Morphology-diet relationships in four killifishes (Teleostei, Cyprinodontidae, Orestias) from Lake Titicaca.

This study explores the relationship between morphology and diet in four Andean killifishes (Orestias) from Lake Titicaca that are known to differ in habitat use. Species that fed preferentially on amphipods (Orestias albus) or molluscs (Orestias luteus) separated in multivariate space from other species that feed on cladocera and algae (Orestias agassii and Orestias jussiei). Generally, specimens feeding on cladocera were characterized by a short, blunt nose with a small mouth; whereas, specimens feeding on amphipods exhibited a long snout with a large mouth. Specimens including molluscs in their diet tended to have a larger posterior part of the head and the larger opercles than others; while the occurrence of substratum in gut content was generally related to a short but deep head. The present analysis suggests that the littoral O. jussiei has an intermediate phenotype and diet between the pelagic (O. agassii) and benthic (O. albus and O. luteus) species. Results suggest that resource partitioning was occurring and that several morphological traits relate to characteristics of the diet, and it is inferred that the benthic, the pelagic and the littoral zones in the lake host different prey communities constituting distinct adaptive landscapes.

River hydrological seasonality influences life history strategies of tropical riverine fishes.

Under a particular set of selective forces, specific combinations of traits (strategies) will be favored in a given population, within the particular constraints of the considered species. For fishes, three demographic strategies have been suggested to result from adaptive responses to environmental predictability (i.e., seasonality): periodic, opportunistic and equilibrium [Winemiller KO, Rose KA (1992) Patterns of life-history diversification in North American fishes: implications for population regulation. Can J Fish Aquat Sci 49:2196-2218]. These strategies optimize fitness within predictable, unpredictable and stable systems, respectively. We tested these predictions of life history trait distribution along a gradient of hydrologic seasonality in West African tropical rivers at the drainage basin scale. We used logistic regression of species presence-absence data to test whether dominant life history traits of species caused community compositional change in response to a gradient of seasonality in hydrologic regime across basins. After accounting for taxonomic relatedness, species body size and statistical redundancy inherent to related traits, we found a higher proportion of species producing a great number of small oocytes, reproducing within a short period of time and presenting a low degree of parental care (the periodic strategy) in highly seasonal drainage basins (e.g., rivers with a short and predictable favorable season). Conversely, in more stable drainage basins (e.g., rivers with a wet season of several months), we observed a greater proportion of species producing small numbers of large oocytes, reproducing within a long period of time and providing parental care to their offspring (the equilibrium strategy). Our results suggest that distributions of tropical freshwater fishes at the drainage basin scale can be partly explained by the match between life history strategies and seasonality gradients in hydrological conditions.

Gold-mining activities and mercury contamination of native amerindian communities in French Guiana: key role of fish in dietary uptake.

In 1994, the French National Public Health Network reported significant mercury exposure of native Amerindians in French Guiana. In 1997, a study was conducted in the Wayana community to quantify the dietary intake and to identify the fish species contributing the most to the contamination. The study was completed by an impregnation analysis based on Hg determination in hair samples. The methodology used was a detailed familial dietary study associated with Hg measurements in fish and some game. The study was conducted over 7 days in two different seasons in the four most populated Wayana villages on the upper part of the Maroni River (521 people; 70% of the Wayana population in French Guiana). Analysis was based on data on consumption obtained from 165 people in a 1-14 day period (i.e., 940 persons [times] days) and involved 270 fish samples from 48 species. Total Hg and monomethylmercury (MMHg) were also determined in hair samples (235 samples for total Hg). The results confirm mercury exposure of the Wayana population related to a diet rich in fish, which are relatively highly contaminated for certain species (up to 1.62 mg/kg fresh weight or 8.1 mg/kg dry weight in skeletal muscle). Results from hair samples showed that 57% of the Amerindians had Hg levels above the World Health Organization (WHO) safety limit (10 microg/g); all those over 1 year of age had a Hg intake greater than the WHO safety limit (200 microg MMHg/week for a 60-kg male). Hg concentrations in fish muscle were closely linked to the feeding regime and position of fish in the food webs. Overall, 14.5% of the fish collected exceeded the 0.5 mg/kg (fresh weight) safety limit. Four carnivorous species accounted for no less than 72% of the metal ingested by the Wayana families, although these represented only 28% of the consumed fish biomass. In conclusion, this study revealed excessive exposure to mercury in the Wayana population in French Guiana related to the consumption of contaminated fish.