There are, in aquaria, coldwater fish species and tropical fishes, the guppy being one of the latter (Bud 2002). However, the guppy has the ability to survive in cooler waters that would certainly kill most tropical fishes (Mag & Bud 2006; Mag et al 2006; Păsărin et al 2007). In their paper “Detection of a low temperature-resistant gene in guppy (Poecilia reticulata), with reference to sex-linked inheritance”, Fujio et al (1990) reported an X-linked gene, responsible of low water-temperature resistance in guppy. Sixteen years later, in the paper: “Effect of temperature on sex ratio in guppy Poecilia reticulata (Peters 1860)”, Karayϋcel et al (2006) emitted the hypothesis according to which the same gene could be involved in high water-temperature resistance of guppy. In that moment, the above mentioned gene became a very important one, especially for guppyculture and generally for aquaculture, because of extrapolation possibility of these studies to many cases of economical and commercial important species.
In a CEEX-Biotech project (Research of Excelence Program, no 140/2006) our team tested a number of 150 random primers (Biosearch Technologies Inc.) in order to identify RAPD markers which could be associated to low temperature resistance in guppy. However, 71 random primers have not amplified DNA at all, 35 primers have not generated DNA polymorphisms, and 44 of them generated (more or less) polymorphisms. Only one random primer (no 77) was associated with cold tolerance (5'd(CCAACGACCA)3'; see Figure 1) in the Red Blond variety.
Figure 1. http://www.bioflux.com.ro/docs/vol1/2008.1.99-110.pdf Polymorphism, induced by the primer 77, associated with cold tolerance in the Red Blond guppy. The supplementary DNA fragment of 878 bp is associated to coldwater resistance (11-20), and the supplementary fragment of 839 bp is associated to coldwater sensitivity (1-10).
UPGMA (Unweighted Pair Group Method with Arithmetic Mean) was used to illustrate the two distinct fish clades: coldwater resistant group and coldwater sensitive group (see Figure 2). However, using the same primer (77), our repeated RAPD analyses failed to discriminate between coldwater resistant and sensitive individuals in other guppy strains. The primer was useless even for identification of coldwater resistant fishes from an FB generation whose father and both grandfathers were Red Blond males.
After the identification of coldwater resistant individuals, the next step forward of the research in the project CEEX 140/2006 was obtaining of a homozygote guppy strain for coldwater resistance gene, and this was possible due to the X-linkage of Nigrocaudatus II (Ni) which was used as color marker gene. The breeding program of the research was based on a ♂Red Blond X ♀Half-Black Black cross, followed by a backcross of F1 females with the initial Red Blond male.
One hundred of individuals, homozygote for the coldwater resistance gene, were further tested for resistance to heat. The results indicated a significant higher tolerance to heat of these ones compared to control lot. These data supported the hypothesis of Karayϋcel et al (2006) and indicated the common identity of coldwater resistance gene and heat tollerance gene. This X-linked gene (for resistance) seems to encode a protein with multiple role, a molecular chaperone, a protein formally included in HSPs group. We concluded at least some of the HSPs were involved in both coldwater resistance and heat tollerance, modulating animal metabolism under different environmental conditions.
Figure 2. http://www.bioflux.com.ro/docs/vol1/2008.1.99-110.pdf The two phenotypic distinct groups illustrated by UPGMA (when genomic DNA was amplified with the primer no 77).
Bud I., 2002 [Aquariophilia]. Academicpres, Cluj-Napoca, Romania. [in Romanian]
Fujio Y., Nakajima M., Nagahama Y., 1990 Detection of a low temperature-resistant gene in the guppy (Poecilia reticulata), with reference to sex-linked inheritance. The Japanese Journal of Genetics 65(4):201-207.
Karayücel I., Ak O., Karayücel S., 2006 Effect of temperature on sex ratio in guppy Poecilia reticulata (Peters 1860) Aquaculture Research 37:139–150.
Mag I. V., Bud I., 2006 Environmental factors’ impact upon sex-ratio in guppies (Poecilia reticulata Peters, 1859). In: 41st Croatian and 1st International Symposium on Agriculture - Opatija, pp. 523-524, Osijek, Croatia.
Mag I. V., Bud I., Petrescu R. M., 2006 Sex-dependent mortality in the guppyfish. Acta Ichtiologica Romanica 1:153-164.
Păsărin B., Gorgan L., Bura M., Botha M., Petrescu-Mag I. V., 2007 The invasive potential of the exotic guppyfish (Poecilia reticulata Peters 1859) in temperate zone. Studia Universitatis Babes-Bolyai, Ambientum 1-2:179-187.