Marcial Arellano Martínez

Unusual High Frequency of Hermaphroditism in the Gonochoric Bivalve Megapitaria squalida (Sowerby, 1835) (Veneridae)

ABSTRACT Through histological analyses, this investigation reveals an unusual high incidence of hermaphroditism in Megapitaria squalida, a gonochoric species. A total of 684 specimens were sampled at monthly intervals from February 2007 to January 2008 at Bahia de La Paz and Bahia Magdalena, Baja California Sur, Mexico. Microscopic examination showed that 21.8% of specimens from Bahia de La Paz and 23.5% from Bahia Magdalena were hermaphroditic; in both areas, hermaphroditism was found throughout the year, although in variable proportions. In general, a significantly higher number of females relative to males (chi-square, P < 0.05) were observed in both areas. Our findings indicate that this unusual incidence of hermaphroditism was likely caused by the low population density resulting from overfishing.ABSTRACT Through histological analyses, this investigation reveals an unusual high incidence of hermaphroditism in Megapitaria squalida, a gonochoric species. A total of 684 specimens were sampled at monthly intervals from February 2007 to January 2008 at Bahia de La Paz and Bahia Magdalena, Baja California Sur, Mexico. Microscopic examination showed that 21.8% of specimens from Bahia de La Paz and 23.5% from Bahia Magdalena were hermaphroditic; in both areas, hermaphroditism was found throughout the year, although in variable proportions. In general, a significantly higher number of females relative to males (chi-square, P < 0.05) were observed in both areas. Our findings indicate that this unusual incidence of hermaphroditism was likely caused by the low population density resulting from overfishing.

USE OF LENGTH-FREQUENCY ANALYSIS FOR GROWTH ESTIMATION OF THE CALIFORNIA TWO-SPOTTED OCTOPUS OCTOPUS BIMACULATUS VERRIL 1883 OF THE GULF OF CALIFORNIA

ABSTRACT Indirect methods such as length—frequency analysis have not been recommended for growth estimation in octopus (length is not a good measure of size for soft-bodied organisms; size is not a good indicator of age because of the high interindividual variability in growth rates and an asymptotic growth is often assumed). However, these methods are still applied in various places where octopus fisheries exist because they are low cost and easy to apply in most fisheries where there are no financial resources or scientific capacity to use direct methods. The purpose of this study was to investigate whether length—frequency analysis is an appropriate method for determining the growth pattern of Octopus bimaculatus from the Gulf of California. We tested the widely used methods ELEFAN I and NSLCA, and a modal progression analysis with a multimodel approach. The results showed that the growth pattern of O. bimaculatus was reasonably described using these analyses. First, the suitability of using mantle length as a measure of size was confirmed through a significant length—weight relationship. A length—age key was also generated in terms of probability to take into account the variability in growth rates, and with the multimodel approach it was not necessary to assume asymptotic growth. Population size structure is the most readily obtained and probably the most commonly used or only available information in a large number of fisheries. Therefore, the usefulness of length—frequency analyses should not be underestimated when direct methods are available.

Female gonad morphology and maturation in Centropages furcatus (Dana, 1852)

Abstract Centropages furcatus is a dominant species of the planktonic community in the Ensenada de La Paz, Baja California Sur, Mexico. Little is known about gonad morphology and maturation of this species, and that knowledge is key for understanding the reproductive activity and the mode of eproduction of C. furcatus. The histological analysis revealed that, similar to most calanoid copepods, the sac-shaped ovary of C. furcatus is located dorsally to the centre of the prosoma; oocyte maturation takes place outside the ovary. Besides, in agreement with the Calanus-type gonad, most oocyte development stages occur simultaneously, and frequently many oocytes mature synchronously. However, the spatial location of oocytes differs from the one described for the Calanus-type gonad. In C. furcatus, previtellogenic oocytes are arranged in an outer layer spreading longitudinally and across the circumference of the prosoma; oocyte growth and maturation takes place radially towards the b dy centre. For this reason, a...Abstract Centropages furcatus is a dominant species of the planktonic community in the Ensenada de La Paz, Baja California Sur, Mexico. Little is known about gonad morphology and maturation of this species, and that knowledge is key for understanding the reproductive activity and the mode of eproduction of C. furcatus. The histological analysis revealed that, similar to most calanoid copepods, the sac-shaped ovary of C. furcatus is located dorsally to the centre of the prosoma; oocyte maturation takes place outside the ovary. Besides, in agreement with the Calanus-type gonad, most oocyte development stages occur simultaneously, and frequently many oocytes mature synchronously. However, the spatial location of oocytes differs from the one described for the Calanus-type gonad. In C. furcatus, previtellogenic oocytes are arranged in an outer layer spreading longitudinally and across the circumference of the prosoma; oocyte growth and maturation takes place radially towards the b dy centre. For this reason, a new gonad morphology type is hereby proposed for C. furcatus, naming it furcatus-type.

Notes on the reproductive cycle of the blotchy scallop Spathochlamys vestalis (Reeve, 1853) at Isla Danzante, Gulf of California

Este trabajo documenta algunas notas sobre el ciclo reproductivo del pectinido manchado Spathochlamys vestalis (Reeve, 1853), el cual se desconoce tanto para las costas del Pacifico como del Atlantico. En el Golfo de California es abundante sobre fondos de arena gruesa y entre las espinas de la concha china Spondylus leucacanthus. Es una especie hermafrodita funcional con la porcion gonadal masculina separada de la porcion gonadal femenina. Se observo alta proporcion de individuos maduros durante diciembre de 1994 (87,5%) y en octubre de 1995 (100%). Los individuos desovados se observaron en baja proporcion. Se encontro un 5,5% en enero, cuando la temperatura del agua de fondo fue menor de 15oC y un 5,1% en abril, cuando la temperatura se incremento a 21oC. El patron reproductivo ocurrio de manera continua sin presentar una alta correlacion con la temperatura del agua de fondo. La abundancia del fitoplancton fue alta en primavera, si embargo presento una relacion negativa con el desarrollo y la madurez del pectinido (P<0,05).