Temperate Freshwater Species Research Articles

Enriched stable isotope marking of hatchery trout via immersion: A method to monitor restocking success

Abstract Suitable habitat for many temperate freshwater species of salmonids is predicted to dramatically decline, yet many hatcheries still release millions of juvenile salmonids into rivers and lakes annually with little or no post release monitoring. This is, in part, because marking of hatchery reared fish is often not compulsory and currently available marking methods are either costly, cause high mortalities, are inconvenient to apply, or have poor long-term retention rates. To help overcome these limitations, we tested two recently validated stable isotope mass marking methods for Atlantic salmon (larval and egg immersion), to determine if a suitable low cost, easy to apply, fish friendly marking method could be achieved for two of the most widely stocked freshwater salmonids worldwide: brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss. Egg immersion using 1000 μg L−1 of 137Ba and 136Ba over a 2 h period did not create detectable marks in the otoliths of brown or rainbow trout. In contrast, larval immersion using 100 μg L−1 of 137Ba and 136Ba over a 24 h period returned a 100% mark-success rate in the otoliths of brown and rainbow trout at an estimated marking cost of $US 0.004 per fish. Larval immersion marks were clearly definable in the otoliths, with isotope ratios in marked fish 11 times greater than ratios measured in control fish. Furthermore, the process of marking was easy to apply, with

Effects of malathion and carbendazim on Amazonian freshwater organisms: comparison of tropical and temperate species sensitivity distributions

The risk assessment of pesticides for freshwater ecosystems in the Amazon has relied on the use of toxicity data and water quality criteria derived for temperate regions due to a lack of ecotoxicological studies performed with indigenous species. This leaves an unknown margin of uncertainty for the protection of Amazonian ecosystems, as differences in environmental conditions and species sensitivity are not taken into account. To address this issue, the acute toxic effects of malathion (an organophosphorus insecticide) and carbendazim (a benzimidazole fungicide) were assessed on five fish and five freshwater invertebrates endemic to the Amazonian region. Subsequently, the intrinsic sensitivity of Amazonian and temperate freshwater species was compared using the species sensitivity distribution (SSD) concept. Amazonian species sensitivity to malathion was found to be similar to that of their temperate counterparts, with LC50 values ranging between 111 and 1507 μg/l for fish species and 2.1–426 μg/l for arthropod species. However, Amazonian fish appeared to be slightly less sensitive for carbendazim than temperate fish with LC50 values ranging between 1648 and 4238 μg/l, and Amazonian invertebrates were found to be significantly more resistant than their temperate counterparts, with LC50 values higher than 16000 μg/l. The results of this study suggest that for these compounds, the use of water quality criteria derived with laboratory toxicity data for temperate species will result in a sufficient protection level for Amazonian freshwater organisms. Recommendations for further research include the validation of threshold concentrations derived with temperate standard test species and with the SSD model with semi-field experiments considering larger assemblages of indigenous species under local environmental conditions.

Fish Cytogenetic Research: Advances, Applications and Perspectives

Methods developed since 1976 for harvesting, preparing and banding fish chromosomes are now commonly used for taxonomic and phylogenetic studies, genetic control and chromosome manipulations in fish breeding and in monitoring aquatic pollutants by examining chromosomal aberrations. These studies have chiefly concerned common temperate freshwater species; the same procedures, when applied to marine and coldwater fish, often provide unsatisfactory results, especially in cell culture. A concerted effort should be made in marine fish, and to develop molecular cytogenetic methods to provide a more powerful tool to study chromosomal evolution.