Barrier mitigation measures trigger the rapid recovery of genetic connectivity in five freshwater fish species

ABSTRACTRivers are heavily fragmented by man-made instream barriers such as dams and weirs. This hyper-fragmentation is a major threat to freshwater biodiversity and restoration policies are now adopted worldwide to mitigate these impacts. However, there is surprisingly little feedback on the efficiency of barrier mitigation measures in restoring riverine connectivity, notably for non-migratory fish species. Here, we implemented a “before-after genetic monitoring” of the restoration of 11 weirs in France using a dedicated genetic index of fragmentation (the FINDEX), with a focus on five fish species from two genera. We found that most obstacles actually had a significant impact on connectivity before restoration, especially the highest and steepest ones, with an overall barrier effect of about 51% of the maximal theoretical impact. Most importantly, we demonstrated for the first time that mitigation measures such as dam removal or fish pass creation significantly and rapidly improved connectivity, with –for some barriers-a complete recovery of the genetic connectivity in less than twelve months. Our study provides a unique and strong proof-of-concept that barrier removal is an efficient strategy to restore riverine connectivity and that molecular tools can provide accurate measures of restoration efficiency within a few months.Graphical Abstract

Functional DNA annotation from a preliminary de novo genome assembly of Brycon orbignyanus, an endangered Neotropical migratory fish

The predicted sequence for thousands of genes revealed by a preliminary low-coverage genome assembly is presented for Brycon orbignyanus, an endangered migratory fish. Neotropical migratory fish stocks have been drastically reduced due to accumulated environmental pressure. Brycon orbignyanus, once one of the main fisheries species in the Platine Basin, is now very rare in nature and relies on spawning programs and a few well preserved or still untouched sites. The use of high-throughput DNA sequencing is still untapped regarding the functional genome information from B. orbignyanus. In order to help bridging this gap, we present a dataset resulting from the first functional annotation from a de novo genome assembly for B. orbignyanus, from short reads (90 bp), obtained by the HiSeq 2000 platform (Illumina). The annotation was performed for scaffolds over 10 kb using the Maker pipeline, with reference sequences taken from the NCBI for the Characiformes order. This annotation resulted in the prediction of 12,734 genes, classified with the aid of PANTHER. The data presented here can facilitate the development of basic research in this threatened species, along with practical biotechnological tools for different areas, such as commercial and environmental fish spawning operations (e.g. hormonal induction, growth) and human health.

Marginal lagoons: natural nurseries of migratory fish

As lagoas marginais constituem ambiente complexo que potencializa o sucesso reprodutivo das espécies migratórias, fornecendo abrigo e recursos. Nosso estudo avalia o papel dessas lagoas no recrutamento de espécies migratórias no rio Jequitaí. Durante um ano, foram realizadas amostragens mensais em quatro lagoas marginais do rio Jequitaí: Lagoão (LAG), Renero (REN), Buriti (BUR) e Tamatião (TAMA). Foram capturados 1.049 indivíduos pertencentes a sete espécies de peixes migradores: Brycon orthotaenia, Megaleporinus obtusidens, Prochilodus argenteus, Prochilodus costatus, Pseudoplatystoma corruscans, Salminus franciscanus e Salminus hilarii. O comprimento médio dos exemplares capturados foi de 13,6 cm e o peso corporal médio de 80,7 g, evidenciando o predomínio de peixes jovens. A espécie mais representativa em números absolutos foi L. obtusidens (41,47%) enquanto P. costatus foi a mais representativa (24,57%) na biomassa. Salminus hilarii e i apresentaram as menores taxas de aumento do comprimento corporal (1,90 e 2,10, respectivamente). S. franciscanus e M. obtusidens aumentaram seu comprimento em 4 e 3,6 vezes, respectivamente. Além disso, S. franciscanus e M. obtusidens aumentaram seu peso em 81,3 e 102,4 vezes, respectivamente. Os resultados do presente estudo mostraram como as lagoas marginais podem funcionar como grandes berçários para o desenvolvimento e recrutamento de peixes migradores, contribuindo assim para a conservação de peixes de importância comercial e ecológica. Além disso, este estudo reduz a escassez de conhecimento sobre o uso de lagoas marginais por espécies de peixes migradores e destaca a importância desses ambientes.

ON THE INVASION OF THE GENUS MARENZELLERIA (POLYCHAETA, SPIONIDAE) REPRESENTATIVES INTO THE CASPIAN SEA BASIN

In 2018, in the bottom fauna of the Caspian Sea, single specimens of a previously unknown species of polyhaetes were discovered. Since 2019, pelagic larvae of this species have been recorded in zooplankton samples. These worms are also found in the nutrition of migratory and semi-migratory fish species. According to morphological features, this polychaete species is identified as Marenzelleria arctia , an Arctic species dominating in the Gulf of Finland and probably invaded the Caspian along the Volga-Caspian invasion corridor.

From drought to deluge: spatiotemporal variation in migration routing, survival, travel time and floodplain use of an endangered migratory fish

We developed a novel statistical model to relate the daily survival and migration dynamics of an endangered anadromous fish to river flow and water temperature during both extreme drought and severe flooding in an intensively managed river system. Our Bayesian temporally stratified multistate mark recapture model integrates over unobserved travel times and route transitions to efficiently estimate covariate relationships and includes an adjustment for telemetry tag battery failure. We applied the model to acoustic-tagged juvenile Sacramento river winter-run Chinook salmon (Oncorhynchus tshawytscha) and found that survival decreased with decreasing river flows and increased water temperatures. We found that fish were likely to enter at a large floodplain during flood conditions and that survival in floodplain was comparable to the mainstem Sacramento river. Our study demonstrates the response of an endangered anadromous fish population to extreme spatial and temporal variability in habitat accessibility and quality. The general model framework we introduce here can be applied to telemetry of migratory fish through systems with multiple routes to efficiently estimate spatiotemporal variation in survival, travel time, and routing.

Evaluation of the reproductive parameters of female neotropical migratory fish from a lotic and lentic environment of a dammed river

The fragmentation of watercourses caused by dams is considered to be one of the main threats to aquatic biodiversity worldwide, especially for ichthyofauna. Several studies have shown that the environmental modifications caused by dammed water bodies can change the various reproductive parameters of freshwater fish. Therefore, the present study aims to comparatively analyze the reproductive potential of female Megaleporinus reinhardti, a migratory species, sampled in the lentic environment of the Três Marias Reservoir and the lotic environment of the São Francisco River. Biometric data were obtained from 79 females and the biological indices were subsequently calculated. Additionally, the microscopic analysis of the gonads was performed, and the follicular atresia index was compared. The results of the study show that fish from the lotic environment presented higher gonadal volume, fecundity, and oocyte diameter, and a lower follicular atresia index when compared to fish from the lentic environment. In summary, the data suggest that environmental changes, i.e. from a lotic to lentic environment, caused by river damming, may negatively affect the reproductive process of migratory fish, such as M. reinhardti, and impair the maintenance of the population of this species in lentic environments