Cannibalism, stress, and low reproduction in captivity. This list of horrors has all but eliminated the matrinxã (Brycon cephalus) from the group of the fresh water fish most used commercially in Brazil, particularly in those establishments known as pay as you fish. A great help for the solution of this problem came from the results of the studies by biologist Gilson Luiz Volpato, a teacher at the Botucatu Biosciences Institute and at the Aquiculture Center, of Unesp, the State University of São Paulo. He achieved a simple and surprising solution to the problem, putting sheets of colored cellophane over the 60 or 200 liter incubators used in the breeding of matrinchã larvae, providing the fish with a colored environment.
Coloring the water blue, for example, calmed the little matrinchãs down, and brought a 15% decrease in cannibalism. A green coloring increased by 50% the reproduction of this species in captivity. Of the nine females used in the study, eight felt at ease in the green environment, and spawned. As if the improved disposition of the females were not enough, the males also showed an increased volume of semen. In the control group, under natural lighting, only four of the nine females reproduced. “This detail is very important, since all the methodological precautions were taken”, explains Volpato.
The study was carried out over a two-year period, in partnership with a company called Fish-Braz, from Botucatu, which had been having problems breeding this kind of fish. The project, entitled Environmental Coloring as a Facilitator of Reproduction and Reducer of Cannibalism in Matrinxã was part of FAPESP’s Pite, the University-Company Program for Technological Innovation.
The study’s solutions have diminished a deep-rooted habit in this species of matrinxã, whose origin is several rivers in the Amazon Basin. This fish has impressive levels of cannibalism. In the incubator, it has no need of any enemies. A few hours after being spawned, the larvae are already extremely voracious, able to reach a level of 92% to 99% of loss from cannibalism. Quite simply, one larva devours another. And this at a stage in their lives when they measure no more than seven millimeters. From what has been discovered, this behavior lasts no longer than two weeks, but its most intense phase is in the first five days.
In the 80’s, this fish was threatened with extinction in its natural habitat. Besides its natural voracity in its infancy, there were other factors that also contributed towards the problem. The matrinxã is a rheophilic species, which means it migrates in the period of reproduction. Thus, dam construction therefore prevents or hinders this migration. But there are other factors, like riverside undergrowth destruction, and thus favoring silting up and reducing the bankside ponds where the larvae develop, and some manage to escape alive. The growing pollution of the watercourses is also a direct fish killer, when the quality of the water is poor. Predatory fishing, which diminishes the adults specimens, may also have contributed towards this process, since the matrinxã only shows good levels of reproduction from the third year of life.
Worse still, as it is common with these rheophilic species, it is only in the process of migration that the matrinxãs manage to achieve naturally the maturity of their gonads and complete their reproductive process. When they are fished prematurely or poisoned in polluted waters, the salvation of the species, as it is with many freshwater fish, ends up in the hands of researchers and fish breeders. They are now inducing these fish to breed, a p.rocess in which reproduction is stimulated by injecting an extract of carp pituitary, which makes the artificial propagation of the species feasible.
Even so, the results take time, and they depend on a deeper knowledge of various aspects of species behavior, according to the account by researcher Paulo Sérgio Ceccarelli, the author of the essay Cannibalism in Matrinchã Larvae, finished in 1997 at Unesp’s Institute of Biosciences, under the supervision of Professor Volpato.
Part of the hurdles to the commercial raising has been got round by adopting breeding in consortiums, in which the matrinxã larvae live together with larvae of other species and feed on them; the cost is lower and perfectly manageable in profitability terms. At the beginning of the 90s, breeding in consortiums with pacu larvae began to become common practice amongst fish breeders.
However, the difficulties have persisted, because, besides the aspect of inducing hormones, there is the limit period in which this species spawns in the southeastern region of Brazil and the high level of cannibalism in the first few days of life. However, the possibility of a profit makes the breeders struggle on. “Everything that is produced is sold”, explains Volpato, in particular to the main segment popularly known as “pay as you fish” ( artificial lakes or ponds where fishermen pay for their catch) , to which over 80 % of the production is directed. In the state of São Paulo alone there are some 1500 “pay as you fish” ventures.
In comparison with the other species of freshwater fish, the prices paid per batch of a thousand little fish (sold in the young stage, when between 2 and 4 centimeters) tilt the balance in favor of the commercial breeding of the matrinxã. A batch of a thousand of this species costs between R$ 200.00 and R$ 450.00, depending on the time of the year and the region, while fish like the pacu are sold at between R$ 70.00 and 120.00. And on top of that, fishing matrinxã is exciting. “They seem to react in a way that gives the fishermen more pleasure”, says Volpato.
This body reaction is different right from the first hours after the larvae break out. With a little over 6.5 mm in length, they weight in the region of 230 milligrams, they have well developed nostrils and eyes, the opening of the mouth in the vertical direction, corresponding to 15% of the total length of the body, and the digestive tract completely formed. It swims on the horizontal plane, but with spells of intensive opening and closing of the mouth, say the researchers. As Ceccarelli’s essay shows, this degree of contortion of the body and of the jawbone joint, plus the possibility of a large dilation of the belly, makes it possible for it to swallow its prey with some ease.
Dynamics of the strike
With matrinxãs, the predatory capacity is intra and inter species, that is, it eats individuals of its own species and of others. This predatory behavior was carefully studied by Ceccarelli. It shows a consistent sequence: fixation, persecution, approximation, strike, bite, seizure, and swallowing. For a martinxã, size is no obstacle. It devours a slightly smaller rival, or one of its own size. “This behavioral pattern may also be associated with the motor dynamics of the strike, which gives the fish greater speed and, as a result, greater power to surprise its prey”, suggests Ceccarelli.
The setting of correct parameters to diminish cannibalism and increase reproduction among the matrinxã had its origin in earlier studies financed by the CNPq , the National Council of Scientific and Technological Development, with other species of fish. The idea of coloring the water is also based on other studies, non-scientific, of chromotherapy. Vopato chose the colors of blue, green, red and white (transparent) for the experiments, for being those that might interfere with the well-being of these larvae. In the project with Fapesp, Volpato’s hypothesis was that a small disturbance in the well-being of these larvae would make them lessen the aggression shown to their peers, and, with this, cannibalism in this stage would be reduced. And the researcher tried to reduce their well-being by changing in the breeding environment coloring of these larvae, which is the incubators. In the first test, Volpato observed that a blue hue made the survival rate reach 15%, against a percentage of 7% under other conditions.
At the beginning of the work on the project for technological innovation, Professor Volpato had to face another feature of this freshwater fish. “The matrinxã dies easily if handled improperly, in particular if the handling takes place at a temperature out of the species thermal comfort range, which is around 26º C”, he explains. The problem faced by Volpato was that the batch of reproducers purchased died between the transport and the handling to separate them in the tanks. “Only two females and a few males survived.”
It was possible to take the research forward because Fish-Braz swiftly financed the replacement of the reproducers. Other problems popped up, as it is common in research, and CEPTA, the National Center for Research into Tropical Fish, linked to Ibama, the Brazilian Institute of the Environment and Renewable Natural Resources, in Pirassununga, also helped a lot to conclude the study.
But the project of Volpato and Fish-Braz with Fapesp also investigated the coloring of the environment in improving the induction of hormones for the matrinxã to reproduce. As stress is a factor that inhibits reproduction, the researcher sought to find some natural environmental coloring that could have a calming effect on the females.
Green is better
Volpato found out that young matrinxã individuals bred under green coloring are more aggressive when they are transferred to a new environment, compared with those kept with the yellow, blue, red, and white colors. But the researcher did not think that green increased aggressiveness, but rather that the other colors abated aggression. In the new environment, he thought that the animals that had been put in the green environment adapted quicker, and were therefore able to begin to fight in defense of their new territory. This idea gained strength, as the researcher saw that the growth of the animals in the green environment was almost three times greater than in the others.
These results are encouraging an incipient area in fish farming, which is the use of alternative techniques (environment coloring) in steering fish behavior. Volpato believes that, in the case of cannibalism, the proposed technique (blue environment), although still on an experimental basis, may be associated with other techniques that already exist (grouping with pacu and curimbatá (Prochilodus scrofa) larvae), to improve production. In the case of reproduction, the reproducers are optimized and a greater success in the crop is ensured. In addition, it is a simple technique, and one that can be used even in the more modest fish farmers. It may also provide better guidance for the manufacturers of incubators and tanks, when they choose the color for these vessels. Volpato warns that his studies show the effects of the coloring, but he still does not know how much in fact the color or the intensity of the light is the main cause of these effects.
To get an idea of the importance of these studies, the financial return in the crop of just one tank for fish breeding producing young matrinxã runs in the order of R$ 25,000.00 (a small fish breeder has some ten of these tanks). Hence the small percentage of technological advance in production are significant.
Another positive point that Volpato sees in the project with Fapesp is that Fish-Braz is very excited with the development of the work and even intends to create a specific sector in the company for scientific research.
Another important study to be published by Volpato, in conjunction with his pupil for a doctorate, Luciana Jordão, he deals with another species, the pacu, in stress situations. He has shown that this fish recognizes a predator from sight only, and, when it moves away from it, it releases chemical substances in the water that alerts the other members of the group to the danger.
An understanding of the natural mechanisms of these fish, both the pacu and the matrinxã, makes it possible for effective technologies to be created to solve the crucial problems of Brazilian fish breeders.
Gilson Luiz Volpato graduated in Biological Sciences from Unesp in Botucatu. He took both his master’s and doctor’s degree at Unesp in Rio Claro. He completed his post-doctorate studies the Fish and Aquaculture Unit, of the Agricultural Research Organization, at Bet-Dagan, Israel. He is head of the Physiology Laboratory of the Physiology Department of Unesp’s Institute of Biological in Botucatu.