The 2 amphidromous gobiids Sicyopterus lagocephalus and Cotylopus acutipinnis from La Réunion Island (Mascarene archipelago, south-western Indian Ocean) are heavily exploited by traditional fisheries during their river colonisation. Traits of their oceanic larval life were investigated to better understand the complex life cycle of these fishes. Age estimates were established using otolith increment counts and an alizarin complexon validation method. Larval duration was longer for the widespread S. lagocephalus (133 to 266 d; mean 199 ± 33 d) than for the endemic C. acutipinnis (78 to 150 d; mean 101 ± 14 d), which reflects their distributional ranges. For both species, no correlation was established between age and size, suggesting a decrease in growth during the larval phase. From the back-calculated birth dates, all S. lagocephalus of a major colonisation episode (December 2002) were hatched during the cool season. All results are discussed in terms of the recruitment origins of S. lagocephalus and C. acutipinnis within the Mascarenes. Recognition of the differences in larval life traits is essential for proposing both management and conservation measures for each species.

Freshwater gobies of tropical islands are amphidromous: adults reproduce in rivers and larvae passively drift down to the sea immediately after hatching. Describing the phenology of this larval drift is essential to understanding the population dynamics of amphidromous gobies and to developing ecologically based recommendations for managing the watersheds. The larval drift patterns of two amphidromous gobies of Réunion Island, Sicyopterus lagocephalus and Cotylopus acutipinnis, were studied on a monthly basis for 1 year using plankton nets at two sites on the Mât River, located 20 km and 7 km from the river mouth. Genetic analyses showed that larval assemblages were dominated at 90% by S. lagocephalus, although the proportion of C. acutipinnis increased during early summer. Our findings highlighted a marked larval drift peak in full austral summer. The diel larval drift dynamic was described using periodic linear models. A diel pattern was only observed downstream, peaking a few hours after sunset. Finally, this study presents a new approach that improves standard methods for sampling and analyzing larval drift of amphidromous species.

Diadromous species of tropical islands face numerous anthropogenic disturbances. Understanding how these disturbances affect the population dynamic of these species is important to develop ecologically based management measures. The upstream migration dynamics of two amphidromous gobies, Sicyopterus lagocephalus (Pallas) and Cotylopus acutipinnis (Guichenot), was described using intensive fishway monitoring (28 sampling dates over 1.5 years, 13 000 S. lagocephalus, 23 000 C. acutipinnis captured). Migration peak occurred for both species during the afternoon at the end of austral winter/beginning of austral summer. Abundance and size of fish caught in the river showed a marked impact of a dam (six sampling dates approximately 4000 individuals of each species captured). This study provides critical data for better management of fishways used by tropical amphidromous gobies. It appears especially important to reduce unwanted rheotactic sources that attract the fish away from the fishway's entrance.

Eel populations from the small rivers on the Island of Reunion (French Overseas Department in the Indian Ocean) were investigated with respect to the occurrence and abundance of helminths during the autumn of 2005. The native species Anguilla marmorata (n = 80), Anguilla bicolor (n = 23), and Anguilla mossambica (n = 15) were studied. Six species of helminths were identified, four of them having a definitely nonnative status. Furthermore, unidentified intra-intestinal juvenile cestodes and extra-intestinal encapsulated anisakid nematode larvae were present in a few eels. We found that the invasive swim bladder nematode Anguillicoloides (Anguillicola) crassus had been introduced into the island. Six specimens were collected, four from A. marmorata, one from A. bicolor and one from A. mossambica. The maximum intensity of infection was two worms. The other helminths also showed a low abundance. These species were the monogenean gill worms Pseudodactylogyrus anguillae and Pseudodactylogyrus bini and the intestinal parasites Bothriocephalus claviceps (Cestodes), Paraquimperia africana (Nematodes), and the acanthocephalan Acanthocephalus reunionensis Warner, Sasal, and Taraschewski, 2007. The latter species, found as intra-intestinal immatures, is thought to utilize amphibians as required hosts; its status, introduced or native, could not be determined. P. africana was described from A. mossambica in South Africa and has not been recorded outside Africa. The other species are known from populations of European and American eels. However, A. crassus and the two Pseudodactylogyrus species originate from East Asia, where they are indigenous parasites of Anguilla japonica. Both an assignment test based on seven specific microsatellite loci and subsequent sequencing of mitochondrial haplotypes of a partial fragment of cytochrome c oxidase 1 strongly suggest that the A. crassus may originated around the Baltic Sea. According to the results presented here, populations of the indigenous eel species from Reunion can be considered to harbor extremely isolationist alien parasite communities. Our findings support the hypothesis that during the present time of global biological change, invasion by a nonnative species into a target island is more likely to reflect the political affiliation of the colonized environment and the pathways of trade and tourism than geographic proximity between donor and recipient areas or other natural circumstances.

Amphidromous gobies living in the rivers of tropical islands display a high continuous reproductive effort in response to environmental unpredictability. Females are usually able to spawn a large number of eggs over an extended season, which contributes to offset the high larval mortality. The increasing human pressure on the insular aquatic systems threatens these gobies and highlights the urgent need to acquire knowledge on their biology for management purposes. The present study investigated the reproductive traits of the endemic amphidromous goby, Cotylopus acutipinnis, in a river of La Réunion Island. Ovarian histology showed that females were multiple spawners with a group-synchronous ovarian follicle development and an indeterminate fecundity. Females reproduced from 28.6-mm TL and laid their eggs in a unique event (from 3226 to 106840 eggs), with a spawning frequency of ~1 month or less. The drop in reproductive activity coincided with lower water temperatures and a decrease in daylight duration. Evidence suggested that spawning activity was not disturbed by flooding events recorded a few days before sampling. We suggested that the temperature threshold inducing the ovarian growth (18.3°C for C. acutipinnis) could be a determinant factor explaining the specific repartition of gobies throughout the river.