A quantitative analysis of exopodite beating in the larvae of the lobster Homarus gammarus (L.).

Raw data on exopodite beating in the first three developmental stages of the lobster Homarus gammarus were collected and analysed for key beating parameters. The analysis was computer assisted and the main procedures used are described. Beating patterns are the same in all three stages and are usually very regular although perturbations do occur (figures 1, 2). When beating stops the deceleration and subsequent re-acceleration is very rapid (figure 1) and limb movement sequences usually start posteriorly and move forwards (figures 1, 2d). Ipsilateral phase relations are generally maintained at 0.4-0.6 (figures, 3,4) and while the coupling between adjacent exopodites is usually stronger than for those further apart various deviations from this are occasionally seen (figure 5). No significant correlation between the ipsilateral phase relations of adjacent exopodites and base cycle duration was detected for any of the stages (figure 6). Contralateral phase relations undergo a constant progression (figures 7, 9) and this was found to be due to a heterodyne effect (figure 8) also described as gliding coordination. The powerstroke/returnstroke ratio for all stages was approximately 0.5 (figure 10) and no significant correlation was found with cycle duration (figure 11). The only substantial difference between the three larval stages which was noted was that of cycle duration, the cycles of stage III being shorter than those of the first two stages. The exopodite beating pattern was discussed in context with other metachronously cycling systems in arthropods and the implications of the present study discussed.     

Ontogeny of intracellular isosmotic regulation in the european lobster Homarus gammarus (L.).

Intracellular free amino acids were measured in the abdominal muscle of the three larval instars, postlarvae, and juveniles of the lobster Homarus gammarus, acclimated to seawater (35 per thousand) and to a dilute medium (22 per thousand), to study intracellular isosmotic regulation throughout the development of this species. Transfer to low salinity was followed by a highly significant drop of free amino acids level in all developmental stages. The main regulated amino acids were glycine, proline, and alanine. The level of regulation of total free amino acids changed at metamorphosis: the decrease in total free amino acids at low salinity was 46% in the three larval instars, but it was only 29% in postlarvae and 20% in juveniles. These results suggest that free amino acids, mainly glycine, proline, and alanine, are involved in intracellular isosmotic regulation in the lobster, with different levels of involvement in pre- and postmetamorphic stages. The ontogenetic changes in intracellular isosmotic regulation are discussed in relation to the changes in extracellular regulation (osmoregulation) in the lobster.     

The structure and function of the labrum in the lobster Homarus gammarus (L.).

The labrum of decapod crustaceans is a soft lobe overhanging the mouth. The labral skeleton, musculature and innervation of Homarus gammarus are described. There are three bilateral groups of sensory neurons innervating the floor, lobe and lateral walls of the labrum. These are probably responsible for the phasic afferent activity that can be recorded from the inner labral nerve on mechanical deformation of the labrum. The labrum undergoes rhythmical retraction-protraction movements during ingestion and is shown to be active during both mandibular activity and oesophageal peristalsis. Studies were made on the duration and frequency of labral "swallowing" activity. The role of the labrum in feeding is discussed.     

Influence of walking on swimmeret beating in the lobster Homarus gammarus

Influence of walking on swimmeret beating in intact lobsters, Homarus gammarus, has been analyzed using a treadmill experimental device. Belt movement activates both leg stepping and swimmeret beating. The simultaneity of the onset of the two motor systems in this situation is demonstrated to be the result of a startle response initiated when the belt begins to move. This reaction consists of a non-specific motor activity involving several antagonist postural and dynamic muscles. Abdominal extension and vigorous swimmeret beating are the main featurs of this reaction. The main characteristics of the swimmeret beating as defined by Davis (1969) has been observed here in sequences without walking. However during long walking sequences a very different swimmeret beating pattern occurs. It is suggested that this slow swimmeret beating is completely subordinate to the walking rhythm during sequences of absolute coordination. In more rapid swimmeret beating a relative coordination with leg stepping is very common. The functional meaning of this linkage between legs and swimmerets is discussed.     

The control of hindgut motility in the lobster,Homarus gammarus (L.)

1. The sixth abdominal ganglion (6 A.G.) of the lobster Homarus gammarus (L.) innervates the rectum via the paired posterior intestinal nerves (P.I.N.’s) and the paired anal nerves. The anterior branches of the P.I.N.’s supply the anterior hindgut, the main faecal expulsion region, whilst the posterior branches (P.I.N.p.’s) supply the posterior region and the 5 extrinsic radial muscle groups around the anus.

2. Stimulation of the ventral nerve cord (V.N.C.) or the oesophageal connectives initiates co‐ordinated hindgut movements, the defaecatory response. The nervous activity eliciting these movements passes down the P.I.N.’s. The anal nerves are devoid of motor function with respect to the hindgut.

3. In addition to neurogenic movements the rectum also undergoes non‐coordinated, low amplitude longitudinal and circular muscle contractions. These are thought to be due to independently acting endogenous oscillators within the muscles themselves. The radial muscles of the anus also exhibit rhythmical contractions after an initial maximal contraction following stimulation of the P.I.N.p.’s.

4. Receptors responding to anal dilation and closure have been shown to exist in the anal nerves. They are non‐specific soft cuticle receptors which are, apparently, positionally sensitive. These receptors are not thought to modulate motor output from the 6 A.G. to the rectum at the level of the 6 A.G.

5. Bifurcating motor axons are thought to exist in the P.I.N.’s.

6. It is concluded that the defaecatory response of the lobster is a centrally programmed phenomenon.     

Crustacean hyperglycemic and vitellogenesis-inhibiting hormones in the lobster Homarus gammarus

Crustacean hyperglycemic hormone (CHH) and vitellogenesis-inhibiting hormone (VIH), produced by the X organ-sinus gland neurosecretory complex, belong to a peptide group referred to as the CHH family, which is widely distributed in arthropods. In this study, genetic variants and post-translationally modified isoforms of CHH and VIH were characterized in the European lobster Homarus gammarus. With the use of RP-HPLC and ELISA with specific antibodies that discriminate between stereoisomers of CHH and VIH, two groups of CHH-immunoreactive peaks were characterized from HPLC fractions of sinus gland extract (CHH A and CHH B); each group contained two variants (CHH and D-Phe3CHH). In the same way, two VIH-immunoreactive peaks (VIH and D-Trp4VIH) were demonstrated in HPLC fractions from sinus gland extract. The masses of these different neuropeptides were determined by FT-ICR MS: CHH A and CHH B spectra exhibited monoisotopic ions at 8557.05 Da and 8527.04 Da, respectively, and both VIH isomers displayed an m/z value of 9129.19 Da. Two full-length cDNAs encoding preprohomones of CHH A and CHH B and only one cDNA for VIH precursor were cloned and sequenced from X organ RNA. Comparison of CHH sequences between European lobster and other Astacoidea suggests that the most hydrophobic form appeared first during crustacean evolution.     

Proteasomal activities in the claw muscle tissue of European lobster, Homarus gammarus, during larval development

Decapod crustaceans grow discontinuously and gain size through complex molt processes. The molt comprises the loss of the old cuticle and, moreover, substantial reduction and re-organization of muscles and connective tissues. In adult lobsters, the muscle tissue of the massive claws undergoes significant atrophy of 40-75% before ecdysis. The degradation of this tissue is facilitated by calcium-dependent proteases and by the proteasome, an intra-cellular proteolytic multi-enzyme complex. In contrast to the adults, the involvement of the proteasome during the larval development is yet not validated. Therefore, we developed micro-methods to measure the 20S and the 26S proteasomal activities within mg- and sub-mg-quantities of the larval claw tissue of the European lobster, Homarus gammarus. Within the three larval stages (Z1-3) we distinguished between sub-stages of freshly molted/hatched (post-molt), inter-molt, and ready to molt (pre-molt) larvae. Juveniles were analyzed in the post-molt and in the inter-molt stage. The trypsin-like, the chymotrypsin-like, and the peptidyl-glutamyl peptide hydrolase activity (PGPH) of the 20S proteasome increased distinctly from freshly hatched larvae to pre-molt Z1. During the Z2 stage, the activities were highest in the post-molt animals, decreased in the inter-molt animals and increased again in the pre-molt animals. A similar but less distinct trend was evident in the Z3 stages. In the juveniles, the proteasomal activities decreased toward the lowest values. A similar pattern was present for the chymotrypsin-like activity of the 26S proteasome. The results show that the proteasome plays a significant role during the larval development of lobsters. This is not only reflected by the elevated activities, but also by the continuous change of the trypsin/chymotrypsin-ratio which may indicate a shift in the subunit composition of the proteasome and, thus, a biochemical adjustment to better cope with elevated protein turnover rates during larval development.     

A new mycosis of larval lobster (Homarus americanus).

Spodoptera exempta larvae were reared on semisynthetic maize diet. Pathogenicity studies were undertaken on first- to fifth-instar larvae fed a high dosage of Nosema necatrix spores. Larvae from the earlier instars were most susceptible to the microsporidan and also developed bacteriosis. A cytoplasmic polyhedrosis virus (CPV) was evident in some infected larvae but not in controls. The development of N. necatrix is redescribed using the light microscope. A disporoblastic life cycle was evident at 25°C and both a disporoblastic and an octosporoblastic life cycle at 20°C. The implications of the occurrence of bacteriosis and CPV and the possible biological significance of the two sporogonic sequences are discussed. The taxonomic position of N.necatrix is reviewed and, after comparison with existing species of the genera Nosema and Parathelohania, it is placed in the new genus Vairimorpha. The implications of polymorphism are discussed in relation to the classification of the Microsporida.     

A long-term mesocosm study on the settlement and survival of juvenile European lobster Homarus gammarus L. in four natural substrata

To date, the natural substratum preferences of early benthic phase (EBP) European lobsters (Homarus gammarus) remain largely unknown. This study utilised a large scale mesocosm experiment to determine if the animal favours cobble ground, similar to its American counterpart (Homarus americanus), or has other substratum preferences. Postlarvae were provided with the choice of settling on four natural substrata: sand, coralline algae, mussel shell and cobble. Over a nine month period, the number and size of juveniles on each substratum was recorded, with loss of chelipeds used as an indication of social interaction. After a 30 day period, a non-random distribution of lobsters was observed on the four substrata. Juveniles were more abundant in substrata which provided pre-existing shelter in the form of interstitial spaces, i.e. cobble and mussel shell, than in sand or coralline algae. The survival of individuals from postlarvae to 30 day old juveniles ranged from 5 to 14% with surviving benthic recruits showing a clear mode at 6-8 mm carapace length (CL) in size distribution. The density of lobsters per m(2) of cobble remained relatively constant (18/m(2)) throughout the study period while the density of juveniles on mussel shell decreased significantly (35 to 5/m(2)). The size distribution of lobsters on each substratum also varied with time. By the conclusion of the trial, lobsters found in mussel shell had a mode of 8-10 mm CL within a range of 6-14 mm CL while those in cobble had a mode of 10-12 mm CL within a range of 8-24 mm CL. Overall, the results underline the importance of shelter-providing habitat such as cobble or crevice-type substrata to EBP European lobsters. They also confirm that for a shelter-dwelling animal such as a lobster, the physical structure of the habitat is a key factor in determining both the size and number of its inhabitants.     

Growth, feeding frequency, protein turnover, and amino acid metabolism in European lobster Homarus gammarus L

The effect of feeding frequency on growth and protein metabolism in the European lobster, Homarus gammarus, was investigated. Fourth (IV) stage lobsters H. gammarus were fed individually a marine animal meal (herring/mussels meal) for 56 days. Feeding a daily ration equivalent to 10% of their body weight gave better growth than feeding daily rations of 5% and 20%. Protein synthesis rates were similar for the three food rations but protein growth rates were significantly lower and protein degradation rates highest in the 5% body weight per day ration group. The efficiency with which synthesised protein was retained as growth was found to be 38% in the in the 10% ratio group. Protein synthesis rates of lobsters were found to be lower than those for shrimps (Penaeus vannamei). The amino acid flux also suggests a lower protein conversion efficiency than shrimps P. vannamei. The results suggests that lobsters are slow, periodic feeders and that growth can be readily increased by manipulation of particular environmental factors such as feeding frequency.     

An approach to the assessment of risk from chronic radiation to populations of European lobster, Homarus gammarus (L.)

The basic principles underlying a four-discrete age group, logistic, growth model for the European lobster Homarus gammarus are presented and discussed at proof-of-concept level. The model considers reproduction, removal by predation, natural death, fishing, radiation and migration. Non-stochastic effects of chronic low linear energy transfer (LET) radiation are modelled with emphasis on ⁹⁹Tc, using three endpoints: repairable radiation damage, impairment of reproductive ability and, at higher dose rates, mortality. An allometric approach for the calculation of LD_50/30 as a function of the mass of each life stage is used in model calibration. The model predicts that at a dose rate of 1 Gy day⁻¹, lobster population reproduction and survival become severely compromised, leading eventually to population extinction. At 0.01 Gy day⁻¹, the survival rate of an isolated population is reduced by 10%, mainly through loss of fecundity, comparable to natural migration losses. Fishing is the main ecological stress and only dose rates in the range 0.03–0.1 Gy day⁻¹ can achieve discernible effects above it. On the balance of radiation and other ecological stresses, a benchmark value of 0.01 Gy day⁻¹ is proposed for the protection of lobster populations. This value appears consistent with available information on radiation effects in wildlife.     

Oesophageal sensors and their modulatory influence on oesophageal peristalsis in the lobster, Homarus gammarus.

The musculature and innervation of the oesophagus of Homarus gammarus are described as a prerequisite to studies on the mechanisms and control of food ingestion. Of particular interest are two paired sensors (the anterior and posterior oesophageal sensors) which are bilaterally situated at the oesophageal-cardiac sac valve. These are similar to contact chemoreceptors previously described in insects and are classified as such on morphological grounds and with indirect electrophysiological evidence. Oesophageal peristalsis is effected by the coordinated contraction of the Oesophageal musculature. This is controlled by rhythmical bursting neuronal activity, which can be recorded from the nerve trunks in the area. A characteristic burst recorded from the superior oesophageal nerve is used as an indication of oesophageal dilatation during peristalsis for studies on the feedback effects of the oesophageal sensors. Electrical and chemical stimulation of the posterior oesophageal sensors can initiate and increase the frequency of oesophageal peristalsis, while stimulation of the anterior oesophageal sensors can slow and terminate oesophageal peristalsis. The results are discussed and a model presented of the role of the oesophageal sensors in feeding.     

An historical overview of the Republic of Ireland's lobster (Homarus gammarus Linnaeus) fishery,with reference to European and North American (Homarus americanus Milne Edwards) lobster landings

Historical developments of the Republic of Ireland's Homarus gammarus fishery are reviewed and compared in the context of landings in Europe and the North American H. americanus fishery. H. gammarus fishing has provided essential income for over a century to many Irish coastal communities. There have been significant fluctuations (greater than 460%) in recorded landings over this time and the relative importance of H. gammarus fishing has changed with the establishment of ancillary crustacean fisheries. In 1994, H. gammarus landings reached an all-time high of 714 tonnes, with a landed value of IR £6.3 million; in 1999 landings were 597 tonnes valued at IR £6.15 million. Current Republic of Ireland lobster fishery regulations are: (a) minimum carapace length of 85 mm, (b) ban on landing lobsters that have been `V-notched' or have a mutilated tail fan, and (c) prohibition of capturing lobsters by SCUBA diving. Chronological details on recent legislation, regulations and landings relating to Ireland's lobster fishery sector are reviewed. In the last 40 years landings of H. gammarus in the Republic of Ireland exhibit signs of an overexploited stock characterised by a reduction in catch per unit effort and there has been a general decline of total landings for H. gammarus throughout Europe. This contrasts with North America, where many regulations govern the H. americanus fishery and landings appear to be in a healthier state.     

Sensory activity of the mandibular muscle receptor organ of Homarus gammarus (L)

The mandibular muscle receptor organ (Mand. M.R.O.) of Homarus gammarus (L) exhibits increased activity to receptor muscle (R.M.) contraction (decrease in length) and to stretch (increase in length).

The sensory units of this receptor differ in their threshold to R.M. tension and in the frequency change they exhibit for a given increment in tension. The units fire tonically during maintained tension once their threshold has been reached.

Both the number of active units and their frequency increase with R.M. tension. The Mand. M.R.O. is velocity sensitive and exhibits a higher degree of activity during rapid stretch. This dynamic response increases with rate of R.M. stretch.

The activity of the Mand. M.R.O. sensory neurones is compared with that of other M.R.O.’s and the authenticity of some aberrant units is discussed.     

Effect of an insect juvenile hormone analogue, Fenoxycarb on development and oxygen uptake by larval lobsters Homarus gammarus (L.)

Little attention has been focused on the effect of anthropogenic compounds that disrupt the endocrine systems in crustaceans. Consequently, this study investigated the effects of the juvenile hormone analogue (JHA), Fenoxycarb on selected physiological and developmental processes of the zoeal stages in the European lobster, Homarus gammarus. Chronic exposure to Fenoxycarb (50microg L(-1)) resulted in a significant (p < 0.05) reduction in moult frequency and size at moult. Fenoxycarb exposure extended zoeal duration between zoea I to II (p<0.05) and resulted in total inhibition of the moult from zoea II to III. Significantly greater rates of O2 uptake were observed in Fenoxycarb-exposed larvae in comparison with controls (p<0.05). All rates of O2 uptake decreased significantly between 7 and 12d of exposure (p<0.05). At 12d, exposure to the solvent control no longer influenced rates of O2 uptake, but it was not possible to attribute increased O2 uptake to Fenoxycarb exposure directly, as treated individuals did not moult beyond zoea III. The low exposure concentrations of Fenoxycarb, comparable to those used in plant protection, resulted in endocrine disrupted responses in H. gammarus (albeit with little clear, demonstrable effect on metabolism) a finding that could have important ecological and commercial implications.     

The mandibular muscle receptor organ of Homarus gammarus (L.) (crustacea,decapoda)

Summary A muscle receptor organ is present in the mandible of macruran decapods. The mandibular muscle receptor organ (Mand. MRO) of Homarus gammarus (L.) consists of a ribbon of muscle innervated at its ventral insertion by 10–20 multiterminal sensory neurones. The sensory cells have a small number of dendritic processes.The receptor muscle exhibits some structural properties of both fast and slow muscle. The mean sarcomere length is similar to that of the slow abdominal MRO but the receptor muscle in cross section has a punctate distribution of myofibril bundles more typical of fast muscle.This work was supported by Science Research Council grants B/SR/1871 and BR/G/585.     

In vitro cytotoxicity of crustacean immunostimulants for lobster (Homarus gammarus) granulocytes demonstrated using the neutral red uptake assay

The neutral red uptake (NRU) cell viability assay was adapted for use with lobster Homarus gammarus (Linnaeus, 1758) granulocytes cultured in vitro. The assay was more sensitive than the conventional trypan blue exclusion assay and facilitated a higher sample throughput than subjective microscope-based assessments of cell viability. The NRU assay was demonstrated to have a linear response from 470 to at least 126000 cells cm(-2). It was used to investigate the acute cytotoxicity of three commercial and two candidate crustacean aquaculture immunostimulants on lobster granulocytes. All five stimulants had a cytotoxic action on the granulocytes and the toxic dose for some of these stimulants was found to be below their commercially prescribed dose. The long term energetic cost of the use of these stimulants and the concomitant potential for a reduction in growth rate of cultured decapod crustaceans, which is fundamental to the success of commercial aquaculture, is identified and discussed.