Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

consumed relative to unexposed fish. By using very young fry, the studies also provide
information on a sensitive early lifestage where swimming behaviors are critical to survival (i.e.,
feeding and predator avoidance). We ranked these studies as highly relevant to a variety of
essential swimming-associated behaviors.
One study tested whether schooling of fish in estuarine waters was affected by a single short-
term exposure of carbaryl at 100 μg/L (Weis and Weis 1974). Carbaryl impaired schooling of
Atlantic silversides (M. menidia) by increasing the school area by up to twice that of control
groups. Recovery of schooling behavior took three days (Weis and Weis 1974). The authors
suggested that increased schooling areas would increase energy expenditures of individual fish
and also increase rates of predation. The study lacked analytical verification of exposure
concentrations; only one concentration was tested; and the study was conducted with a nonsalmonid
fish. The study is relevant because it addressed an important swimming behavior (i.e.,
schooling), which juvenile salmonids use at times, and presented data on time to recovery
following an adverse behavioral affect. However, it remains uncertain at which concentrations
juvenile salmonids that school would be affected.
Neurological effects on the startle response and ability to avoid predation by juvenile medaka
(Oryzias latipes) were evaluated following exposures of 2.5, 5.1, 7.0, and 9.4 mg/L carbaryl
(Carlson, Bradbury et al. 1998). At 5.1 mg/L and higher, carbaryl increased the time between
motor neuron peak and initiation of muscle activity (i.e., swimming response) and at 7.0 mg/L
and higher response to stimuli ratios were also higher. Predation trials showed no differences
between medaka exposed to carbaryl and unexposed fish. While these concentrations are
extremely high compared to concentrations affecting salmonids, the results indicate that
neurological-associated swimming behaviors are affected by carbaryl. Given that the 48 h LC50
of juvenile medaka is estimated at 9.4 mg/L and that detectable sublethal neurological effects
occurred at 5.1 mg/L, roughly half the LC50, it is uncertain at what concentrations juvenile
salmonids neurological endpoints would be affected. We ranked this experiment as relevant as it
provided evidence that neurological effects manifest at lower concentrations than 48 h LC50s.
339