Social and reproductive physiology and behavior of the Neotropical cichlid fish Cichlasoma dimerus under laboratory conditions

In this work we describe for the first time the social and reproductive behavior of the Neotropical fish Cichlasoma dimerus (Heckel, 1840) [Perciformes: Cichlidae], endemic to the Paraná River basin, using a comprehensive-integral approach, including morphological and physiological features. This substrate breeding fish has biparental care of the fry and presents a dominance hierarchy that determines access to breeding territories among males, and to males with territories among females. Gregarious behavior associated with a pale body color, was observed before reproductive behaviors started. Afterwards, a dominance hierarchy was established through aggressive interactions. Territorial individuals had bright body color patterns and non territorial an opaque grey one. Black ventral coloration was associated with reproductive individuals. Courtship displays, which were similar to threatening displays, had the common effect of increasing the visible area of the individual. The dominant male was always the largest one suggesting that size is probably a major factor determining the hierarchy establishment and that these intra-sexually selected traits may have been reinforced by inter-sexual selection. Reproductive males had higher pituitary levels of β-follicle stimulating hormone (β-FSH) and somatolactin (SL) than non reproductive ones, while no differences were found among females. No differences were found among male gonadosomatic indexes. Non reproductive individuals had higher plasma cortisol levels for both sexes. It is possible that dominant reproductive individuals may be inhibiting reproduction of subordinate fish through physical contact, increasing their cortisol levels and diminishing FSH and SL pituitary content. However, this was not reflected as an inhibition at the gonadal level in our experimental design.

En este trabajo se describen por primera vez el comportamiento social y reproductivo del pez cíclido neotropical Cichlasoma dimerus (Heckel, 1840) [Perciformes: Cichlidae], endémico de la cuenca del Paraná, desde un enfoque integral y abarcador, incluyendo características morfológicas y fisiológicas. Éste pez incubador de substrato, tiene cuidado biparental de las crías y presenta una jerarquía de dominancia que determina el acceso a territorios reproductivos entre los machos, y a machos con territorios entre las hembras. Se observó un comportamiento gregario con una coloración corporal pálida característica, antes que comenzaran los comportamientos reproductivos. Luego, una jerarquía de dominancia se estableció a través de interacciones agresivas. Los individuos territoriales presentaron patrones de coloración corporal brillantes y los individuos no territoriales uno gris opaco. Una coloración ventral oscura fue observada asociada a individuos reproductivos. Los despliegues de cortejo fueron similares a los de amenaza y tuvieron la característica común de aumentar el área visible de los peces. El macho dominante fue siempre el más grande, sugiriendo que probablemente la fuerza (tamaño) es un factor preponderante determinando el establecimiento de las jerarquías y que éstas características seleccionadas intrasexualmente pueden haber sido reforzadas por selección intersexual. Los machos reproductivos presentaron un mayor contenido hipofisario de β-FSH y SL que aquellos no reproductivos, mientras que no se encontraron diferencias entre las hembras. No se encontraron diferencias entre los índices gonadosomáticos de los machos. Los individuos no reproductivos presentaron niveles plasmáticos mayores de cortisol para ambos sexos. Aunque los individuos reproductivos dominantes podrían estar inhibiendo la reproducción de los peces menos dominantes a través de interacciones de contacto físico, aumentando sus niveles de cortisol y disminuyendo el contenido hipofisario de FSH y SL, esto no se vería reflejado a nivel gonadal en nuestro diseño experimental.

Studies on the reproductive and developmental biology of Cichlasoma dimerus (Percifomes, Cichlidae): [review]

Many characteristics of the South American teleost fish Cichlasoma dimerus (body size, easy breeding, undemanding maintenance) make it amenable to laboratory studies. In the last years, many of the fundamental aspects of its reproductive and developmental biology have been addressed in our laboratory. Rather recently, the immunohistochemical localization of pituitary hormones involved in reproduction and in background color adaptation has been described in both adult and developing individuals, and the role of FSH in ovarian differentiation has been established. These findings have been correlated with mapping of some of their brain-derived controlling hormones. The latter include brain-derived gonadotropins which were shown to be active in vitro in the control of pituitary hormone secretions. The emerging picture shows C. dimerus as an interesting species in which many of their basic features have already been investigated and which conform a solid platform for comparative studies correlating neurohormones, pituitary hormones and behavior, from the molecular to the organismic level.