Comparison of the abilities of ?-ecdysone and 20-hydroxyecdysone to induce precocious proecdysis and ecdysis in the fiddler crab, Uca pugilator

Evaluation of different induced molting methods in Callinectes ornatus (Crustacea, Decapoda, Portunidae) as a tool for the commercial production of soft-shell crabs

We investigated the effects of eyestalk ablation and cheliped autotomy in inducing molting in Callinectes ornatus. The specimens in intermolt stage were divided into two size classes: 1 (30-50 mm) and 2 (51-70 mm) and were further divided into four experimental groups. In the CA group (Cheliped Autotomy, n=76), crabs were submitted to cheliped autotomy; in the UA group (Unilateral Ablation, n=66) and BA group (Bilateral Ablation, n=66) to unilateral and bilateral eyestalk ablation, respectively. The C group (Control, n=70) was used as control. The animals were individually kept in tanks interconnected to a recirculation system for 30 days. The highest frequency of premolt was recorded in the BA group (32%), followed by the CA group (16%). The premolt frequency of class 1 (28%) was significantly higher (p<0.05) than of class 2 (8%). The mean time until molt in the BA group was significantly lower (p <0.05) than other groups tested. The highest mortality rates were 55% and 25% in crabs from the BA and CA groups, respectively. The results indicate bilateral eyestalk ablation and cheliped autotomy are potentially capable of inducing molt in C. ornatus, but these techniques have limited efficiency for the commercial application of large-scale soft-shell crab.

Chitinase activity in the epidermis of the fiddler crab, Uca pugilator, as an in vivo screen for molt-interfering xenobiotics

We describe an in vivo screening assay that uses epidermal chitinase activity as the endpoint following a 7-day exposure of Uca pugilator to test chemicals. Chitinase, a chitinolytic enzyme, is the end product of endocrine cascades of a multi-hormonal system for control of crustacean molting. Wherever a molt-interfering agent adversely impacts the Y-organ-ecdysteroid receptor axis, the effect should be manifested by the activity of chitinase in the epidermis. Therefore, epidermal chitinase activity is an ideal endpoint for molt-interfering effects of xenobiotics. The validity of epidermal chitinase activity being used for such a purpose is supported by our finding that two injections of 20-hydroxyecdysone at 25 microg/g live weight induced a twofold increase in chitinase activity in the epidermis of U. pugilator. A total of nine chemicals were screened for molting hormone and anti-molting activities. o,p'-DDT was found to significantly inhibit epidermal chitinase activity while kepone and methoxychlor exhibited a tendency of inhibition of enzymatic activity. None of the remaining six chemicals, namely, p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), atrazine, tributyltin (TBT), methoprene, dieldrin and permethrin, had an effect on epidermal chitinase activity.

Hormonal coordination of molting and female reproduction by ecdysteroids in the mole crab Emerita asiatica (Milne Edwards)

The measurement of hemolymph ecdysteroids using radioimmunoassay (RIA) indicates a biphasic increase during intermolt and premolt stages of the mole crab Emerita asiatica. The gradual rise during intermolt stage corresponds to vitellogenic activities in the ovary; whereas a distinctive premolt peak is characteristic of molting crustaceans. Injection experiments with 20-hydroxyecdysone (20E) during different molt cycle stages revealed the onset of precocious premolt changes, as determined by the epidermal retraction and setal development. Injection of 20E augmented protein synthesis in the ovary, hepatopancreas and integumentary tissues. Quantification of ecdysteroids in different developmental stages of ovary also indicated a progressive increase of ovarian ecdysteroids. Interestingly, the ovarian ecdysteroids after reaching a peak at C3 stage, start declining drastically to reach the lowest level at D(3-4) stage. This decline in the ovarian ecdysteroids is inversely related to rising hemolymph ecdysteroids during these active premolt stages. The hatching of the embryos, attached to the pleopods of the ovigerous females also occurs under a high titer of hemolymph ecdysteroids. In support, 20E injection at C3 stage crabs indicated a significant reduction in time duration of pleopodal embryonic development leading to hatching of zoea larvae. Understandably, the augmented hemolymph ecdysteroid titer helps in the synchronization of embryo hatching and the premolt changes, as occurring under the normal premolt conditions.

Patterns of N-acetyl-beta-glucosaminidase isoenzymes in the epidermis and hepatopancreas and induction of N-acetyl-beta-glucosaminidase activity by 20-hydroxyecdysone in the fiddler crab, Uca pugilator

A new staining method for detection of N-acetyl-beta-glucosaminidase on denaturing SDS polyacrylamide gels was developed. The isoenzyme pattern of N-acetyl-beta-glucosaminidase in the epidermis of the fiddler crab, Uca pugilator, is different from that in the hepatopancreas. Two isoforms of N-acetyl-beta-glucosaminidase, with molecular weights of 89 and 45.6 kDa, are present in the hepatopancreas while there is only one form of N-acetyl-beta-glucosaminidase, 89 kDa, in the epidermis. No sexual dimorphism was found in these patterns of N-acetyl-beta-glucosaminidase isoenzymes. The characteristic isoenzyme patterns in the epidermis and hepatopancreas occurred consistently throughout the molting cycle. Injections of the molting hormone, 20-hydroxyecdysone, at 25 microg/g live weight, into crabs in premolt substage D1, significantly increased N-acetyl-beta-glucosaminidase activity in the epidermis by 86%. Since only one form of N-acetyl-beta-glucosaminidase, 89 kDa, is present in the epidermis, the elevation in epidermal enzymatic activity after 20-hydroxyecdysone administration is entirely accounted for by this N-acetyl-beta-glucosaminidase isoenzyme. The results reported herein are the first direct evidence that in a crustacean N-acetyl-beta-glucosaminidase activity is regulated by the steroid molting hormone.

Ecdysteroid titers and Y-organ activity during late anecdysis and proecdysis in the fiddler crab, Uca pugilator

The titer of ecdysone in hemolymph and the ratio of ecdysone to other radioimmunoassay(RIA)-active hemolymph ecdysteroids were compared to in vitro secretion of ecdysone in Y-organs removed from eyestalkless fiddler crabs at various times following eyestalk ablation. Using high-pressure liquid chromatography (HPLC) and RIA it was established that ecdysone, 20-hydroxyecdysone, and RIA-active metabolites are present in the hemolymph at the end of anecdysis and throughout proecdysis. There was little correlation between in vitro secretory activity and total ecdysone in circulation. Ratios of ecdysone and 20-hydroxyecdysone changed during proecdysis as did the percentage of total RIA activity attributable to both. Positive correlations were observed between in vitro Y-organ secretion rates and amounts of ecdysteroids extracted from hemolymph and added to incubation media.

Effects of exogenous ecdysterone upon moulting, proecdysial development, and limb regeneration in the prawn Palaemon elegans

Injection of small doses of ecdysterone accelerated moulting and proecdysis in the prawn Palaemon elegans. Injection of large doses of ecdysterone (1-10 micrograms) markedly accelerated proecdysis, but death always occurred prior to or during moulting and was accompanied by abnormal setal development and retarded cuticle formation. Dose-response curves were obtained for a range of hormone doses from 10 to 0.01 micrograms by administering ecdysterone during postmoult (stages A-B) and early premoult (stages DE0-DL0). Accelerated proecdysis and viable moulting were more marked in the group injected during early premoult (stages DE0-DL0). The sensitivity threshold for prawns injected during this time was less than 40 ng g-1 but could not be determined more precisely in view of the range of ecdysterone concentrations used. In contrast, the sensitivity threshold for ecdysterone administered during postmoult (stages A-B) was much higher, between 0.4 and 2 micrograms g-1. The possible mechanisms controlling sensitivity thresholds for ecdysterone are discussed. The effect of ecdysterone on limb regeneration was also studied. Within the concentration range used, ecdysterone was found to have no effect on the rate of limb regeneration.

The successful induction of molting in the adult male lobster (Homarus americanus) with a slow-release form of ecdysterone

In an initial, and then a confirmatory experiment, adult, male lobsters were injected with solvent, ecdysterone (E, 2.0 mug/g live weight) or ecdysterone acetate (EAc, 2.5 or 5.0 mug/g live weight) emulsions in Freund's incomplete adjuvant (FIA). Control lobsters underwent no molts and only one death in the two cases. The E treated animals all died (average: exp. 1, 19.2 +/-2.1 days; exp. 2, 25.3 +/- 8 days). After the lobsters were treated twice with 2.5 mug EAc/g live weight, in the first experiment, four out of five molted and one died; in the second experiment six out of eight molted, one died and one remained refractory. The high EAc dose resulted in five deaths, one molt and two pseudomolts after one treatment. It is concluded that the use of the oil emulsion and EAc sufficiently slowed the release of free ecdysterone to allow complete premolt development in the lobster.