Anomalies on capture nets of Hydropsyche slossonae larvae (Trichoptera; Hydropsychidae) following a sublethal chronic exposure to cadmium L. Tessier a , J.L. Boisvert a, *, L.B.-M. Vought b , J.O. LacoursieÁre b a Universite  du Que Âbec a Á Trois-Rivie Áres, De Âpartement de chimie-biologie, C.P. 500, Trois-RivieÁres (Que Âbec), Canada G9A 5H7 b University of Lund, Department of Ecology, Ecology Building, S-223 62 Lund, Sweden Received 17 February 1999; accepted 26 July 1999 ``Capsule'': Capture net anomalies of hydropsychid larvae may re¯ect sublethal toxicity of metals. Abstract A laboratory study on the sublethal eects of cadmium (Cd) on the net-spinning process of the larvae of Hydropsyche slossonae was conducted in order to assess the potential of net anomalies as an indicator of chronic exposure to Cd. Two major anomalies with dierent frequency levels were identi®ed after chronic exposure to 0.37, 1.2, 11.6, 21.4 and 43.3 mgl 1 of Cd. The ®rst was a distortion of the midline meshes where the diamond-shape structure is disrupted and the meshes are separated by extra strands (called `midline' anomaly). The second aberration consisted of a distortion of the rectilinear structure of net opening by strands being fused or added over the meshes (called `crossover' anomaly). The midline distortion may be linked to a physio- logical stress caused by Cd, which can aect the control of the net-spinning process. It was not possible to relate the crossover aberrations to a speci®c toxic action of Cd, but data indicated that both anomalies are independent from each other and that two modes of action could be implicated. Protein analyses of capture nets have revealed silk polypeptide modi®cations at the highest Cd concentration tested, indicating a possible eect of Cd interaction with silk proteins. However, neither a gradient-concentration nor a time-dependent response could be established with both aberration frequencies. Silk protein modi®cations would rather play a secondary role in the appearance of both net anomalies, and mostly at a high concentration level. Finally, the toxicity curves (EC 50 ) show that the sensitivity threshold for both types of aberration ranged from 1 to 5 mgl 1 which is highly sensitive compared with other sublethal eects of Cd on other macroinvertebrate species. Hence, the use of capture-net anomalies of hydropsychid larvae would represent a valuable indicator of sublethal toxicity induced by Cd and possibly by other metals in running waters. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Anomalies; Aberrations; Hydropsyche slossonae; Trichoptera; Capture net; Larvae; Cadmium; Sublethal; Chronic exposure 1. Introduction During recent decades, researchers have focused on the development of standardized laboratory bioassays for assessing the toxicity of aquatic ecosystem con- taminants. Lethal, sublethal and chronic toxicity may be estimated in the laboratory by exposing single species to samples of contaminated waters on a short-term basis. However, predicting the potential toxicity of pol- lutants on parameters such as growth, reproduction or survival from short-term laboratory toxicity tests is questionable because of the variability of biochemical and physiological responses and dierences in sensitiv- ity of individuals within a population observed during acute and chronic exposures (Giesy and Graney, 1989; Camargo, 1991a). Nevertheless, individual parameters are likely to be more sensitive and accurate indicators of increased stress than parameters utilizing whole com- munities (Vuori and Parkko, 1996). In this sense, in situ assessment of a contaminant's toxicity using a repre- sentative macroinvertebrate species is preferable since it may give a more realistic measure of pollution impact on freshwater ecosystems. In situ determination of toxic eects at the organism level is suitable since it may be linked to the eect at population level and even give some information of possible mechanisms of toxicity at the community level (Vuori, 1995; Vuori and Parkko, 1996). 0269-7491/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(99)00219-5 Environmental Pollution 108 (2000) 425±438 www.elsevier.com/locate/envpol * Corresponding author. Tel.: +1-819-376-5053; fax: +1-819-376- 5084. E-mail address: jacques_boisvert@uqtr.uquebec.ca (J.L. Boisvert).