Biología reproductiva y contenido bioquímico gonadal de la cabrilla arenera, Paralabrax maculatofasciatus en la región de Bahía de Kino, Sonora//Reproductive biology and biochemical gonadal content of the spotted sand bass, Paralabrax maculatofasciatus in Kino Bay, Sonora

A pesar de la importancia económica que representa la cabrilla arenera, Paralabrax maculatofasciatus, la información acerca de sus aspectos reproductivos es escasa, por lo que se investigó su biología reproductiva así como su composición proximal de la gónada. Para ello, se capturaron 30 organismos mensualmente de marzo 2017 a febrero 2018. Los peces se midieron, pesaron y disectaron para obtener el factor de condición (K), el índice hepatosomático (IHS) y el índice gonadosomático (IGS). Adicionalmente, se preservó tejido de gónada para llevar a cabo el proceso histológico y la tinción hematoxilina-eosina. Los resultados indicaron que el IHS y el IGS fueron afectados significativamente (P<0.05). El análisis histológico evidenció la presencia de machos maduros en abril, así como de octubre a noviembre, y para las hembras, se observó la presencia de organismos desarrollados en abril y de octubre a diciembre. Adicionalmente, se detectó la presencia de organismos en transición de hembra a macho. El análisis proximal mostró el valor máximo de grasa en abril, lo cual coincidió con el menor valor de humedad. El análisis de proporción mostró una significativa dominancia de machos. Los datos obtenidos en la presente investigación coadyuvarán en la implementación de programas de protección para la especie.ABSTRACTDespite the economic importance of sand bass, Paralabrax maculatofasciatus, little information regarding its reproductive aspects is known. In this study, gonadal maturity stage, biological indexes, proximate gonad composition and sex ratio proportion were determined. A total of 30 wild spotted sand bass were monthly obtained from March 2017 to February 2018. Organisms were measured, weighted and dissected in order to obtain the condition factor (K), hepatosomatic index (IHS) and gonadosomatic index (IGS). A small portion of gonad was preserved to perform the histological procedure, and stained with Harris´ hematoxilineosin technique. The results indicate that somatic indexes were significantly affected (P<0.05) in terms of IHS and IGS. Histological analysis showed the presence of ripe males in April and from October to November, and for females, the presence of developed organisms was observed in April and from October to December. Additionally, the presence of transitional organisms from female to male was observed. The proximate analysis showed the maximum crude fat value in April, which coincides with the lowest moisture value. Sex proportion showed a significant male dominance. These data provide valuable information for the development of protection programs to encourage a sustainable fishery of the species.

Effects of a luteinizing hormone-releasing hormone analogue (LHRHa) on the reproductive performance of spotted sand bass Paralabrax maculatofasciatus (Percoidei: Serranidae)

Hormonal induction of spotted sand bass Paralabrax maculatofasciatus, was investigated in order to induce and synchronize spawning. Three experiments were conducted using wild fish captured in the Gulf of California: 1) LHRHa (luteinizing hormone-releasing hormone analogue) induced spawning with concentrations of 25, 50, 100 µg kg-1 and saline solution, 2) Effects of LHRHa on motility and sperm density, and 3) Induction and incubation of spawns obtained using LHRHa. In experiments 2 and 3 using concentrations of 12.5, 25, 50 µg kg-1 and saline solution. In experiment 1, a higher spawning ratio was observed for the concentration of 25 µg kg-1; however, no significant differences were observed in the proportion of floating (viable) eggs. In experiment 2, significant differences (P < 0.05) were observed in duration of sperm motility and sperm density, with highest duration registered for wild fish (control group) and highest density registered for laboratory control group and concentration of 12.5 µg kg-1. In experiment 3, significant differences (P < 0.05) were observed between treatments in volume of spawned eggs and proportion of fertilized eggs, with higher values shown for the concentrations of 50 and 12.5 µg kg-1, respectively. Survival at hatching and proportion of live yolk-sac larvae were significantly higher (P < 0.05) for the concentration of 12.5 µg kg-1. LHRHa was effective in inducing and synchronizing the spawning of spotted sand bass, a process which will be used for massive egg production.

EVIDENCIA DE LA ESTABILIDAD CARIOTÍPICA DURANTE LA DIVERGENCIA EVOLUTIVA ENTRE Paralabrax maculatofasciatus Y P. nebulifer (PERCIFORMES: SERRANIDAE)

La información sobre la estructura cromosómica es básica dentro del conocimiento biológico de cualquier especie y fundamental para la comprensión de fenómenos citogenéticos que subyacen a procesos fisiológicos, ontogénicos y evolutivos. En este último ámbito, el conocimiento del grado de similitud de los cromosomas de especies filogenéticamente cercanas complementa la información necesaria para plantear hipótesis causales sobre procesos de divergencia evolutiva. El objetivo del presente estudio fue determinar la similitud citogenética entre Paralabrax maculatofasciatus y P. nebulifer, especies filogenéticamente cercanas que se distribuyen en el Pacífico oriental, mediante la comparación del número, tipo y tamaño de los cromosomas. El examen de células mitóticas de eleuteroembriones en ambas especies mostró un cariotipo constituido por 48 cromosomas acrocéntricos (2n = 48A; número fundamental = 48), sin la presencia de cromosomas heteromórficos. No se detectaron diferencias significativas entre especies, tanto en el tamaño promedio, como en la longitud relativa (LR) de los pares cromosómicos homeólogos que presentaron un valor máximo de 4 μm (LR = 5.5 %; par 1) y un mínimo de 1.7 μm (LR = 2.3 %; par 24). Este cariotipo es considerado ancestral dentro del Orden Perciformes y está presente en la mayoría de las especies de la Familia Serranidae. Con base en estos resultados se sustenta la hipótesis de que la divergencia evolutiva entre P. maculatofasciatus y P. nebulifer se originó a través del establecimiento de barreras reproductivas precopulatorias sin alteración cariotípica ni formación de barreras postcopulatorias, tanto precigóticas como postcigóticas. Evidencen of karyotypic stasis during the evolutionary divergence between Paralabrax maculatofasciatus and P. nebulifer (Perciformes: Serranidae) Information on chromosome structure is basic within the biological knowledge of any species and fundamental to the understanding of the cytogenetic phenomena underlying physiological, ontogenic and evolutionary processes. Knowledge on the degree of similarity of chromosomes in phylogenetically close species supplements the necessary information to raise causal hypotheses on the processes of evolutionary divergence. The objective of this study was to determine the cytogenetic similarity between Paralabrax maculatofasciatus and P. nebulifer, closely (phylogenetically) related species distributed in the Eastern Pacific, by comparing number, type and size of chromosomes of these taxa. The examination of mitotic cells from eleutheroembryos of both species showed a karyotype consisting of 48 acrocentric chromosomes (2n = 48A; fundamental number = 48), without the presence of heteromorphic chromosomes. No significant differences between species were observed in size and relative length (RL) of homeologous chromosome pairs which showed maximum and minimum values of 4 μm (RL = 5.5 %; pair 1) and 1.7 μm (RL = 2.3 %; pair 24), respectively. This karyotype is considered ancestral within the Order Perciformes and is present in most of the species of the Family Serranidae. The results found in this study supported the hypothesis that evolutionary divergence between P. maculatofasciatus and P. nebulifer occurred through the establishment of pre-mating reproductive barriers, without karyotype modification or formation of post-mating barriers, either pre-zygotic or post-zygotic.