A recirculating culture system for larvae of the American lobster, Homarus americanus

A recirculating culture system is described, suitable for mass rearing of larvae of the American lobster (Homarus americanus) and other larval forms.     

Spawning,egg attachment and egg retention in captive lobsters (Homarus americanus)

The numbers of eggs spawned, attached, and carried through to hatching were examined in three groups of captive lobsters (Homarus americanus). Wild born/lab spawned H. americanus, lab born/lab spawned H. americanus, and hybrids of H. americanus ♂ × H. gammarus ♀ spawned 8800–11500 eggs per female (weight range 336–945 g). Hybrid females attached 77% of all spawned eggs. Purebred females attached either most eggs of a spawn or fewer than 10%. In some instances where attachment was poor, females were known to be virgins or had been mated to a sterile hybrid male. Unfertilized eggs could attach, but the percentage which did was low. Some wild born/lab spawned H. americanus carried portions of their clutches through until hatching; however, many purebreds and all hybrids dropped their clutches before hatching. Possible factors which cause eggs to drop prematurely are discussed.     

A collector trap for lobster larvae

The paper describes and illustrates the design of a collector trap to facilitate the collection and holding of newly hatched larvae of the North American lobster, Homarus americanus. The trap insures vigorous water circulation, thereby reducing cannibalism by keeping the larvae in constant motion.     

A comparison of techniques for the measurement of growth in adult lobsters

Four non-destructive measures of growth (wet weight in air, wet weight in water, displacement volume and carapace length) were correlated to two destructive measures of growth (dry weight and total body protein level) in adult American lobsters (Homarus americanus). All non-destructive parameters were significantly (P < 0.05) correlated to dry weight and protein for female lobsters. Only wet weight in water was significantly correlated to dry weight and total body protein level in male lobsters.     

Isolation of Pediococcus homari, etiological agent of gaffkemia in lobsters,from a California estuary

Virulent Pediococcus homari, the etiological agent of gaffkemia, a disease enzootic in Atlantic lobsters (genus Homarus), was isolated from two sites in Anaheim Bay, Calif. The concentration of P. homari was in the order of 1–10 bacteria per ml of sample. This is the first known report of free-living P. homari in the Pacific; the bacterium was previously reported to exist in infected decapod Crustaceae and sediments from the Atlantic. Introduction of P. homari may have occurred through transport of infected Homarus americanus (Atlantic lobster), or by discharge of water in contact with them.     

A recirculating system for small-scale experimental work on juvenile lobsters (Homarus americanus)

A refrigerated closed system unit for performing small-scale experimental studies on juvenile lobsters (Homarus americanus) is described. Water is recirculated through a series of filters to juvenile lobsters housed in trays and separated from each other by movable dividers. Tests showed that there was minimal fluctuation in water quality and that lobster development and survival were more a function of nutritional variation than of changes in physical parameters. The system is compact, inexpensive and well suited to small-scale research with aquatic animal culture.     

Microbial diseases of cultured lobsters: A review

Six microbial diseases of cultured American lobsters (Homarus americanus) determined to be of significant concern to commercial aquaculture are discussed in relation to present knowledge of characteristics of the causative microorganisms, lobster susceptibility, environmental influence, severity, gross and microscopic recognition, physiological changes, contagion and control. The diseases reviewed here include shell disease, Gaffkemia, microbial epibiont disease, Lagenidium disease, Haliphthoros disease, and Fusarium disease.     

The influence of wind and temperature on the catch rate of the American lobster (Homarus americanus) during spring fisheries off eastern Canada

The effects of wind and temperature on catch rate of American lobster (Homarus americanus) in the Baie des Chaleurs and off Cape Breton Island in Eastern Canada were investigated. Data on lobster catch and the number of trap hauls were available through a fishermen's volunteer logbook program, bottom temperatures were measured from thermistors either moored nearby or placed inside lobster traps and wind measurements were obtained from local airports. In the Baie des Chaleurs and off the east coast of Cape Breton, a positive and significant correlation was found between the mean temperature change during the 24 h prior to the traps being hauled and the change in the average catch of lobsters per trap haul. Catch rates rose with increasing bottom temperatures and fell with declining bottom temperatures. Higher correlations between changes in temperature and catch rates occurred at sites where the temperature variance was greater. The short‐term fluctuations in lobster catch rates corresponding to temperature changes are hypothesized to result from behavioral changes affecting lobster activity. In both study areas, the large temperature variability was mainly forced by alongshore winds producing upwelling and downwelling, consistent with a classical Ekman response. The effect of the winds on lobster catch is shown to be principally due to their influence on ocean bottom temperatures. Along the south coast of Cape Breton, no relationship was found between catch rates and either temperature or wind, perhaps because lower lobster abundance resulted in a lower signal‐to‐noise ratio. The results of this study qualitatively support the observations by fishermen of a wind‐induced effect on lobster catch rates.     

Large‐scale coherence in New England lobster (Homarus americanus), settlement and associations with regional atmospheric conditions

Time series of American lobster (Homarus americanus) postlarval settlement from southern New England to Atlantic Canada exhibit many common features, and a cluster analysis indicates a block of regions extending from Massachusetts to Maine that have coherent interannual variations. The spatial scale of this block suggests that variability in settlement is related to large‐scale, rather than local, processes. We examined the association between settlement at six reference regions and monthly mean atmospheric conditions (temperature, geopotential height, westerly and southerly wind components, and wind curl) from the North American Regional Reanalysis. We first extracted the dominant modes of variability in monthly averaged geopotential height, temperature, and wind curl. The leading mode from September, which represents high geopotential height, warm temperatures, and negative wind curl throughout the study area, was strongly correlated with settlement at most of the regions. The third mode from August, which represents enhanced southwesterly winds, was correlated with settlement in Rhode Island. Correlations between local atmospheric conditions and lobster settlement confirm the principal component results. Settlement was correlated to varying degrees with geopotential height (positive), temperature (positive) and wind curl (negative) with lobster settlement at the northern sites, with temperature being a stronger indicator in the north and curl a stronger indicator in the south. Rhode Island settlement was strongly correlated with August westerly winds. The correlation between settlement and atmospheric conditions could improve our understanding of stock‐recruit relationships for lobster populations and provides one mechanism for how climate change could impact lobsters.     

Lobster,Homarus americanus,Gastric Fluid Is a Barrier to the Ciliate,Anophryoides haemophila,in an in vitro Study

ABSTRACT

Ciliated protozoan disease caused by Anophryoides hae-mophila, also called “bumper car” disease, has been noted in impounded American lobsters, Homarus americanus, in the Gulf of Maine from 1990 to the present. One possible infection route for ciliated protozoan disease in the American lobster is through the digestive tract. The survival of A. haemophila in gastric fluid from healthy lobsters was tested in vitro. “Bumper cars” did not survive exposure to diluted gastric fluid for longer than one minute. Most ciliates (99%) died within 30 seconds of exposure to gastric fluid. All ciliates died within one minute. Disruption of the ciliate cuticle was apparent after two minutes. The cuticle was completely lysed in six minutes. All ciliates were digested in 8 minutes. These data suggest ciliate infection of American lobsters through the digestive tract is unlikely and cannibalism of infected lobsters is unlikely to result in transfer of the disease.     

Bait-subsidized diets and their effects on ovigerous North American lobsters (<Emphasis Type="Italic">Homarus americanus</Emphasis>)

Ovigerous American lobsters (Homarus americanus) display a protracted period of ovary maturation and maternal care when incubating their eggs, potentially influencing offspring fitness. Lobsters consume a wide range of food items; however, trap bait may comprise a larger proportion of their diet in some fished areas compared to non-fished areas, and the long-term consequences of a bait-based diet remain largely unexplored in lobsters. We tested the hypothesis that disproportionate amounts of bait in the diets of pre-ovigerous females affect the quality of their ovaries and eggs. We held pre-ovigerous lobsters (n?=?29) over a period of ~?300 days (range?=?270–378) and fed them diets of herring bait, natural prey items (crab, mussel, urchin, macroalgae), or a combination of both diet types. Nutritional status, measured as biweekly blood indices and total glucose levels, suggest differences between lobsters fed a natural or combination diet and lobsters fed a bait-based diet (ANOVA; P?<?0.05). We found that bait diets contained more protein (58.5%) and lipids (31.6%) compared to natural diets (34.5 and 13.2%, respectively) and lipid levels in ovaries and eggs significantly correlated with each other for all treatments (r?=?0.76, n?=?15, P?=?0.028). Histopathological analysis indicates that ovaries contained more variable maturation in starved lobsters or those fed with bait, with some animals showing delayed gonad maturation. Results suggest that a varied diet promotes the overall fitness of ovigerous lobsters and the associated reserves that are used for ovarian development and subsequent oocyte formation.     

Acute toxicity of emamectin benzoate (SLICE™) in fish feed to American lobster, Homarus americanus

SLICE? (active ingredient 0.2% emamectin benzoate (EMB)), a feed premix developed by Schering‐Plough Animal Health for the control of sea lice on cultured salmonids, is registered for use in several countries and is being prescribed on an emergency basis in Canada and the United States. The concentration of EMB in feed administered to farmed salmon ranges from 1 to 25 μg g^?1. To determine the acute toxicity of the compound to juvenile and adult American lobster (Homarus americanus), commercial salmon feed was coated with SLICE? at a range of concentrations and provided to the animals for 7 d in the laboratory. The LC₅₀ is estimated to be 644 μg g^?1 (95% CI=428, 1275) for adult lobsters and >589 μg g^?1 for stage V and VI juvenile lobsters. The consumption of medicated pellets by adult lobsters decreased significantly with increasing concentration of EMB. Adult lobsters that died during the study had a significantly greater concentration of emamectin B1a in their muscle tissue than those that survived. These results support the conclusion that salmon feed medicated with EMB at the concentrations used by the aquaculture industry is unlikely to pose an acute lethal threat to adult and small juvenile American lobsters.     

Missing claws in a commercial catch of the American lobster: Implications for life history and the fishery

In most crustaceans, including the American lobster (Homarus americanus), a high frequency of individuals with missing claws is often reported. As lobsters with missing claws (“culls”) are less valuable in terms of weight and market value than uninjured lobsters, returning of culls to the sea has been suggested as a conservation strategy. To assess the potential benefits of such strategy, the frequency and types of claw loss were documented during the fishery season of 2007 (34 days, 6900 trap hauls) in an area of Prince Edward Island, southern Gulf of St. Lawrence. On average, culls accounted for ～7% of the total catch in weight and such percentage remained fairly constant along the study period. The raw frequency of culls, however, was higher in the first 9–12 days of the study and decreased progressively afterwards, reflecting the pattern followed by actual total catches. A single missing claw (pincher or crusher in similar proportions) was the most common type of injury for both males and females, followed by the presence of a single regenerating claw. The male:female ratio for the culls (～1:2) did not deviate from the one estimated for uninjured lobsters of the same size range (canners). These results are used to further discuss life history implications and the potential benefits and limitations of a conservation strategy based on the return of culls to the water.     

Effect of Neguvon® and Nuvan® treatment on crabs (Cancer pagurus,C. maenas), lobster (Homarus gammarus) and blue mussel (Mytilus edulis)

Survival tests were carried out with crabs, lobsters and blue mussels held in tanks of flowing seawater and subjected to Neguvon at 10, 1, 0.5 and 0.1 ppm and to Nuvan at 1, 0.01 ppm. Homarus gammarus was the most susceptible species; the animals died within 24 h at Neguvon levels of 0.5 ppm and higher and at Nuvan levels of 0.1 ppm and higher. The use of these chemicals in salmon farming appears to have deterious effects on marine invertebrate species.     

Sea Lice Control II

ABSTRACT

Sea lice, Lepeophtheirus salmonis, mobile stages were caught using a light trap, in cages holding Atlantic salmon, Salmo salar, and their abundance determined through calculation. Seasonal changes were shown with an increase in abundance as the temperature increased toward the end of the season. Analysis of manual lice-count data indicated variations in lice abundance between cages with and without deployed light traps. Analysis indicated that these variations were in larval presence (P = 0.006) and presence of gravid females (P = 0.015), but not in abundance of in pre-adults (P = 0.172). Cage net condition also affected the abundance and infection intensity of sea lice on Atlantic salmon within aquaculture cages. Abundance of larvae were affected by net condition (P = 0.01), as were abundance of pre-adults on salmon (P = 0.04). The infection intensity of gravid females, however, did not vary with net condition (P = 0.74). Other species of zooplankton such as, American lobster, Homarus americanus, larvae and various Brachi-pod larvae, were also collected with the light trap. The light trap, as presented in this research, could provide an alternate method of lice control in aquaculture cages.     

Effects of container transparency and reflectivity upon oxygen consumption of hybrid lobsters

The effect of intra-specific visual communication on the rate of oxygen consumption of hybrid lobsters (Homarus americanus × H. gammarus) was tested in a partitioned metabolic chamber. Three partition linings were tested: opaque rubber, clear plexiglass, and glass mirror. Short-term mean oxygen comsumption rates observed for lobsters separated by rubber-lined partitions were 8% lower than those of lobsters separated by the clear partitions, and 29% lower than those of lobsters separated by mirrored partitions (P < 0.001).     

Gaffkemia in the California spiny lobster, Panulirus interruptus: Infection and immunization

Infection (gaffkemia) can be induced in the California spiny lobster (P. interruptus) with injections of Pediococcus homari (formerly Gaffkya homari). An LD_{5 0} of 10³ microbes per ml hemolymph is observed at 17°C. Prior immunization of lobsters (P. interruptus) with an avirulent strain of P. homari protects lobsters against 100 × LD_{5 0}. This is the first report of acquired immunity to P. homari in a susceptible species. The high incidence of gaffkemia in American lobsters (Homarus americanus) held in live holding facilities makes prophylactic measures essential in regions outside the enzootic area of the North Atlantic to avoid inadvertent transplantation of the disease to other susceptible populations of animals.     

Hatchery performance of early benthic juvenile American lobsters (Homarus americanus) fed enriched frozen adult Artemia diets

One of the main factors hindering aquaculture production of American lobsters (Homarus americanus) is the need for a cost‐effective and nutritionally sound diet. Live Artemia results in good growth, but is expensive and is a constant source of contamination. Frozen Artemia, although lower in cost, generally results in decreased survivorship and growth relative to live Artemia. The recent advent and mass production of enriched frozen Artemia products may provide for a cost‐effective and nutritionally complete food source for culturing American lobsters. Here, commercially available frozen adult Artemia enriched with either n‐3 fatty acids, or Spirulina was fed to juvenile American lobsters, and their growth and survivorship for three months was compared with that of animals fed unenriched frozen adult Artemia. Both enriched Artemia products produced survivorship superior to that for animals fed unenriched Artemia. Results for growth were equivocal although animals fed the Spirulina‐enriched Artemia had the greatest condition factor. Although more costly by the end of the experiment, enriched diets were more economically efficient than unenriched Artemia. This research demonstrates that enriched feedstuffs are cost‐effective over longer time intervals, and benefits may continue beyond the hatchery‐rearing phase. Enriched diets may also yield animals with a better condition factor, which may further influence their survivorship when released to the wild in enhancement programmes.