Nano-plastics in the aquatic environment.

The amount of plastics released to the environment in modern days has increased substantially since the development of modern plastics in the early 1900s. As a result, concerns have been raised by the public about the impact of plastics on nature and on, specifically, aquatic wildlife. Lately, much attention has been paid to macro- and micro-sized plastics and their impact on aquatic organisms. However, micro-sized plastics degrade subsequently into nano-sizes whereas nano-sized particles may be released directly into nature. Such particles have a different impact on aquatic organisms than larger pieces of plastic due to their small size, high surface curvature, and large surface area. This review describes the possible sources of nano-sized plastic, its distribution and behavior in nature, the impact of nano-sized plastic on the well-being of aquatic organisms, and the difference of impact between nano- and micro-sized particles. We also identify research areas which urgently need more attention and suggest experimental methods to obtain useful data.

Sex identification and PIT-tagging: tools and prospects for studying intersexual differences in freshwater fishes.

This study evaluated a technique to allow the long-term monitoring of individual fishes of known sex in the wild using sex confirmation in close proximity to the reproductive period combined with individual tagging. Hundreds of partially migratory roach Rutilus rutilus were tagged with passive integrated transponders (PIT) following sex determination in spring and various performance measures were compared with fish tagged outside the reproductive period in autumn. Short-term survival was >95% for R. rutilus sexed and tagged under natural field conditions. Total length (LT ) did not affect the probability of survival within the size range tagged (119-280 mm), nor were there differences in timing of migration the following season between individuals sexed and tagged in spring and individuals tagged in autumn (i.e. outside the reproductive period). Also, a similar per cent of R. rutilus sexed and tagged in spring and tagged in autumn migrated the following season (34·5 and 34·7%). Moreover, long-term recapture data revealed no significant differences in body condition between R. rutilus individuals sexed and tagged in spring, individuals tagged in autumn and unmanipulated individuals. The observed sex ratio of recaptured fish did not differ from the expected values of equal recapture rates between males and females. Hence, there is no observable evidence for an adverse effect of tagging close to the reproductive period and therefore this method is suitable for studying intersexual differences and other phenotypic traits temporarily expressed during reproduction at the individual level in fishes.

Partial migration in fishes: causes and consequences.

Partial migration, where only some individuals from a population migrate, has been widely reported in a diverse range of animals. In this paper, what is known about the causes and consequences of partial migration in fishes is reviewed. Firstly, the ultimate and proximate drivers of partial migration are reflected upon: what ecological factors can shape the evolution of migratory dimorphism? How is partial migration maintained over evolutionary timescales? What proximate mechanisms determine whether an individual is migratory or remains resident? Following this, the consequences of partial migration are considered, in an ecological and evolutionary context, and also in an applied sense. Here it is argued that understanding the concept of partial migration is crucial for fisheries and ecosystem managers, and can provide information for conservation strategies. The review concludes with a reflection on the future opportunities in this field, and the avenues of research that are likely to be fruitful to shed light on the enduring puzzle of partial migration in fishes.

Partial migration in fishes: definitions, methodologies and taxonomic distribution.

Partial migration, where populations are composed of both migratory and resident individuals, is extremely widespread across the animal kingdom. Researchers studying fish movements have long recognized that many fishes are partial migrants, however, no detailed taxonomic review has ever been published. In addition, previous work and synthesis has been hampered by a varied lexicon associated with this phenomenon in fishes. In this review, definitions and important concepts in partial migration research are discussed, and a classification system of the different forms of partial migration in fishes introduced. Next, a detailed taxonomic overview of partial migration in this group is considered. Finally, methodological approaches that ichthyologists can use to study this fascinating phenomenon are reviewed. Partial migration is more widespread amongst fishes than previously thought, and given the array of techniques available to fish biologists to study migratory variation the future of the field looks promising.

Effects of enrichment on simple aquatic food webs.

Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.

Induced pigmentation in zooplankton: a trade-off between threats from predation and ultraviolet radiation.

Ultraviolet (UV) radiation is harmful to all life, and the ongoing depletion of the ozone layer is likely to affect interactions among both terrestrial and aquatic organisms. Some organisms have evolved adaptations to reduce radiation damage, such as the various types of protective pigmentation of freshwater zooplankton. However, strong pigmentation also increases vulnerability to visually hunting predators. Hence, where both UV radiation and predation are intense, zooplankton may be sandwiched between conflicting selective pressures: to be pigmented and to be transparent at the same time. Here, I show that the level of pigmentation in copepods is up to ten times higher in lakes without predatory fishes than where fishes are present. Moreover, animals from the same population exposed to either UV light or predator scent showed a 10% difference in pigmentation after only four days, suggesting that pigmentation is an inducible trait. Hence, individual copepods are not passive victims of selective predation or radiation damage, but adjust the level of pigmentation according to the prevailing threat. The ability to adjust pigmentation level rapidly may be especially useful in situations where risk assessment is difficult due to strong seasonal and spatial variation in risk variables, such as in Arctic regions. With progressive thinning of the ozone layer, the ability of some but not other organisms to adjust protection against UV radiation may lead to counter-intuitive, large-scale alterations in freshwater food webs.

Physicochemical characterization of specific and nonspecific polyaromatic hydrocarbon binders in rat and mouse liver cytosol.

The aryl hydrocarbon hydroxylase inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3-methylcholanthrene, and benzo(a)pyrene were all shown to bind in a saturable manner to a distinct component in cytosol from both rat and C57BL/6J mouse liver. This component was analyzed by gel permeation chromatography on Sephacryl S-300 and by sucrose density gradient centrifugation and was found to have a Stokes radius of 61 +/- 1.5 A and a sedimentation coefficient of 4.4 S under high salt conditions. Based on these parameters, which were identical for the rat and mouse receptor, a molecular weight of 111,000 was calculated. The same Stokes radius and sedimentation coefficient were observed regardless of the ligand used for labeling of the receptor protein [(3H]TCDD, 3-[3H]methylcholanthrene or [3H]benzo(a)pyrene). On the other hand, 3-[3H]methylcholanthrene and [3H]benzo(a)-pyrene exhibited much more nonspecific binding than [3H]TCDD, at least partially due to contaminating serum components, and it cannot be excluded that some previous findings on low molecular weight hepatic "receptors" for these polyaromatic hydrocarbons may actually be explained in this way. Clearly, use of thoroughly perfused livers would seem to be a prerequisite for investigations on specific binding of aryl hydrocarbon hydroxylase inducers to liver cytosol. The rat hepatic TCDD receptor was also shown to be retained on DEAE-Sepharose (eluted at 0.2-0.3 M NaCl), hydroxylapatite (eluted at 0.15-0.17 M phosphate), and heparin-Sepharose (eluted at 0.3-0.4 M NaCl). In conclusion, the TCDD receptor showed similar physicochemical and chromatographic characteristics to those previously reported for the androgen and glucocorticoid receptors. However, ligand competition experiments indicated that the TCDD receptor is not identical to any steroid receptor. In line with this, monoclonal anti-glucocorticoid receptor-IgG antibodies did not react with the TCDD receptor.