Tropical Freshwater Research Articles

Molecular phylogeny and systematics of the South Asian freshwater‐fish genus Puntius (Teleostei: Cyprinidae)

AbstractDuring the past decade, the ca 120 species of small, colourful tropical Asian freshwater fishes previously referred to the cyprinid genus Puntius have been shown to consist of multiple morphologically distinct evolutionary lineages that resolve as monophyletic groups in molecular studies. Many of these clades have been allocated to new genera such as Dawkinsia, Desmopuntius, Haludaria, Oliotius, Pethia, Puntigrus, Sahyadria, Striuntius and Waikhomia. Others have been assigned to existing but previously poorly delineated genera such as Barbodes and Systomus, while some 40 species remain in Puntius. The divergent morphology of several species retained in Puntius suggests, however, that the systematics of this group requires further attention. Here, based on a phylogeny incorporating newly generated data from the mitochondrial cytochrome b (cytb), mitochondrial cytochrome c oxidase subunit 1 (cox1), nuclear recombination activating protein 1 (rag1), and interphotoreceptor retinoid‐binding protein (irbp) gene markers, we investigate the interrelationships of the species of Puntius in Sri Lanka in the wider context of their Indian and Southeast Asian congeners. We identify three well‐supported monophyletic groups that warrant recognition as new genera: Rohanella (type species Puntius titteya), Plesiopuntius (type species Gnathopogon bimaculatus) and Bhava (type species Puntius vittatus). The first of these is endemic to rainforest streams in Sri Lanka's perhumid southwestern wet zone, whereas the latter two are widely distributed in both Sri Lanka and southern India, including the Western Ghats. Our study highlights the presence of distinct evolutionary lineages among several widespread species.

Environmental Risk Assessment of Drugs in Tropical Freshwaters Using Ceriodaphnia silvestrii as Test Organism.

In this study we evaluated the acute (immobility/mortality) and chronic (survival and reproduction) effects of the drugs caffeine, diclofenac sodium salt, ketoprofen, paracetamol and salicylic acid on the cladoceran Ceriodaphnia silvestrii. The environmental risks of these substances for tropical freshwaters were estimated from the risk quotient MEC/PNEC. Sensitivity in acute exposures varied up on the drug as follows: salicylic acid (EC50 = 69.15mg L- 1) < caffeine (EC50 = 45.94mg L- 1) < paracetamol (EC50 = 34.49mg L- 1) < ketoprofen (EC50 = 24.84mg L- 1) < diclofenac sodium salt (EC50 = 14.59mg L- 1). Chronic toxicity data showed negative effects of the drugs on reproduction. Paracetamol and salicylic acid caused reduction in fecundity in concentrations starting from 10mg L- 1 and 35mg L- 1, respectively. Ketoprofen caused total inhibition at 5mg L- 1. MEC/PNEC values were relatively low for all drugs. The risk was estimated as low or insignificant, except for caffeine, whose MEC/PNEC value was greater than 1 (moderate risk).

De Novo Transcriptomic and Life-History Responses of Moina Micrura Under Stress Environment Conditions.

Moina micrura represents a promising model species for ecological and ecotoxicological investigations in tropical freshwater ecosystems. Illumina NovaSeq™ 6000 sequencing was employed in this study to analyze M. micrura across three distinct developmental stages: juvenile, adult, and male. Current study successfully annotated 51,547 unigenes (73.11%) derived from seven (7) different databases. A total of 554 genes were found to be significantly upregulated, while 452 genes showed significant downregulation between juvenile and male. Moreover, 1001 genes were upregulated, whereas 830 genes exhibited downregulation between the adult and male. Analysis of differentially expressed genes revealed upregulation of chitin, cuticle, myosin (MYO), mitogen-activated protein kinases (MAPK), fibrillin (FBN), cytochrome (CYP), glutathione s-transferase (GST), vitellogenin (VTG), acetylcholinesterase (AChE), and transforming growth factor beta (TGFB) under unfavorable environmental conditions (male), as compared to favorable environmental conditions (juveniles and adults). These alterations in gene expression significantly impact the phenological and life-history traits of M. micrura. Furthermore, the upregulation of hemoglobin (HMB), doublesex (DSX), juvenile hormone analogs (JHA), heat shock protein (HSP), and methyltransferase (METT) genes in males initiates the sex-switching effects observed in M. micrura. These findings hold substantial value for researchers interested in determining M. micrura sequences for future investigations of gene expression and comparative reproductive genome analysis within the Moina genus and cladoceran families.

Development of a cell line from skeletal trunk muscle of the fish Labeo rohita.

Labeo rohita is a widely cultivated tropical freshwater carp and found in rivers of South Asian region. A new cell line, designated LRM, has been developed from the muscle tissue of L. rohita. Muscle cells were subcultured up to 38 passages in a Leibovitz's-15 (L-15) supplemented with 10% FBS (Fetal Bovine Serum) and 10 ng/ml bFGF. The LRM cells exhibited fibroblastic morphology with a doubling time of 28h, and a plating efficiency of 17%. A maximum growth rate was observed for LRM cells at 28°C, 10% FBS and 10 ng/ml bFGF. A cytochrome C oxidase subunit I (COI) gene sequence was used to authenticate the developed cell line. Chromosome analysis revealed 50 diploid chromosomes. The fibroblastic characteristics of the of the LRM cells was confirmed by immunocytochemistry. The expression of MyoD gene in LRM cells was analyzed by quantitative PCR in comparison with passages 3, 18 and 32. The expression of MyoD was higher at passage 18 compared to the passages 3 and 32. The LRM cells attached properly onto the 2D scaffold and the expression of the F-actin filament protein was confirmed by phalloidin staining followed by counter staining with DAPI to observe the distribution of the muscle cell nuclei and the cytoskeleton protein. A revival rate of 70-80% was achieved when the LRM cells were cryopreserved at - 196°C using liquid nitrogen. This study would further contribute to understanding the in vitro myogenesis and progress toward cultivated fish meat production.

Individual specialization is the highest in generalist populations from intermediary to high trophic positions in tropical freshwater fishes

AbstractIndividual specialization (IS) refers to intrapopulation variation in resource use unrelated to ontogeny, sexual dimorphism, or discrete morphological variation. A broad niche increases individual specialization because individuals might segregate in niche space. If trophic position influences niche breadth, it would indirectly constrain the degree of individual specialization. Intermediate trophic levels, usually associated with omnivory, might display fewer constraints on their trophic niche, leading to high levels of individual specialization. We investigate the degree of individual specialization and its relationship to the trophic position in 121 fish populations belonging to 32 species from the upper Tocantins River, Central Brazil. We calculated IS using the index V based on the stomach contents of individuals, whereas values close to 1 indicate strong IS. IS ranged from 0 to 0.87 and greatly varied among species. We showed that niche breadth positively affects a population's individual specialization regardless of its trophic position. Populations occupying intermediate and high trophic positions displayed the highest degrees of individual specialization. Omnivory has no significant effect over individual specialization values. We argue that the intricate relationship among individual specialization, trophic position, and niche breadth relates to the great ecological opportunity and trophic plasticity in tropical fishes.

Prospecting the Photosynthetic Flatworm Symsagittifera roscoffensis as a Novel Fish-Feed

Symsagittifera roscoffensis is an intertidal Acoel flatworm that forms a symbiotic relationship with the alga Tetraselmis convolutae. Members of the genus Tetraselmis are known to have a high nutritional value and have been widely used to enrich intermediate prey for fish within the aquaculture industry; therefore, S. roscoffensis could be a good candidate as a trophic shortcut to deliver algal nutrition to fish. In this study, we investigated the likelihood of five ornamental tropical freshwater and six ornamental marine fishes to consume this worm, either as live feed or in freeze-dried form. We also tested the ability of S. roscoffensis to form a symbiotic relationship with alternative algal species, analysing the nutritional profile of S. roscoffensis when grown in different media. All the experimental fish consumed live worms to some degree, with the exception of one species (Meiacanthus grammistes); the response time to the worms ranged from 1.1–68.6 s for freshwater ornamental species to 1–24 s for marine ornamental species, and in most cases, this was comparable to or shorter than their response time to the reference diet Artemia. The fishes showed no negative effects after consuming the worms. We obtained similar results with freeze-dried worms in terms of the number of worms eaten, response time, and feeding time. Symsagittifera roscoffensis was able to form a symbiotic relationship with all the tested algal species of the genus Tetraselmis, but not with members of other genera. Worms grown in nutrient media (f/2 and f/4) had significantly higher contents of protein, pigments, and total and polyunsaturated fatty acids, including eicosapentaenoic acid (20:5n − 3) and α-linolenic acid (18:3n − 3), than those grown in seawater. These results show that S. roscoffensis was acceptable to many ornamental fish species, delivering key algal ingredients that are beneficial to fish health; hence, it is a promising alternative to conventional fish feeds for the ornamental pet trade.

Conservation for sustaining livelihoods: Adaptive co-management of fish no-take zones in the Mekong River

A major challenge in natural resource management in developing countries is to pursue conservation objectives while avoiding negative impacts on local livelihoods. Inland capture fisheries provide opportunities to demonstrate an integration of conservation and livelihood objectives when managed as a social-ecological system. While numerous marine no-take reserves have been found effective for the recovery of fisheries, few well-documented examples exist in the freshwater realm. Research gaps also remain in the role of co-management in balancing various management objectives and resolving conflicts. This paper offers critical reflection on adaptive co-management of fish conservation zones (FCZs) in the Mekong River in Cambodia and its social-ecological outcomes as perceived by local stakeholders. The management approach was found generally effective for the local stakeholders to negotiate between conservation and livelihood objectives at key stages of the implementation, and resolve conflicts; however, the lessons learned were not uniform across all sites. The degree of difficulty in conflict resolution was mainly a function of the fishing dependency of local communities on the protected site, the prevalence of severe poverty in adjacent villages, and the availability of livelihood options other than fishing. Growing stakeholder perception over time, of the FCZs as yielding positive outcomes—for both conservation and livelihood—motivated the local communities to create more FCZs. We argue clear recognition by local stakeholders of the achievements and the fairness in the FCZ management, facilitated through participatory approaches, can improve their acceptance of conservation rules and enhance their effectiveness. However, long-term mechanisms to support these community initiatives technically and financially are needed. Simple yet scientifically robust approaches for tropical freshwater fisheries monitoring, including periodical assessments of indicator species, are also needed to facilitate performance evaluation of specific management measures locally.

The role played by tropical cyclones-induced freshwater flux forcing in the upper-ocean responses: A case for Typhoon Yutu (2018)

Tropical cyclones (TCs) produce heavy precipitation and provide excessive freshwater flux (FWF) to the ocean, which alters surface salinity and upper-ocean stratification, leading to changes in ocean physical processes. At present, roles played by TC-induced FWF (FWFTC) forcing in the upper-ocean responses have received less attention than those by TC-induced wind stress (τTC) forcing. An ocean model is used to investigate the role played by FWFTC forcing in upper-ocean responses in the Pacific; several numerical experiments and observation-based analyses are performed, focusing on Typhoon Yutu (2018) . The FWFTC and τTC components are explicitly extracted from atmospheric reanalysis fields and are then taken into account or not in model sensitivity experiments. As expected, the FWFTC forcing acts to freshen the ocean surface, enhance the ocean stratification and reduce the mixing and entrainment of subsurface cold water into the mixed layer (ML), leading to potentially favoring surface warming; this FWF effect is opposite to that induced by τTC forcing (i.e., a cooling effect on sea surface temperature (SST)). The combined effects of FWFTC and τTC forcings lead to local ocean responses to Typhoon Yutu that are characterized by surface cooling and salting, which are dominated by the τTC forcing and are also modulated by the FWFTC forcing, depending on their relative magnitudes. When FWFTC forcing reaches a certain intensity and the τTC forcing is weak, however, the warming effect on SST due to FWFTC forcing can even exceed the cooling effect due to τTC forcing. When FWFTC forcing is relatively stronger than τTC forcing (e.g., TC-induced precipitation >10.37mmh−1 and τTC∼0.14Nm−2), the warming effect on SST due to FWFTC forcing can even exceed the cooling effect due to τTC forcing. Meanwhile, with the combination of τTC forcing, the FWFTC forcing can also promote SST cooling induced by the τTC forcing, which is dominated by mixing and entrainment. In this case, the FWFTC forcing increases surface heat loss from the ocean due to enhanced stratification, which contributes to τTC-induced vertical mixing and surface cooling. Further case studies are needed to thoroughly evaluate FWFTC-related effects on the upper ocean.

Normoxia exposure reduces hemoglobin concentration and gill size in a hypoxia-tolerant tropical freshwater fish

Hypoxia is a widespread environmental stressor that shapes fish physiology and morphology. Plasticity in traits that improve oxygen uptake and delivery or reduce oxygen requirements may be critical for fish to cope with fluctuating dissolved oxygen (DO) conditions in their natural habitat or adapt to new environments. In this study, we characterized a suite of morpho-physiological respiratory traits of a naturally hypoxia-acclimated weakly electric mormyrid fish, Petrocephalus degeni, and quantified their plasticity in response to long-term normoxia exposure. We captured P. degeni from a hypoxic swamp habitat (PO2 = 2.43 ± 1.85 kPa) surrounding Lake Nabugabo, Uganda, and acclimated them to normoxia (PO2 > 16 kPa) for up to 75 days. At various time points throughout normoxia exposure, we measured blood hemoglobin and lactate concentration, gill size, routine metabolic rate (RMR), regulation index (RI), and critical oxygen tension (Pcrit). We found that 62–75 days of normoxia exposure significantly reduced blood hemoglobin concentration (− 17%), gill filament length (− 14%), and hemibranch area (− 18%), whereas RMR, RI, Pcrit, and blood lactate showed no significant change. Our results support earlier findings that swamp-dwelling P. degeni are well adapted to life in chronic and severe hypoxia and indicate that they possess a limited capacity for phenotypic plasticity in response to a change in their DO environment.

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.