Tropical Freshwater Research Articles

Too cold is better than too hot: Preferred temperatures and basking behaviour in a tropical freshwater turtle

AbstractThermoregulation is critical to the survival of animals. Tropical environments can be particularly thermally challenging as they reach very high, even lethal, temperatures. The thermoregulatory responses of tropical freshwater turtles to these challenges are poorly known. One common thermoregulatory behaviour is diurnal basking, which, for many species, facilitates heat gain. Recently, however, a north‐eastern Australian population of Krefft's river turtles (Emydura macquarii krefftii) has been observed basking nocturnally, possibly to allow cooling. To test this, we determined the thermal preference (central 50% of temperatures selected) of E. m. krefftii in an aquatic thermal gradient in the laboratory. We then conducted a manipulative experiment to test the effects of water temperatures, both lower and higher than preferred temperature, on diurnal and nocturnal basking. The preferred temperature range fell between 25.3°C (±SD: 1.5) and 27.6°C (±1.4) during the day, and 25.3°C (±2.4) and 26.8°C (±2.5) at night. Based on this, we exposed turtles to three 24 h water temperature treatments (‘cool’ [23°C], ‘preferred’ [26°C] and ‘warm’ [29°C]) while air temperature remained constant at 26°C. Turtles basked more frequently and for longer periods during both the day and night when water temperatures were above their preferred range (the ‘warm’ treatment). This population frequently encounters aquatic temperatures above the preferred thermal range, and our results support the hypothesis that nocturnal basking is a mechanism for escaping unfavourably warm water. Targeted field studies would be a valuable next step in understanding the seasonal scope of this behaviour in a natural environment.

Water Chestnut (Trapa natans L.): Functional characteristics, nutritional properties and applications in food industry: A review

An annual floating-leaved aquatic plant, the water chestnut (Trapa natans L.), is found in temperate and tropical freshwater wetlands, rivers, lakes, ponds, and estuaries. Hydrophytes that produce starch called water chestnut has the potential to serve as a reliable food supply, particularly in flood-prone wasteland areas. It is loaded with minerals and essential nutrients. Water chestnuts are not actually nuts, despite their name. They are aquatic tuber vegetables that may be found in shallow lakes, paddy fields, marshes, and ponds. Water chestnuts are indigenous to numerous islands in the Indian and Pacific oceans, as well as Southeast Asia, Southern China, Taiwan, Australia, and Africa. When the corm, or bulb, acquires a dark brown hue, they are picked. They are a typical ingredient in Asian recipes including stir-fries, chop suey, curries, and salads because of their crisp, white meat, which may be eaten raw or cooked. The huge, nourishing seed of the water chestnut, a native of Eurasia and Africa, has been widely collected since the Neolithic, and it is now grown for food throughout Asia. Water chestnuts have several advantages over other foods, including being particularly nutrient-dense and low in calories. A wonderful source of fibre, water chestnuts may aid in promoting bowel movements, lowering blood cholesterol, neuro-protective, controlling blood sugar levels, and maintaining the health of your gut. In addition, carbohydrates account for the majority of the calories in water chestnuts. Although they are abundant in fibre, potassium, manganese, copper, vitamin B6, and riboflavin, uncooked water chestnuts are 74% water, which means they are often low in calories. Due to its usage in the treatment of gastrointestinal illnesses, genitourinary system disorders, liver, kidney, and spleen disorders, Trapa natans is one of the most significant medicinal plants in Indian Ayurveda.

Redclaw, Cherax quadricarinatus sex-separated rearing strategy enhances reproduction in females

Redclaw crayfish Cherax quadricarinatus, a tropical freshwater species, native to Northern Australia and is regarded as a promising species for global expansion of aquaculture. However, poor female fertility is a hindrance towards the commercial production of redclaw. The present study investigated if dissociated; pre-exposure of female redclaw to males can stimulate spawning and increase reproductive efficiency. The study was conducted in dissociated (111 days) and associated (34 days) phases. Redclaw were held in vertical recirculating aquaculture systems with each system consisting of 42 individual compartments (45 cm length x 33 cm width x 25 cm height) arranged as six compartments horizontally and seven compartments vertically. The average body weight of females was 66 ± 2.2 g. In the dissociated phase, females were either kept alone (0M, n = 36) or were exposed to either 1 (1M, n = 36) or 2 (2M, n = 36) males suspended in the uppermost row of the system. During the associated phase, females (n = 108) were maintained at a sex ratio of 1M:1F. During the dissociated phase, the spawning rate was less in the control compared to the male exposed groups (2.8%, 1/36, 18.1%, 13/72 respectively; p = 0.026). However, the moulting rate was greater in the control compared to the male exposed groups (22.2%, 8/36; 5.6%, 4/72 respectively; p = 0.009). During the associated phase, there were no significant differences in spawning rate (22.2%, 8/36 and 33.3%, 24/72), mean days to spawning (21.88 ± 3.06 and 16.38 ± 2.35), moulting rate (11.1%, 4/36 and 6.9%, 5/72) and mean days to moulting (24.50 ± 3.97 and 22.40 ± 3.93) in the control and male exposed groups, respectively (p > 0.05). However, the mean total number of eggs (670.9 ± 26.0 and 507.0 ± 29.36), fecundity (11.00 ± 0.59 and 6.14 ± 0.47), the hatching rate (89.70 ± 1.31% and 77.50 ± 9.24%) and the total number of juveniles produced (545.70 ± 42.50 and 343.30 ± 37.47) during the associated phase were greater in the male exposed groups compared to the control group respectively; p < 0.05). It was concluded that pre-exposure of redclaw females to males in a dissociated recirculation system, increases spawning rate during a dissociated phase, and after exposure to males improves egg and juvenile production during an associated phase. Such a breeding strategy has potential to increase hatchery productivity.

Occurrence Prediction of Riffle Beetles (Coleoptera: Elmidae) in a Tropical Andean Basin of Ecuador Using Species Distribution Models

Genera and species of Elmidae (riffle beetles) are sensitive to water pollution; however, in tropical freshwater ecosystems, their requirements regarding environmental factors need to be investigated. Species distribution models (SDMs) were established for five elmid genera in the Paute river basin (southern Ecuador) using the Random Forest (RF) algorithm considering environmental variables, i.e., meteorology, land use, hydrology, and topography. Each RF-based model was trained and optimised using cross-validation. Environmental variables that explained most of the Elmidae spatial variability were land use (i.e., riparian vegetation alteration and presence/absence of canopy), precipitation, and topography, mainly elevation and slope. The highest probability of occurrence for elmids genera was predicted in streams located within well-preserved zones. Moreover, specific ecological niches were spatially predicted for each genus. Macrelmis was predicted in the lower and forested areas, with high precipitation levels, towards the Amazon basin. Austrelmis was predicted to be in the upper parts of the basin, i.e., páramo ecosystems, with an excellent level of conservation of their riparian ecosystems. Austrolimnius and Heterelmis were also predicted in the upper parts of the basin but in more widespread elevation ranges, in the Heterelmis case, and even in some areas with a medium level of anthropisation. Neoelmis was predicted to be in the mid-region of the study basin in high altitudinal streams with a high degree of meandering. The main findings of this research are likely to contribute significantly to local conservation and restoration efforts being implemented in the study basin and could be extrapolated to similar eco-hydrological systems.

Population Status of the Tropical Freshwater Shrimp Xiphocaris elongata in Urban and Forest Streams in Puerto Rico

Most of the human population lives in cities, and understanding their impact on freshwater environments is essential. Streams in cities face many environmental challenges that have been described in the concept of Urban Stream Syndrome. This concept illustrates urban streams’ biological, hydrological, chemical, and physical stressors. In tropical streams, these stressors impact shrimp, fish, insects, and other macroinvertebrates that inhabit the freshwater ecosystems. Freshwater shrimp are vulnerable to urban activities, physical, chemical, and ecological impacts. For this reason, these organisms have been used as biological indicators of stream health in the tropics. The shredder shrimp Xiphocaris elongata plays a fundamental role in the organic matter process and decomposition. The objectives of this study were to characterize the population of X. elongata and to identify differences in the abundance of X. elongata between urban and forest streams. Our results showed that highly urbanized areas have a significantly lower abundance of the shredder shrimp X. elongata than medium or low urban reach in the urban and forested watersheds. This study also showed that physicochemical and geomorphological variables are important environmental factors that influence the abundance of X. elongata in Puerto Rican streams.

The Effects of Nickel and Copper on Tropical Marine and Freshwater Microalgae Using Single and Multispecies Tests.

Microalgae are key components of aquatic food chains and are known to be sensitive to a range of contaminants. Much of the available data on metal toxicity to microalgae have been derived from temperate single-species tests with temperate data used to supplement tropical toxicity data sets to derive guideline values. In the present study, we used single-species and multispecies tests to investigate the toxicity of nickel and copper to tropical freshwater and marine microalgae, including the free-swimming stage of Symbiodinium sp., a worldwide coral endosymbiont. Based on the 10% effect concentration (EC10) for growth rate, copper was two to four times more toxic than nickel to all species tested. The temperate strain of Ceratoneis closterium was eight to 10 times more sensitive to nickel than the two tropical strains. Freshwater Monoraphidium arcuatum was less sensitive to copper and nickel in the multispecies tests compared with the single-species tests (EC10 values increasing from 0.45 to 1.4 µg Cu/L and from 62 to 330 µg Ni/L). The Symbiodinium sp. was sensitive to copper (EC10 of 3.1 µg Cu/L) and less sensitive to nickel (EC50 >1600 µg Ni/L). This is an important contribution of data on the chronic toxicity of nickel to Symbiodinium sp. A key result from the present study was that three microalgal species had EC10 values below the current copper water quality guideline value for 95% species protection in slightly to moderately disturbed systems in Australia and New Zealand, indicating that they may not be adequately protected by the current copper guideline value. By contrast, toxicity of nickel to microalgae is unlikely to occur at exposure concentrations typically found in fresh and marine waters. Environ Toxicol Chem 2023;00:1-13. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Exceptional levels of species discovery ameliorate inferences of the biogeography and diversification of an Afrotropical catfish family

Endeavours in species discovery, particularly the characterisation of cryptic species, have been greatly aided by the application of DNA molecular sequence data to phylogenetic reconstruction and inference of evolutionary and biogeographic processes. However, the extent of cryptic and undescribed diversity remains unclear in tropical freshwaters, where biodiversity is declining at alarming rates. To investigate how data on previously undiscovered biodiversity impacts inferences of biogeography and diversification dynamics, we generated a densely sampled species-level family tree of Afrotropical Mochokidae catfishes (220 valid species) that was ca. 70 % complete. This was achieved through extensive continental sampling specifically targeting the genus Chiloglanis a specialist of the relatively unexplored fast-flowing lotic habitat. Applying multiple species-delimitation methods, we report exceptional levels of species discovery for a vertebrate genus, conservatively delimiting a staggering ca. 50 putative new Chiloglanis species, resulting in a near 80 % increase in species richness for the genus. Biogeographic reconstructions of the family identified the Congo Basin as a critical region in the generation of mochokid diversity, and further revealed complex scenarios for the build-up of continental assemblages of the two most species rich mochokid genera, Synodontis and Chiloglanis. While Syndontis showed most divergence events within freshwater ecoregions consistent with largely in situ diversification, Chiloglanis showed much less aggregation of freshwater ecoregions, suggesting dispersal as a key diversification process in this older group. Despite the significant increase in mochokid diversity identified here, diversification rates were best supported by a constant rate model consistent with patterns in many other tropical continental radiations. While our findings highlight fast-flowing lotic freshwaters as potential hotspots for undescribed and cryptic species diversity, a third of all freshwater fishes are currently threatened with extinction, signifying an urgent need to increase exploration of tropical freshwaters to better characterise and conserve its biodiversity.

Seasonality and growth in tropical freshwater ectotherm vertebrates: Results from 1-year experimentation in the African gray bichir, giraffe catfish, and the West African mud turtle.

Growth in ectotherm vertebrates is strongly rhythmed by seasonal variation in environmental parameters. To track the seasonal variation in ancient times in a continental and tropical context, we aim to develop a method based on the use of the growth rate of fossil ectotherm vertebrates (actinopterygians and chelonians) influenced by seasonal environmental fluctuations they experienced in their lifetime. However, the impact of environmental parameters on growth, positive or negative, and its intensity, depends on the taxa considered, and data are scarce for tropical species. For 1 year, an experiment was conducted to better understand the effect of seasonal variation in environmental parameters (food abundance, temperature, and photoperiod) on the somatic growth rate of three species of tropical freshwater ectotherm vertebrates: the fishes Polypterus senegalus and Auchenoglanis occidentalis and the turtle Pelusios castaneus. Mimicking seasonal shifts expected to be experienced by the animals in the wild, the experiment highlighted the preponderant effect of food abundance on the growth rate of those three species. Water temperature variation had a significant effect on the growth rate of Po. senegalus and Pe. castaneus. Moreover, the photoperiod demonstrated no significant effect on the growth of the three species. The duration of application of starvation or cool water conditions, ranging from 1 to 3months, did not affect the growth rate of the animals. However, Pelusios castaneus showed a temporary sensitivity to the return of ad libitum feeding or of warm water, after a period of starvation or cool water, by a period of compensatory growth. Finally, this experiment revealed, in the three species, fluctuations in the growth rate under controlled and constant conditions. This variation, similar to the variation in precipitation and temperature observed in their native environment, could be linked to a strong effect of an internal rhythm controlling somatic growth rate.

Species Checklistand DNA Barcoding of Baung (Bagrid Catfish) Hemibagrus Hoevenii from Muar River, Johor

Of Asia, Africa, and the Middle East, there are 15 genera in the Bagridae family. The tropical freshwater catfish Hemibagrus hoeveniiis found in Asian waters. Bagrids are also known as Old World pimelodids, while New World bagrids may be more accurate. In Muar, Johor, DNA barcoding has never been utilised to determine the species of bagrid catfish. Therefore,this study was done to updatethe species checklist of Baung (bagrid catfish)in Muar River,and DNA barcoding of protein-coding cytochrome coxidase I (COI) mitochondrial gene was donefor species identification and phylogenetic analyses. A number of two partial COI gene sequencesranging 674-687 nucleotide baseswere successfully obtained for two specimens of Baung Lawi and the Nucleotide Basic Local Alignment Search Tool (BLAST) analysis suggested theirspecies status as from the genus Hemibagrus. Furthermore, the results of the phylogenetic analyses showedthat the neighbour joining tree, the maximum parsimony tree and the maximum likelihood tree grouped the COI mtDNA gene sequencesof Baung Lawifrom MuarRiverin one single cluster, thusconfirming the species status and showed the presence of H. hoeveniiin MuarRiver, Johor.

Toxicity of Zinc to Aquatic Life in Tropical Freshwaters of Low Hardness.

Zinc (Zn) is a metal of potential concern for a uranium mine whose receiving waters are in the World-Heritage listed Kakadu National Park in northern Australia. The chronic toxicity of Zn was assessed using seven tropical species in extremely soft freshwater from a creek upstream of the mine. Sensitivity to Zn was as follows (most sensitive to least sensitive based on 10% effect concentrations [EC10s]): mussel Velesunio angasi > gastropod Amerianna cumingi > fish Mogurnda mogurnda > cladoceran Moinodaphnia macleayi > green hydra Hydra viridissima > green alga Chlorella sp. > duckweed Lemna aequinoctialis, with EC10s (<0.45 µm filtered fraction) ranging from 21 to 320 µg/L Zn and EC50s ranging from 52 to 1867 µg/L Zn. These data were used to inform the risk assessment for the rehabilitation of the mine-site and contribute to the global Zn dataset. Environ Toxicol Chem 2023;42:679-683. © 2023 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2023 SETAC.

Nitrous oxide emission from a flooded tropical wetland across a vegetation and land use gradient

Abstract This study investigated, using the closed chamber method, the impact of (1) vegetation community type (Typha latifolia, Cyperus papyrus and Phragmites mauritianus) in a natural tropical freshwater marsh wetland (marsh) and (2) conversion of a natural tropical freshwater marsh into a rice paddy wetland (rice paddy), on nitrous oxide (N2O) emission. Both the marsh and the rice paddy were continuously flooded, while the rice paddy was unfertilized. Average N2O emission from the marsh did not vary significantly (p &amp;gt; 0.05) among the vegetation communities, ranging from 0.5 to 0.6 μg m−2 h−1. Similarly, these N2O emission rates were not significantly different (p &amp;gt; 0.05) from those recorded in the rice paddy (0.7 ± 2.8 [SE] μg m−2 h−1). There was no significant correlation (p &amp;gt; 0.05) between environmental parameters and N2O emission. We concluded that vegetation community type does not affect N2O emission from natural tropical freshwater marshes under continuous flooding. Further, converting natural tropical freshwater marshes into continuously flooded and unfertilized rice paddies does not affect N2O emission but instead enhances carbon emission, as was depicted by the significantly lower (p &amp;gt; 0.05) soil organic carbon content in the rice paddy. In view of climate change mitigation, therefore, wetland management should give priority to the conservation/protection of natural wetlands.

Environmental DNA survey to detect an endemic cryptic fish, Anablepsoides cryptocallus, in tropical freshwater streams

Abstract Martinique island is a biodiversity hotspot in the Lesser Antilles that harbours many endemic species. One of these, Anablepsoides cryptocallus, also known as ‘Poisson gale’, is the only endemic freshwater fish of Martinique and a species with a poorly understood distribution range. In this study, an environmental DNA (eDNA) detection protocol was developed, validated, and optimized, targeting a short fragment (125 bp) of the A. cryptocallus COI mitochondrial gene, to investigate the presence of this species in Martinique. Fifty‐seven sites spread over 43 permanent rivers and two wetlands were sampled using both eDNA and conventional fishing (dip net capture). Presence was confirmed in 27 sites using eDNA detection, and in nine sites by dip net fishing. eDNA‐based detection of A. cryptocallus was effective and less time‐consuming than conventional fishing, making it a relevant tool for future studies throughout the island. Even though A. cryptocallus was found to be present in a significant number of sites, many sites previously known for this species were found to be negative, highlighting the need for continuous monitoring. There is now an urgent need to propose protection status for this endemic species to preserve its preferential habitats, as these are being increasingly threatened by human activities that are leading to habitat loss and fragmentation.

Recent Production and Marketing Scenarios of Water Chestnut (Trapa spp.) in India: A Review

Water chestnut (Trapa spp.) is an important annual, floated but rooted aquatic plant of temperate and tropical freshwater wetlands of India. The water chestnut is native to Europe, Asia and Africa and has been widely cultivated for a long time for food in Asia. It thrives best in nutrient-rich water with a pH range of 6.7 to 8.2. The plant Trapa spp. has also been recognized as analgesic, anti-inflammatory, anti-diabetic and anti-microbial. The kernels of water chestnut act as a diuretic, aphrodisiac, nutrient, appetizer, astringent, coolant, anti-diarrheal and tonic. It is an excellent source of minerals such as K, Ca and Mg, as well as carbohydrates and protein. In the creation of mixed products, many food products derived from the chestnut kernel and its flour are used. The yield per hectare is approximately 4-4.5 tones of fresh fruit and 1-1.5 tones of dry nuts. As fresh, canned fruit, dry nuts and flour, it has a very promising market in India and internationally. Fresh fruits are extremely delicious. TSS values varied from 7.0 to 9.00B. It is a very lovely and low-cost nutritious food that has the potential to manipulate the food market by making available various water chestnut mix flour items that might play an essential role in addressing malnutrition in India. This study of enumerated areas, production and marketing potential may be of immense value and great interest to researchers and academicians.

Effects of turbidity and introduced tilapia (Oreochromis spp) on macrophytes and invertebrates in a shallow tropical lake

Tropical freshwater wetlands are subject to multiple stressors but there is little information on which stressors cause wetland degradation. Increased turbidity is considered a major cause of degradation, but the effects of introduced fish are often overlooked. Tilapia are frequently introduced in tropical regions, especially species in the genus Oreochromis, and the ecological effects of introducing tilapia are poorly studied. We used enclosure experiments in a shallow lake in Madagascar to assess the effects of tilapia and turbidity on macrophytes and benthic invertebrates, and to test management interventions designed to increase both. Tilapia at high and low stocking densities had negative effects on survival of Charophyte algae and water lilies, but no direct effect on benthic invertebrate abundance or diversity. Invertebrate abundance was highest on submerged Charophytes, so herbivory by tilapia indirectly affected invertebrates. Turbidity affected Charophyte survival, and abundance and diversity of non-Dipteran insects. As a complication, tilapia may increase turbidity by re-suspending the lake sediment. Our results suggest that herbivory by tilapia is a plausible cause of the removal of macrophytes from the lake and an impediment to their re-establishment. Tilapia are widely introduced in tropical areas as a food resource. Our results demonstrate serious consequences to these introductions.

Assessment of the current trophic state and water quality of Lake Naivasha, Kenya using multivariate techniques

AbstractLake Naivasha is a tropical freshwater body in Kenya, providing a source of livelihoods to the surrounding communities. The lake ecosystem, however, has become degraded over time because of increasing pollutant loads from multiple sources, including human settlements and agricultural and surface runoff in its basin. Thus, it is vital to study the lake's water quality to determine its current status to inform appropriate management measures. Accordingly, the present study analysed water quality parameters and the trophic state of Lake Naivasha on the basis of water samples collected at eight sampling sites during the dry and wet seasons from December 2019 to May 2020. The physico‐chemical parameters were measured in situ, while nutrients were analysed in the laboratory. The results indicated high turbidity, total nitrogen (TN), ammonium‐nitrogen (NH4+‐N), nitrate‐N (NO3‐N) and total phosphorus (TP) levels during the wet season, and at the Malewa and Karati River mouths, while pH, electrical conductivity (EC) and chlorophyll‐a values were relatively high during the dry season. The water temperature and dissolved oxygen (DO) concentration, however, did not vary between sampling sites or seasons. Cluster analysis (CA) classified the sites into three clusters based on water quality spatial and seasonal variations. Cluster 1 was comprised of the isolated region (Crescent), while clusters 2 and 3 mainly comprised sites sampled during wet and dry seasons, respectively. Similarly, principal component analysis (PCA) revealed spatial and seasonal physico‐chemical variations, indicating nutrient parameters (TN, TP, NO3‐N and NH4+‐N), pH, Secchi depth and turbidity are the major variables influencing water quality variations. Furthermore, factor analysis (FA) identified nutrients, sediment and organic sources as the main lake pollution sources. The trophic state index (TSI = 60–72) indicated the lake varied from a eutrophic to hypertrophic state during the study period. The lake was found to be more eutrophic than reported in previous studies, indicating a progressive deterioration of its water quality. The overall results demonstrated some of the sampling sites in the lake are heavily contaminated with pollutants from various sources, attributable primarily to land use patterns and anthropogenic activities. The results of the present study are useful to inform decisions regarding management of the lake water quality.

Combined effects of landscape composition and agrochemicals on frog communities amid sugarcane-dominated agroecosystems.

Global demand for crops will continue increasing over the next few decades to cover both food and biofuel needs. This demand will put further pressure to expand arable land and replace natural habitats. However, we are only beginning to understand the combined effects of agrochemicals and land-use change on tropical freshwater biodiversity. In this study, we analyzed how pond-dwelling anuran larvae responded to pond characteristics, landscape composition, and agrochemical contamination in a sugarcane-dominated agroecosystem in Brazil. Then we used an information theoretical approach with generalized linear models to relate species richness and abundance to predictor variables. The variation in tadpole abundance was associated with both agrochemical concentration (e.g., ametryn, diuron, and malathion) and landscape variables (e.g., percentage of forest, percentage of agriculture, and distance to closest forest). The relationship between species abundance and agrochemicals was species-specific. For example, the abundances of Scinax fuscovarius and Physalaemus nattereri were negatively associated with ametryn, and Dendropsophus nanus was negatively associated with tebuthiuron, whereas that of Leptodactylus fuscus was positively associated with malathion. Conversely, species richness was associated with distance to forest fragments and aquatic vegetation heterogeneity, but not agrochemicals. Although we were unable to assign a specific mechanism to the variation in tadpole abundance based on field observations, the lower abundance of three species in ponds with high concentrations of agrochemicals suggest they negatively impact some frog species inhabiting agroecosystems. We recommend conserving ponds near forest fragments, with abundant stratified vegetation, and far from agrochemical runoffs to safeguard more sensitive pond-breeding species.

A Review of Zebrafish as an Alternative Animal Model and Its Benefits over Other Animal Models in Various Disease Conditions

The zebrafish (Danio rerio) model has been exponentially adopted because it is a small tropical freshwater fish with crucial genetic, anatomical, and physiological homology with humans. Therefore, zebrafish constitute an excellent experimental model for behavioral, genetic, and toxicological studies that unravel the mechanisms of various human diseases. The zebrafish is a vertebrate, as it shares many organs with humans, including the blood, muscles, kidneys, and eyes. Genome organization and the pathways involved in controlling signal transduction appear to be highly conserved between zebrafish and humans, and therefore zebrafish may be used for modeling human diseases. The zebrafish genome has been sequenced, allowing scientists to study the functions of more than 14,000 genes by inducing mutations in those genes. Zebrafish have a special ability to repair their heart muscle, and scientists are attempting to determine the specific factors involved in this process to help people with heart problems. This review focuses on the use of zebrafish as a potential alternative model and its advantages over other animal models for conducting biomedical research on various human disease conditions.

Drivers of species richness and beta diversity of fishes in an Afrotropical intermittent river system.

Tropical freshwater ecosystems are some of the most threatened systems yet remain understudied relative to temperate systems. Here, we look at the drivers of community structure of fishes in a tropical and intermittent system in central Kenya. We conducted monthly sampleswithin the upper Northern Ewaso Ng'iro to assess variation in community composition and abiotic characteristics. We analyzed species richness along the longitudinal gradient, computed beta diversity within the system, relative contributions of each site, and partitioned beta diversity metrics into nestedness and turnover components. We found that, similar to temperate intermittent systems, species richness varied along the longitudinal gradient, nestedness contributions to beta diversity exceeded those of turnover, and environmental and spatial variables determined patterns of beta diversity. Sites at the highest and lowest ends of the species richness gradient showed the highest contributions to beta diversity, suggesting sites important for preservation or restoration initiatives, respectively. With ongoing water extraction and conflict over resources throughout the region, this study highlights the need for further investigations of the effects of multiple stressors on biodiversity patterns and ecosystem functioning in tropical stream communities.

Risk assessment of bisphenol analogues towards mortality, heart rate and stress-mediated gene expression in cladocerans Moina micrura.

Bisphenol A (BPA) is a well-known endocrine-disrupting compound that causes several toxic effects on human and aquatic organisms. The restriction of BPA in several applications has increased the substituted toxic chemicals such as bisphenol F (BPF) and bisphenol S (BPS). A native tropical freshwater cladoceran, Moina micrura, was used as a bioindicator to assess the adverse effects of bisphenol analogues at molecular, organ, individual and population levels. Bisphenol analogues significantly upregulated the expressions of stress-related genes, which are the haemoglobin and glutathione S-transferase genes, but the sex determination genes such as doublesex and juvenile hormone analogue genes were not significantly different. The results show that bisphenol analogues affect the heart rate and mortality rate of M. micrura. The 48-h lethal concentration (LC50) values based on acute toxicity for BPA, BPF and BPS were 611.6µg L-1, 632.0µgL-1 and 819.1µgL-1, respectively. The order of toxicity based on the LC50 and predictive non-effect concentration values were as follows: BPA > BPF > BPS. Furthermore, the incorporated method combining the responses throughout the organisation levels can comprehensively interpret the toxic effects of bisphenol analogues, thus providing further understanding of the toxicity mechanisms. Moreover, the output of this study produces a comprehensive ecotoxicity assessment, which provides insights for the legislators regarding exposure management and mitigation of bisphenol analogues in riverine ecosystems.

Aquatic Insects in Habitat-Forming Sponges: The Case of the Lower Mekong and Conservation Perspectives in a Global Context

Shallow water sponges settled on a raft along the Pong River (Lower Mekong Basin, Thailand) were investigated to highlight the taxonomic richness, composition, relative abundance and lifestyle of sponge-dwelling aquatic Insecta. The three-dimensional biogenic structures of the model sponges hosted 4 orders of Insecta, belonging to 10 families and 19 genera/species, able to strictly coexist at the level of the sponges in aquiferous canals and/or at the body surface, and/or dwelling in the extracellular matrix. On the basis of the identified 379 larvae and pupae, Trichoptera and Diptera were found to be the dominant inhabitants of Corvospongilla siamensis (Demospongiae: Spongillida), endemic to Southeast Asia. In the focused lotic ecosystem, dominated by soft bottoms, sponges play a functional role. Insecta use sponges as a substratum, nursery ground, food source, and shelter microhabitat, protecting them from predation and environmental aggression. Moreover, their feeding behavior indicates the insects’ adaptive traits to recycle sponge siliceous spicules as a source of exogenous material to strengthen the larval–pupal cases and the digestive system. The results of the Thai sponge model contribute to the inventory of global engineering species richness, ecosystem types, and biogeographic diversity, thus raising awareness for freshwater biodiversity conservation. In this regard, the present data, along with the worldwide inventory, focus on sponges as (a) key habitat-forming species for aquatic insect assemblages, (b) ecosystem engineers in river/lake/wetland ecosystems, providing water purification, the processing of organic matter, recycling of nutrients, and freshwater–terrestrial coupling, and (c) promising candidates in restoration projects of tropical freshwater ecosystems by bioremediation.