond for nursing Tilhpia fl

320

Stripping and artificial fertilization A selected female is removed from the aquarium and wrapped in a towel (Fig. 1C) in order to reduce damage to her scales. With a light squeezing of the abdomen the eggs of a ripe female are easily stripped into a container. After stripping, the female may be returned into her aquarium, and a ripe male of the second species is chosen and stripped into the same container in the same manner (Fig. 1D). The eggs and the milt are stirred with a feather for 1-2 min, then a small quantity of about 10 cm3 physiological solution is added while stirring is continued for another 2 min. The fertilized eggs are now washed under a slow current of tap water to remove all excess matter that may contaminate the fertilized eggs. The individual spawners may be marked by colored plastic tags that are shot into their back, or tail muscles by a tagging gun (Thorson, 1967; Dell, 1968). Coded cuts along the margins of the tags may be used for individual identification. Artificial incubation and nursing Incubation was carried out in small (5 1.) plastic containers filled with tap water to about three-quarters of their volume. These containers were placed on a shelf attached by an acentric arm to a ‘/4 h.p. low speed electric motor. A suitable transmission further reduced the number of revolutions to 40 rpm (Fig. 1E). This system created a back-forth movement of about 10 cm of the shelf. The constant shaking of the water and the eggs, which is similar to the movement of eggs in the female’s mouth, ensured sufficient oxygen supply needed for successful hatching. At temperatures of 25-27 “C the eggs hatch 50 h after spawning. The larvae may be kept on the shaker for another 8-10 days till the yolk sac is completely absorbed. Daily inspection and removal of spoiled eggs (unfertilized or dead embryos) during the incubation is essential since the presence of spoiled eggs may cause infection and loss of the whole spawn. Whenever the water in an incubating container becomes turbid due to decomposition of spoiled eggs the container should be refilled with fresh water and the eggs should be washed under a slow current of fresh water of the same temperature. After incubation and absorption of the yolk sac the fry may be transferred to ponds, to larger containers or to wire cages placed in ponds (Fig. IF). The fry may be kept in these cages until they are sufficiently large for their sex to be distinguishable by inspection. ACKNOWLEDGEMENTS

We are indebted to Professor R. Moav and to .Dr G. Wohlfarth for their valuable advice in planning the experiments and help in preparation of the manuscript.

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REFERENCES Dadzie, S., 1970 a. Preliminary report on induced spawning of Tilapia aurea. Bamidgeh, 22(1):9-13 Dadzie, S., 1970 b. Laboratory experiment on the fecundity and frequency of spawning in Tilapia aurea. Bamidgeh, 22(1):14-18 Dell, M., 1968. A new fish tag and rapid cartridge fed applicator. Trans. Am. Fish. Sot., 97(1):57-59 Fishelson, L., 1966. Cichlidae of the genus Tilapia in Israel. Bamidgeh, 18(3-4):67--80 Mires, D., 1974. On the high percent of Tilapia males encountered in captive spawnings and the effect of temperature on this phenomenon. Bamidgeh, 26(1):3-11. Nussbaum, M. and Chervinsky, J., 1968. Artificial incubation of Tilapia nilotica. Bamidgeh, 20(4):120-124 Rothbard, S. and Pruginin, Y., 1972. Hybridization of two Tilapia species to obtain males. Fish. Fish Breed. Isr., 7(2-3):10-13 (in Hebrew) Shehadeh, Z.H., 1973. Induced breeding techniques. A review of progress and problems. EIFAC workshop on controlled reproduction of cultivated fishes. May 21st-25th, 1973. Hamburg, Federal Republic of Germany Thorson, K., 1967. A new high speed tagging device. Calif. Fish Game, 53(4):289-292