Reproductive aspects of Chiton virgulatus in Bahía de La Paz, Gulf of California, Mexico

This study analyzed the reproductive cycle of Chiton virgulatus and its relationship with air temperature (AT) sea and surface temperature (SST), photoperiod, and tidal cycle (TC) in Bahía de La Paz, in the coast of the Gulf of California. Monthly samples were collected from September 2008 to September 2009. The parameters recorded included total length, total weight, and gonad weight of each organism; the gonad was processed using a histological technique, and the gonadal index and length at first maturity (L50) were estimated. C. virgulatus displays partial spawning with a reproductive peak in summer and autumn (July to December). The frequency of ripe organisms was associated with rises in SST (30.6 ºC), AT (29.9 ºC), and TC (68 cm, high tidal), while photoperiod (longer days) regulated the frequency of developing organisms. The length at first maturity was 29.7 mm. Chiton virgulatus is a polyplacophoran species in which high temperatures and high tides influence reproductive timing, while an increase in daylight boosts gonad development.

Reproductive cycle of the barred sorubim Pseudoplatystoma fasciatum (Linnaeus, 1766), in the upper delta of the Orinoco River, Delta Amacuro State, Venezuela

Pseudoplatystoma fasciatum represents one of the most important items in the continental fisheries of Venezuela. The great fishing pressure exerted on this species has decimated the populations in the Orinoco River Delta and other regions of the country. The current condition of the population in the delta region is unknown and information about basic biological parameters is unavailable. Hence, population and reproductive parameters of this catfish were determined in this region. Results showed that the size interval was from 30 to 105 cm total length (TL), generally smaller than the size range found in other regions of the country. The largest value for the gonadal index for females was 116, recorded in July. Size at maturity of 50% of females was 46.38 cm TL, a smaller value than others reported for the Orinoco River Basin. Maturation of oocytes was synchronous, showing a single total spawning per year. The capture of P. fasciatum was continuous throughout the year, including mature individuals during the reproductive season, suggesting a possible utilization of the delta region as reproductive site. A total of 61% of the individuals were below the minimum legal size, indicating deficient management of this fishery resource in the Orinoco River Delta.

Occurrence of abnormal sexual dimorphic structures in the gonochoristic crustacean, Upogebia major (Thalassinidea: Decapoda), inhabiting mud tidal flats in Japan

Normal females of the mud shrimp, Upogebia major, have a pair of pleopods on the first abdominal segment, while normal males do not. We have investigated nine populations in the Seto-Inland Sea, Japan, and found morphological disorders on the first abdominal segments of both males and females. In males, the first pleopods occurred. Morphology and arrangement of these additional pleopods were classified into four types. The pleopods of Types M-1 and M-2 were similar in structure to those of normal females. These males could be considered as de-masculinized individuals, and the occurrence of males with these morphological disorders showed local variation: while their frequency was high in two specific sites in Kasaoka Inlet (11.5% in Site 6 and 5.5% in Site 7), it was less than 3.5% in other sites. Other types had abnormal additional appendages similar to the walking legs (pereiopods) (Type M-3) or biramous leaf-like pleopods (Type M-4), but their frequency was extremely low (only 3 out of 1558 males inspected). Morphological disorders in males (Types M-1 and M-2) occurred independently of gonadal development, and did not affect the sexual characteristics as revealed by analyses of allometric growth and gonadal index. In females, morphological disorders were classified into five types: incomplete first pleopods (Type F-1); lack of the first pleopods (Type F-2 and F-3); transformation into the pereiopod-like pleopods (Type F-4); and biramous leaf-like pleopods (Type F-5). The frequency of Types 1–3 was especially high in Site 6 in Kasaoka Inlet (24.4%), but was less than 9.4% in other sites. A feature was that cuticular lesions often co-occurred with the morphological disorders. Possible causal factors of these abnormalities are discussed.

Spawning and fecundity of king weakfish, Macrodon ancylodon, in the Río de la Plata estuary, Argentina–Uruguay

The reproductive biology of the king weakfish, Macrodon ancylodon, inhabiting the estuarine waters of the Río de la Plata (Argentina–Uruguay), was studied using macroscopic and histological analysis of the gonads. The samples were collected from commercial landings and from three research cruises carried out between 1999 and 2001. King weakfish is a multiple spawner with indeterminate annual fecundity. Spawning of this species extends from October to March with two main peaks of gonadal index in November and March. Based on the incidence of females with new postovulatory follicles, the evening near sunset was the estimated time of spawning for M. ancylodon. Spawning frequency, determined using the percentages of females with postovulatory follicles, was about 17% during March 2001, indicating that females spawn once every six days at the second peak of the reproductive season. Batch fecundity ranges from 12,400 to 225,700 hydrated oocytes and was fitted to a linear function of total length and ovary-free female weight. The number of hydrated oocytes decreased at the end of the spawning season. In addition, a decline in hydrated oocyte size and weight was also observed during this period.

L’ INFLUENCE DE L’ALIMENTATION ET DE LA DENSITÉ DE LA POPULATION SUR LE DÉVELOPPEMENT DES GONADES CHEZ TROIS ESPÈCES DE POISSONS

Foi realizado o estudo do comprimento total, peso total e peso das gônadas; dos índices gonadais e do fator de condição (K), em relação à variação da densidade populacional em três diferentes tratamentos do experimento com Trichogaster trichopterus e, além dos estudos citados, também foi realizada no experimento com Hemichromis bimaculatus, a análise dos estádios de maturação gonadal encontrados, em relação à quantidade de alimento ofertado em quatro diferentes tratamentos. O estudo do fator de condição em relação à quantidade de alimento ofertado em três diferentes tratamentos dos experimentos com Hyphessobrycon callistus e Trichogaster trichopterus também foi realizado. O comprimento total, peso total e peso das gônadas revelaram a tendência de serem inversamente proporcionais à densidade populacional. Porém o comprimento total e o peso total, de H. bimaculatus, revelaram a tendência de serem diretamente proporcionais à quantidade de alimento ofertado. Tanto o índice gonadal como o índice gônado-somático foram mais elevados no tratamento de densidade populacional intermediária, em T. trichopterus. Os menores valores destes índices, em H. bimaculatus, foram registrados no tratamento 3 e os maiores valores nos tratamentos 1 e 2, respectivamente. Em T. trichopterus, experimento quanto à variação da densidade populacional, observaram-se valores muito semelhantes do fator de condição entre os tratamentos 1 e 2. O maior e o menor valor do fator de condição em H. bimaculatus foram observados nos tratamentos 1 e 4, respectivamente. Em H. callistus, o maior e o menor valor do fator de condição foram encontrados, respectivamente, nos tratamentos de maior oferta alimentar e de oferta alimentar intermediária. Em T. trichopterus, o fator de condição revelou a tendência de ser diretamente proporcional à quantidade de alimento ofertado. A espécie H. bimaculatus não evidenciou apresentar tendência à correlação positiva entre maturação gonadal e quantidade de alimento ofertado. Abstract Studies on the Trichogaster trichopterus gonadal development in regard to the variation of the population density were carried out. The following parameters were studied: the total length, total weight and gonads weight; the gonads indexes and the condition factor (K). In the experiment with Hemichromis bimaculatus was concomitantly analysed the maturity stages of the gonads in relation to the quantity of nourishment offered. The nourishment influence in the condition factor (K) of Hyphessobrycon callistus and Trichogaster trichopterus has been analysed. The total length, total weight and gonads weight were estimated to be inversely proportional to the population density. However, the total length and total weight in H. bimaculatus were estimated to be directly proportional to the amount of nourishment offered. The gonadal index and the gonadosomatic index were higher in the treatment of the intermediate population density, in T. trichopterus. The smallest values of these gonads indexes, in H. bimaculatus, were recorded in treatment 3 and the biggest values in treatment 1 and 2, respectively. In T. trichopterus, an experiment about the variation of the population density, similar values were observed between treatment 1 and 2, in relation to the conditional factor. The biggest and smallest values about the conditional factor, in H. bimaculatus, were observed in treatment 1 and 4, respectively. In H. callistus, the highest and the lowest values of the conditional factor were observed, respectively, in the treatment of the highest level of nourishment offered and in the treatment of the intermediate nourishment offered. In T. trichopterus, the conditional factor tended to be directly proportional to the amount of nourishment offered. In the species H. bimaculatus the tendency on the positive correlation between gonadal maturation and amount of nourishment offered is not evident.

Variation in the reproductive strategy of the sea urchin Sphaerechinus granularis (Echinodermata: Echinoidea) related to food availability

Changes in the reproductive strategy of Sphaerechinus granularis (Echinodermata: Echinoidea) according to food availability were examined by comparing gonadal index changes from two populations with different food conditions. The better nutritional situation was confirmed by a repletion index always higher without significant inverse relationships with the gonadal index. The two populations exhibited a different reproductive strategy during their life cycle. The food limited population showed a delay in reproductive competence, a lower gonadal index and an increase in relative gonadal growth with age. This population showed a seasonal inverse relationship between the consumption index and the gonadal index during the spawning period. A discussion based on the variations in the main life history parameters between the two populations: reproduction, somatic growth, longevity, underlines the plasticity of this species which must maximize its reproductive output in terms of changes in food availability. The adaptive value of this plasticity was observed by the reduction in somatic growth which decreases the energetic cost of maintenance and by the increase in size of the feeding structure (Aristotle's lantern) which improves food acquisition.

Annual reproductive cycle of the Japanese holothurian Eupentacta chronhjelmi

The reproductive cycle of the small temperate dendrochirote holothurian Eupentacta chronhjelmi was studied in the intertidal zone of Aoshima Island, in the Seto Inland Sea of Japan, from July 1989 to January 1991. Reproductive status was assessed by the gonadal index method and histological analysis of the largest (tertiary) gonadal tubules. The primary and secondary tubules are cryptic and difficult to find, so no reference to the animal's annual cycle in terms of gametogenesis is made. The gonad wall was thickest in September for females and October for males, when the gonadal index was at its peak the rapid final stages of vitellogenesis in females (and completion of spermatogenesis in males) depleted reserves in the gonad wall, producing gametes that were spawned in October to December. When gametes were spawned in December the gonadal index and gonad wall thickness decreased. We suggest that the gonadal index reflects gonadal growth by oocyte production and an increase in gonad wall thickness. In the laboratory, spawning occurred from midnight to 04:00, at ambient seawater temperature (12 °C). Individuals elevated their anterior, oral end, waved their tentacles, and released gametes for about an hour. Based on its large egg size (300 ± 5 μm (mean ± SE) diameter) and low fecundity (1500 ± 10 ripe oocytes per individual), we infer lecithotropic development with an abbreviated larval stage.