1. Abnormal hydroclimatic years in the Amazon have been increasingly frequent in the last two decades, creating more prolonged droughts and severe floods. These events are expected to impact organismal phenology, including seasonal reproduction of fish. Droughts are also expected to increase fish mortality and vulnerability to fishing. However, empirical evidence on the impact of these novel conditions on fish reproduction and demography is still limited.2. Here, we evaluate how changes in hydrological conditions and fishing affected reproduction and demographic parameters for the 16 most common floodplain fish species in the central Amazon. We used water level data collected for 113 years together with a 19-year dataset of fish biology, sampled monthly from a floodplain lake at the confluence of Amazon and Negro rivers.3. We observed a lower proportion of ripe females after long, drier low-water and abrupt rising-water seasons. For many species, we detected a progressive reduction in the female's size at sexual maturity, the average size of the ripe females and in the abundance of larger adult females. These effects were observed for both fished and non-fished species, suggesting that the effect of the recent hydroclimatic events might be affecting most fish species. However, fished species showed a steeper decline in the average body size of ripe females, suggesting that size reduction is a combined effect of drought severity and fishing pressure.4. Policy implications. Our results for the proportion of females in reproduction mediated by hydrological conditions and temporal changes of demographic and lifehistory parameters suggest that drought events can reduce the resilience of fish populations in the central Amazon. The increasing frequency of droughts and rapid changes in fish reproductive parameters highlight the need for conservation policies to consider the impact of droughts in addition to fisheries and habitat degradation. Our results should be taken as an early warning regarding the conservation and sustainable use of Amazon aquatic biodiversity. Conserving fish diversity and fish stocks will require substantial ecosystem management in a large portion of the Amazon floodplains and a greater enforcement of fisheries management regulations in years of predicted drought.
Length-weight relationship (LWR) is likely the most useful tool to estimate indirect growth, body condition, and to understand the life cycle of fishes (Camara, Caramaschi, & Petry, 2011; Froese, 2006). Length and weight are biometrics data easily taken and available in most datasets from monitoring studies. Despite the simplicity, it provides highly useful information for fisheries management and can be used in different applications like the estimation of biomass from length data or comparisons between growth patterns and morphologic differentiation of the same species from different populations (Imorou, Alphonse, Edmond, & Youssouf, 2019; Karachle & Stergiou, 2012). The Amazon basin shelters a very highly diverse freshwater fish fauna that occupy a wide variety of environments. The middle stretch of the Amazon River sustains very important fishery activities, which targets about 100 species coming from its main channel and associated floodplain environments (Santos, Ferreira, & Zuanon, 2006). Here we present LWRs for 39 fish species based on 18 years of monthly fish sampling in the Catalão Lake, at the confluence of Amazonas and Negro rivers.
This research aimed to investigate the ecological indexes of the helminths of the digestive system and coelom of Prochilodus argenteus Spix & Agassiz, 1829. A total of 150 specimens (53 males and 97 females) taken from the upper reaches of the São Francisco River in the municipality of Três Marias (18º12'32"S, 45º15'41"W), State of Minas Gerais, Brazil, were examined. The specimens were collected in July, 2003 and January, 2004. Ninety-eight fish (65.3%) were infected by at least one species of helminth. Five helminth species were found: one digenean, Saccocoelioides nanii Szidat, 1954; two Eucestoda, Valipora sp., and one undetermined metacestode; one nematode, Spinitectus asperus Travassos, Artigas & Pereira, 1928; and one acanthocephalan, Neoechinorhynchus prochilodorum Nickol & Thatcher, 1971. The sex of the host did not influence parasite indexes. The total length of the hosts influenced the abundance of S. nanii (r s = -0.21, p = 0.01) and the prevalence of the metacestode (r = -0.91, p = 0.01). Saccocoelioides nanii was the dominant species in the parasite fauna of P. argenteus. Saccocoelioides nanii, Valipora sp., S. asperus and N. prochilodorum are reported here for the first time in P. argenteus and their known distribution is expanded to the São Francisco River
Length‐weight relationships (LWRs) were estimated for 16 ornamental fish species from Amanã Lake and nine tributary streams, in Central Brazilian Amazonia. Sampling was carried out bimonthly for a year (2007–2008), using two sets of four gillnets (20 m × 2 m, 2,5; 3,5; 04; 4,5 cm stretch mesh size); trawls were performed with seine nets (35 m × 6 m, 3 mm stretch mesh size); native fish‐traps (fyke‐net like fish‐traps woven from local lianas), and dip nets (0.5 m × 0.5 m stretch mesh size). Measurements were done for standard length (SL – 0.1 cm precision) and total weight (Wt – 0.01 g precision). This study provides information on the length–weight relationships for all sampled species and, in addition, provides new maximum standard lengths for six species.
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