Aquiculture Biotechnology

With financing of a Fondef Project, a team of researchers from the department of Oceanography is working on the optimization of the cultivation technology for the mussel Choromitylus chorus in its diverse stages to promote the development of its industrial activity and strengthen its exportation potential.

An important part of this initiative– that is based in the University’s hatchery in the Marine Biology Station in Dichato – is oriented at solving, using biotechnological techniques, a problem that has reduced the viability of this resource’s foreign commercialization: the female’s gonads brownish-black color produces disgust in the consumer. To solve this problem, the researchers are striving to increase the percentage of the male exemplars in cultivation and/or lighten the color of the female gonads. Three alternatives have been planted to solve this problem: selective crossing with lighter individuals, hormone treatment to induce a sex change, and chromosome manipulation. The first line of research was oriented towards researching different populations throughout the country to identify lighter-colored individuals. These individuals would then be used to obtain through successive crossings over several generations, lightercolored organisms. Population analysis, however, found little difference in tonalities, and this area of intervention was abandoned.

Hormonal treatment Animal and vegetal substances, such as the hormones contained in the masculine mussel gonads, have been tested to induce the formation of males. The hormonal treatment is applied during the first development stages, before sexual differentiation, at a size between 2 and 2.5 centimeters.

In the first tests, the direct injection of substances was rejected for being highly invasive and the use of vegetal products was rejected for its toxicity. The best results have been obtained with animal and the mussel’s own hormones, which are administered through periodic bathes. The greatest difficulty in the case of their own hormones lies in the large number of adults that need to be squeezed to extract the hormones. Tests with androgenic substances, which are used in humans, have also been performed, to increase the masculine expression.

Triploid and neo-male organisms In the area of genetic manipulation, two paths have been defined that are based on a detailed knowledge of the species’ chromosome characteristics: the use of triploid individuals (with three sets of chromosomes) and the generation of neo-males through gynogenesis.

The triploid produces, between 98 and 99%, asexual beings with stunted gonad development, concentrating most of their energy in tissue production, which implies greater growth rates and, in the case of this mussel, the disappearance of the brown color from the female gonads.

The triploid intervention takes places at the moment of fecundation. In the natural process of the bivalves, the masculine gamete arrives with a chromosome set, while the ovum comes with two. When the sperm enters the ovum, it liberates two polar corpuscles, forming a
haploid cell that fuses with the male gamete’s nucleus, generating a diploid individual.

With the use of chemical substances, which have been successfully applied in oysters and scallops, the expulsion of the second polar corpuscle is avoided.

In this way, the organisms remain with three sets of chromosomes, two supplied by the female and one by the male.

The second alternative in chromosomal management consists in the generation of gynogenetic organisms, where only the maternal DNA
intervenes. The technique consists in eliminating the genetic material of the masculine gametes by ultraviolet radiation treatment. Without their DNA, the sperm, when united with the ovule, only fulfills the inductor function of cellular division, where diploid restitution is necessary to avoid the expulsion of the second polar corpuscle. As a result, diploid individuals of feminine character are generated, which are subsequently submitted to hormone treatments for their masculinization.

The definitive results of these experiments will be confirmed when the individuals reach the size of 5 centimeters.