The effect of repeated exposure to azamethiphos on survival and spawning in the American lobster (Homarus americanus).

The azamethiphos formulation Salmosan has been used to control sea lice on Atlantic salmon. To determine the effect of this pesticide on spawning in the American lobster, pre-ovigerous females acclimated to 13 degrees C were given biweekly 1-h exposures to Salmosan at concentrations of 1.25-10 microg/L azamethiphos. In March and April, four exposures to 1.25, 2.5, or 5.0 microg/L had no significant effect on survival or spawning incidence, while three or four exposures to 10 microg/L caused high mortality (43-100%). Spawning incidence in the surviving lobsters in the 10 microg/L groups was significantly reduced in the group given four treatments, but not in the group given three treatments. In December and January, four exposures to 10 microg/L azamethiphos had no significant effect on either survival or spawning incidence. The results demonstrate that repeated 1-h biweekly exposures to azamethiphos can have a negative effect on survival and spawning in female American lobsters. The response to this pesticide appears to be influenced by time of year, as well as concentration and number of exposures.

Relationship between dose of emamectin benzoate and molting response of ovigerous American lobsters (Homarus americanus).

A widely-prescribed treatment to control sea lice on cultured salmon is the administration of feed medicated with SLICE (active ingredient emamectin benzoate (EMB)). High doses of EMB can disrupt the molt cycle of ovigerous American lobsters, causing them to enter proecdysis prematurely and lose their attached eggs when the shell is cast. To determine the dose response to EMB, lobsters were forced to ingest doses that ranged from 0.05 to 0.39 microg g(-1). A significant proportion of lobsters given doses of 0.39 and 0.22 microg g(-1) (37% and 23%, respectively) molted prematurely, almost a year earlier than the control group. All the lobsters in the 0.05 and 0.12 microg g(-1) groups molted at the normal time and the mean time of molt was similar to that of the control group. Thus, the no-observed-effect level (NOEL) and lowest-observed-effect level (LOEL) of EMB on the molt cycle were 0.12 and 0.22 microg EMB g(-1) lobster, respectively. To acquire the LOEL, a 500-g lobster would have to consume 22 g of salmon feed medicated with SLICE at a level of 5 microg EMB g(-1) feed.

Seasonal lethality of the organophosphate pesticide, azamethiphos to female American lobster (Homarus americanus).

The organophosphate pesticide azamethiphos is the active ingredient in Salmosan, a product formerly registered in Canada for the treatment of cultured Atlantic salmon against infestations of the ectoparasite Lepeophtheirus salmonis. The 48-h LC50 of azamethiphos to female American lobsters was determined bimonthly for 2 years to determine whether the sensitivity of lobsters to azamethiphos varied with time of year, molt stage, or reproductive stage. The LC50's ranged from 0.61 to 3.24 microg/L. The lobsters were most sensitive to azamethiphos during the spawning and molting seasons which occur in the summer and early fall when seawater temperatures are highest. Testing of compounds on this species for regulatory purposes should take into account that there may be variations in sensitivity during the molt and reproductive cycles.

Expression of the crustacean hyperglycaemic hormones and the gonad-inhibiting hormone during the reproductive cycle of the female American lobster Homarus americanus.

Crustacean reproduction is regulated by a complex chain of hormonal interactions in which the crustacean hyperglycaemic hormones A and B (CHH-A and CHH-B) and the gonad-inhibiting hormone (GIH) play a primary role. These neurohormones are produced in the same neuroendocrine cells of the X-organ sinus gland complex, situated in the eyestalks of the American lobster, Homarus americanus. In order to obtain more information on the synthesis, storage, release and function of these three neuropeptides during the reproductive cycle, we studied the levels of their mRNAs in the X-organ, their peptide storage in the sinus gland and their concentration in the haemolymph at different stages of the female reproductive cycle. A high CHH-A mRNA level was found only in the previtellogenic stage, while elevated mRNA levels were determined for CHH-B in the mature as well as the previtellogenic stage. High CHH storage levels in the sinus gland were found during previtellogenesis. The total amount of CHH (CHH-A plus -B) in the haemolymph was significantly higher during maturation. A low level of GIH mRNA in the X-organ and a low amount of the GIH I isoform in the sinus gland were found only in the immature stage. In contrast, GIH haemolymph levels were high during the immature and previtellogenic stages. We conclude that CHH-A and -B are involved in triggering the onset of vitellogenesis and that CHH-B in particular is responsible for stimulating oocyte maturation before spawning, while GIH prevents the start of vitellogenesis in the ovary. Moreover, our results show that the balance between the haemolymph levels of the CHHs and GIH may tune the synchronization of reproduction and molting during the biannual reproductive cycle of the American lobster.