Crime Scene San Francisco: Who Is Responsible for the Disappearance of Delta Smelt?

Delta smelt are becoming harder and harder to find in the San Francisco Estuary. Some of the suspects in their disappearance are invasive fish species that were introduced from other places into the Estuary. These invasive fish can impact their new habitat by eating the native species that were originally there. However, it is hard to understand what the invasive fish are eating. We found that we can use the DNA in the stomachs of invasive fish to figure out what they have eaten. We caught a common invasive fish in the Estuary, called the Mississippi silverside, and analyzed the DNA from their stomachs to see if it matched delta smelt DNA. We discovered that some Mississippi silversides had delta smelt DNA in their stomachs! We therefore believe that Mississippi silversides are one of the culprits causing the disappearance of delta smelt.

Concentration of Metals in Native and Invasive Species of Fish in the Fluvial-Lagoon-Deltaic System of the Palizada River, Campeche

Aquatic organisms, such as fish, are important indicators of the bioavailability of metals in coastal environments, demonstrating the capacity of different species to bioaccumulate these metallic elements. The fluvial-lagoon system of the Palizada River is an important ecosystem for its terrestrial and aquatic biological diversity where fishing is an important productive activity in this system. The objective of this research was to evaluate the concentration of Pb and Cd in the muscle tissue of native and invasive fish species in this area. For this, the digestion of fish muscle samples was carried out with a CEM MARS 5 Digestion Microwave System, while the quantification of metals was performed with an atomic absorption equipment. All analysis muscle samples from native and invasive fish showed Pb and Cd in their content. By sampling site there was a statistically significant difference (p < 0.05), with a maximum Pb concentration of 7.760 µg g−1 at the LLAR site (Laguna Larga). In terms of species, the maximum Cd concentration was obtained in the Cyprinus carpio with 6.630 ± 0.127 and in Pterygoplichthus pardalis with 6.547 ± 0.873 µg g−1 (dry weight). The presence of metals such as Pb and Cd in muscle tissue of native and invasive fish species represents an important bioindicator of environmental exposure in the study area and a potential risk to public health, as these species are commonly consumed.

Introduction to the Biology and Control of Invasive Fishes and a Special Issue on This Topic

Across the globe, dozens of species of invasive fish are now found in fresh as well as marine waters, where they alter habitats, compete with native fish for food, and prey on native fishes, exerting both indirect and direct effects on ecosystems and economies. While efforts to understand and control these species are growing, most are still in their infancy; however, a few examples stand out. This special issue is comprised of 11 notable articles on freshwater invasive fish and is the first to address this topic. This introductory article serves as an introduction to these articles which focus on 5 topics on invasive freshwater fish: (1) the damage they cause (one article); (2) techniques to ascertain their presence (one article); (3) techniques to restrict their movement (one article); (4) strategies to control them (three articles); and (5) lessons learned from ongoing management efforts (five articles). This introduction notes that successful management efforts share a few approaches: (1) they develop and use a deep understanding of local species and their abundance as well as distribution; (2) they focus on reducing reproductive success; (3) they use multiple complimentary control strategies; and (4) they use a long-term approach.