Internal anatomy and ultrastructure of the male reproductive system of the Norway lobster Nephrops norvegicus (Decapoda: Astacidea)

The Norway lobster (Nephrops norvegicus) is economically important in Europe. However, apart from the female reproductive system, very little is known about its internal anatomy. This article focuses on studying the internal anatomy and ultrastructure of the male reproductive system. This system follows the general pattern found among decapod crustaceans, with several peculiarities. Testes are composed of lobular sperm ducts in which the spermatozoa are fully constituted. The spermatozoa present three lateral arms and a long acrosome, which gives a false appearance of flagellated spermatozoa. The two testes form a double H under the heart, and the vas deferens (VD) arise from each side at the posterior edge of the double H. The main characteristic of the VD is the presence of a sphincter in the enlarged area of the distal end of the middle VD. The MVD here shows an increase in musculature of the wall as compared to the VD, which regulates the passage of the sperm cord to the distal VD (DVD) and thence to the thelycum of the female. The wall of the spermatophore is formed in the distal part of the proximal VD, which surrounds the unique sperm cord present in the VD. Isolated spermatophores are not observed in the VD. The sperm cord is pinched off during copulation by the musculature of the DVD. Then, a portion of the sperm cord is transferred from each VD to form the isolated spermatophores. The wall of the spematophores and the spermatozoa that are observed inside the thelycum have the same morphology as those observed in the VD. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

The effect of temperature on the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) tail meat during storage

Aims: The aim of this study was to update and extend our knowledge of the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) under commercially relevant storage conditions to optimize handling procedures. Methods and Results: Total viable counts were performed at different storage temperatures (0, 4, 8, 10, 12 or 16°C) and after different storage times (1–7 days). Storage at 16°C was found to be most detrimental, and storage at 0°C was found to be optimal. 16S‐rRNA sequencing was utilized to determine the composition of the bacteria within the microflora. In this way, Photobacterium isolates, especially Photobacterium phosphoreum, were identified as the main specific spoilage organisms. The abilities to reduce trimethylamineoxide (TMAO) and to produce H₂S were analysed in a selection of bacterial isolates. The higher the incubation temperature during storage, the more isolates were found to reduce TMAO and produce H₂S. Conclusions: Nephrops norvegicus possesses an unusually high initial microbial load when fresh. Storage temperature is the most crucial factor affecting microbial growth, microbial activity and spoilage potential in N. norvegicus produce. Spoilage can be attributed mainly to P. phosphoreum. Significance and Impact of the Study: This study presents significant new findings with regard to the progression and causative agents of spoilage in N. norvegicus. Based on the results, we can recommend that N. norvegicus tails should be stored in a 0°C environment immediately after catch. Stored this way, the growth and spoilage activity of the microflora may be reduced significantly and an extension of shelf life might be attained.     

The reproductive cycle of Norway lobster

The reproductive biology of female Norway lobster Nephrops norvegicus was studied throughout an annual cycle from January to December 2007 in Pagasitikos Gulf, a large semi-enclosed Gulf in the central west Aegean Sea, in Greece. Six ovarian maturation stages were described to follow gonadal development, based on the combined external observation and histological examination of the ovary. Reproduction showed clear seasonality both in terms of ovarian maturation and brooding period. The proportion of fully mature females in the catch increased from January to the summer months with a peak in June. The species has a protracted brooding period that peaks in November and December, while the release of eggs from females' pleopods occurs from January to March. The size at which 50% of females reached sexual maturity was estimated, using a logistic model, to be 28.1 mm of carapace length. The undiscovered reproductive dynamics will be valuable for optimizing population models and management strategies for this important fishery resource.     

Mitochondrial DNA variation in Northeast Atlantic and Mediterranean populations of Norway lobster, Nephrops norvegicus

Analysis of the genetic structure of the Norway lobster (Nephrops norvegicus), a marine crustacean with high commercial value, was undertaken to gain information regarding the differentiation of Atlantic from Mediterranean populations of marine invertebrates. Restriction fragment length polymorphism analysis of two mitochondrial DNA segments, 3.6 kilobases in total, was performed. Twelve populations from the North Sea, Irish Sea, Portuguese coast and Aegean Sea were analysed. Low levels of differentiation were found among them (F(ST) = 0.018, P < 0.001) and there were no signs of an Atlantic-Mediterranean divide or of an isolation-by-distance scheme of differentiation. Possible reasons for these low levels of differentiation can be found in the recent expansion of N. norvegicus populations. This is supported by the mismatch distribution of pairwise haplotype differences, as well as by the high mean haplotype diversity (h = 0.93) combined with medium nucleotide diversity (pi = 0.0057) (in comparison to values for marine crustaceans or teleosts) found in this study. This combination of high levels of haplotype diversity with moderate to low levels of nucleotide diversity has also been frequently attributed to a recent time of divergence for various marine species. No evidence was found for a Mediterranean refugium during glaciation periods, separate from the Atlantic, as has been reported for some marine species. The Irish Sea population was the most differentiated as a result of reduced levels of diversity. Results are also discussed in the light of future management of N. norvegicus stocks.     

The reactions of the Norway lobster,Nephrops norvegicus (L.), to water currents

Observations were made on the reactions of the Norway lobster, Nephrops norvegicus, to water currents in a sea‐water flume tank. Blind animals were used to prevent visually‐guided behaviour. Nephrops adopted a downstream orientation, and usually walked downstream, in response to water current speeds in the range of 0.07 to 0.20 ms^?1. Patterns of water flow around the body revealed that it was most effectively streamlined when the animal adopted a downstream orientation. Direct measurements of the forces acting on the body revealed that animals with a downstream orientation experienced the least hydrodynamic drag and the greatest downforce.     

A parasitic scuticociliate infection in the Norway lobster (Nephrops norvegicus)

A histophagous ciliate infection was discovered in a number of Norway lobsters (Nephrops norvegicus) from the Clyde Sea Area, Scotland. Silver-carbonate staining of cultured ciliates revealed an oral apparatus and additional structural features that are morphologically similar to scuticociliates in the genus Mesanophrys, which are known to parasitize crustaceans. However, ribosomal DNA sequences (ITS1/5.8S/ITS2) of the ciliate were identical to Orchitophyra stellarum, a parasitic scuticociliate of sea stars with a different morphology from Mesanophrys spp. and to the ciliate from N. norvegicus. Associated pathology included degeneration and necrosis of the myocardial heart muscle, and large numbers of ciliates in the gill filaments.     

Differences in the condition of Norway lobsters (Nephrops norvegicus (L.)) from trawled and creeled fishing areas

The condition of trawled and creeled Norway lobsters, Nephrops norvegicus, was compared in individuals caught along the Swedish west coast. Female and male N. norvegicus were collected from trawled and creeled areas in the spring and autumn. Their nutritional state was determined by analysing individuals for haemocyanin concentration, the dry weight/wet weight relationship in muscle and hepatopancreas and the percentage dry weight of muscle and hepatopancreas of total animal dry weight. All parameters were measured on an individual basis and checked for size dependence. Creeled individuals were generally found to be in better condition than individuals from trawled areas, and animal condition increased from spring to autumn. Autumn males from creeled sites were overall in the best condition, having the highest mean haemocyanin concentration, muscle and hepatopancreas dry weight/wet weight relationship and percentage dry weight of muscle tissue. Claw symmetry (paired cutters) was suggested as an indicator of limb loss, with the highest occurrence found in females from trawled sites. Crusher absence had no effect on the animal's individual percentage dry weight of muscle, although the mean was lower in trawled females than in other groups. Resource limitation and physical stress are discussed as possible underlying factors affecting the observed differences.     

The effects of the metal ions Mn2+ and Co2+ on muscle contraction in the Norway lobster Nephrops norvegicus (L.)

The effects of the metal ions manganese and cobalt on force production by the abdominal superficial flexor muscle of the Norway lobster, Nephrops norvegicus, have been studied in response to both neuronal stimulation and electrical field stimulation applied to an isolated neuromuscular preparation, and by selectively blocking synaptic transmission with ivermectin. In response to both forms of stimulation, low concentrations of manganese added to the standard N. norvegicus saline increased the contractile force produced by the muscle, whereas higher concentrations of manganese inhibited both responses in a dose-dependent manner, until force was completely abolished at concentrations above 2.9 mM manganese. Cobalt ions produced similar effects, and no significant difference was found between the concentration of the two ions at 50% force inhibition (K_m) or between the two stimulation methods (manganese: 1.22 mM; cobalt: 1.29 mM, P = 0.86). This suggests that they have a similar mode of action, and a postsynaptic site of inhibition. These K_m values are considerably higher than the concentrations of these ions known to accumulate in the haemolymph of N. norvegicus under eutrophic conditions, and it therefore seems unlikely that accumulations of manganese or cobalt ions under such conditions would cause any significant inhibition of muscle contraction force. Accepted: 28 April 1999     

The time course of early post-mortem biochemical processes in the abdominal muscle of a commercially important decapod crustacean (Nephrops norvegicus): implications for post-catch processing

The post-mortem processes in the fast abdominal muscle of the Norway lobster Nephrops norvegicus have been investigated by simulating the first 24-h post-harvest in a controlled experiment. Tissue pH and the concentrations of arginine phosphate, glycogen, L-lactate, ATP, ADP, AMP, IMP, HxR, and Hx were measured at the time of sacrifice and 3, 6, 12 and 24 h thereafter. Additionally from the nucleotide values the corresponding adenylate energy charge (AEC) was calculated. The results reveal that the post-mortem biochemical processes in the abdomen of the Norway lobster after sacrifice and during storage at 10°C are comparable to those of vertebrates. It was found that arginine phosphate was depleted from 38.5 ± 5.2 to 10.9 ± 2.9 µmol g^?1 within 3 h, and anaerobic glycolysis was enhanced, so that glycogen was depleted and L-lactate accumulated. The muscle pH decreased significantly from 7.6 ± 0.1 to 7.0 ± 0.15 within 20 min and then continued to decrease at a slower rate. Most interestingly, the ATP concentration was maintained at approximately 3.5 ± 0.3 µmol g^?1 for up to 12 h post-mortem. This is unusually long and indicates a special characteristic of this fast-type crustacean muscle. AMP accumulated to a maximum after 12 h and was then slowly transformed into IMP. The AEC fell from an initial value of 0.88 to only 0.17 after 24 h. When viewed in context with the fishing industry the results demonstrate that when the product is tailed (removal of the cephalothorax) upon catch, as is common practice in this industry, the result will always be an extensive post-mortem glycolytic response that will lead to an unavoidable and rapid depletion of the energy reserves resulting in a product of lesser quality.     

Microsatellite loci from the pink shrimp Farfantenaeus notialis (Crustacea,Decapoda)

Farfantepenaeus notialis is an important resource for fisheries in Cuba. For this reason and for a sustainable exploitation it is important to study their population structure and genetic variability. We report and characterize microsatellites as genetic markers from this species. Fifteen microsatellite polymerase chain reaction (PCR) primers were designed and tested in some individuals from different populations. Seven pair of primers showed reliable amplification products and five were polymorphic. The allele number ranged from 4 to 33, and the observed and expected heterozygosities were relatively high with values between 0.63 and 0.74 and 0.56 and 0.81, respectively. Departures from Hardy–Weinberg equilibrium were observed for all loci.     

Survival of discarded plaice (Pleuronectes platessa) from Norway lobster (Nephrops norvegicus) otter‐trawl fishery

The introduction of landing obligations in the European Union common fisheries policy, has increased the focus on discard survival. Since species with scientifically proven high survival rates may be exempted from the landing obligations, the economic significance for the fishing industry is large. Landing obligations include individuals below the minimum conservation reference size (MCRS), which are not allowed to be sold for human consumption. The Norway lobster (Nephrops norvegicus) fishery is a high value fishery, but with a substantial amount of bycatch of plaice (Pleuronectes platessa) below the MCRS. In the present study, observations were made on the short‐term survival of plaice at or below the MCRS, discarded from a small otter board trawler targeting Nephrops in Skagerrak (ICES 3a). The average short‐term survival of plaice was 15% at haul level, ranging from 0% to 39%, after 10 days of captive observation. Survival significantly decreased with time on deck and the retention of debris in the codend (p < 0.0001), while survival was not correlated to size. Vitality assessments, using a combined reflex impairment and injury score, were tested as predictor of survival and were significantly associated to survival (p < 0.0001) both for individual fish and when grouped by hauls. Seabird predation behaviour was assessed and it was estimated that seabirds predated or pursued 85% of discarded plaice below the MCRS.     

Histological investigation on the ovarian cycle of the bluefin tuna in the western and central Mediterranean

The histological analysis of eastern Atlantic bluefin tuna Thunnus thynnus ovaries caught from February to September 1999–2000, made it possible to distinguish the presence of seven oocyte developmental stages and allowed the characterization of six time-dependent ovary maturity stages. The ovaries of mature (fork length, L _F ≥ 110 cm) bluefin tuna were non-active from August (spent period) to March (quiescent period) when they contained only perinucleolar-stage oocytes. Ovary development started in April to early May (recrudescent period) with the appearance of oocytes at the lipid stage. Vitellogenesis appeared in mid-May (ripening period) and post-vitellogenesis occurred in late May to mid-June (pre-spawning period). In late June to early July, hydrated oocytes, a sign of imminent spawning, were found only in specimens caught in Balearic waters. Females ranging between 100 and 110 cm L _F, captured during the recrudescent and ripening periods, had the largest oocytes at the lipid stage, most of which were degenerating. An extensive vitellogenic atresia was observed in the ovaries of five females caught during the spawning period in non-spawning areas.     

Elemental and biochemical composition of<Emphasis Type="Italic"> Nephrops norvegicus</Emphasis> (Linnaeus 1758) larvae from the Mediterranean and Irish Seas

The Norway lobster, Nephrops norvegicus, is a commercially exploited decapod which is widely distributed throughout the north-eastern Atlantic and the Mediterranean Sea. Ovigerous females originating from the Mediterranean and the Irish Seas were held in the laboratory until larvae hatched. Biomass and biochemical composition, as well as digestive gland structure, were examined in newly hatched larvae from these two regions. In addition, previously published data from a North Sea population were included in our comparison. Elemental analyses showed that the absolute quantities of dry mass (DM), carbon (C), nitrogen (N) and hydrogen (H) (collectively referred to as CHN) per individual, and the C:N mass ratios, were significantly lower, while the relative CHN, protein and lipid values (in % of DM) were higher in samples from the Irish Sea compared to larvae originating from either the Mediterranean or the North Sea. As in CHN, the absolute level of protein per individual was higher in larvae from the Mediterranean, while no significant differences were observed in the individual lipid contents. Likewise, the digestive gland structure at hatching did not show any differences between study areas. Intraspecific variability in biomass and chemical composition of newly hatched larvae from different regions may be related to differential patterns of reproduction in regions with different climatic conditions. Lobster larvae hatch in the Mediterranean Sea predominantly in winter when both water temperature and planktonic food availability are at a minimum, while hatching in the Irish Sea occurs under more favourable conditions in spring. Hence, significantly higher wet mass, dry mass and protein values in Mediterranean larvae may represent adaptive traits allowing for early posthatching survival and development under food-limited conditions in an oligotrophic environment.Communicated by H.-D. Franke     

Taxonomy and distribution of the hydrozoan and protozoan epibionts on Pagurus bernhardus (Linnaeus, 1758) (Crustacea, Decapoda) from Scotland

Protozoan and hydrozoan epibionts on the hermit crab Pagurus bernhardus and its shell, collected near Cumbrae Island (Scotland) were studied. The epibionts found were the following: (1) protozoans: the suctorian ciliates Ephelota plana, Acineta compressa, Conchacineta constricta, Corynophrya anisostyla; the peritrich ciliates Cothurnia mobiusi and Zoothamnium plumula; the chonotrich ciliate Chilodochona quennerstedti; and (2) hydrozoans: the species Leuckartiara sp. and Clytia sp. The morphological characteristics of the epibionts were analysed, as well as their taxonomic position. The distribution of epibionts on the crab surface and its shell was studied, and the density and biomass of epibionts were calculated on each anatomic unit. There was a differential distribution according to the type of epibiont: hydrozoans dominated in biovolume and were present mainly on the shell, meanwhile protozoans represented the highest fraction of density and they were found exclusively on the crab (principally on eyes, antennulae, antennae, maxillipeds, pereopods and uropods). The anterior area of the cephalothorax was the most colonized. On this area, the maxillipeds and second pereopods showed the highest densities. The location of each epibiont species was described. There was a correlation between the length of the crab and the total number of hydrozoans. There was a significant correlation between the right and the left units of the crab, taking into consideration the mean densities of epibionts on each anatomical unit. The shell was colonized by the same species of hydrozoa that appeared on the crab, although in a much higher density (mean 3024.38 per shell; 6.9 per crab). There was a significant difference between both species of hydrozoan epibionts with respect to the mean densities on the different areas of the shell. The zone of the shell more occupied by Clytia sp. was the apical zone of the shell, while the highest densities of Leuckartiara sp. were registered near the aperture of the shell. The hydrozoan and protozoan epibiont species found on P. bernhardus in this study represent the first mention of their presence on this hermit crab.     

Larval development and spawning of Citharus linguatula (Linnaeus, 1758) in the western Mediterranean

Larval development from the early stages to metamorphosis ofthe Pleuronectiform Citharus linguatula is described and illustratedfor the first time; until now only its eggs and newly hatchedlarvae were known. The specimens used in this study were collectedon plankton samples taken from the Catalan continental shelf(western Mediterranean) on two surveys made in September andOctober 1983. The descnption of larval development includesmorphological and morphometnc characters and pigmentation. Relationshipsbetween various parts of the body and standard length duringdevelopment are also considered. Information of their seasonaland spatial distribution along the studied area is provided.     

The complete mitochondrial genome of the American lobster, Homarus americanus (Crustacea, Decapoda)

Although relatively a large number of the complete mitochondrial genome sequences have been determined from various decapod species (29 mtDNA sequences reported so far), the information for the infraorder Astacidea (including lobsters, crayfishes, and their relatives) is very limited and represented by only one complete sequence from the Australian freshwater crayfish species Cherax destructor. In this study, we determined the complete mitochondrial DNA sequence of Homarus americanus, the first representative of the family Nephropidae to be fully characterized. Comparison of the gene arrangement reveals that H. americanus mtDNA is identical to those of other pancrustacean species but differs from the other astacidean species (C. destructor). Based on these data, it can be assumed that an idiosyncratic gene order discovered in C. destructor mtDNA may be secondarily acquired from the ancestral lineage of the Astacidea.     

The genetic population structure of Thunnus thynnus (Linnaeus, 1758) in the Mediterranean Sea,a controversial issue

The Atlantic bluefin tuna (ABFT), Thunnus thynnus (Linnaeus, 1758), is an important commercial species managed as two different stocks, western and eastern Atlantic, with their spawning grounds in the Gulf of Mexico and in the Mediterranean Sea, respectively. The eastern Atlantic stock has been overexploited in the last decades, leading to the application of specific management measures introduced by the International Commission for the Atlantic Tuna (ICCAT). A clear understanding of the genetic structure of ABFT Mediterranean population should be pursued in order to support management decisions. To date the genetic studies on the Mediterranean ABFT, carried out with different molecular markers and sampling procedures, have produced unclear results. Here, we analysed ABFT samples from central and western Mediterranean Sea with mitochondrial sequences and 11 microsatellite loci to investigate, among the others, the area of the Strait of Messina, where environmental conditions seem to support a resident population of ABFT. Furthermore, genetic analyses of mitochondrial sequences were carried out including nucleotide sequences of Adriatic ABFT wild larvae retrieved from GenBank. Among the investigated areas a genetic differentiation was detected between the Strait of Messina and the Tyrrhenian Sea with microsatellite loci according to the exact G test, but not to the Bayesian analyses carried out with STRUCTURE. The analyses with mitochondrial sequences do not reveal any differentiation among sampled areas, however, a highly significant genetic divergence was observed between the Adriatic mitochondrial sequences retrieved from GenBank and the central‐western Mediterranean sequences obtained in the present work. Our results provide some evidence of population structure of Mediterranean ABFT adding pieces to a still unclear picture.     

Physiological changes in the Norway lobster Nephrops norvegicus (L.) escaping and discarded from commercial trawls on the West Coast of Scotland: 1. Body fluid volumes and haemolymph composition after capture and during recovery

The Norway Lobster Nephrops norvegicus (L.) was captured by trawling at depths of 120 to 150 m off the West Coast of Scotland using commercial fishing gears. Discarded animals (normally <25–35 mm carapace length) were sampled immediately after capture, and following emersion (exposure to air) on deck for 1 or 2 h. Their recovery from, and survival of, the stresses of being fished were examined in separate groups of animals transferred by SCUBA divers to underwater (u/w) cages on the seabed at a mean depth of 24 m. “Escaped” N. norvegicus were collected in a small-meshed (40 mm) “cover” around the cod-end and sampled without emersion. It was assumed that the physiological state of these animals would be similar to those passing through the cod-end meshes directly back into the surrounding sea during normal fishing operations. Groups of escaped animals were also transferred to u/w cages for recovery and survival studies. Control animals (creel-caught from the same fishing grounds) were sampled after recovery in u/w cages. Total body water content, haemolymph (blood) volume and composition were examined at various stages after capture and during recovery of control, discarded and escaped animals. Discarded animals showed significant reductions in total body water content compared to controls but recovered after 24 h. Controls that had been artificially damaged by puncturing also showed a reduction in water content. Escaped animals showed significantly higher mean water content compared to discards. Haemolymph volumes were also reduced in discarded animals suggesting that significant blood loss occurs during capture. There was also evidence of a shift of fluid from haemolymph to tissues in discarded animals. Pericardial (haemolymph) pressures were much reduced in discards compared to undisturbed control animals but showed significant recovery in surviving animals. Pressure reduction was less in escapes but was seen in control animals that had been exercised to exhaustion. Haemolymph osmotic concentrations, [Na⁺] and [K⁺] showed increases after discarding, notably after emersion, but haemocyanin [Hcy] and total haemolymph protein concentrations were less affected. The effect of these changes on longer term survival and recovery from the stress of capture are discussed.