Molecular Footprint of Parasite Co-introduction with Nile Tilapia in the Congo Basin

Nile tilapia, one of the most popular aquaculture species worldwide, has been introduced into the Congo Basin several times. In previous morphological studies, we showed that some of the monogenean gill parasites were co-introduced with Nile tilapia and some spilled over to native Congolese cichlids. In this study, we investigated the co-introduced monogeneans of Nile tilapia genetically from three major parts of the Congo Basin; Upper, Middle and Lower Congo. We generated sequences of Congolese native and introduced monogeneans from native and introduced tilapias and evaluate their position in a phylogeny. Additionally, we generated sequences of the same species of monogeneans co-introduced with Nile tilapia in Madagascar and of a native population of Nile tilapia from Burundi. Our results confirm the co-introductions in the Congo. We found that co-introduced parasites are less genetically diverse than native ones, and that there was no geographical pattern between introduced populations. Furthermore, our COI haplotype networks suggest multiple introduction events of Nile tilapia into the Congo Basin. Additionally, we tested the barcoding gap and the performance of mitochondrial COI and nuclear ribosomal ITS-1, 28S and 18S markers. We found a significant intra/interspecific barcoding gap of 15% for COI, but none for the other markers. Our molecular results reveal that Cichlidogyrus halli, C. papernastrema, C. tiberianus, C. cirratus and C. zambezensis are in need of taxonomic revision.

The role of phylogeny and ecological opportunity in host-parasite interactions: network metrics, host repertoire, and network link prediction.

Hosts and parasites have often intimate associations. Therefore, the evolution of their interactions is crucial for understanding species-rich host-parasite communities. Yet relatively few studies investigate eco-evolutionary feedbacks in these systems as large datasets remain scarce. Here, we explore African cichlid fishes and their flatworm gill parasites (Cichlidogyrus spp.) including 9901 reported infections and 473 different host-parasite combinations collected through a survey of peer-reviewed literature. We apply network metrics, estimate host repertoires, and use network link prediction (NLP) algorithms to investigate meta-community structures and their predictors including evolutionary, ecological, and morphological parameters. Host repertoire was mostly determined by the hosts’ evolutionary history. Both ecological and evolutionary parameters predicted host parasite associations but many interactions remain undetected according to NLP. We conclude that ecological opportunity paired with ecological fitting has shaped interactions. The cichlid-Cichlidogyrus network is a suitable study system for eco-evolutionary feedbacks but taxonomic research remains key to finding undetected interactions.

De novo developed microsatellite markers in gill parasites of the genus Dactylogyrus (Monogenea): revealing the phylogeographic pattern of population structure in the generalist parasite Dactylogyrus vistulae

Approaches using microsatellite markers are considered the gold standard for modern population-genetic studies. However, though they have found application in research into various platyhelminth taxa, they remained substantially underutilized in the study of monogeneans. In the present study, a newly-developed set of 24 microsatellite markers was used to investigate the genetic diversity of the generalist monogenean species D. vistulae. The analyzed parasite specimens were collected from 13 cyprinoid species from 11 sites in the Apennine and Balkan peninsulas. A total of 159 specimens were genotyped at each of the loci and the number of alleles per locus ranged from 2 to 16, with a mean number of 6.958 alleles per locus. Exceptionally high genetic diversity was observed among D. vistulae individuals in the southern Balkans, suggesting that this region might represent the center of diversification of the genus in Europe, from where Dactylogyrus parasites expanded into the north. The initial clustering analysis divided all investigated specimens into three major clusters; however, the results of the subsequent analyses revealed the existence of various subpopulations, suggesting that the population structure of D. vistulae is associated with the diversification of their cyprinoid hosts. In addition, partition of the parasite population was observed in regions of the sympatric occurrence of two host species, indicating that these hosts may represent a barrier to gene flow, even for generalist parasite species.

Community structure of protozoan parasites in Heteropneustes fossilis (Bloch 1794) in Bangladesh

The study was conducted to prepare a database for the infection status of protozoan parasites on an important host fish species of Bangladesh, Heretropneustes fossilis. Host samples were collected from the freshwater habitats of six different districts of Bangladesh- Manikganj, Faridpur, Mymensingh, Kishoreganj, Bogura, and Jashore. H. fossilis was noted to be infected by 6 parasite species, of which 3 belonged to myxozoa (Henneguya singhi, Henneguya qadrii and Henneguya mystusia); 1 belonged to ciliophora (Trichodina siddiquae) and 2 (Trypanosoma singhii and Piscinoodium pillulare) belonged to mastigophora.The parasites, Trypanosoma singhii and Henneguya singhi were recorded as new locality record in H. fossilis. The three parasites Piscinoodium pillulare, Henneguya qadrii and Henneguya mystusia were the first recorded parasites in this fish and the first locality record in Bangladesh. The parasites were observed to occupy gill, body slime, and blood. Gill parasites were abundantly found compared to body slime and blood parasites. The highest prevalence (67.21%) of infection of H. fossilis was observed in Manikganj and the lowest prevalence (54.67%) of infection was observed in Bogura. Parasites of H. fossilis showed the highest diversity in fishes of Faridpur (2.63). Species richness of parasites was highest in Manikganj (0.38) and species evenness was relatively low (0.13-0.19) in almost all the study sites. Dhaka Univ. J. Biol. Sci. 30(2): 307-316, 2021 (July)

EFFECT OF POULTRY LITTER AS AN ORGANIC FERTILIZER, IN WATER QUALITY, PARASITIC ABUNDANCE, AND GROWTH NILE TILAPIA

Nile tilapia feed on plankton in natural environments. This food source can be increased in ponds through fertilization and can reduce feed expenses or improve fish performance when used as supplementary food. Organic fertilization is an alternative to commercial fertilization; however, its use increases concerns regarding water quality and sanitary aspects. This study aimed to evaluate the effects of the use of poultry litter as organic fertilizer on the physical and chemical parameters of water, gill ectoparasite metazoan abundance, and growth of Nile tilapia (Oreochromis niloticus) during the culture cycle lasting 240 days. Four earthen ponds, two fertilized with poultry litter and two non-fertilized ponds, as fertilized and non-fertilized treatments, respectively, were used. Stocking density was 3 fish per m2 with an average initial weight of 0.64 ± 0.15 g. The mean water quality values and the growth performance parameters of Nile tilapia did not show significant differences between the two treatments. The gill parasites found in the fish belonged to the class Monogenea, comprising two genera, Cichlidogyrus and Scutogyrus, with significant differences between treatments. The non-fertilized treatment showed a high abundance of parasites throughout the culture cycle months, with peak abundance in the months with low concentrations of dissolved oxygen in the water.