Parasiticides (PARA)


In addition to antibiotic use to treat bacterial infection in farmed marine finfish, parasiticides are frequently used to reduce parasite infestations in farmed fish. Most parasiticides are applied in a similar manner to antibiotics, either in medicated baths or within formulated feeds. When used in open net pen aquaculture systems, the effects of parasiticides typically manifest beyond the fish farm, and thus it is important to consider the ecological implications of their application within the marine environment.

Many parasiticides are toxic to non-target organisms, especially aquatic invertebrates (Burridge et al. 2008a). Toxicity varies by the type of parasiticide and type of organisms affected (Burridge et al. 2008a). Similarly, the persistence of parasiticides in the sediment and water column range significantly (Bright and Dionne 2005; Burridge et al. 2008a; SEPA 1999 in Burridge et al. 2008b; Mayor et al. 2008). Overuse of certain parasiticides can lead to chemical resistance, such as the documented resistance to parasiticides in Scottish sea lice (Jones et al. 1997).

The parasiticides indicator (PARA) was designed by a workshop of experts brought together by the project to determine indicators for waste-related impacts. While the amount of chemical used and the level of toxicity were considered key components of the indicator, consulted experts agreed that the persistence of the chemicals should also be incorporated. LC50 and half-life, the major components of the formula, were chosen because they are both accepted and readily available measures of toxicity and persistence, respectively.



PARA = ∑(Amount (kg) x [(1/LC50) + 1] x Persistence (Days))

Amount (kg) = Amount of active ingredient of the parasiticide used
LC50 (mg/L) = Lethal concentration of a chemical in water that kills 50% of the test animals in a given time (represents the organisms most harmed by each substance)
Persistence (half-life) = Residency time of a chemical in the environment measured by its half-life in that environment

Units: Kilograms

Sample Calculation

Sample Normalised Calculation: Coho Salmon from Chile, 2007


GAPI employed the following decision rules to treat gaps in parasiticide data: