The taxonomy and growth of a Crypthecodinium species (Dinophyceae) isolated from a brackish-water fish aquarium

An unidentified heterotrophic dinoflagellate found growing in abundance in a brackish-water fish aquarium was isolated and serially cultivated using a fish cell line as the food source. Prominent characteristics of this dinoflagellate included a cingulum that did not fully encircle the motile cell, cell division in non-motile cysts, and a theca composed of thin but structured plates. Morphological analysis of flagellate cells by scanning electron microscopy revealed a Kofoid thecal plate tabulation of 4’, 4a, 4’’, ‘X’, 5 or 6c, ?s, 5’’’, 1p, 1’’’’, most consistent with the original description of Crypthecodinium setense Biecheler. This Crypthecodinium species exhibited a high maximum division rate (3.2 divisions day–1) and cell yield (>106 cells ml–1) when fed cultured fish cells. Small sub-unit rDNA phylogenetic analyses supported relatedness with a previously studied Crypthecodinium-like dinoflagellate, but a significant difference in aligned gene sequences was found. This study provides the first clear demonstration of the plate tabulation of a Crypthecodinium speciessince the original description over 60 years ago, allowing the original morphological conception of Crypthecodinium to be linked with molecular phylogenetic information.