Motivation: TCS is a widely used haplotype network reconstruction software, but lacks the capability of overlapping genetic with geographic structure, which is often a first step in phylogeographic analysis.

Effective conservation of species and ecosystems requires the understanding of important ecological traits, such as dietary habits, food webs, and trophic niches. In diet studies, the visual identification of partially digested prey has been enhanced with the recent more powerful and accurate technique, DNA barcoding. Here, we summarize the contribution of this recent methodology to the investigation of both terrestrial and aquatic taxa diet, and compare the level of novelty uncovered through the use of this technique regarding species' ecology. From a total of 150 studies analyzed, focusing on more than 250 vertebrate wild species, seven domesticated taxa, and humans, we suggest that barcoding has led to more significant findings for aquatic taxa and ecosystems, where direct observations of feeding events and consequent trophic niche understanding are typically limited. Finally, we introduce the term dietary DNA (dDNA) to describe environmental approaches that use DNA extracted from gut, stomach, or fecal contents, aiming to assess both species dietary habits and describe local biodiversity. Particularly, we highlight the complementarity of environmental DNA (eDNA) and dDNA as a new tool for biodiversity assessments in remote areas, including most of the aquatic realm.

Fish microbiome plays an important role in maintaining host homeostasis, with many bacterial functions directly linked to host fitness. Fish microbiome research is advancing fast, especially in the context of aquaculture where several stressors are known to disrupt stability of host‐associated bacteria, prompting dysbiosis. Therefore, understanding the signatures of dysbiosis in different fish mucosae and their association with such stressors is fundamental to set up efficient health‐monitoring strategies, as well as sound and objective working hypothesis for future research. Herein, we reviewed studies that employed culture‐independent approaches to assess the effects of disease, chemotherapeutics and water quality changes on several diversity metrics of gut, skin and gill microbiomes. We conclude that increases in abundance of potential pathogens and changes to bacterial community structure are reliable indicators of dysbiosis in fish. The gut microbiome emerged as being highly susceptible to salinity changes and chemotherapeutics, whereas external microbiota seems to be more susceptible to dysbiosis caused by disease and temperature changes. Our analysis showed that treatments with tetracyclines and florfenicol are more likely to elicit severe dysbiosis compared to quinolones and disinfectants that cause lesser disturbance to fish microbiome. Bacterial diseases also frequently elicit severe dysbiosis (enteritis in particular), whereas parasitic diseases are far less deleterious. Regarding impacts on water quality, only changes to salinity and temperature are reasonably studied. Recent developments in metagenomics, that include a fast turn‐around time of results, can be used to detect changes to fish homeostasis during critical periods of fish production, assisting aquaculture management.

The mucosal surfaces of fish harbour microbial communities that can act as the first-line of defense against pathogens. Infectious diseases are one of the main constraints to aquaculture growth leading to huge economic losses. Despite their negative impacts on microbial diversity and overall fish health, antibiotics are still the method of choice to treat many such diseases. Here, we use 16 rRNA V4 metataxonomics to study over a 6 week period the dynamics of the gill and skin microbiomes of farmed seabass before, during and after a natural disease outbreak and subsequent antibiotic treatment with oxytetracycline. Photobacterium damselae was identified as the most probable causative agent of disease. Both infection and antibiotic treatment caused significant, although asymmetrical, changes in the microbiome composition of the gills and skin. The most dramatic changes in microbial taxonomic abundance occurred between healthy and diseased fish. Disease led to a decrease in the bacterial core diversity in the skin, whereas in the gills there was both an increase and a shift in core diversity. Oxytetracycline caused a decrease in core diversity in the gill and an increase in the skin. Severe loss of core diversity in fish mucosae demonstrates the disruptive impact of disease and antibiotic treatment on the microbial communities of healthy fish.

The ocean sunfish (Mola mola) is the world’s heaviest bony fish reaching a body mass of up to 2.3 tonnes. However, the prey M. mola consumes to fuel this prodigious growth remains poorly known. Sunfish were thought to be obligate gelatinous plankton feeders, but recent studies suggest a more generalist diet. In this study, through molecular barcoding and for the first time, the diet of sunfish in the north-east Atlantic Ocean was characterised. Overall, DNA from the diet content of 57 individuals was successfully amplified, identifying 41 different prey items. Sunfish fed mainly on crustaceans and teleosts, with cnidarians comprising only 16% of the consumed prey. Although no adult fishes were sampled, we found evidence for an ontogenetic shift in the diet, with smaller individuals feeding mainly on small crustaceans and teleost fish, whereas the diet of larger fish included more cnidarian species. Our results confirm that smaller sunfish feed predominantly on benthic and on coastal pelagic species, whereas larger fish depend on pelagic prey. Therefore, sunfish is a generalist predator with a greater diversity of links in coastal food webs than previously realised. Its removal as fisheries’ bycatch may have wider reaching ecological consequences, potentially disrupting coastal trophic interactions.