Captive reproductive performance of <i>Mayaheros urophthalmus</i> from four different regions of Southeastern Mexico

Summary A total of 966 cichlids, Cichlasoma urophthalmus, was sampled from three karstic water bodies (cenotes) in the Yucatan Peninsula. Sex ratio was not different from 1. Specimens with ripe eggs were found during the dry and rainy seasons in the inland cenote and during the dry, rainy, and north winds seasons in the two wetland cenotes. With respect to relative fecundity, data show the C. urophthalmus inland population as two- to three-fold greater (53.1 ± 27.7) than the wetland populations (15.7 ± 5.1 and 18.2 ± 3.1). This is attributable to the different breeding strategies of C. urophthalmus populations inhabiting these two types of cenotes. In particular, the ichthyofauna from the two wetlands showed not only higher species richness (17 and 16 species) but also a higher number of potential predators (nine and eight species) as compared to the inland cenote (six species; two potential predators). It is hypothesized that C. urophthalmus adjusts its clutch size and extends its breeding periods as a response to riskier sites as compared to more secure ones; a higher competition for breeding sites and to increased fishing mortality.

Metabolic physiology of the Mayan cichlid fish (Mayaheros uropthalmus): Re-examination of classification as an oxyconformer

Various plant communities developed along the Usumacinta River, adjacent streams and lagoons which are all considered part of the wetlands region. The wetlands are characterized for the presence of water, which plays a fundamental role in the development of the soil, and the ecological and structural functions of the system. The vegetation on the borders of the river and streams are known as riverine plant communities, whereas vegetation floating in the bodies of water is known as hydrophytic vegetation \citep{j2006}. Three types of plant species in the wetlands could be distinguished: a) Strictly aquatic: plants that complete their life cycle either totally submerged, partially emerging, or floating on the surface; b) Subaquatic: plants that complete most of their life cycle on the border of the water, in water-saturated soils and can tolerate temporary dry seasons with minor humidity; and c) Drought tolerant: plants which complete most of their life cycle in dry areas, but support being partially submerged during rainy periods. The last category includes trees, bushes, climbers, and some palms \citep{2015}.The aquatic and border vegetation are physically and biologically connected and are of ecological importance, providing complex habitats and resources for a high variety of other aquatic organisms \citep{j2006}. The knowledge of the aquatic and subaquatic vegetation in Mexico is fragmentary. In particular for the Usumacinta River (the most important river of Mexico) where watershed has been only partially studied. In this study, we revised and created the knowledge available on the plant communities, the riparian and aquatic plant species along the Usumacinta River watershed, and supplemented this knowledge with data collected in the study area. The data of floristic inventory of the Usumacinta river watershed was integrated with data provided by the National System of Information on Biodiversity of the National Commission for the Knowledge and Use of the Biodiversity (SNIB-CONABIO), literature, herbaria samples of UAC, ENCB, UJAT, Ecosur-SCLC and MEXU, and field data.We registered 212 families and 3,501 species; the families with most species were those of legumes (342), followed by orchids (295), the composite family (214), and grasses (195) \citep{delgado2018}. Such numbers of plant species is a good indication of the great diversity and floristic richness of aquatic and border plants in the Usumacinta River watershed. We registered 36 families and 148 aquatic and subaquatic plant species, numbers which confirm the importance of the Usumacinta watershed for these species groups.The borders of the Usumacinta River are threatened by human activity. The villages’ are planting ornamental and fruit trees, both native as introduced species. However, it is still possible to find original plant communities either in the lagoons, or along the Usumacinta river; for example, shrublands of muco (Dalbergia brownei or D. glabra) \citep{santiago2005}. The most common tree species registered are typical of riverine forest communities, such as: Bucida buceras (pucte), Inga vera (jinicuil), Haematoxylum campechianum (tinto), Pithecellobium lanceolatum (tucuy) and Salix humboldtiana (sauce), all of which are still present in border-forested fragments along the Usumacinta, San Pedro and Palisade rivers \citep{e1963} \cite{santiago2005}. The border vegetation near the coast is dominated by mangroves, such as Rhizophora mangle (red mangle), associated with Laguncularia racemosa (white mangle), Avicennia germinans (mangle prieto) and Conocarpus erectus (botoncillo) \cite{j2006}.We registered five species which had value and/or use: Annona glabra (anona) which is edible, Crescentia cujete (jicaro) which is ornamental, Guatteria anomala (palo de zope) which is used as food of turtles and parakeets, Sagittaria lancifolia (tule), and Vallisneria americana (sargazo) which is also known to be in the diet of turtles. This work highlights the importance of the riverine and aquatic vegetation for human communities, besides the service of food, nesting sites, refuge and rest for the regional fauna.This diversity of plants is integrated in plant communities which stabilizes the silt, oxygenates the water, provides refuge and material for nest sites, are habitats for different species of fauna, and provides multiple ecosystem services which depend partly on the population that lives in the region \citep{a2010}. The villagers depend on the hydrological functions because fishing is an important source of economic income, and a local food source. Many of people that live in the watershed recognize the importance of the plants as a source of food for the aquatic fauna. As such, the management and conservation of the wetlands is of great importance.Diversidad de Plantas en Humedales de la Cuenca del rio Usumacinta, Mexico

Background. The Lacandon mojarra, Eugerres castroaguirrei González-Acosta et Rodiles-Hernández, 2013, was described from the Grijalva–Usumacinta River basin (Mexico). According to the diagnosis E. castroaguirrei differs from the only other freshwater Gerreidae, the Mexican mojarra, Eugerres mexicanus (Steindachner, 1863) by the combination of certain morphological characters. However, a comparison of materials obtained in the Usumacinta River, besides of type materials and other preserved specimens, yielded contradictory results. Therefore, the objective of this paper was to clearly determine if E. mexicanus and E. castroaguirrei are subjective synonyms applying morphological and molecular analyses. Materials and methods. A total of 44 specimens were included in this study including the specimens collected specifically for this study, the type and non-type materials of Eugerres castroaguirrei from Colección de Peces de El Colegio de la Frontera Sur, Unidad San Cristóbal, Chiapas, México, and the types of Eugerres mexicanus, belonging to the Museum of Natural History, Wien, Austria. The morphological comparison also included data from the 42 specimens of E. castroaguirrei reported in the new species description. Biometric data were analysed as body proportions. We used Friedman’s test to compare our biological materials with those used in the new species description. Molecular genetics comparisons on both putative freshwater gerreid species were made based on three mitochondrial gene fragments: 12SrRNA, 16SrRNA, and Cytochrome Oxidase subunit I (COI), and the nuclear gene: Recombination-Activating protein 1 (RAG1). Results. Neither the non-parametric Friedman’s test nor the Nemenyi’s procedure showed differences among individuals for both putative species in multiple pair-wise comparisons of body proportions. Moreover, the genetic divergence from all genes indicated that all individuals exhibited almost identical sequences, with inter-specific pair-wise genetic distances that ranged from 0.00% to 0.100% in all of the fragments. Conclusion. Our morphological and molecular genetics analyses demonstrated that E. mexicanus and E. castroaguirrei are subjective synonyms, therefore, Eugerres mexicanus (Steindachner, 1863) must be considered a valid species name, and Eugerres castroaguirrei González-Acosta et Rodiles-Hernández, 2013 a junior synonym.

Length-weight relationship and condition factor (K) are descriptors of the biology of fish populations, providing fundamental information on growth strategies, nutritional status, and reproduction. These parameters are used to compare the condition of fish populations in aquatic systems with different degrees of anthropogenic intervention. This study aimed to explore the length-weight relationship of Pterygoplichthys sp., to observe whether the physiological condition factor reveals variation from a dammed river (Grijalva) to a free-flowing river (Usumacinta). Given the physiological characteristics of armored catfish (benthic consumer, tolerance to hydrological disturbance and aquatic pollution, and wide reproductive range), we predict that this fish will have a better welfare condition in the Grijalva River than in the Usumacinta. Highest abundance of armored catfish was obtained in the Grijalva River (282 specimens). However, the largest and heaviest fish were caught in the Usumacinta River (34.4 ± 5.31 cm and 389 ± 138 g, respectively). Length-weight ratio of armored catfish showed a negative allometric growth rate in both rivers (b>3), i.e., the fish grew more in length than in weight. However, the condition factor revealed that armored catfish have better physiological conditions in the Usumacinta River. Food availability, species population density, intra- and interspecific competition probably played an important role in fish welfare. Information generated in this study can be used as a guide to analyze more detailed the populations of armored catfish, taking into consideration sex and different bodies of water, to adequately monitor the populations of Pterygoplichthys sp., in the Mexican southeast.

Invasive species cause substantial changes to the biodiversity of freshwater systems. The African Nile tilapia (Oreochromis niloticus) is now widely distributed in tropical freshwaters globally. Despite indications that feral populations can influence native species through competitive effects, direct evidence of competition between Nile tilapia and native species is rare. Moreover, it is not clear if environmental variables such as temperature and oxygen concentration modulate competition. Here, interactions between Nile tilapia and the native Mayan cichlid (Mayaheros urophthalmus) were studied in experimental mesocosms in south-eastern Mexico. We found that Nile tilapia was the more active and aggressive of the two species, and their movement was only weakly influenced by temperature and oxygen concentration. By contrast, movement of the Mayan cichlid was strongly predicted by the movement and aggression of Nile tilapia, and the Mayan cichlid showed a steep decline in behaviours with increased water temperature and reduced oxygen. Our results suggest that broad environmental tolerance of the intrinsically aggressive Nile tilapia provides it with an advantage over native species. Collectively these traits may help to exacerbate its invasive success as those environmental conditions become more commonplace in a changing world.

We investigated the reproductive biology of the Mayan cichlid, Cichlasoma urophthalmus, for twenty consecutive months in a southern Florida mangrove creek and compared it to that of available published accounts where this species is native. Mayan cichlid reproduction occurred during a period of the year when physical conditions facilitated the best growth and survival of the young, and was influenced more by changes in water level and salinity than by temperature. Most nests were observed along mangrove shorelines in April. The majority of reproduction and parental care of the young followed in May, and was completed by June when rising water levels flooded shallow habitats and dispersed young-of-year fish. Mayan cichlids in Florida became reproductively mature at a greater size than in native regions, but produced roughly the same number of eggs at a given body mass. The similarity of environmental conditions between southern Florida and areas where Mayan cichlids naturally occur imparts a very favorable reproductive potential for this species in southern Florida, and facilitates their continued presence within the ichthyofauna of the region.

Ecological studies on Potamogeton pectinatus L. I. General characteristics, biomass production and life cycles under field conditions

Reproductive isolation in Chara aspera populations

BackgroundThe number and spatial distribution of wild boars (Sus scrofa) has increased remarkably in Sweden as well as in other European countries. To understand the population dynamics of the wild boar, knowledge of its reproductive period, oestrus cycle and reproductive success is essential. The aim of this study was therefore to describe the seasonal reproductive pattern and reproductive potential of a wild boar population in Sweden. The study was based on findings from macroscopic examinations of the reproductive organs from 575 hunter-harvested female wild boars (>30 kg body weight). Samples were collected between December 2011 and December 2015 in the southern and middle parts of Sweden. The age of the sampled animals was determined and dressed weight was noted. The stage of the reproductive cycle was defined according to ovarian structures and in relation to the appearance of/and findings in the uterus. The crown-rump length (CRL) of the embryos/foetuses was used to calculate the oestrus/mating month and month for the expected farrowing.ResultsThe macroscopic examination revealed a seasonal variation of reproductive stages, although cyclic and pregnant females were found in all seasons. Moreover, the estimated oestrus/mating and farrowing months based on the CRL showed that mating and farrowing may occur ‘off-season’. The average litter size (no. of embryos or foetuses) per pregnant female was 5.4. Sow weight and age had significant effect on both the reproductive potential (ovulation rate and litter size) and pregnancy rate, respectively.ConclusionsThe reproductive potential in the studied wild boar population was high compared to studies from other countries and farrowing may occur ‘off-season’. This suggests that the environmental conditions in Sweden, including supplemental feeding, are favourable for wild boar reproduction.

Modelling immersion corrosion of structural steels in natural fresh and brackish waters

The freshwater eels of the genus Anguilla, which are catadromous, migrate between freshwater growth habitats and offshore spawning areas. A number of recent studies, however, found examples of the temperate species Anguilla anguilla, Anguilla rostrata, Anguilla japonica, Anguilla australis and Anguilla dieffenbachii that have never migrated into fresh water, spending their entire life history in the ocean. Furthermore, those studies found an intermediate type between marine and freshwater residents, which appear to frequently move between different environments during their growth phase. The discovery of marine and brackish-water residents Anguilla spp. suggests that they do not all have to be catadromous, and it calls into question the generalized classification of diadromous fishes. There has been little available information, however, concerning migration in tropical Anguilla spp. Anguilla marmorata, shows three fluctuation patterns: (1) continuous residence in fresh water, (2) continuous residence in brackish water and (3) residence in fresh water after recruitment, while returning to brackish water. Such migratory patterns were found in other tropical species, Anguilla bicolor bicolor and Anguilla bicolor pacifica. In A. b. bicolor collected in a coastal lagoon of Indonesia, two further patterns of habitat use were found: (1) constantly living in either brackish water or sea water with no freshwater life and (2) habitat shift from fresh water to brackish water or sea water. The wide range of environmental habitat use indicates that migratory behaviour of tropical Anguilla spp. is facultative among fresh, brackish and marine waters during their growth phases after recruitment to the coastal areas. Further, the migratory behaviours of tropical Anguilla spp. appear to differ in each habitat in response to inter and intra-specific competition. The results suggest that tropical Anguilla spp. have a flexible pattern of migration, with an ability to adapt to various habitats and salinities. The ability of anguillids to reside in environments of various salinities would be a common feature between tropical and temperate species without a latitudinal cline. Thus, the migration of Anguilla spp. into fresh water is clearly not an obligatory behaviour. This evidence of geographical variability among Anguilla spp. suggests that habitat use is determined by environmental conditions in each site.

The vulnerability of microhylid frogs, Cophixalus spp., to climate change in the Australian Wet Tropics

We analysed the morpho-functional response of grassland species to a grazing intensity gradient (1–3.5 sheep ha−1) in the Mediterranean-type climate region of Chile. A total of nine morpho-functional traits (with a total of 24 attributes) were determined for 79 herbaceous plant species. Valuation of the traits enabled calculation of the reproductive, vegetative and defensive potentials for each species. A classification analysis for species x potentials identified five groups of plant functional strategies, and we analysed their responses along a grazing intensity gradient both for native and non-native species. The defensive potential of the species was negatively correlated with reproductive but was not significant in relation to vegetative potential. Grazing intensification favoured the presence of species with high defensive potential, to the detriment of those with high reproductive potential. This process affected both native and non-native species, but was more intense in the former presenting higher defensive potential. The functional group with a higher defensive strategy showed an increase in relative frequency with grazing intensity. However, self-defence alone is insufficient. This group also presents a certain reproductive potential that ensures the persistence of its annual or biennial species. The functional group combining high reproductive and vegetative potentials is the one that exhibits the biggest decrease in relative frequency due to intensified grazing. This group, however, is dominant in all the stocking treatments. All the functional groups identified include both native and non-native species, although the former dominate in those with greater defensive potential.

Rotifer trophic state indices as ecosystem indicators in brackish coastal waters