ABSTRACT It can be challenging to determine the identity of tilapia species in aquaculture using morphological characteristics alone. In central Tanzania, there is ongoing expansion of small‐scale inland aquaculture, mainly focused on the large‐bodied non‐native Nile tilapia (Oreochromis niloticus) and the native Wami tilapia (Oreochromis urolepis). The spread of Nile tilapia has been accompanied by blue‐spotted tilapia (Oreochromis leucostictus), a small‐bodied non‐native species that has the potential to compromise fisheries production. Given the phenotypic similarity of the three species, particularly at the juvenile stage, we developed an environmental DNA (eDNA)‐based assay to determine the distribution and relative abundance of the three Oreochromis species within aquaculture and natural settings in Tanzania. In a field test of the assay in 15 water bodies—comparing eDNA results with genotyping of sampled fish—we found that the confirmed presence of a species, as inferred from their mitochondrial DNA (mtDNA) ND1 haplotypes, led to an on average one‐thousand‐fold increase in eDNA copies relative to water bodies where the species was not confirmed. In a more expansive eDNA field survey across 52 water bodies from 32 locations, we found that the vast majority of water bodies were dominated by O. niloticus or O. urolepis, with O. leucostictus widespread but typically present in low relative abundance. Collectively, our results indicate that O. leucostictus is currently unlikely to compromise the productive capacity of aquaculture of the region. However, caution should be exercised to reduce the influence of the species on yield. We conclude that eDNA‐based methods can be a valuable source of information for the identification of fish in mixed cultured stocks and may, in the future, have a role in optimising regional aquaculture.
Lake Malawi/Nyasa/Niassa (LMNN) contains exceptional fish diversity with more than 800 species recognised, yet the rivers flowing into LMNN also contain a rich variety of fish species. Here, we report a study, using a combination of morphological and genetic evidence, that shows that the Malagarasi sardine Engraulicypris spinifer Bailey and Matthes, 1971 is present in the northern sector of the LMNN catchment. Previously, the species was only known from the Lake Rukwa, Rufiji River and Malagarasi River catchments. We found that individuals from the LMNN catchment possess the same mitochondrial COI haplotype as those in the Malagarasi River catchment, and that both groups share key diagnostic morphological traits of the species. These findings support theories of past hydrological connectivity between LMNN and the neighbouring Rukwa and Rufiji catchments. They also indicate potential for further discoveries of novel fish diversity in riverine habitats of the LMNN catchment.
Despite previous research on small fish (Dagaa) postharvest losses, a comprehensive assessment of the entire regional supply chain remains limited. The study aimed to quantify Dagaa losses, identify their causes and propose mitigation strategies. Using FAO’s load tracking method, Informal Fish Loss Assessment Method (IFLAM) and Questionnaire Loss Assessment Method (QLAM), we monitored changes in product weight, quality and nutritional profile. Results highlight processing and transportation as the most critical loss points. Processing stage accounted for 19.5
Mangroves are a critical habitat that provide a suite of ecosystem services and support livelihoods. Here we undertook a global analysis to model the density and abundance of 37 commercially important juvenile fish and juvenile and resident invertebrates that are known to extensively use mangroves, by fitting expert-identified drivers of density to fish and invertebrate density data from published field studies. The numerical model predicted high densities throughout parts of Southeast and South Asia, the northern coast of South America, the Red Sea, and the Caribbean and Central America. Application of our model globally estimates that mangroves support an annual abundance of over 700 billion juvenile fish and invertebrates. While abundance at the early life-history stage does not directly equate to potential economic or biomass gains, this estimate indicates the critical role of mangroves globally in supporting fish and fisheries, and further builds the case for their conservation and restoration.
Microbial trait variation along environmental gradients is crucial to understanding their ecological adaptation mechanisms. With the increasing availability of microbial genomes, making full use of the genome-based traits to decipher their adaptation strategies becomes promising and urgent. Here, we examined microbial communities in water and sediments of 20 East African lakes with pH values ranging from 7.2 to 10.1 through taxonomic profiling and genome-centric metagenomics. We identified functional traits important for microbial adaptation to the stresses of alkalinity and salinity based on the significant trait-environment relationships (TERs), including those involved in cytoplasmic pH homeostasis, compatible solute accumulation, cell envelope modification, and energy requisition. By integrating these significant traits, we further developed an environmental adaptation index to quantify the species-level adaptive capacity for environmental stresses, such as high pH environments. The adaptation index of pH showed consistently significant positive relationships with species pH optima across regional and global genomic datasets from freshwater, marine, and soda lake ecosystems. The generality of the index for quantifying environmental adaptation was demonstrated by showing significant relationships with the species niche optima for the gradients of soil temperature and seawater salinity. These results highlight the importance of TERs in facilitating the inference of microbial genomic-based adaptation mechanisms and expand our understanding of ecological adaptive strategies along environmental gradients.
