The body of most fishes is fully covered by scales that typically form tight, partially overlapping rows. While some of the genes controlling the formation and growth of fish scales have been studied, very little is known about the genetic mechanisms regulating scale pattern formation. Although the existence of two genes with two pairs of alleles (S&s and N&n) regulating scale coverage in cyprinids has been predicted by Kirpichnikov and colleagues nearly eighty years ago, their identity was unknown until recently. In 2009, the ‘S’ gene was found to be a paralog of fibroblast growth factor receptor 1, fgfr1a1, while the second gene called ‘N’ has not yet been identified. We re-visited the original model of Kirpichnikov that proposed four major scale pattern types and observed a high degree of variation within the so-called scattered phenotype due to which this group was divided into two sub-types: classical mirror and irregular. We also analyzed the survival rates of offspring groups and found a distinct difference between Asian and European crosses. Whereas nude × nude crosses involving at least one parent of Asian origin or hybrid with Asian parent(s) showed the 25% early lethality predicted by Kirpichnikov (due to the lethality of the NN genotype), those with two Hungarian nude parents did not. We further extended Kirpichnikov's work by correlating changes in phenotype (scale-pattern) to the deformations of fins and losses of pharyngeal teeth. We observed phenotypic changes which were not restricted to nudes, as described by Kirpichnikov, but were also present in mirrors (and presumably in linears as well; not analyzed in detail here). We propose that the gradation of phenotypes observed within the scattered group is caused by a gradually decreasing level of signaling (a dose-dependent effect) probably due to a concerted action of multiple pathways involved in scale formation.
Successful artificial propagation of black scorpionfish (Scorpaena porcus), in captivity is reported for the first time. Broodfish were collected from the Adriatic Sea after the natural spawning season. Maturation stage of the gonads was determined using histological analysis. Broodfish were kept in two 700-L aquaria within a recirculation system and held under controlled conditions. Fish were stimulated to reach pre-ovulatory stage by weekly IP injections of common carp pituitary at 3mg.kg-1 and the speciments showing soft and swollen abdomen were induced to ovulate by 6mg.kg-1 CP. Frequency of ovulation and pGSI of the females were recorded. The mean pseudo gonado-somatic index (pGSI) reached 29% and the average egg number per stripping ranged 5-6000. The dry fertilisation method proved to be more efficient than the wet method. Fertilised eggs, which floated on the water surface in gelatinous mass, were incubated in a fine net cage. Fry hatched out 53-59 hours post-fertilisation and began exogenous feeding three days after hatching at 20°C. This method could be adapted to the largescaled scorpionfish (Scorpaena scrofa L.), an endangered close relative, which is a commercially valuable candidate species for marine aquaculture.
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