The life history parameters of the speckled skate, Raja polystigma were investigated through the vertebral centra analysis. A total of 183 specimens (97 females, ranging from 11.5 to 59 cm in TL and 87 males with TL among 11.8 and 52.1 cm) were caught during experimental (MED.I.T.S.) and commercial trawl surveys in the period 2012-2013. The vertebrae centra extracted from a subsample of at least 10 individuals, belonging to different size classes, were employed to state which technique among the EDTA decalcification process, the analysis of unstained centra and two staining methods (Alizarin Red and Silver Nitrate), allowed a better band enhancement. The unstained centra and those treated with Alizarin red provided a better band visibility, so these techniques were applied to the entire sample. The annuli counts were carried out by two different readers and repeated two times for both treatments. The obtained readings showed a good reproducibility with both techniques, even though band counts executed on stained centra (PA = 86.8, %Cv = 7.0, IAPE = 5.177) seemed slightly more accurate than those made on unstained samples (PA = 86.6, %Cv = 7.9, IAPE = 5.96). These differences were stastically proved through the Kolmogorov-Smirnov test (p < 0.005). The von Bertalanffy Growth Functions were determined for both stained and unstained samples (respectively Linf = 75.93, s.e. = 7.29; k = 0.10, s.e. = 0.02; t0 = -2.29, s.e. = 0.25; Linf = 74.97, s.e. = 7.35; k = 0.10, s.e. = 0.02; t0 = -2.16, s.e. = 0.24). Given these results is recommended to apply the Alizarin red staining methods for future age estimations, through vertebral centra, of the speckled skate, before trying other more expensive and less time-efficient techniques.
Life history parameters of the small Mediterranean-endemic skate, Raja polystigma Regan 1923, from Sardinian seas
BELLODI, ANDREA;MARONGIU, MARTINA FRANCESCA;Mulas A;VITTORI, STEFANIA;
2014-01-01
Abstract
The life history parameters of the speckled skate, Raja polystigma were investigated through the vertebral centra analysis. A total of 183 specimens (97 females, ranging from 11.5 to 59 cm in TL and 87 males with TL among 11.8 and 52.1 cm) were caught during experimental (MED.I.T.S.) and commercial trawl surveys in the period 2012-2013. The vertebrae centra extracted from a subsample of at least 10 individuals, belonging to different size classes, were employed to state which technique among the EDTA decalcification process, the analysis of unstained centra and two staining methods (Alizarin Red and Silver Nitrate), allowed a better band enhancement. The unstained centra and those treated with Alizarin red provided a better band visibility, so these techniques were applied to the entire sample. The annuli counts were carried out by two different readers and repeated two times for both treatments. The obtained readings showed a good reproducibility with both techniques, even though band counts executed on stained centra (PA = 86.8, %Cv = 7.0, IAPE = 5.177) seemed slightly more accurate than those made on unstained samples (PA = 86.6, %Cv = 7.9, IAPE = 5.96). These differences were stastically proved through the Kolmogorov-Smirnov test (p < 0.005). The von Bertalanffy Growth Functions were determined for both stained and unstained samples (respectively Linf = 75.93, s.e. = 7.29; k = 0.10, s.e. = 0.02; t0 = -2.29, s.e. = 0.25; Linf = 74.97, s.e. = 7.35; k = 0.10, s.e. = 0.02; t0 = -2.16, s.e. = 0.24). Given these results is recommended to apply the Alizarin red staining methods for future age estimations, through vertebral centra, of the speckled skate, before trying other more expensive and less time-efficient techniques.
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