Effects of mercury and magnetic fields on the activity of proteinases and glycosidases in the intestine of common carp Cyprinus carpio.

Aquatic ecosystems are increasingly affected by anthropogenic pollution, including heavy metals like mercury, which accumulate in organisms and cause harmful effects. At the same time, human activities such as industrial operations and the use of electric power lines also alter the magnetic background in natural water bodies. However, the interaction between mercury exposure and magnetic fields remains poorly understood. This study aimed to investigate the combined effects of mercury and magnetic fields on the digestive enzyme activity of common carp (Cyprinus carpio), focusing on the relevance of magnetic fields due to their increasing presence in industrialized environments. Two groups of fish were fed diets with low (0.02 mg/kg) or high (0.27 mg/kg) mercury content for 6 months and exposed to extremely low-frequency magnetic fields or hypomagnetic conditions. Results showed significant differences in mercury accumulation between groups, with higher levels in carps fed with high-mercury content diets. These fish also exhibited increased body length and weight compared to those on a low-mercury diet. The amylolytic activity (total activity of enzymes hydrolyzing starch: α-amylase, glucoamylase, and maltase) and proteolytic activity (total activity of serine proteinases) in the fish intestine were assessed. Magnetic exposure had contrasting effects on enzyme activity, depending on mercury levels in the diet. Fish fed the low-mercury diet exhibited decreased amylolytic activity following magnetic field exposure, while fish on the high-mercury diet showed increased activity. Proteolytic activity followed a similar pattern, with opposite effects observed between the two dietary groups. These findings suggest that mercury accumulation alters the biological response to magnetic fields, possibly through compensatory biochemical mechanisms. Understanding the interactions between toxic substances and magnetic fields is critical for improving environmental risk assessments.

Unveiling the molecular identity of the diminutive cyprinid, Horadandia brittani (Teleostei: Cyprinidae), a species endemic to Southern India.

BACKGROUND: Horadandia brittani is a small cyprinid fish species initially discovered in the coastal floodplains of southern India. For almost 50 years, the genus Horadandia was monotypic with a single species confined to Sri Lanka. In 1992, a new species H. brittani was described from south-western India. Despite being described as a separate species, H. brittani was later considered a synonym of H. atukorali, but in 2013, researchers recognized it as a distinct species based on morphological differences. Despite this clarification, there was still a need to validate the identity of H. brittani and determine its evolutionary relationship with its closely related species using DNA sequences. METHODS: To address the uncertainties surrounding the identity of H. brittani, the present study utilized molecular techniques to generate DNA sequences. Sample collection involved obtaining specimens of H. brittani from their natural habitats. Subsequently, DNA was extracted from the collected samples, and the mitochondrial cytochrome C oxidase (COI) gene was amplified using appropriate methods. RESULTS: The analysis of DNA sequences obtained from the COI gene revealed significant genetic distinctions between H. brittani and H. atukorali. The genetic distance values between these two species ranged from 3.21 to 3.63%, clearly indicating that these two species are genetically separate entities. The study successfully established the phylogenetic relationships between H. brittani and H. atukorali based on the COI gene sequences, further confirming the validity of H. brittani as a distinct and separate species. CONCLUSION: The findings of this study conclusively demonstrate that H. brittani is a valid and separate species, distinct from H. atukorali. The genetic analysis based on mitochondrial COI gene sequences provided strong evidence for the differentiation between these two species. The molecular data generated in this research can be used to identify H. brittani quickly and accurately in the future.

Comprehensive analysis of full-length transcriptomes of Schizothorax prenanti by single-molecule long-read sequencing.

Schizothorax prenanti (S. prenanti) is one of the most important aquaculture species in the southwest of China. However, information of the full-length transcripts in S. prenanti remains unknown. In this study, single-molecule real-time (SMRT) sequencing was performed to generate full-length transcriptomes of S.prenanti. In total, 23.26 Gb of clean reads were generated. A total of 312,587 circular consensus sequences (CCS) were obtained with average lengths of 2634 bp and 84.16% (270,662) of CCS were full-length non-chimeric reads. After being corrected with Illumina library sequencing, 18,005 contigs were obtained, with 17,797 (98.81%) successfully annotated in eight public databases, including 15,839 complete open reading frames (ORFs) with an average length of 1330 bp. Furthermore, a total of 4152 alternative splicing (AS) events and 250 long non-coding RNA (lncRNA) transcripts were detected. Additionally, a total of 1129 putative transcription factors (TFs) members from 56 TF families and 11,660 simple sequence repeats (SSRs) were identified. This study provided a valuable resource of full-length transcripts for further research on S. prenanti.

Antibiotic resistance and virulence factor gene profile of A. hydrophila isolated from carp (Cyprinidae) suspected with hemorrhagic septicemia in Gilan, Iran.

The present study was conducted to determine the antibacterial resistance profile of Aeromonas hydrophila (n = 42) isolated from the 100 hemorrhagic septicemia-suspected carp in Gilan, Iran. The prevalence of class 1 and 2 integrons, antibiotic resistance genes (ARG) and virulence factor genes (VFG) among these isolates was investigated using PCR. Also, the possible association between the presence of VFGs and the antibiotic resistance profile of isolates was assessed. The majority of A. hydrophila isolates (83·33%) exhibited multi-drug resistance (MDR) profile, and all isolates were resistant to clindamycin, while all isolates were susceptible to amikacin. intI1 and intI2 gene was found in 26·2 and 4·8% isolates, respectively. This is the first report of the presence of the intI2 gene in A. hydrophila isolates in Iran. The blaTEM (40·5%) and tetA (33·3%) genes were found as the predominant ARGs. The most frequently detected VFGs were lip and ahh1(90·5%), while the examined isolates carrying at least three VFGs and the most prevalent VFGs profile was ast+, act+, alt+, ahhl+, aerA+, ahyB+ and lip+. The results of this study indicate a positive association between the presence of VFGs and antibiotic resistance, and most MDR A. hydrophila isolates showed high frequencies of VFGs.

Towards the phylogenetic placement of the enigmatic African genus Prolabeops Schultz, 1941.

The small cyprinid genus Prolabeops Schultz, 1941 is restricted to the Nyong and Sanaga River systems in Cameroon. In the past, the genus had been suggested to be either a member of the Labeoninae, Torinae or the Smiliogastrinae mainly on the basis of morphological similarities, and it is nowadays considered as incertae sedis within the Cypriniformes. This study provides the first attempt to reveal the phylogenetic position of Prolabeops using molecular data. For this purpose, the authors sequenced a large fraction of the mitochondrial genome (c. 13,600 bp), including all mitochondrial protein coding genes, of two Prolabeops melanhypopterus specimens and an additional four Enteromius specimens. The large-scale phylogenetic analysis was based on an alignment including all mitochondrial protein coding genes of 902 specimens representing c. 899 cypriniform species. Prolabeops was clearly recovered within the African Smiliogastrinae, forming a weakly supported clade together with Enteromius jae, Enteromius hulstaerti and Barboides gracilis. The study data underline the urgent need of a thorough taxonomic revision of the small African barbs collectively placed in the genus Enteromius.

Selected freshwater fish species for assessing the water quality of the lower catchment of the Kelani River, Sri Lanka.

Kelani River is the most polluted river in Sri Lanka and the lower catchment is more polluted than the upper catchment. In the present study, freshwater fish species of the lower catchment of the river were investigated for the use of assessing the water quality. Cast net sampling and identification recorded 34 freshwater fish species from the lower catchment, the majority represented by family Cyprinidae. Fish species richness, diversity indices, distribution, abundance and the regression analysis of fish species with water quality parameters revealed high sensitivity and tolerance of three fish species with certain water quality parameters. Dawkinsia singhala was tolerant to the fluctuations of the chemical parameters of the water, while Rasbora daniconius and Pethia reval were tolerant to the physical parameters. Positive correlations were evident between the ammonium and phosphate concentrations of the water and distribution and abundance of D. singhala, while R. daniconius and P. reval showed positive correlations with turbidity of water and pH value respectively. Furthermore, the study reveals that D. singhala is more suitable for predicting the water quality of urban and peri-urban locations of the river, while P. reval and R. daniconius are more suitable for assessing the water quality of rural locations. Thus, the present study reveals a strong possibility of using D. singhala, R. daniconius and P. reval, as biological indicators for assessing the variation of water quality of the lower catchment of the Kelani River. However, despite the fact that such a study has been conducted for the first time in Sri Lanka, it is restrained by certain limitations, and seasonal variations of water quality parameters with fish parameters, adaptations inherent to fish species and food availability in different locations combined with long-term monitoring of fish assemblages have not been considered. Future studies investigating these aspects will further enhance the value of the study.

Redescription of Aspidogaster limacoides Diesing, 1834 (Aspidogastrea: Aspidogastridae) from freshwater fishes of northern Germany.

Aspidogaster limacoides Diesing, 1834 (Aspidogastridae) is redescribed based on light and scanning electron microscopy of specimens from the stomach and intestine of Abramis brama, Rutilus rutilus and Scardinius erythrophthalmus (Actinopterygii: Cyprinidae). The fishes were sampled during 2018 and 2019 at Lake Tollense in Mecklenburg-Western Pomerania, Germany. The prevalence of A. limacoides was highest in R. rutilus (61.7%) followed by Scardinius erythrophthalmus (7.7%) and A. brama (2.9%), while it was absent in Perca fluviatilis from the same lake. The following structures of A. limacoides are described for the first time: a depression on the ventral side of the neck, variations in the number and the arrangement of alveoli, numerous pits scattered all over the body surface, the presence of a few papillae-like structures posterior lateral to the mouth, the number of marginal organs represented by openings of exocrine multicellular glands as shown in histology and the subterminal position of the excretory pore. These characters can be used to distinguish three species of Aspidogaster, namely, A. ijimai, A. conchicola and A. limacoides, suggesting that SEM is a useful and promising tool in differentiating Aspidogaster species. Comparison of molecular data of the ITS1-5.8S-ITS2 regions showed a 94% similarity to A. limacoides from the European part of Russia. Phylogenetic analysis showed that the present specimens clustered in the same clade with A. limacoides sensu stricto, forming a distinct group to the exclusion of congeners.

Characterization of the complete mitochondrial genome of Barilius malabaricus and its phylogenetic implications.

Bariliine fishes are important components of the ornamental as well as subsistence fishery sectors in India. Many of the species in the genus Barilius are threatened by habitat loss and therefore need to be met with conservation initiatives. Effective conservation measures, however, require clarification of species identities and resolution of the validity of many species currently treated as synonymous or sub-species. The complete mitochondrial genome data provide better insight into phylogenetic information than the short fragment or single gene based analysis. Thus, we have sequenced the complete mitochondrial genome of Barilius malabaricus, one of the important fish species in the fresh water ornamental sector, for better understanding its phylogenetic status. The 16,519 bp mitochondrial genome consists of 37 genes which classifies as 22 tRNA, 13 protein coding and 2 ribosomal RNA genes and a control region. Overall, the mitochondrial genome bears the typical gene order and composition as in other fishes. Further, the COI, cytochrome b and 16S rRNA gene sequences revealed that, B. malabaricus is genetically closer to B. canarensis and B. bakeri compared to other Barilius species. Also, the Barilius species of west flowing rivers in Western Ghats were consistently recovered as a clade distinct from other species. We therefore suggest to retain the genus name Barilius for the species from the Western Ghats until a comprehensive analysis based on both morphological and molecular markers reveals the relationship between species now variously placed in the genera Barilius and Opsarius in greater detail.

A comparison of avoidance to acoustic stimuli in fish with different auditory capabilities: juvenile chum salmon (Oncorhynchus keta) and common carp (Cyprinus carpio).

This study compared the repulsive effects of sound playbacks of intermittent 30, 150, 300, 600 and 900 Hz tones on two fish with different auditory capabilities: juvenile chum salmon (Oncorhynchus keta) and common carp (Cyprinus carpio). When 150 and 300 Hz tones were emitted from an underwater speaker, O. keta exhibited a moderate repulse reaction. Conversely, C. carpio exhibited a moderate repulse reaction to a tone with a frequency of 30 Hz, which indicates that a low-frequency component in complex broadband sound may be important for inducing a repulse reaction in cyprinids.

High Endemicity with Clonorchis sinensis Metacercariae in Fish from Yongjeon-cheon (Stream) in Cheongsong-gun, Gyeongsangbuk-do, Korea.

The infection status with Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fishes from Yongjeon-cheon (a branch of Nakdong-gang) located in Cheongsong-gun, Gyeongsangbuk-do, the Republic of Korea (Korea). A total of 750 fishes in 19 species were examined by the artificial digestion method for 2 years (2019 and 2020). CsMc were detected in 378 (51.4%) out of 735 fishes in 14 species (73.7%), and the infection intensity was 666 per fish infected. In 2019, CsMc were found in 172 (68.0%) out of 253 fishes in 10 species, and the infection intensity was 565 per fish infected. In 2020, CsMc were detected in 206 (62.2%) out of 331 fishes in 10 species, and the infection intensity was 751 per fish infected. The other zoonotic trematode, ie. Metagonimus spp., Centrocestus armatus, Echinostoma spp. and Clinostomum complanatum, metacercariae were also detected in fishes from the survey streams, but their endemicities were relatively low. Conclusively, it was first confirmed that CsMc are highly endemic in fishes from Yongjeon-cheon in Cheongsong-gun, Gyeongsangbuk-do, Korea.

Ultramorphology and Molecular Studies of Contracaecum Larvae (Nematoda: Anisakidae) Collected in Five Cyprinid Fish Species from Sulaimani Province, Kurdistan Region-Iraq.

A total of 1134 freshwater fishes belonging to Cyprinidae (Acanthobrama marmid (n=20), Alburnus caeruleus (n=7), Alburnus mossulensis (n=62), Arabibarbus grypus (n=123), Barbus lacerta (n=7), Capoeta trutta (n=222), C. umbla (n=161), Carasobarbus kosswigi (n=5), C. luteus (n=89), Carassius auratus (n=54), Chondrostoma regium (n=52), Cyprinion kais (n=10) and C. macrostomum (n=322)) were collected in different water bodies in Sulaimani Province, Kurdistan Region-Iraq for the presence of larval nematode of the genus Conteacaecum. This investigation revealed that 17 fishes belonged to five species (A. marmid, A. grypus, C. trutta, C. luteus and C. regium) were infected with Contracaecum larvae with prevalence of 35 %, 0.81 %, 0.90 %, 4.49 % and 5.76 %, respectively. The third- larval stage was morphologically studied by optical microscopy, and the ultrastructure was investigated using scanning electron microscopy (SEM). In addition, molecular analysis was carried out by amplifying, sequencing and comparing different gene loci, including internal transcribed spacers (ITS-1 and ITS-2) and cytochrome oxidase c subunit-II (COX-2), of the different isolated Contracaecum larvae. These sequences were also compared with closely related nematode sequences from the GenBank. Fifteen sequences were obtained for this study from the collected Contracaecum larvae. ITS-1, ITS-2 and COX-2 were amplified by polymerase chain reaction (PCR) and sequenced. The sequences of ITS-1, ITS-2 and COX-2 revealed that the collected Contracaecum larval specimens from all infected fish species represented one species (Contracaecum rudolphii B) based on the identity percentage in the GenBank database. The genetic characterisation of the parasite in the present study is available in the GenBank database, and the obtained ITS-1, ITS-2 and COX-2 sequences were deposited in GenBank. The present study provides information on the accurate identification and molecular analysis of Contracaecum larvae in the infected fish species in Sulaimani Province, Kurdistan Region-Iraq.

Substantially adaptive potential in polyploid cyprinid fishes: evidence from biogeographic, phylogenetic and genomic studies.

Whole genome duplication (WGD) is commonly believed to play key roles in vertebrate evolution. However, nowadays polyploidy exists in a few fish, amphibian and reptile groups only, and seems to be an evolutionary dead end in vertebrates. We investigate the evolutionary significance of polyploidization in Cyprinidae-a fish family that contains more polyploid species than any other vertebrate group-with integrated biogeographic, phylogenetic and genomic analyses. First, polyploid species are found to be significantly frequent in areas of higher altitude and lower mean annual temperature compared with diploid species in Cyprinidae. Second, a polyploidy-related diversification rate shift is observed in Cyprinidae. This increased net diversification rate is only seen in three polyploid lineages, and other polyploid lineages have similar net diversification rate as well as diploid lineages in Cyprinidae. Interestingly, significant 'lag times' existed between polyploidization and radiation in Cyprinidae. Multiple polyploid lineages were established approximately 15 Ma through recurrent allopolyploidization events, but the net diversification rate did not start to increase until approximately 5 Ma-long after polyploidization events. Environmental changes associated with the continuous uplift of the Tibetan Plateau and climate change have probably promoted the initial establishment and subsequent radiation of polyploidy in Cyprinidae. Finally, the unique retention of duplicated genes in polyploid cyprinids adapted to harsh environments is found. Taken together, our results suggest that polyploidy in Cyprinidae is far more than an evolutionary dead end, but rather shows substantially adaptive potential. Polyploid cyprinids thus constitute an ideal model system for unveiling largely unexplored consequences of WGD in vertebrates, from genomic evolution to species diversification.

Isolation and characterization of 20 polymorphic microsatellites loci for Xenocypris davidi based on high-throughput sequencing.

Xenocypris davidi is one of the most economically important freshwater fish in China. However, few molecular markers have been reported for this species, impeding in-depth population genetic, dispersal, and gene flow studies. In the present study, a batch of novel polymorphic microsatellites from the genome of X. davidi were isolated and characterized using high-throughput sequencing. A total of 20 microsatellite markers were isolated. Analysis of 33 individuals revealed an average of 7.35 alleles per locus, ranging from 3 to 18. The observed and expected heterozygosities ranged from 0.3 to 1 and from 0.426 to 0.93, respectively. Only one tested locus significantly deviated from Hardy-Weinberg equilibrium. 18 microsatellite loci were highly polymorphic (PIC > 0.5). These newly isolated microsatellite markers would be useful to study the population genetics and stock management of X. davidi.

Carp (Cyprinidae) Fisheries in Swedish Lakes: A Combined Environmental Assessment Approach to Evaluate Data-limited Freshwater Fish Resources as Food.

The role of aquatic resources to food security is both promising and constrained since the global seafood consumption is increasing while marine fisheries approach the limit of what it can produce. In Sweden, the seafood consumption per capita is higher than the European and world average but the current dietary advice is to increase consumption. Freshwater fisheries have in general been paid less attention in food security discussions. Carp fishes (Cyprinidae) in Sweden have lost their historical value and are currently, both understudied and underutilized. Here we use a combined environmental assessment approach to examine the environmental sustainability of current and potential cyprinid fisheries. We found that current commercial fisheries for Swedish cyprinids in lakes have an average carbon footprint of 0.77 kg CO2e per kg of edible product, substantially smaller than most of the popular marine and terrestrial protein sources consumed in Sweden today. This could be even lower if cyprinid resources were better utilized than currently. The cyprinids however exhibited different vulnerability to fishing pressure and are today associated with data deficiencies. Hence, it is currently uncertain how much food for human consumption they can contribute to. Improved consumer interest and management attention is needed, but to the Swedish diet, cyprinids offer a promising opportunity for future more sustainable and nutritious food systems.

Seminal plasma fractions can protect common carp (Cyprinus carpio) sperm during cryopreservation.

This study aimed to investigate the effect of fractionated seminal plasma on characteristics of common carp Cyprinus carpio cryopreserved sperm. Nanosep® centrifugal devices yielded four seminal plasma fractions with different total protein content ranging in molecular weight from less than 17 to almost 74 kDa. Each protein fraction was added to semen extender medium prior to freezing. Spermatozoon motility characteristics and DNA integrity were analyzed in supplemented and non-supplemented cryopreserved samples. The cryopreservation process strongly affected the swim-up sperm quality. Treatment with fractions 1, 2, 3, and 4 was associated with significantly higher spermatozoon motility rate and curvilinear velocity than seen in extender only, with highest values obtained with fraction 4 (78.21 ± 2.41% and 168.05 ± 4.46 µm/s, respectively). Significantly less DNA damage, expressed as percent tail DNA (12.23 ± 1.27) and olive tail moment (0.68 ± 0.12), was recorded in fraction 4. The findings indicated that addition of fractionated seminal plasma to cryopreservation medium can preserve the quality of common carp sperm. The protective effect of each fraction varied, suggesting the presence of distinct components exerting different effects on cryopreserved sperm function.

Phylogeny, phylogeography and hybridization of Caucasian barbels of the genus Barbus (Actinopterygii, Cyprinidae).

Phylogenetic relationships and phylogeography of six species of Caucasian barbels, the genus Barbus s. str., were studied based on extended geographic coverage and using mtDNA and nDNA markers. Based on 27 species studied, matrilineal phylogeny of the genus Barbus is composed of two clades - (a) West European clade, (b) Central and East European clade. The latter comprises two subclades: (b1) Balkanian subclade, and (b2) Ponto-Caspian one that includes 11 lineages mainly from Black and Caspian Sea drainages. Caucasian barbels are not monophyletic and subdivided for two groups. The Black Sea group encompasses species from tributaries of Black Sea including re-erected B. rionicus and excluding B. kubanicus. The Caspian group includes B. ciscaucasicus, B. cyri (with B. goktschaicus that might be synonymized with B. cyri), B. lacerta from the Tigris-Euphrates basin and B. kubanicus from the Kuban basin. Genetic structure of Black Sea barbels was influenced by glaciation-deglaciation periods accompanying by freshwater phases, periods of migration and colonization of Black Sea tributaries. Intra- and intergeneric hybridization among Caucasian barbines was revealed. In the present study, we report about finding of B. tauricus in the Kuban basin, where only B. kubanicus was thought to inhabit. Hybrids between these species were detected based on both mtDNA and nDNA markers. Remarkably, Kuban population of B. tauricus is distant to closely located conspecific populations and we consider it as relic. We highlight revealing the intergeneric hybridization between evolutionary tetraploid (2n = 100) B. goktschaicus and evolutionary hexaploid (2n = 150) Capoeta sevangi in Lake Sevan.

High cryptic diversity of bitterling fish in the southern West Palearctic.

South-east Europe, along with the adjacent region of south-west Asia, is an important biodiversity hotspot with high local endemism largely contributed by contemporary continental lineages that retreated to southern refugia during colder Quaternary periods. We investigated the genetic diversity of the European bitterling fish (Rhodeus amarus) species complex (Cyprinidae) across its range in the western Palearctic, but with a particular emphasis in the region of Balkan, Pontic and Caspian refugia. We genotyped 12 polymorphic microsatellite loci and a partial sequence of mitochondrial gene cytochrome b (CYTB) for a set of 1,038 individuals from 60 populations. We used mtDNA sequences to infer phylogenetic relationships and historical demography, and microsatellite markers to describe fine-scale genetic variability and structure. Our mtDNA analysis revealed six well-supported lineages, with limited local co-occurrence. Two lineages are distributed throughout central and western Europe (lineages "A" and "B"), with two zones of secondary contact. Another two lineages were restricted to the Ponto-Aegean region of Greece (lineages "C" and "D") and the final two lineages were restricted south of the Caucasus mountains (lineage "E" from the Black Sea watershed and lineage "F" from the Caspian watershed). A signal of recent expansion was revealed in the two widespread lineages and the Ponto-Aegean lineage "C". The geographic distribution of clusters detected by nuclear microsatellites corresponded well with mitochondrial lineages and demonstrated finely sub-structured populations. A profound population structure suggested a significant role of genetic drift in differentiation among lineages. Lineage divergence in the Ponto-Aegean and Caspian regions are substantial, supporting the validity of two described endemic species (Rhodeus meridionalis as lineage "D" and Rhodeus colchicus as lineage "E") and invite taxonomic evaluation of the other two southern lineages (Thracean "C" and Caspian "F").

Otolith shape analysis and daily increment validation during ontogeny of larval and juvenile European chub Squalius cephalus.

This assesses features of otoliths from laboratory-reared embryos, larvae and juvenile European chub Squalius cephalus from hatching to 180 days post-hatching (dph). We observed the development of the three pairs of otoliths (lapilli, sagittae and asterisci) and more precisely shape changes, as well as timing and deposition rate of increments of the lapilli. The lapilli and the sagittae were present at hatching, whereas the asterisci formed between 20 and 30 dph. The lapillus and sagitta shapes were round until 20 dph. From 60 dph the anterior and the posterior rostra of the sagittae were well developed, but very thin, making this otolith too fragile to manipulate for further studies of shape and validation of otolith increment deposition rate. The lapilli provided reliable age estimates for free embryos, larvae and juveniles up to 120 dph. However, caution should be taken when ageing fish older than 150 dph as an underestimation was noticeable. The regression of the number of otolith increments on age showed a slope and an intercept not significantly different from 1 and 0, respectively, which indicated that otolith growth increments were deposited on a daily basis, with the first microincrement occurring at hatching. Increment counts were consistent between three interpreters, indicating a consistent and reliable age estimate. This study validates that the otolith increment deposition rate can be used to assess hatching dates and daily growth of wild S. cephalus under 150 dph and in environments similar to the conditions used in this study.

Daily growth increments in otoliths of wild-caught honmoroko Gnathopogon caerulescens.

Otolith growth increments in wild-caught alizarin complex one (ALC)-marked honmoroko Gnathopogon caerulescens were examined to verify the veracity of the age determination method in cyprinids. ALC-marked G. caerulescens recaptured from their natural environment had lapilli increment counts outside the ALC ring mark that had formed on a daily basis during the juvenile stage. This apparently being the first direct evidence of daily periodicity of otolith increment formation in wild-caught cyprinids.

Variation in thermal tolerances of native freshwater fishes in South Africa's Cape Fold Ecoregion: examining the east-west gradient in species' sensitivity to climate warming.

The Cape Fold Ecoregion (CFE) is a biodiversity hotspot with high levels of endemism in its freshwater fish fauna. This study examined inter and intra-specific variation in critical thermal maxima (TCmax ) for eight native species of freshwater fish from the CFE. Cape galaxias Galaxias zebratus, Breede River redfin Pseudobarbus burchelli, Berg River redfin Pseudobarbus burgi, Clanwilliam redfin Pseudobarbus calidus and fiery redfin Pseudobarbus phlegethon were the most thermally sensitive (TCmax = 29.8-32.8°C). Clanwilliam rock-catfish Austroglanis gilli, Eastern Cape redfin Pseudobarbus afer and Cape kurper Sandelia capensis were moderately sensitive (TCmax = 33.0-36.8°C). An increase in intra-specific thermal sensitivity of S. capensis was observed from east to west. The results were related to in situ water temperature, which influenced TCmax for all species, suggesting that thermal history is a major driver of variation in thermal tolerance amongst populations. These thermal tolerance data for freshwater fishes in the CFE demonstrate that resilience to climate warming follows a geographical cline and that the more sensitive western species and regions are conservation priorities.