The Lateral-Line System in the Rio Grande Perch, Cichlasoma cyanoguttatum (Baird and Girard)

Abstract

The lateral-line system of Cichlasoma cyanoguttatum is similar to that of other perciforms but there are many peculiarities. The tubes of the lateralis scales do not make contact with each other but the innervation of the organs in this part of the system is normal. The exter- nal morphology and osteological components of the system are described in detail and compared with that of serranids and centrachids; the text is copiously augmented with illustrations. The lozenge-shaped canal neuromasts are in general like those of sunfishes but much larger. The sensory cells, unlike most of the cells seen in other fishes, bear multiple sensory hairs. All of the supporting cells penetrate to the free surface of the organ and intercellular bridges connect each with the others, thus forming a kind of syncytium. Cichlasoma cyanoguttatum is the only member of the family Cichlidae known to occur naturally in continental United States. Its range extends eastward from the Rio Grande in Texas as far north as the Rio Colorado near Austin. Material for this study was col- lected from the Blanco River, 25 miles northwest of San Marcos and from San Marcos Springs, Hayes County on July 14, 1958. Dr. Kirk Strawn of Lamar Institute of Technology, Beaumont, Texas, assisted in the collecting and Dr. G. A. Moore of Oklahoma State University offered helpful criticisms. I am grateful for their assistance. Several specimens were fixed in PFA3, one of Allen's modifica- tions of Bouin's fluid, and others in 10 per cent formalin. Three of the formalin-fixed specimens were stained by the alizarin method of Hollister (1934). In addition, four large specimens were packed in dry ice and subsequently disarticulated for bone study. Other formalinized fish were dried by means of jets of air and the canal system injected with India ink. Innervation was determined by gross dissection under the lens of a stereomicroscope. The lachrymal bone was chosen for microscope sections because of its constancy and ease of removal. Material for sectioning was decalcified in two per cent hydrochloric acid, embedded in pyroxylin and cut at five microns. Some sections were stained with iron hematoxylin and others wifth Mallory's triple connective tissue stain; all were mounted in picrolyte. Measurements were taken by means of a filar micrometer mounted on a compound microscope. Drawings were made with the assistance of a camera lucida. EXTERNAL MORPHOLOGY In its external appearance the cephalic lateral-line system of