Trends in biomarkers, biotic indices, and fish population size revealed contrasting long-term effects of recycled water on the ecological status of a Mediterranean river.

Recycled water is important for maintaining river flow in semi-arid regions. However, it has ecological risk, as suggested by comparison of habitat and white and red blood cell count in two wild fish species (Barbus meridionalis and Squalius laietanus) before and after an input of recycled water in Ripoll River (NE Spain) in 2009. Due to the lack of normal ranges for blood variables in wild fish, we surveyed seasonally the same river reaches in 2013 to test if blood alterations from 2009 compromised the viability of the fish populations. By examining other indicators of river health in baseline and polluted sites (fish abundance, mass-length relationships, and community indices in fish, diatoms and invertebrates), we tested for the superior utility of blood tests in biomonitoring. The comparison of water quality and scores of diatoms and invertebrate indices between polluted and reference sites showed that polluted sites improved from 2009 to 2013. The abundance of B. meridionalis also increased in polluted sites, but that of S. laietanus declined in 2013 compared to 2009. These results contrast with results of blood analyses in 2009, which suggested that B. meridionalis was more seriously affected by pollution than S. laietanus. The fish index did not reveal the risk of recycled water to fish health, whereas fish mass-length relationships suggested that S. laietanus individuals in 2013 had a better body condition in polluted than in reference sites. Given that the two fish species had opposite results in reference sites, and that the physical habitat was more suitable for B. meridionalis in polluted sites in 2013 than was for S. laietanus, trends in population size are not only explained by pollution. The role of phenology is suggested by peaks in blood disorders during the breeding season. However, more long-term studies combining indicators of river health at the individual and community scales are needed to fully assess the ecological risk of recycled water in this river. These studies will also help to develop blood tests as reliable health indicators in wild fish populations.

Interactions of warming and exposure affect susceptibility to parasite infection in a temperate fish species.

Predicting how elevated temperatures from climate change alter host-parasite interactions requires understandings of how warming affects host susceptibility and parasite virulence. Here, the effect of elevated water temperature and parasite exposure level was tested on parasite prevalence, abundance and burden, and on fish growth, using Pomphorhynchus laevis and its fish host Squalius cephalus. At 60 days post-exposure, prevalence was higher at the elevated temperature (22 °C) than ambient temperature (18 °C), with infections achieved at considerably lower levels of exposure. Whilst parasite number was significantly higher in infected fish at 22 °C, both mean parasite weight and parasite burden was significantly higher at 18 °C. There were, however, no significant relationships between fish growth rate and temperature, parasite exposure, and the infection parameters. Thus, whilst elevated temperature significantly influenced parasite infection rates, it also impacted parasite development rates, suggesting warming could have complex implications for parasite dynamics and host resistance.

Life history characteristics of a lightly exploited stock of Squalus suckleyi.

The purpose of this study was to examine the basic life history of a lightly exploited stock of Squalus suckleyi in the Gulf of Alaska to establish a baseline for future comparison and to provide critical information for stock assessments. Average total length (total length extended) of females (87·7 cm) was significantly larger (t-test, t = -12·57, d.f. = 1533, P < 0·01) than males (80·3 cm); size at 50% maturity (74·5 and 97·3 cm, males and females, respectively) and age at 50% maturity (21 and 36 years, respectively) were also significantly different between the sexes (i.e. bootstrapped 95% c.i. did not overlap). Total average fecundity was 8·5 pups per female, and individual fecundity was a linear function of either length or whole mass. The best estimate of instantaneous natural mortality was 0·097. The delayed age of maturity, low natural mortality and low rates of reproduction imply that only very low rates of fishing mortality are sustainable. Finally, this paper provides the first reported evidence that a small percentage of the adult females may undergo an extended resting period between pregnancies of ≥ 1 years.