Elise Mayrand

Changes in muscle of postmoult snow crabs Chionoecetes opilio (O. Fabricius) fed different rations

Somatic growth, muscle cell condition and metabolism, and gonadal production have been studied in male snow crabs Chionoecetes opilio fed 0, 0.4 and 2 g·animal−1·day−1 and sampled 5, 25, and 60 days after the terminal moult. Twenty-five days after moulting, muscle growth rate was low in crabs fed a high ration and negative in the other groups, and no gonadal production took place. This suggests that the energy was utilised in priority to sustain a high maintenance metabolism. Between 25 and 60 days post-moult, maintenance costs were apparently lower and more energy was directed, in decreasing order of priority, towards gonadal production, which was independent of food ration, muscle growth and reserve build-up in the digestive gland, the two latter being directly related to food ration. Starvation caused the death of merus muscle cells, as indicated by the significant decrease in DNA content, but after 60 days the size of the remaining cells (protein:DNA ratio) had increased as much as that of crabs fed a high ration. It may be a better strategy to maintain fewer cells, by using material and energy obtained from the sacrificed ones, than to keep all cells in a deficient state. Crabs fed a high ration filled the new larger exoskeleton through hypertrophy and hyperplasia. After 25 days of undernutrition, the reduced number of muscle cells relatively to the merus volume was counterbalanced by an enhanced activity of phosphofructokinase (PFK), citrate synthase (CS) and cytochrome C oxidase (CCO) per g of muscle dry weight. An inverse relationship between food ration and enzyme activity per g dry weight further attenuated the effect of food ration on the enzyme total activity in the whole merus muscle. After 60 days of starvation, the still high enzyme activity per g dry weight could no longer compensate for the continuing loss of cells and, at that time, the enzyme total activity was directly related to food ration. Our results suggest that the feeding status of wild crabs may affect their locomotor ability through effects on muscle capabilities.

Biochemical indicators of muscle growth in the snow crab Chionoecetes opilio (O. Fabricius)

This study examined the relationships between muscle growth rate, the activity of metabolic enzymes and the RNA:DNA ratio, in adult snow crabs Chionoecetes opilio. After moulting, crabs were assigned to three feeding rations to attain a range of tissue growth rates. Muscle growth rate, estimated by the variation in dry tissue content per ml of merus of the first walking leg, was positively correlated with changes in muscle cell number, as evaluated by the DNA content per ml of merus. However, no significant correlation was detected between growth rate and the variation in muscle cell size, the latter being estimated by the change in the protein:DNA ratio. This is due to the fact that, in starved crabs, a reduction in the number of cells is partly compensated by a size increment of the remaining ones. This phenomenon also weakened the overall relationship between muscle growth rate and the phosphofructokinase (PFK) capacity per ml of merus. The simple correlation between those two variables was significantly positive for animals which increased their mass of muscle but insignificant for those which were loosing muscle mass. The lactate dehydrogenase (LDH), citrate synthase (CS) and cytochrome c oxidase (CCO) capacity per ml of merus did not match growth rate. The significant simple correlations that were detected between growth rate and the various enzyme activity expressed per g of protein, per µg of DNA and per g of dry mass did not hold when partial correlations were computed. Variations in muscle cell size were related to adjustments in the quantity of RNA per cell, as depicted by the RNA:DNA ratio. Since muscle growth was not correlated with the variation in muscle cell size, it was not correlated with the RNA:DNA ratio either.

Effect of Morphometric Maturity and Size on Enzyme Activities and Nucleic Acid Ratios in the Snow Crab Chionoecetes Opilio

Indicators of metabolic capacity and the potential for protein synthesis in male snow crabs, Chionoecetes opilio, were measured to estimate how these factors are affected by morphometric maturity and body size. The metabolic capacity of muscle, as depicted by cytochrome C oxidase (CCO), citrate synthase (CS), and lactate dehydrogenase (LDH) activity, was greater in adults than in adolescents, while that of the digestive gland was not affected by maturity. These differences may reflect the different locomotory habits of adults and adolescents. Indicators of the potential for protein synthesis, the RNA:DNA and protein:RNA ratios, did not differ between adult and adolescent crabs, presumably because the animals were in late intermolt stage and flesh growth was already completed. The total mass of muscle, as estimated by the flesh content of the merus, and the total capacity of muscle CCO scaled isometrically with body mass, while that of CS scaled with an exponent <1. The mass of the digestive gland, as well as the total capacity of both mitochondrial enzymes in this organ, increased more slowly than body size. These results support the hypothesis that the negative allometry generally observed for aerobic metabolism may be caused by the decreasing size of the metabolically most active tissues with an increase of body mass. In contrast with the positive allometry of the anaerobic capacity of fast-swimming fish with body mass, we noted an isometric relationship between these two variables in the rather slow-moving C. opilio. This supports the hypothesis that an enhanced anaerobic capacity is necessary for the largest individuals of a fast-moving species in order to maintain their burst swimming speed despite the increased friction generated by increased speed and body size. The effects of body size on the aerobic capacity of vertebrates have been thoroughly investigated during the last two decades (reviewed by Robinson et al., 1983; SchmidtNielsen, 1984; Goolish, 1991). Far fewer allometric studies have been concerned with invertebrates, on the one hand, or with glycolytic capacity, on the other hand. Given the differences in locomotory strategies and dependency upon aerobic and anaerobic metabolism, the relationships between body size and metabolic capacities may differ between mammals, fish, and invertebrates. Growth not only leads to increases in body size, but may also be associated with changes in maturity, morphology, and behavior. For example, immature males of many crustacean species, including crabs and shrimps, undergo molt cycles until they reach the adult stage. Whether the molt leading to morphometrical maturity is terminal or not in majid male crabs is still subject to controversy (Hartnoll, 1963; Conan and Comeau, 1986; Dawe et al., 1991; Sainte-Marie and Hazel, 1992), although the general opinion favors the terminal molt hypothesis. Adult males have larger gonads as well as a higher chela height to carapace width ratio than adolescent males, and th y display mating behaviors more frequently (Donal son an Adams, 1989; Claxton, 1992; Cassier et al., 1997). Adult males of various crab species also migrate over longer distances than immature males (SainteMarie and Hazel, 1992; Hines et al., 1995). Maturity is thus likely to affect muscle metabolic capacities and should be considered in allometric studies. Whether an adjustment in enzyme activities with maturity or body size is strictly due to locomotory habits can be inferred by comparison with enzymatic responses in nonlocomotory tissues such as the digestive gland. To our knowledge, the effect of maturity on the relationship between metabolic capacity and body mass in invertebrates has not been investigated. The equation describing the relationship between metabolic rate (Y) and body mass (M) is Y = aMb, where a is a constant and b the scaling factor. Numerous studies have demonstrated that the oxygen consumption of a given endothermic species is proportional to the body mass to the power 0.67. Interspecifically, an exponent of 0.75 is often reported for ectothermic animals, although

Physiological Responses of Rock Crab Cancer Irroratus Exposed to Waterborne Pollutants

Abstract This study investigates the impact of waterborne xenobiotics on the rock crab Cancer irroratus. Male rock crabs were caged at two polluted sites for five weeks. One site was highly polluted while the other was slightly polluted mainly by metals. A control group was caged in a raceway tank supplied with clean sea water. The activity of branchial ATPases was increased in crabs exposed to pollution, presumably to compensate for the competition of metals with electrolytes and to facilitate the transport of metals out of the cytoplasm. The rock crab was characterized as having high basal levels of glutathione in the digestive gland (∼ 3500 nmol GSH equivalents/g dry weight). Exposure to waterborne pollutants failed to trigger an increase in glutathione concentration, but over time in crabs caged at the highly polluted site it elicited a 26% increment in the relative mass of the digestive gland which is an important site for glutathione synthesis. Neither cytochrome C oxidase, nor lactate dehydrogenase activity in the merus muscle was affected by pollution. By the end of the experiment, somatic growth rate was highest in the control crabs though the crabs caged at the polluted sites also maintained a positive energy balance. Gonadal growth was delayed at the highly polluted site but the size of the gonads caught up with that of the controls by the termination of the experiment.

Physiological changes during overwintering of the Eastern oyster Crassostrea virginica (Gmelin, 1791)

This study aims at better understanding of the physiological changes that occur during the winter months in Eastern oysters (Crassostrea virginica) living at their northernmost distributional limit (48°N). It was conducted in northeastern New Brunswick, Canada (47°49′N, 64°46′W). Oysters were held in Vexar bags on the bottom of a bay and collected before (December) and during (January–April) the ice-cover period. Winter mortality was <5%. A significant decrease in the concentration of lipids stored in the digestive gland (from 42.0 to 22.5 mg/g wet tissue) indicated that the animals had access to oxygen, probably through minimal shell openings. Proteins were also used, although less heavily (decrease from 68.0 to 59.1 mg/g wet tissue), leading to an accumulation of ammonia in the intrapallial fluid (up to 0.83 μM), which is modest considering the length of time the animals lived as almost closed systems. In contrast, carbohydrates appear to play a minor role in winter energetics. Low pH values of intrapallial fluid were noted in late winter (c. 7.0) as compared with those measured at the onset of winter and in spring (c. 7.7). The animals used more energy substrates in late than in early winter, which might be partly related to the necessity to intensify detoxification mechanisms as toxic metabolites accumulate. Despite the fact that oysters do not filter-feed at temperatures <0 °C, the mass of the digestive gland increased by a factor of 1.5 during early winter, presumably as the result of nutrient transfer from other tissues. The ability of C. virginica to use energy-rich substrates and to minimize the accumulation of catabolic byproducts could partly explain the ability of the species to survive prolonged subzero conditions.