HATCHERY PRINCIPLES AND PRACTICES
1. BREEDING BEHAVIOR
The male tilapia’s goal in life once he reaches breeding age is to establish a territory that he can defend and to attract into his territory as many females as possible. The male tilapia seeks females who are ready to drop eggs for him to fertilize and to keep out of this territory any tilapia or other fish that is not ready to breed with him.
The female tilapia’s biological goal is to reach breeding maturity. She then searches for a suitable male who is able to keep other fish out of his breeding territory while they are breeding.
In natural ponds, dams or rivers the male generally chooses a site to establish his territory up against a barrier of some sort such as the edge of the pond bank, a tree stump, an outcropping a large rock or anything that allows him to restrict the area which he will need to defend while undergoing the breeding ritual. When he finds a suitable territory, the male will start by chasing out any other fish and then he will attempt to dig a shallow bowl shaped hole in the mud, sand, gravel or other substrate where he has chosen his territory.
The size of the territory he will usually choose to defend is generally 2 to 4 times his body length in diameter in a circle or semicircle if he is successful in establishing his territory against a natural barrier. The actual size depends also on visibility. The pit he digs is formed by scooping out a mouthful of the substrate and spitting it out over the top edge of what is to be his spawning site until he has created a pit with a diameter of about 1.5 times his body length.
The size of his territory and of the pit in its center is important to understand because we are trying to create in our breeding tanks acceptable substitutes for these areas.
The breeding follows a very precise pattern with the male first establishing a territory, which in the case of controlled breeding we help to establish by placing a flowerpot in the breeding. Then, when a female is ready to breed, she will swim into the “arena” the male is defending, and they will do a shake rattle and roll sort of dance while circling each other.
When she is properly courted, the female will lay 3 to 5 eggs at a time in the center of the male’s territory, usually in the flower pot, and then she will swim a little distance away.
The male will swim over the eggs and fertilize them, then she will return and pick them up in her mouth and repeat the dance with the male while they circle each other head to tail wriggling and vibrating the whole time. She will often on this occasion suck at the area of the sperm tube as if to draw extra sperm to insure fertilization of the eggs.
When they have done this for a minute or so she will return to the center of the pit and lay more eggs, and so on until she has a full mouth of fertilized eggs.
The number of eggs the female produces is related to several factors.
The most important is her size in grams and her condition in terms of being well fed. The female mossambica for instance start breeding at 20 to 30 grams and continue up to and over 1,000 grams. A well-fed healthy female can lay one to two eggs per breeding for each gram of weight she has attained. This means that even a small 30gram female can produce as many as 50 or more eggs per breeding and up to 2,000 or more when she is fully-grown.
The male and female continue their spawning until the female has a full mouth and this can take from 3-0 or 40 minutes to 2 or 3 hours for a large female. Once she has these eggs in her mouth she will leave the breeding area and join the other females in an area of the pond or tank where she is out of sight of the male. She must be able to do this, as he will continue to harass her as long as she remains in the breeding area.
Once she has left the area she will continue to hold the eggs for 7 to 10 days depending on how warm the water is.
During the incubation process she slowly and continuously rolls the eggs gently to keep them well oxygenated and clean. The female tilapia is capable of telling sick or dead eggs from healthy live eggs and swallows any that are not right.
The fertilized eggs begin development almost immediately after the female picks them up in her mouth and within 48 hours at 290C, the beginnings of eyes and tails can be seen on the eggs.
By the fourth day the fry begin to resemble small fish attached to little yellow balls, which are the egg sacks. These are called appropriately egg sac fry, and usually by this stage if separated from the mother are easy to keep alive.
By the fifth day the fry can swim and navigate well enough to be released by the mother for brief excursions out into the world. At first she lets them out for a brief swim and sucks them back in within a few minutes.
By the sixth day she allows them to browse on bacteria, algal, and fungal growths on the surface of plants or walls. While the fry are out the mother tilapia keeps a sharp eye out for any intruders such as other fish and will aggressively chase them away if they approach the area where the fry are feeding.
If she perceives any danger she will signal the fry by a sideways wiggle of her body and an open mouth at which signal the fry will immediately swim towards and into her mouth. When this is viewed it looks like a film in slow motion reverse where she just spit out a mouthful of tiny pebbles.
The older the fry get, the longer the time the mother allows them to spend outside and by the tenth day she will often no longer tend them or allow them oral sanctuary.
It is also true that the older the fry are when the mother is disturbed, the more likely she is to spit them out to fend for them if she feels her life is in danger.
3. BREEDER MANAGEMENT
Each day after the breeders are set up in the tanks we need to observe each of the females and the male to be sure that they are healthy and active. One thing we need to watch for is damage to the skin and fins of the females from the male’s constant harassment. If the females show signs of sluggishness or there are obvious sores or skin lesions and the male is chasing them to distraction sometimes they need to be separated until the females are healthy and ready for breeding.
Another possibility is to place into the aquarium rocks with holes in them or pieces of plastic pipe with openings big enough for the females but too small for the males. This will give the females a place to hide if they need it.
3.1 Breeder Clues
If the male begins dancing around a female and she joins in the dance there is a good chance they will breed soon. Once they have bred, the female will have a mouth full of eggs and will not show much interest in eating.
When a female is observed in that state a note should be made and then in three or four day’s time she should be gently removed from the aquarium and placed in another aquarium until her eggs have developed into free-swimming fry.
The best way to do this is to take two 20cm by 20cm nets and very slowly herd her into one. Then, gently hold the net against the side of the aquarium and bring it up over the side and transfer her immediately into a bucket with water from the aquarium. Quickly transport the female and pour her and the water into the waiting aquarium.
The nursery aquarium should have water at the same temperature and from the same source as the breeding aquarium.
3.2 Post Breeding Behaviour
Tilapia males in general are very aggressive and territorial. To a certain extent, mother tilapia also becomes territorial for a period of time after breeding.
Besides the obvious full mouth, the female develops a dark marking on her forehead and often darker vertical stripes on her body when brooding eggs. She also becomes more sensitive to many things and can be upset rather easily.
Unbred females also have personalities which appear to border on jealousy in that they often will swim forcefully into a pregnant mother and make her spill some of her eggs. They will then often eat the eggs. Whether this is just a way to get a free meal or a sort of jealous attack to insure lower survival of the other female’s eggs is difficult to analyze. The males can also cause a bred female more difficulty by chasing her aggressively after she is finished breeding.
The unbred females do not always bother the bred females. The males may in some cases actually share the brooding behaviour with the female by taking some of the eggs into their mouth and rolling them as the female does until the fry are free swimming. Females in the tank that also have bred, may, if the female drops some eggs, actually pick them up and adopt them with her own brood. Many times in large group breeding tanks I have found both eggs and fry in the mouth of the same female.
I have also witnessed a single male breeding simultaneously with four different females. As each female dropped her eggs in his nest site, the male fertilizes them and then each of the females would move in and pick up some of the eggs. Understanding which type of behaviour a female will practice is not always easy. Less than one set of circumstances the same fish may exhibit entirely different behaviour than under another set.