|
|
Faktory ovplyvňujúce nástup pohlavnej dospelosti u rýb a možnosti skrátenia generačného intervalu - prehľadová štúdia
GARAYOVÁ, Margaréta
The aim of the this thesis was to develop a comprehensive overview study on the onset of sexual maturity, the factors that affect the onset and the possibilities of shortening of generation interval. Sexual maturity can be understood as a trait, resp. phenotypic expression, with individuals undergoing puberty before reaching adulthood. Puberty in fish is very important for farmers or breeders, as it affects a number of important parameters. The onset of puberty is influenced by many factors, either internal or external. Internal factors include fish species, genetic predisposition, health and fitness condition, the size and age of fish, sex of fish, and most importantly, the endocrine system. Based on the role of sex, we can state that in most species of fish in the Czech Republic and Slovakia, females mature later than males. The fact that individuals are sexually mature points out the functionality of the brain-pituitary-gonadal axis, which role is indispensable. GnRHs (gonadortropin-releasing hormones) or otherwise so-called hormone triggers with their effect on the pituitary gland and the secretion of LH (luteinizing hormone) and FSH (follicle-stimulating hormone), which further affect the gonads, are the center of this axis. Another gland with internal secretion that influences the onset of puberty is the pineal gland with the hormone melatonin. There are many external factors, but the thesis focuses on factors influencing the onset of sexual maturity of our fish and these are water temperature and photoperiod. From the obtained information, we can claim that in carp fish the key factor is the temperature, whereas in salmonid fish it is the photoperiod. For perch fish, this is still not clear. Taking into consideration carp fish, we can shorten the generation interval with a constant higher temperature. On the other hand, in the case of perch (Perca fluviatilis), we can achieve the shortening of the generation interval by shortening the photoperiod simultaneously with the decreasing of the temperature at the right time. Concerning a two-year old pikeperch (Sander lucioperca), we can achieve the same result at a temperature of 12 ° C for the period of three months. In the case of rainbow trout (Oncorhynchus mykiss), early maturation may be best achieved by continuous light in the spring followed by a sudden reduction of the photoperiod together with an increased temperature. In the case of atlantic salmon (Salmo salar), brook trout (Salvenilus fontinalis) and artic charr (Salvenilus alpinus), continuous fotoperiod causes a delay in puberty, however, the increased temperature has a stimulating effect on the onset of puberty for them, too. To sum up the gained information, I conclude that even though one factor may play a primary role on the maturation, other factors also have an impact, sometimes even significant. By manipulating with the above mentioned and other factors, we can achieve a shortening of the generation interval in our fish, which may be the goal of breeders in the Czech Republic and Slovakia.
|
guest ::
