Behavior of juvenile American lobsters, Homarus americanus, under predation risk

The influence of predation risk and food deprivation on the behavior and activity of juvenile American lobsters, Homarus americanus Milne Edwards, was examined in single and paired individuals in laboratory experiments performed during 1988 and in the winter of 1991/92. In the presence of a predator (the tautog Tautoga onitis Linnaeus) restrained behind a barrier, single lobsters significantly reduced the time spent feeding at night, consumed fewer mussels, and quickly brought them back to shelter. Single lobsters did not forage during the day in any treatment. If deprived of food for 60 h, they consumed more mussels and spent more time walking than recently fed (12-h food-deprived) lobsters. Paired lobsters did forage during the day in the presence of a predator. The smaller lobsters (subdominant) in the pairs foraged for a longer time in the presence than in the absence of a predator and significantly longer than single individuals. Shelter occupancy was significantly shorter in single, recently fed lobsters in the presence of a predator compared to time spent sheltering in its absence. Among food-deprived lobsters, paired individuals spent a significantly shorter time within the shelter than single lobsters in the absence of a predator. Larger (dominant) lobsters, however, spent more time than subdominant lobsters within the shelter during all periods of the day. Without a predator, paired lobsters spent significantly more time than single ones in shelter-related activities. Under predation risk, subdominant lobsters concentrated shelter-building time during the day and built a higher percent of alternative shelters than either single or dominant lobsters. In the absence of a predator, paired lobsters walked in the open area for a significantly longer time than single ones in the absence of a predator. This apparently was associated with fighting between dominant and subdominant lobsters and the attempts of the larger lobster to drive the smaller one from its shelter. During the day, lobsters fought for a significantly longer time in the presence than in the absence of a predator. When the tautog was not constrained, mortality rate was similar in both single and paired lobsters. Mortality rate among subdominant lobsters, however, was seven times higher than among dominant lobsters. We suggest that the risk of predation interferes with the ability of single juvenile lobsters to acquire and consume food. They appear to trade off energetic consideration against risk of predation when foraging away from the shelter. The introduction of a conspecific competitor to the system may further increase risk (of the subdominant) to the predator. Intraspecific interactions tend to increase the risk of predation to smaller lobsters but increase the survival rate among larger lobsters. Received: 6 February 1995 / Accepted: 2 September 1997     

Movements of lobsters (Homarus americanus) tagged in the Bay of Fundy,Canada

Of the 18 359 American lobsters (Homarus americanus) tagged and released at three locations in the Bay of Fundy during 1977–1980, 5 375 lobsters (29.3%) were recaptured within 6 yr of release. Mature lobsters (95-mm carapace length, CL) on average moved significantly greater distances than immature lobsters (<95-mm CL). Many (16.4%) of the mature lobsters were recaptured >92.6 km (50 nautical miles) from the release sites; the farthest distance moved was 798 km for a male at liberty for 3.5 yr. Examination of the direction of movements indicates some intermixing of lobsters within the Bay of Fundy, and throughout the Gulf of Maine and the adjoining Continental Shelf and slopes. Mature lobsters were recaptured in deeper waters during winter than during summer. The seasonal shallow-deep migration of mature lobsters in the Bay of Fundy is possibly associated with maximizing degree-days for molting, growth, gonadal development, and egg development. In some areas, mature females on average moved farther and seasonally earlier into deeper waters than mature males. Although the seasonal migration resulted in many lobsters returning to the original release area year after year, some lobsters made extensive long-distance movements away from the Bay of Fundy. Temperature-dependent, seasonal deep-shallow migration can explain both the local returns and the long distance migrations of mature lobsters in the Bay of Fundy and the Gulf of Maine. To achieve appropriate seasonal temperature regimes, mature lobsters have to move different distances and directions, depending on local topography.     

Primary cell-culture of the digestive gland of the marine mussel Mytilus edulis: a time-course study of antioxidant- and biotransformation-enzyme activity and ultrastructural changes

The extent to which the American lobster, Homarus americanus (H. Milne-Edwards), utilizes estuarine habitats is poorly understood. From 1989 to 1991 we examined lobster movements in and around the Great Bay estuary, New Hampshire using tag/recapture and ultrasonic telemetry. A total of 1212 lobsters were tagged and recaptured at sites ranging from the middle of Great Bay, 23.0 km from the coast, to Isles of Shoals, 11.2 km offshore. Twenty-six lobsters equipped with ultrasonic transmitters were tracked for periods ranging from 2 weeks to >1 year. Most lobsters moved <5 km toward the coast, with those furthest inland moving the greatest distance. Lobsters with transmitters moved in a sporadic fashion, with residency in one area for 2 to 4 weeks alternating with rapid movement to a new location (mean velocity = 0.3 km d⁻¹, 1.8 km d⁻¹ max.). Site of release influenced distance moved, but there was no significant relationship between lobster size and distance traveled, days at large, or rate of movement. Most movement into the estuary occurred in the spring, while during the remainder of the year there was a strong tendency to move downriver, toward the coast. These seasonal migrations of estuarine lobsters may enhance their growth and survival by enabling them to avoid low salinity events in the spring and fall, and to accelerate their growth in warmer estuarine waters during the summer. Received: 26 January 1996 / Accepted: 22 January 1999     

A laboratory energy balance for the larvae and juveniles of the American lobster Homarus americanus

A laboratory energy budget was constructed for the larvae and juveniles of the American lobster Homarus americanus Milne-Edwards fed brine shrimp, Artemia saline L. Measured energy flows included ingestion, egestion, excretion of ammonia, routine and fed metabolism, growth, and production of exuvia. Digestion and assimilation were calculated and minimum ration of protein necessary to sustain larval lobsters was estimated. No change associated with metamorphosis was observed in rates of excretion, fed metabolism, and production of exuvia. Routine metabolism is not significantly higher for larvae than for juveniles. Growth changes from exponential in larvae to a slower increase in post-larvae. Consumption reflects changes in other variables. Changes in energy partitioning and energetic efficiencies associated with metamorphosis are largely due to change in rate of growth.     

Survival of communally reared larval and juvenile lobsters,Homarus americanus

Survival of individually reared larval and juvenile stage lobsters, Homarus americanus (Milne-Edwards), was significantly higher than in corresponding groups of communally reared individuals. Among communally reared lobsters, the mortality rate was highest in the second-stage larvae and then progressively decreased in the later stages. The relationship between survival and duration of molt period of each life-cycle stage indicates that asynchronous molting in the groups of communally reared lobsters is a contributing factor to the higher mortality rate. The molting and mortality curves of communally held lobsters reared from the first larval to first or second juvenile stage showed best cross correlation at 0- or 1-day time lag. The decreased mortality rate observed in the later larval and juvenile stages appears to have resulted from the establishment of new behavior patterns. Group interactions which are influenced by numerous extrinsic and intrinsic factors lead to higher mortality rate (cannibalism) among communally reared lobsters.     

Effects of environmental manipulation on the locomotor activity and agonistic behavior of cultured juvenile American lobsters,Homarus americanus

The locomotor activity patterns and agonistic encounters of cultured juvenile (IX–XIII stage) American lobsters, Homarus americanus (Milne-Edwards) held in 8 experimental environments were investigated to examine their relative contribution to aggressive level. Three variables: (1) lobsters individually or communally maintained, (2) shelters present or absent, and (3) open or closed seawater system were tested in a set of factorial experiments. Locomotor activity of lobsters held in a 12 h: 12 h light: dark regime was recorded for individually separated lobsters for the first 5 days and for communally held lobsters for the next 5 days of a 10-day experimental period. All lobsters maintained individually had similar levels of activity. When the same individuals were communally maintained, there appeared to be social inhibition of activity. In addition, communally held lobsters without shelter were twice as active as those provided with shelter. The activity levels of groups of communally held lobsters with shelter progressively decreased over the experimental period. All lobsters became somewhat entrained to the light: dark cycle and were nocturnally active. However, the degree of entrainment was strongly influenced (P<0.001) by the presence or absence of shelter and other lobsters. Individually maintained lobsters all showed good entrainment, although those provided with shelter were slightly better entrained. The presence of conspecifics desynchronized activity patterns when shelter was not provided. Aggressive level, as measured by the frequency of agonistic encounters per 15-min observation period and the number and types of displays per encounter, decreased over an 8-day period for groups of 3 lobsters in all experimental environments. Lobsters maintained in a closed system initially showed higher frequencies of agonistic encounters than those held in an open system. The observed decrease in aggressive level with time primarily resulted from decreased activity levels. When two lobsters met, the probability of an agonistic encounter was about 0.8 throughout the experimental period, but decreasing activity levels resulted in progressively fewer encounters. The results suggest several approaches for limiting aggression among communally maintained lobsters in culture systems by environmental manipulation.     

Astaxanthin deposition in the cuticle of juvenile American lobster (<Emphasis Type="Italic">Homarus americanus</Emphasis>): implications for phenotypic and genotypic coloration

The phenotypic brownish-green color of an American lobster (Homarus americanus Milne-Edwards, 1837) is determined by genetic and dietary mechanisms. Diet influences color through the carotenoid astaxanthin. This pigment can appear red or blue depending if it is bound to protein, and the relative amounts of each form influence lobster color. Carotenoprotein formation was examined in sibling American lobsters rendered white by a diet low in astaxanthin, by feeding a diet containing 0, 55, 110, or 220 g astaxanthin g^–1 for 110 days beginning on 7 February 2004. The relative levels of red and blue in these lobsters were assessed through the analysis of digital photographs of the lobsters, which were taken monthly. The red/blue ratio was used to assess if free (red) or protein-bound astaxanthin (blue) was the dominant form in the lobsters, or if the two forms occurred in ratios allowing for natural coloration. Naturally colored lobsters developed only in the highest astaxanthin diet group, while lobsters fed the 55-g diet were blue. Differences were observed among different parts of the body, and were presumed to be a function of cuticle thickness. However, within each diet treatment, some lobsters initially became red, suggesting an accumulation of free astaxanthin, while other lobsters initially became blue, suggesting an accumulation of protein-bound astaxanthin. This variation may be a result of differences in the uptake of astaxanthin, the rate of carotenoid-protein complexing, or in the total amount of protein available for binding. This variability is likely to be the key to understanding the underlying basis of genetically determined color in American lobsters.Communicated by J.P. Grassle, New Brunswick     

Cryptic speciation in the recently discovered American cycliophoran <Emphasis Type="Italic">Symbion americanus</Emphasis>; genetic structure and population expansion

Symbion americanus was recently described as the second species in the phylum Cycliophora, living commensally on the American commercial lobster Homarus americanus. A previous genetic analysis of American and European populations of cycliophorans suggested that haplotype divergence in S. americanus was much greater than in its European counterpart S. pandora. This study examined the population structure and demographics of 169 individuals thought to belong to S. americanus collected from lobsters over 13 North American localities (Nova Scotia, Canada to Maryland, USA) between October 2003 and January 2006. Cytochrome c oxidase subunit I sequence data clearly suggested the presence of three cryptic lineages in a species complex, often co-occurring in the same lobster specimens. One of these lineages, named the “G” lineage, was represented by very few individuals and therefore was excluded from subsequent statistical analyses. The other two sympatric lineages, named the “T” and “C” lineages, showed different population structure and demography. Although limited geographic structure was found in the T lineage, the C lineage showed higher nucleotide and haplotype diversity values, as well as more variation between localities. The data also indicated that the T lineage underwent a recent population expansion, suggesting that the C and T lineages may have speciated in allopatry but a subsequent population expansion may have been responsible for their current sympatric distribution. Studies on the anatomy and ecology of the sympatric lineages of this species complex should provide further information on the identity of the holotype of S. americanus, which currently cannot be ascribed to any of the three cryptic lineages.     

The timing of chemical signaling with urine in dominance fights of male lobsters (Homarus americanus)

Chemicals carried in the urine are a rich source of information about the identity, sex, aggressive motivation, and other attributes of an animal. In agonistic interactions, animals should be careful about disclosing such information, since it can be used by receivers to the disadvantage of the sender. By adjusting the timing of urine release, the signaler may still influence the behavior of the receiver to its own benefit. Here we investigate the urine signaling of American lobsters (Homarus americanus), necessary for the maintenance of dominance, using a catheter technique with high temporal resolution. We hypothesize that urine release in lobster fights is not continuous but restricted to moments that may elicit a reaction in the receiver beneficial to the sender. We found that eventual winners signaled more readily in the initial phase of the fight. Eventual losers did not show such initial urination. This suggests that a confident lobster may use urine signals to influence the behavior of its opponent into giving up the fight at an early stage. For both winners and losers, urine release is linked to offensive behavior and increases as the intensity of agonistic behavior increases. The coupling of urine release to offensive behaviors appears to improve both the reliability and efficacy of the chemical signal. Releasing urine under the increasing risk of inflicting injury during the fight provides a handicap that may ensure reliability of the threat signal. Furthermore, the immediate coupling of urine components to offensive behavior may help to consolidate the receiver"s memory of the signaler"s individual scent and thus facilitate future recognition of the dominant animal. Received: 6 October 1999 / Accepted 28 August 2000     

Effect of aerial exposure on concentrations of selected metabolites in blood of the Norwegian lobsterNephrops norvegicus (Crustacea: Nephropidae)

The Norwegian lobsterNephrops norvegicus (L.) collected from Firth of Clyde, Scotland between December 1987 and March 1988, was unable to survive longer than 18 h experimental emersion at 10°C. During this time the partial pressure of oxygen (P O₂) in the venous blood decreased rapidly and the lobster supplemented cellular energy requirements by anaerobic metabolism. This was indicated by the rapid accumulation ofL-lactate in the blood. Although the survival rate increased (to ca 36 to 48 h) if lobsters were kept on ice, the accumulation ofL-lactate in the blood was not significantly different from lobsters at 10°C, despite the temperature difference. There was no indication thatN. norvegicus was able to further metabolize circulatingL-lactate during emersion. On emersion there was also a marked hyperglycemia in the blood due to the stress of handling and asphyxiation. There was fairly good agreement between results obtained during laboratory studies and simulated fishing activity in the Firth of Clyde. Both sets of results are discussed in the context of adaptation to air breathing within the Crustacea and an assesment of post-harvest treatment of lobsters.     

Circadian shelter occupancy patterns and predator–prey interactions of juvenile Caribbean spiny lobsters in a reef lagoon

The spiny lobster, Panulirus argus, is predominantly nocturnal, remaining inside shelters during the day and foraging outside at night, presumably to minimize predation risk. Predation risk generally decreases with increasing lobster size. Therefore, this study examined the hypothesis that size would influence this basic circadian pattern. Video cameras continuously recorded the shelter occupancy of juvenile lobsters (n = 72) having a carapace length (CL) of 30–62 mm that were tethered to shelters in a shallow reef lagoon. The lobsters’ shelter occupancy was 100% during the day, but declined linearly from shortly before sunset to a minimum of 50% shortly after midnight and then increased linearly, reaching 100% by 1 h after sunrise. The percent time the lobsters spent in the shelters followed a similar trend, but there was wide variability at night (0–100%) for individual lobsters. Lobsters left their shelters 2–30 times night⁻¹, with a majority of excursions lasting <10 min. These results suggest that juvenile P. argus minimize predation risk by remaining in their shelters as long as possible but offset the energetic cost of this behavior by foraging close to their shelters for several short periods at night. This emergence pattern contrasts with those of early benthic phase lobsters (<15 mm CL), which seldom leave their shelters, and adults (>80 mm CL), which have a dusk/early evening peak in activity and leave the shelter for extended periods of time during the night. Furthermore, a minimum shelter occupancy in the middle of the night appears especially well adapted to avoid exposure to daytime predators. Videotaped observations also included interactions between lobsters and two dominant lobster predators, the triggerfish, Balistes capriscus, and the octopus Octopus cf. vulgaris. Lobsters responded differently to these predators: remaining in the shelter when attacked by a triggerfish and fleeing the shelter when attacked by an octopus. Triggerfish were nearly twice as likely to attack a lobster that was outside of the shelter than inside. Once under attack, however, a lobster had nearly the same chance of surviving if it was inside or outside. Results suggest that the patterns of shelter use and emergence change as lobsters grow, probably reflecting the interplay between perception of predation risk and the need to forage. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Manipulation of the seasonal reproductive cycle in winter flounder,Pleuronectes americanus,using a gonadotropic hormone releasing hormone

A gonadotropic hormone-releasing hormone analogue ([D-Ala⁶, Pro⁹-NHEt]LHRH, GnRH-A) was administered to the winter flounder, Pleuronectes americanus (Walbaum) at different stages of the reproductive cycle from September 1988 to July 1989. Both males and females responded to releasing hormone treatment throughout the year except for a brief summer period in post-spawned fish when the gonads were regressed. In females, GnRH-A markedly increased plasma estradiol-17 and testosterone levels and accelerated growth of the ovaries during the period of early gonadal recrudescence beginning in August. In prespawning females, GnRH-A treatment increased plasma testosterone levels in association with a stimulation of germinal vesicle migration and ultimately ovulation. During the fall, GnRH-A treatment of males increased plasma androgen levels (testosterone and 11-ketotestosterone) and stimulated growth of the testes. In February, a time when spermiation is initiated in only half of the males, the proportion of spermiating males was increased by treatment with releasing hormone, indicating that spermiation can be advanced in some males by ca. 2 mo.A portion of this work was given as a poster presentation at the XIth International Symposium on Comparative Endocrinology, Malaga, Spain, May 14–20, 1989     

Creation of a Gilded Trap by the High Economic Value of the Maine Lobster Fishery

Abstract: Unsustainable fishing simplifies food chains and, as with aquaculture, can result in reliance on a few economically valuable species. This lack of diversity may increase risks of ecological and economic disruptions. Centuries of intense fishing have extirpated most apex predators in the Gulf of Maine (United States and Canada), effectively creating an American lobster (Homarus americanus) monoculture. Over the past 20 years, the economic diversity of marine resources harvested in Maine has declined by almost 70%. Today, over 80% of the value of Maine's fish and seafood landings is from highly abundant lobsters. Inflation‐corrected income from lobsters in Maine has steadily increased by nearly 400% since 1985. Fisheries managers, policy makers, and fishers view this as a success. However, such lucrative monocultures increase the social and ecological consequences of future declines in lobsters. In southern New England, disease and stresses related to increases in ocean temperature resulted in more than a 70% decline in lobster abundance, prompting managers to propose closing that fishery. A similar collapse in Maine could fundamentally disrupt the social and economic foundation of its coast. We suggest the current success of Maine's lobster fishery is a gilded trap. Gilded traps are a type of social trap in which collective actions resulting from economically attractive opportunities outweigh concerns over associated social and ecological risks or consequences. Large financial gain creates a strong reinforcing feedback that deepens the trap. Avoiding or escaping gilded traps requires managing for increased biological and economic diversity. This is difficult to do prior to a crisis while financial incentives for maintaining the status quo are large. The long‐term challenge is to shift fisheries management away from single species toward integrated social‐ecological approaches that diversify local ecosystems, societies, and economies.     

Thermal histories of brooding lobsters, <Emphasis Type="Italic">Homarus americanus</Emphasis>, in the Gulf of Maine

Although it is widely accepted that migration by ovigerous lobsters (Homarus americanus Milne Edwards) optimizes thermal conditions for embryonic development, temperatures experienced by freely moving lobsters have never been measured. The precise thermal histories of 30 ovigerous lobsters at large in the Gulf of Maine were recorded to compare thermal conditions experienced during a brooding season. Analysis of both the temperature and movement data revealed a clear difference between lobsters smaller and larger than the size when 50% of individuals are mature (carapace length 93 mm). Although small and large lobsters ultimately experienced a similar number of degree-days above 3.4°C (952.8 for small and 983.6 for large) from 25 September 2002 until 27 July 2003, large lobsters and their embryos experienced less extreme and less variable temperatures. They were exposed to more gradual cooling in the fall and more gradual warming in the spring. These data, which are the first to document the seasonal temperatures experienced by ovigerous lobsters, suggest that migrations do not necessarily increase the number of degree-days experienced by developing embryos, but do reduce the variation in their thermal regime.     

Viability of embryos of the winter flounder Pseudopleuronectes americanus exposed to combinations of cadmium and salinity at selected temperatures

Developing eggs of the winter flounder Pseudopleuronectes americanus (Walbaum) were exposed to 9 combinations of cadmium and salinity at 5° and 10°C. Overall mean times to 50% hatch ranged from 7.7 days at 10°C to 17.9 days at 5°C. Mean percentages of total hatches ranged from 50 to 100% for all treatment combinations. Response-surface analyses indicate percentages of viable hatches were generally lowest at 10% S and highest in the 25 to 30% S range. Regression analyses of viable hatch data show that at both temperatures cadmium significantly influenced viable hatch in all experiments. Viable hatch was also significantly influenced by the linear and quadratic effect of salinity in both tests at 5°C and in 2 of 3 tests at 10°C. The interaction between cadmium and salinity also significantly affected viable hatch at 10°C.     

Estimation of the abundance of the tropical lobster Panulirus ornatus in Torres Strait,using visual transect-survey methods

The Panulirus ornatus stock in a 25 000 km² area of Torres Strait was estimated by making visual counts of the number of lobsters in strip transects. Pilot studies in 1988 to assess the feasibility of a full-scale survey and optimize the sampling design showed that: 4×500 m transects were the most cost-effective of the different sizes trialled; two transects per location comprised the most optimal allocation of replication; and 300 locations were necessary to achieve a 95% confidence interval of ±10% of the mean density found in the pilot study. Satellite imagery was used to map habitats in Torres Strait, and areas likely to be inhabited by lobsters were classified broadly into three strata: windward reef slope, submerged reef, and deep areas. The 300 locations were allocated to each stratum in proportion to its area and the estimated variance of lobster abundance within it; once allocated, the locations were positioned at random within each stratum. The main survey was undertaken over a period of 7 wk in May–June 1989, and the resulting estimate of lobster abundance was 14 million with a 95% confidence interval of ±21%. The surveyed population was sampled concurrently to determine its size structure: the pre-fishery year-class comprised 43% of the population; lobsters greater than legal-size comprised 57% and their average tail weight was 346 g. Thus, the estimate of stock size for the study area was 2200 to 3350 t tail weight, which is roughly ten-fold greater than the annual catch of about 250 t. The current catch is approaching the lower estimates of potential yield, calculated using simple maximal sustainable yield estimators, which suggests that the fishery is unlikely to be under threat at present and may support greater effort.     

Age and growth in Nephrops norvegicus (Decapoda: Nephropidae)

The growth of the lobster Nephrops norvegicus (L.) in laboratory tanks was studied. The moult increments of males and females were not significantly different. The growth per moult was of the progressive geometric type throughout the life of the lobster, including the larval instars. Moulting in both the laboratory and the natural population occurred throughout the year in males, but there was a peak of moulting activity in females from June to August. There was no indication of a terminal anecdysis. Size-frequency histograms from monthly samples taken 10 to 20 miles south-west of the Isle of Man over a period of 21/2 years provided data on the growth of the year classes. It is possible to recognise the year classes in females at least, until the lobsters are 3 to 4 years old. Instar determination based on the numbers of aesthetasc-bearing segments of the antennule and on the numbers of lamellae in the endocuticle was unsuccessful. Estimates of the numbers of moults occurring in each year, and the expected mean sizes of the year classes are given.     

Structural changes in the hepatopancreas of the rock lobster,Jasus edwardsii (Crustacea: Palinuridae) during development from the puerulus to post-puerulus

There is evidence for non-feeding in pueruli of palinurid lobsters during their long-distance swim to the coast and the succeeding post-settlement phase until they molt to the juveniles. For a better understanding of the nutritional supply during the puerulus stage, structural changes in the hepatopancreas were studied in post-settlement pueruli and first-molt, postpueruli of the rock lobster, Jasus edwardsii, collected on the southeast coast of the North Island, New Zealand between 1989 and 1990. In newly settled (transparent) pueruli, the epithelium of the hepatopancreas is dominated by presumed young R-(resorptive) cells, which are devoid of lipid droplets, but show active uptake of material from the hemolymph through pinocytosis at the basal region. In the fully pigmented puerulus, the hepatopancreas is dominated by R-cells containing massive lipid droplets; also present are small numbers of F-(fibrillar) and B-(blister-like) cells. This increase of lipid inclusion in the R-cells corresponds to the reduction in size of the fat bodies as the lobster develops from the transparent to the pigmented puerulus. After the molt to the post-puerulus, the R-cells are compressed, and the lipid droplets almost disappear, while the B-cells increase both in size and number. A mechanism is proposed in the present paper to explain energy storage and utilization during the puerulus and post-puerulus stages, wherein the fat bodies and the lipid inclusions play a vital role.     

Effect of ammonia on survival and osmoregulation in different life stages of the lobsterHomarus americanus

Acute toxicity of ammonia was determined for cultured larval, postlarval, and wild adult lobsters (Homarus americanus) in 1988. Ammonia tolerance was found to increase with ontogenetic development. Based on 96-h LC₅₀ values of 58 mg l^–1 NH₄ ⁺ + NH₃ l^–1 seawater (0.72 mg NH₃ l^–1) for Stage I larvae, 87 mg NH₄ ⁺ + NH₃ l^–1 (1.7 mg NH₃ l^–1) for Stage II larvae, 125 mg NH₄ ⁺ + NH₃ l^–1 (2.13 mg NH₃) for Stage III larvae, 144 mg NH₄ ⁺ + NH₃ l^–1 (2.36 mg NH₃ l^–1) for Stage IV postlarvae, 377 mg NH₄ ⁺ + NH₃ l^–1 (5.12 mg NH₃ l^–1) for adult lobsters at 5°C and 219 mg NH₄ ⁺ + NH₃ l^–1 (3.25 mg NH₃ l^–1) for adult lobsters at 20°C, recommendations for safe levels of total ammonia and un-ionized ammonia were calculated using an application factor of 0.1. Effects of ammonia on osmoregulatory capacity were studied on postlarvae and adults. Ability of postlarvae and adults to hyper-regulate in low-salinity media decreased after exposure to ammonia. In postlarval lobsters, osmoregulatory capacity was significantly affected in ammonia concentrations exceeding 32 mg l^–1. Osmoregulatory capacity in adult lobsters (5 and 20°C) was affected at 150 mg l^–1. In postlarval lobsters, a minimum exposure time of 12 h was required to impair osmoregulatory capacity. The decrease in hemolymph osmotic pressure was caused by lower hemolymph sodium concentrations. The presence of ammonia in the external medium could markedly affect the Na⁺/NH₄ ⁺ transport mechanism by permanently, temporarily, or partially impairing the transport sites for sodium.     

Seasonal variations in sperm production and sperm quality in male winter flounder, Pleuronectes americanus: the effects of hypophysectomy, pituitary replacement therapy, and GnRH-A treatment

The pattern of sperm release and changes in sperm quality were investigated throughout the normal spawning season of male winter flounder, Pleuronectes americanus (Walbaum), caught in Conception Bay, Newfoundland, Canada in April and November 1994. In addition, the impact of hormonal manipulation on sperm production and sperm quality was examined through gonadotropin-releasing hormone analogue (GnRH-A) treatment, hypophysectomy, and pituitary extract injection – pituitary replacement therapy (PRT). While a lengthy period of spermiation, lasting ∼6 months (December to July), can be detected in some males, the major period for sperm release occurred in May to July in the summer spawning season. The spawning period started with peak levels of plasma testosterone (T) and 11 ketotestosterone (11-KT). By late July sperm production fell rapidly along with a notable deterioration in sperm motility. While GnRH-A treatment advanced the period of sperm release, and the milt became diluted and increased in volume, the treatment did not increase total sperm output over the spawning season. In hypophysectomized male flounder, by contrast, milt was more concentrated and sperm production declined along with reduced plasma androgen levels during the spawning season. Increased plasma T and 11-KT levels in hypophysectomized males followed PRT in December and January. Moreover, PRT appeared to be responsible for advancement of spermiation in a large number of prespawning males, which released an increased amount of milt. Finally, these studies indicated that both sperm motility and egg fertilization rates remained unchanged after these hormonal treatments. Received: 5 September 1997 / Accepted: 6 January 1999