Abstract
The visual system of Teleost fishes has a wide range of adaptations. The eye has suffered modifications, mainly towards better sensitivity and visual resolution according to specific environmental conditions. In that way, this organ is so important for survival. In spite of being the most commercialized Orinoquia species, and one of the most important ornamental fish worldwide, there are almost no studies on the communication systems of P. axelrodi (including vision). We studied the eye in ten individuals of P. axelrodi, with a mean total length of 2.7 cm (SD = 0.2, n = 20). We measured eye relative size (TRO) after sacrifice. Heads were processed for hematoxylin-eosin, and 8 microm thick sections were obtained. Images were digitalized for histological identification and morphometrics. The relation between TRO and body length was 9.8% (SD= 1.1, n= 20); lens was spherical with a relative size of 64.3% (SD = 4.9, n = 20). Rete mirabilis choroid was composed mainly by capillaries, while sclera was composed of cartilaginous tissue. Retina with eight layers and two membranes. An areae centrales was observed in the posterior retina. Iris covered by a simple cubic epithelium. Cornea of endotelial tissue with two membranes. Pupil almost circular, with a naso-caudal elongation. Measures of retina thickness were as follows: lateral retina 144.5 microm (SD = 5.4, n = 20), temporal retina 210.4 microm (SD = 14.8, n = 20). Lens measurements were: dorso-ventral 759.6 microm (SD = 31.7, n = 20), antero-posterior 763.4 microm (SD = 30.7, n = 20). Cornea thickness was 27.6 microm (SD = 4.3, n = 20); iris thickness was 18.9 microm (SD = 1.9, n = 20); rete mirabilis choroid 22.2 microm (SD = 3.2, n = 20) and sclera: 15.9 microm (SD = 1.2, n = 20). This species has a typical Teleost eye conformation. The retina was thicker in the posterior area, probably related to the presence of neuron groups. This modification allows for a better sharpness and visual resolution. The TRO, areae centrales in the retina, and thin cornea, suggests the need of a well developed visual system resulting from a predatory diet.
Highlights
P. axelrodi pertenece al orden de los Characiformes, que es el grupo más representativo en número de especies en la Orinoquía Colombiana con el 15.69% del total de especies ornamentales de interés comercial (Mancera y Álvarez 2008)
Según registros de captura y comercialización de peces ornamentales en Puerto Carreño e Inírida (Ramírez et al 2001), P. axelrodi es una de las especies más comercializadas en nuestro país, ocupando el primer lugar entre 1998 y 2004
El tamaño relativo del ojo, relacionado con la presencia de areae centrales y una córnea delgada, muestra las necesidades visuales del neón cardenal (cazador) para adaptarse al hábitat, lo que hace necesario tener un sistema visual desarrollado que le permita tener mejor sensibilidad y resolución visual
Summary
P. axelrodi pertenece al orden de los Characiformes, que es el grupo más representativo en número de especies en la Orinoquía Colombiana con el 15.69% del total de especies ornamentales de interés comercial (Mancera y Álvarez 2008). La retina externa está formada por el epitelio simple cuboidal, que es el epitelio pigmentario con gránulos de melanina; este tiene las prolongaciones típicas recubriendo los segmentos externos de las células fotorreceptoras, los cuales conforman la capa de fotorreceptores.
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