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The morphology of an individual can improve its ability to escape predators and ultimately its chances of survival. Sicydiine fishes reproduce in rivers, and their larvae develop in the sea. Once juveniles arrive in rivers, they face numerous predatory fish species. Some juveniles can climb above the first waterfall where the abundance of predatory species is reduced. For individuals that do not climb waterfalls, survival only depends upon their ability to avoid predation. While the factors that affect climbing performance of sicydiines have been extensively described, the information is scarce concerning their predator escape performance. Our experimental study aimed to describe how the predation pressure imposed by three predatory fish species (Eleotris klunzingerii, Kuhlia rupestris, and Anguilla marmorata) affects the individual morphology of juveniles of two sicydiine species from Reunion Island (Cotylopus acutipinnis and Sicyopterus lagocephalus). Individuals which survived predation had a more streamlined body and larger and/or longer pectoral fins for the two sicydiine species, whereas others morphological variables differed with the predator species. Body form of individuals that survived predation also differed from the body form of individuals that climbed waterfalls. The different prey's body forms under selection by the three predator species should be considered in further studies that could address the tradeoff in sicydiines between climbing waterfalls and escaping predation in the field. For example, a careful description of the predator community would help to understand which predator(s) sicydiines juveniles need to escape in downstream reaches and how this particular predation pressure can select body forms. [ABSTRACT FROM AUTHOR]

Dams and other man‐made barriers impair upstream fish migration and thus threaten fish populations that need access to upper river reaches to complete their life cycle. For many years, fishways have been used to mitigate this impact. Fishways around the globe are typically built based on recommendations made for northern hemisphere species, particularly salmonids. These recommendations do not consider the locomotor characteristics and skills of other species, especially those living in the tropics. Among tropical species, freshwater eels and gobies of the Sicydiinae subfamily are important cultural and economic species that are particularly sensitive to the impact of man‐made barriers. Our experimental study aimed to test different substrates and slopes for ramp‐like fishways adapted to tropical eels and sicydiines. Among the five substrates tested for 368 eels Anguilla marmorata, elastomer pins appeared to be the most efficient. Elastomer pins also appeared to be more efficient than the fine concrete which is currently used in fishways for sicydiines (Sicyopterus lagocephalus, N = 1797, and Cotylopus acutipinnis, N = 1303). The slope had a lesser effect on the climbing success of sicydiines compared to substrate type, except for gradients greater than 50° that induced a slight decrease in success. Our results indicated that ramp‐like fishways fitted with 1.0 cm diameter elastomer pins, positioned in staggered rows with a diagonal spacing of 1.3 cm, wetted with low‐flow and angled less than 50°, are well adapted to accommodate the different locomotor characteristics and skills of tropical eels and sicydiines. [ABSTRACT FROM AUTHOR]

The morphology of an individual can affect functional performance and, ultimately, survival and fitness. To study these links, a first step is to evaluate the relationship between morphology and performance. Sicydiine fishes are an interesting model for such studies, because successful completion of their life cycle depends on a functionally demanding task: climbing waterfalls when they return to freshwater from the ocean. Previous studies identified two different climbing modes among sicydiines: 'inching' and 'powerburst'. Relationships between morphology and climbing performance have been found for inching and powerburst species present on different islands from distant oceans (Pacific and Caribbean), but species from the same island have not been compared. In this study, we challenged two different sicydiine species from Réunion Island to an artificial climbing ramp: the inching climber Sicyopterus lagocephalus and the powerburst climber Cotylopus acutipinnis. For each species, we evaluated differences in morphology between successful and unsuccessful climbers. We predicted that species with similar climbing styles (S. lagocephalus and S. stimpsoni) would show differences between successful and unsuccessful climbers that more closely resembled each other than differences between successful and unsuccessful climbers across species from the same island (S. lagocephalus and C. acutipinnis). This prediction was only partially met. S. lagocephalus individuals with a streamlined body showed better climbing performance, as observed for S. stimpsoni. However, the size of the pelvic sucker, which fish use to attach to the substrate while resting, appeared less important for S. lagocephalus than for S. stimpsoni and C. acutipinnis. Instead, the size of the mouth, which inching species use to attach to the substrate while moving up, seemed important for S. lagocephalus but not for other species. Thus, differences in the morphology–performance relationship among sicydiines may relate not only to differences in climbing mode, but also to species‐specific specializations within each climbing mode. The morphology–performance relationship was described for the waterfall‐climbing function of two sicydiine fish species in Réunion Island and compared to similar studies for sicydiine species of Hawai'i and Dominica. Differences in the morphology–performance relationship were observed between species using different climbing mode in Réunion Island, but also between species using the same climbing mode on different islands. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]