George Katselis

Discrimination of two picarel species Spicara flexuosa and Spicara maena (Pisces: Centracanthidae) based on mitochondrial DNA sequences

A DNA methodology based on PCR and sequencing analysis of the mtDNA 16S rRNA gene was developed for the discrimination of picarel Spicara flexuosa and blotched picarel Spicara maena (Pisces: Centracanthidae). The molecular results indicated that there is a clear discrimination between the two species, as all the individuals of S. flexuosa revealed the same 16S rDNA haplotype while the S. maena haplotype differs in 15 distinct nucleotides.

Development and evaluation of an automated digital image analysis software for obtaining seagrass leaf metrics

Abstract We developed a simple and inexpensive digital image analysis method for measuring leaf area and the length of strapped-shaped seagrass leaves. The method uses specialized software that permits automatic leaf and scale recognition in digital images along with batch image processing. The leaf biometrics of 80 Posidonia oceanica and Cymodocea nodosa leaves were used for the evaluation of the method for accuracy, precision, and speed in comparison to manual measurements. Each leaf was measured 90 times under different combinations of several factors that might affect software estimation. The factors examined included leaf shape, leaf orientation in the image, scale dimensions, image resize, and binary conversion. Estimates of leaf length and leaf area were highly correlated between the new image analysis procedure and manual measurements. Relative error values between the two methods were <10% in 99% of leaf length measures and in 75% of leaf area measures. The factors examined explained <10% of the relative error variance; the remaining variance was mostly attributed to technical issues concerning leaf size and image illumination. The digital method proved to be approximately 2.5 times faster than the manual one.

Yolk-sac larval development of the substrate-brooding cichlid Archocentrus nigrofasciatus in relation to temperature.

In order to conserve and culture the cichlid fish Archocentrus nigrofasciatus, more information about its reproductive biology and its larval behavior and morphogenesis is necessary. Currently, temperatures ranging from 21 to 27 °C are used in ornamental aquaculture hatcheries. Lower temperatures are preferred to reduce the costs of water heating, and 23 °C is usually the selected temperature. However, there is limited information on culturing protocols for ornamental species and most of the information generated on this topic remains scarce. Thus, the present study examines the morphological development of Archocentrus nigrofasciatus during the yolk-sac period up to the age of 100 h post-hatching in relation to 2 temperature regimes used in ornamental aquaculture: a temperature of 27 °C (thermal optimum) and a decreased temperature of 23 °C (thermal tolerance). The results of this study suggest that the 27 °C temperature generates intense morphological changes in yolk-sac development in a shorter period. This has advantages as it reduces the time of yolk-sac larval development, and, thus, minimizes the transition phase to exogenous feeding and maximizes the efficiency at which yolk is converted into body tissues. The present paper provides necessary information to produce freshwater ornamental fish with better practices so as to increase larval survival and capitalize on time for growth.