The West African dwarf cichlid Pelvicachromis taeniatus has been found to have extraordinarily long sperm.
Scientists from the Institute for Evolutionary Biology at the University of Bonn, Germany, used scanning electron microscopy to analyse the sperm of Pelvicachromis taeniatus for intraspecific variation.
The study revealed that the size of sperm in Pelvicachromis taeniatus varied from male to male, with a mean size of nearly 70 micrometres - the longest so far recorded in any cichlid species.
For more information see the paper: Thnken T, Bakker TC, Kullmann H (2007) - Extraordinarily long sperm in the socially monogamous cichlid fish Pelvicachromis taeniatus. Naturwissenschaften, 2007, June; 94 (6): 489-491.