Distribution pattern, population structure, and growth of Septifer bilocularis (Bivalvia: Mytilidae) on reefs of Southern Vietnam

The features of the spatial distribution, size and age structure of populations, and growth of the bivalve mollusk Septifer bilocularis (Linnaeus, 1758) were investigated for the first time in the waters of Vietnam. It is shown that in the subtidal area, on reefs well protected from wave effects, S. bilocularis occupies a corallogenous substrate constructed of dead branchy colonies of Acropora and Porites and forms settlements there with a population density and biomass exceeding those in populations located along the open coast and developing on massive coral colonies of the genera Porites, Favia, and Favites. The extensive accumulation of sediments in the inner part of Vanphong Bay (Khanh Hoa Province) correlated with a decrease in the size and age ranges for populations of S. bilocularis. It is found that in places with regularly active hydrodynamics the mollusks grew somewhat more slowly and formed a more convex shell than on reefs protected from surf. The longevity of S. bilocularis estimated both from the greatest observed age and from the growth equation of Bertalanffy was somewhat greater in the former case compared with the latter one, but in general did not exceed 11 years for both cases. The results of the studies are discussed from the position of morphophysiological adaptations of sessile bivalve mollusks to life in contrasting environmental conditions of the upper subtidal zone.     

滆湖入湖河流春季大型底栖动物群落结构及水质生物学评价

分别于2018年4月和2019年4月对滆湖入湖河流底栖动物开展调查,并利用生物指数对水质进行生物学评价。结果表明:共鉴定滆湖入湖河流底栖动物28种,以重度耐污种霍甫水丝蚓(优势度为0.46)和中等耐污种铜锈环棱螺(优势度为0.11)占据绝对优势。生物多样性方面以鹤溪河最高,湟里河、扁担河次之,夏溪河及入湖河口最低,水生植物分布是影响各区域底栖动物多样性的重要因素。卡尔森营养状态指数(TSI)与水质污染等级生物评价结果基本一致,以新孟河延伸拓浚工程沿线为界,鹤溪河、夏溪河、湟里河中上游河段处于中度富营养化水平,水体为轻-中污染状态,而下游河段、扁担河及入湖河口处于重度富营养化水平,水体为中-重污染状态。     

Function of identified nerves in orientation to water flow in Tritonia diomedea

We determined which sensory and motor nerves mediate orientation to flow in the marine slug Tritonia diomedea, and tested the hypothesis that the slug orients to water flow by comparing the intensities of water flow stimulation on each side of its body. Lesion experiments revealed which nerves carried information necessary for flow orientation. The lateral branches of Cerebral Nerve # 2 were the only cerebral nerves necessary for flow orientation. Cutting all cerebral nerves except the lateral branches of Cerebral Nerve # 2 did not eliminate flow orientation. Thus, the lateral branches of Cerebral Nerve # 2 were both necessary and sufficient (among the cerebral nerves) for flow orientation. Denervation of one side of the head by cutting Cerebral Nerves # 1–4 on one side did not eliminate normal flow orientation. We have revised our model of how Tritonia diomedea orients to flow to allow for this unilateral determination of flow direction. Unilaterally cutting Pedal Nerve # 3, which contains many pedal motor axons, reduced turning toward that side, but did not affect final orientation to flow. The ability to detect flow direction was not compro mised by the inability to initially turn towards flow.Abbreviations CeN cerebral nerve - PeN pedal nerve - PlN pleural nerve     

Genetic structure,phylogeography, and demography of Anadara tuberculosa (Bivalvia) from East Pacific as revealed by mtDNA: Implications to conservation

Wild populations of the pustulose ark, Anadara tuberculosa (Bivalvia), an emblematic species of the East Pacific mangrove ecosystem declined in South American countries (Colombia, Ecuador, and Peru) mainly due to overharvesting and habitat loss or degradation. Understanding the genetic aspects of geographic variations and population structure of A. tuberculosa, currently unknown, appears as a priority to fishery authorities in order to elaborate integrated and collaborative conservation policies for fishery management, aquaculture, and stock enhancement programs. We used mtDNA sequence data to investigate haplotype diversity, genetic structure, and demography of A. tuberculosa. Results indicate genetic homogeneity of populations distributed north and south of the equator, respectively. However, statistically significant differentiation emerged between northern and southern populations with pairwise ф_ST values ranging between 0.036 and 0.092. The oceanic current system acting in the area (Panama Current and Humboldt Current) might play a role in limiting the larval dispersal of the species, still poorly understood. Demography reconstruction supported recent population expansion, possibly started after last glacial maximum. Our results would suggest separate and independent management of populations north and south of the equator.     

Putative neoplastic disorders in mussels (Mytilus edulis) from Southern Vancouver Island waters,British Columbia

Histologic examination of wild populations of Mytilus edulis in Saanich Inlet, British Columbia, Canada, revealed the presence of a highly invasive neoplasm. Two types of neoplasms were recognized; most were of hematopoietic origin, except in one mussel which had a presumptive gonadal neoplasm. Both types were apparently malignant neoplasms, based on their anaplastic appearance, invasiveness, mitotic activity, and associated tissue necrosis. This condition was observed from what is believed to be the earliest stage of the disease to the terminal stage, in which the connective tissue was almost completely replaced.     

Diet of an endangered Neotropical catfish (Kalyptodoras bahiensis) from the Paraguaçu River,Bahia, Brazil

ABSTRACT

The present study investigates the diet composition and the feeding strategy of Kalyptodoras bahiensis by verifying variations during the hydrological cycle and between males and females. Samples were collected during the periods of rain and drought using various fishing gears adapted to each microhabitat. In laboratory, the fishes were weighed and measured. An abdominal incision was made to observe the gonads for sex determination and the stomach was removed for identification and quantification of food items. The importance of each item in the diet was calculated using the Feeding Index. Amundsen graphic analysis was used to define the feeding strategy. Kalyptodoras bahiensis was classified as an omnivorous species with an invertivorous tendency. The species presented a generalist feeding strategy and many individuals fed on Melanoides tuberculatus, an exotic mollusk that has spread to Brazilian rivers, causing damages to the native community. The high amount and frequency of M. tuberculatus in the diet of K. bahiensis suggest that the species may have a predatory impact on the local population of this mollusk. However, further studies are needed to better understand the interaction between K. bahiensis and M. tuberculatus.