Biomass-dependent Effects of Age-0 Common Carp on Aquatic Ecosystems

Fishes play a functional role in structuring aquatic ecosystems through top-down and bottom-up processes. Adult common carp (Cyprinus carpio) are well recognized for their middle-out effects on aquatic ecosystems that can shift shallow lakes from the clear- to turbid-water stable state through benthic foraging activities. However, less is known about ecosystem effects of age-0 common carp. Age-0 common carp are planktivorous and can be highly abundant, suggesting that large year classes may also produce undesirable ecosystem effects. We evaluated the effects of four age-0 common carp densities (0, 175, 475, and 812 kg/ha) on water quality (ammonium, total phosphorus, total Kjeldahl nitrogen, and turbidity) and primary (macrophytes and phytoplankton) and secondary (zooplankton and benthic invertebrates) production. Common carp increased nutrient availability and phytoplankton production and decreased water transparency with effects increasing with carp biomass. Common carp also reduced macrophyte coverage and cladocera density (through effects on chydorus and ceriodaphnia) and body size, but effects were not density dependent. In contrast, common carp did not appear to affect copepod, rotifer, chironomid, or gastropod densities. These results suggest that even relatively low age-0 common carp densities (\u3e175 kg/ha) may have many comparable ecosystem effects as adult carp, although effects may be accrued through different pathways

An assessment of age determination in fossil fish: the case of the opercula in the Mesozoic actinopterygian Saurichthys

Analyzing and interpreting life history data (e.g., aging and longevity, age at sexual maturity) are fundamental in many paleontological studies. In the case of extant and fossil fishes, otoliths, and to a lesser degree other incrementally growing hard tissue structures such as scales and bones, have been utilized to reveal these data. We investigated the microanatomy and internal microstructure of opercula of Saurichthys, one of the most easily recognized and globally distributed fishes in the Triassic, to elucidate whether these prominent skull bones provide reliable age estimates. Opercula, and where the subopercula is present, of several outgroup taxa were sectioned to provide a phylogenetic framework for the study. The external protrusions and ridges or internal concentric bands or wrinkles are not related to internal age-related bone tissue structures such as annuli and growth zones, but are instead purely ornamental in the case of the former and probably structural/taphonomic in case of the latter. Opercular morphogenesis of Saurichthys opercula differs from that of the extant outgroups examined in that they show rostro-medial to caudo-lateral extending growth increments instead of ones that extend sub-parallel to the opercular bone surfaces. Individual age data could thus not be reliably extracted from those opercula. Furthermore, an odontode-like complex was not encountered in Saurichthys opercula, but a few specimens show a peculiar, weakly birefringent thin tissue layer of unknown origin filling the valleys between the external ornamental ridges. Although all Saurichthys opercula showed growth marks, these could not be counted to produce reliable individual age data, whereas bones with a more concentric cross section, such as the ceratohyal, appear better suited for this purpose