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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.

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Osmoregulatory capacity (OC) decreased by approximately 50% after eyestalk ablation in adult Homarus americanus when in dilute media. OC was used to assay sinus gland extracts. Injection of total extracts and of some HPLC-separated fractions of sinus glands into destalked lobsters increased OC. One of the described crustacean hyperglycemic hormone isoforms influences osmoregulation. Another fraction of the sinus gland extracts modifies osmoregulation but its nature remains unknown. Variations in OC were examined in response to ecdysterone, Phe-Met-Arg-Phe-NH2, and atrial natriuretic factor but effects were minimal.

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Larval and postlarval lobsters, injected with human somatotropin (STH, or growth hormone), grew at a more rapid rate than untreated control animals over succeeding molts. Their mean carapace length was significantly longer than that of controls and they were heavier, although the moisture content of treated and control animals was similar. Injected STH increased the growth rate of individual animals by 10 to 20%. This is the first evidence for a growth enhancing effect of human somatotropin on a Crustacean.

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Removal of eyestalks of Homarus americanus on different days and molting stages during larval development revealed that eyestalk tissue is involved in the larval and postlarval molting rhythm and in preparation for metamorphosis as early as the end of Stage II. Eyestalk removal in stages II and III reduced the duration of larval and postlarval stages. Eyestalk removal up to the end of Stage II delayed the completion of metamorphosis by one or two molts and caused additional development stages (designated IVa, IV', and V'). In this study, the critical stage for eyestalk ablation to delay metamorphosis occurred at the end of molt stage D1 of larval Stage II (the seventh day of development at 20 degrees). Injection of juvenile hormone before the critical stage resulted in a few intermediate stage IV' animals. This study demonstrates the involvement of eyestalk neuroendocrine tissue in the control of metamorphosis and investigates a possible involvement of juvenile hormone.

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Neither gill nor hepatopancreas exhibited significant differences in Na+, K+-ATPase activity with molt stage. Hepatopancreatic residual ATPase activity was significantly higher (F = 6.273) in post-molt animals; while gill residual ATPase activity exhibited no significant differences. Muscle AEC did not change with molt stage, but levels of ATP (F = 8.050) and ADP (F = 4.130) were significantly higher in premolt (D3 pleopod stage 5.0-5.5) animals; while levels of arginine phosphate (F = 6.981) were significantly higher in post-molt animals. Arginine phosphate/ATP and ATP/ADP ratios were highest in post-molt animals, but were not statistically significant. Although not significant, changes in Na+, K+-ATPase activity and AEC did suggest alterations in: enzyme activity that correlate with known osmotic compensations occurring during the water uptake and hardening/mineralization processes; and energy metabolism which occur during the molt cycle, respectively.

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Sodium regulation in Homarus americanus changes from isoionic in Stage III to slightly hyperionic in Stage IV, and this is paralleled by improved survival of Stage IV lobsters in dilute media. Bilateral eyestalk ablation converts Stage IV and V lobsters to isoionic sodium regulation, but implantation of Stage IV or V eyestalk neuroendocrine tissue restores their normal hyperionic regulation. These results indicate that sodium regulation is controlled from Stage IV by eyestalk neuroendocrine factors. It is suggested that these changes between stages are part of a true metamorphosis that occurs between the last larval stage (III) and the first postlarval stage (IV).

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Juvenile lobsters survive well in salinities above 10.2% (300 mOsm/kg), and their osmotic and ionic (Cl-, Na+, Ca2+) regulation in dilute sea water is slightly hyperosmotic, similar to that of adults. Approximately a month after eyestalk ablation, osmotic and ionic (Cl-, Na+) regulation becomes isosmotic, water content increases, and survival rate in dilute sea water declines, but these changes can be partially reversed by implantation of eyestalk neuroendocrine tissue. Regulation of Ca2+, in contrast, is only slightly affected by eyestalk ablation. These results indicate that osmotic regulation and regulation of hemolymph Na+ and Cl- concentrations are at least partly controlled by eyestalk neuroendocrine factors in this species.

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The lobster mandibular organ is well vascularized and its polygonal cells are arranged loosely around blood vessels and blood sinuses. Numerous mitochondria and microbodies (peroxisomes) give the acidophilic cytoplasm a finely granular appearance, but there is no evidence of secretory granules. The abundant endoplasmic reticulum is almost entirely agranular and occurs in two morphologically distinct forms: tubular and cisternal. The tubular reticulum is randomly distributed and may represent the site of synthesis and transport of the mandibular organ product. The cisternal reticulum is frequently associated with microbodies. Both forms of endoplasmic reticulum proliferate during mid to late premolt. Mandibular organ ultrastructure closely resembles that of cells known to synthesize steroids or lipids, which suggests that this organ may have a similar function. There is no functional evidence of involvement in molt control in Homarus, but ultrastructural and other evidence suggests an analogy with insect corpus allatum.

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An industrial discharge of yellow phosphorus killed fish and crustaceans in Long Harbor, Placentia Bay, Newfoundland, in 1969. During subsequent toxicity studies various organs from lobsters killed by exposure to suspensions of yellow phosphorus were examined for histological damage. Anitennal gland and hepatopancreas both showed degenerative changes, and cellular damnage in the latter was extensive.

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