Dictionary of Ichthyology  

spleen = an elongate element of the viscera lying on the posterior dorsal surface of the fundic part of the stomach, concerned with production and maintenance of blood cells. Deep red, almost black, in colour in teleosts.

Guts of Protopterus from Kingsley's "Textbook of Vertebrate Zoology, 1906. C = caecum, G = gall bladder, HV = hepatic vein, L = liver, O = oesophagus, OD = oviduct, PV = pyloric valve, R = rectum, RD = renal (mesonephric) duct, S = stomach, SP = spleen, SV = spiral valve, V = vent. Photograph by Brian W. Coad.

Canadian Museum of Nature