Fishing causes direct removal of individuals from wild populations but can also cause a physiological disturbance in fish that are released or discarded after capture. While sublethal physiological effects of fish capture have been well studied in commercial and recreational fisheries, this issue has been overlooked for the ornamental fish trade, where it is common to capture fish from the wild and discard non-target species. We examined metabolic responses to capture and discard procedures in the three-striped dwarf cichlid Apistogramma trifasciata, a popular Amazonian aquarium species that nonetheless may be discarded when not a target species. Individuals (n = 34) were tagged and exposed to each of four treatments designed to simulate procedures during the capture and discard process: 1) a non-handling control; 2) netting; 3) netting +30 seconds of air exposure; and 4) netting +60 seconds of air exposure. Metabolic rates were estimated using intermittent-flow respirometry, immediately following each treatment then throughout recovery overnight. Increasing amounts of netting and air exposure caused an acute increase in oxygen uptake and decrease in available aerobic scope. In general, recovery occurred quickly, with rapid decreases in oxygen uptake within the first 30 minutes post-handling. Notably, however, male fish exposed to netting +60 seconds of air exposure showed a delayed response whereby available aerobic scope was constrained <75% of maximum until ~4-6 hours post-stress. Larger fish showed a greater initial increase in oxygen uptake post-stress and slower rates of recovery. The results suggest that in the period following discard, this species may experience a reduced aerobic capacity for additional behavioural/physiological responses including feeding, territory defence and predator avoidance. These results are among the first to examine impacts of discard practises in the ornamental fishery and suggest ecophysiological research can provide valuable insight towards increasing sustainable practises in this global trade.

Albinism is the most common color variation described in fish and is a fascinating trait of some ornamental fish species. Albino mutants can be generated by knocking out core genes affecting melanin synthesis like slc45a2 in several fish species. However, genetic mutation remains challenging for species with unknown genome information. In this study, we generated albino mutants in two selected ornamental fish species, royal farlowella (Sturisoma panamense), and redhead cichlid (Vieja melanura). For this purpose, we carried out phylogenetic analyses of fish slc45a2 sequences and identified a highly conserved region among different fish species. A pair of degenerate primers spanning this region was designed and used to amplify a conserved slc45a2 fragment of 340 bp from the two fish species. Based on the amplified sequences, a target site in the 6th exon was used for designing guide RNA and this targeted site was first verified by the CRISPR/Cas9 system in the zebrafish (Danio rerio) model for the effectiveness. Then, specific guide RNAs were designed for the two ornamental fish species and tested. Most of the injected larvae completely lost black pigment over the whole body and eyes. DNA sequencing confirmed a high degree of mutation at the targeted site. Overall, we described a fast and efficient method to generate albino phenotype in fish species by targeting the conserved 6th exon of slc45a2 gene for genome editing via CRISPR/Cas9 and this approach could be a new genetic tool to generate desirable albino ornamental fish.

Plant polyphenol supplementation may improve fish health in aquaculture systems. To assess the potential benefits and function mechanism of plant polyphenols in aquaculture, fish were fed either basal feed (CON) or the basal feed supplemented with 500 mg/kg of curcumin (CUR), oligomeric proanthocyanidins (OPC), chlorogenic acid (CGA), or resveratrol (RES). After an 8-week feeding experiment, blood samples were used to analyze the concentrations of biochemical indices. Gut samples were collected to evaluate microbiota, short chain fatty acid (SCFA) levels, and gene expression. The results indicated that polyphenol administration reduced serum glucose and insulin. Lysozyme activity was enhanced by OPC and CGA, and superoxide dismutase activity was increased by CUR, OPC, and CGA. The gut microbial structure of the RES group was segregated from that of the CON, and the genus Bacteroides was identified as a potential biomarker in the CUR, CGA, and RES groups. Total gut SCFA increased in the CUR, CGA, and RES groups. A strong correlation was observed between Bacteroides and SCFA. In conclusion, dietary polyphenols have distinct anti-inflammatory, anti-oxidant, and anti-hyperglycemic activities that may be closely associated with their microbiota-modulation effects.

The Pygmy corydoras Corydoras pygmaeus Knaack, 1966, is the smallest member of the genus Corydoras, belonging to the family Callichthyidae and order Siluriformes. The complete mitochondrial genome of C. pygmaeus was sequenced and assembled using next-generation sequencing technology, and phylogenetically compared with those of other species of this genus. The mitochondrial genome of C. pygmaeus is a circular DNA molecule with a size of 16,840 bp (GenBank no. ON729306). A phylogenetic tree was constructed based on 13 protein-coding genes of C. pygmaeus and 13 species of the family Callichthyidae, which showed that C. pygmaeus clustered with other species of this genus, but was the first branch to differentiate. These results could provide basic data for phylogenetic analysis and population genetic diversity protection of Corydoras and Callichthyidae fish in the future.

Cyprinid herpesvirus 2 (CyHV-2), a member of the Alloherpesviridae family belonging to the genus Cyprinivirus, is a fatal contagious aquatic pathogen that affects goldfish (Carassius auratus) and crucian carp (Carassius carassius). Although crucian carp and goldfish belong to the genus Carassius, it is unclear whether they are susceptible to the same CyHV-2 isolate. In addition, the origin of the crucian carp-derived CyHV-2 virus isolate remains unclear. CyHV-2 SH01 was isolated during herpesviral hematopoietic necrosis disease (HVHN) outbreaks in crucian carp at a local fish farm near Shanghai. CyHV-2 SH01 was confirmed by PCR and Western blot analysis of kidney, spleen, muscle, and blood tissue from the diseased crucian carp. Moreover, histopathological and ultra-pathological analyses revealed pathological changes characteristic of CyHV-2 SH01 infection in the tissues of the diseased crucian carp. In the present study, goldfish and crucian carp were challenged with CyHV-2 SH01 to elucidate viral virulence. We found that CyHV-2 SH01 could cause rapid and fatal disease progression in goldfish and crucian carp 24 h post-injection at 28 °C. Experimental infection of goldfish by injection indicated that the average virus titer in the kidney of the goldfish was 103.47 to 103.59 copies/mg. In addition, tissues exhibited the most prominent histopathological changes (cellular wrinkling and shrinkage, cytoplasmic vacuolation, fusion of the gill lamellae, and hepatic congestion) in CyHV-2 SH01-infected goldfish and crucian carp. Thus, crucian carp and goldfish showed a high sensitivity, with typical symptoms, to HVHN disease caused by CyHV-2 SH01.

The ornamental fish industry is growing quickly globally. Asia represents 51% of the export market for this industry and in Singapore alone, it has an estimated market value of US$66 million. Despite the economic importance of this industry for Australasia, aquatic veterinary support for the ornamental fish sector is scarce. In many cases, ornamental fish owners do not seek advice from veterinarians. While the reasons behind this are difficult to elucidate, the low perceived value of fish compared to the cost of consulting a veterinarian, and limited knowledge about the availability of veterinary services for aquatic animals may contribute to the lack of interaction with veterinarians. Considering the growing importance of the ornamental fish industry, more education and data are needed about the services offered by veterinarians with aquatic animal health expertise. Knowledge on aquatic veterinary medicine is limited, reinforcing the need for more educational programmes and dissemination of aquatic veterinary services within the Australasian region.

The yellowbar angelfish Pomacanthus maculosus (Forsskål) (Perciformes: Pomacanthidae) is a beautiful, marine ornamental fish with very important commercial value. However, to date, no information is available on nematode parasite infection in P. maculosus. In the present study, the integrated approaches including light and scanning electron microscopy, and sequencing and analysing ribosomal [small ribosomal DNA (18S) and internal transcribed spacer (ITS)] and mitochondrial [cytochrome c oxidase subunit 1 (cox1)] target regions, respectively, were employed for the systematic evaluation of the nematode parasites firstly isolated from P. maculosus in the Iraqi coral reef. The results revealed that these nematodes represent a new species of Cucullanus (Ascaridida: Cucullanidae). The phylogenetic analyses based on 18S, ITS and cox1 sequences were constructed, respectively, to assess the phylogenetic relationships between the new species and the other cucullanids, and the monophyly of Cucullanus, as well as some its related genus-level taxa. The results supported C. extraneus n. sp. appear to be sister to C. hainanensis, and the genera Cucullanus, Dichelyne and Truttaedacnitis may be not monophyletic assemblages. This is the first report of the occurrence of nematode parasites in P. maculosus.