Aquatic environment and differentiation of vibrissae: comparison of sinus hair systems of ringed seal, otter and pole cat.

This study investigated the structure and innervation of the vibrissal systems of the pole cat (Mustela putorius), European otter (Lutra lutra) and ringed seal (Phoca hispida) in order to find adaptations to aquatic environment. The number of myelinated nerve fibers of deep vibrissal nerve (DVN) of the entire vibrissal system was considerably greater in the ringed seal (10x, aquatic mammal) and in the otter (4x, semi-aquatic mustelid) compared to the pole cat which is a terrestrial mustelid. Similarly, the number of neural end organs in the vibrissae of ringed seals was about ten times more numerous than in pole cats. The number of the vibrissae in the heads of otters was almost two times more than in pole cats, and all vibrissa groups had similar structures and innervation. The asymmetrically developed carpal vibrissae of otters were, however, more poorly innervated than the vibrissae of the head and had only smooth musculature. In the ringed seal the orientation of lanceolate end organs differed in different vibrissae, indicating the specialization of these vibrissae for different kinds of sensory functions. Ringed seal vibrissae contain structures which obviously are developed as adaptations to an aquatic environment. These include the modified mitochondria of Merkel cells, with Merkel cell-neurite complexes very often associated ciliated cells, liquid filled vesicles or intercellular spaces below the basal cell layer of the outer root sheath at the ring sinus level, a long upper cavernous sinus and a flattened beaded structure of the vibrissa hairs. As the vibrissae of aquatic mammals have analogous functions to the lateral line organ of fishes, we suggest using the term 'vibrissal sense' for the vibrissa system of aquatic mammals.

Bisphenol A accumulation in the freshwater clam Pisidium amnicum at low temperatures.

Toxicokinetics of (14)C-labeled bisphenol A (BPA) was studied in the small freshwater clam Pisidium amnicum at four ecologically relevant low temperatures (2, 6, 8, and 12 degrees C). The uptake clearance (k(u)) of BPA increased from 1.49 to 6.55 ml x g(-1) x h(-1) as temperature increased from 2 to 8 degrees C but decreased slightly again at the highest temperature. The depuration of BPA was very slow and statistically insignificant at 2 degrees C, but the depuration rate ( k(d)) increased linearly as temperature increased from 2 to 12 degrees C. The longest half-life of BPA in clam tissues, 221 h, was found at the lowest temperature, and the highest bioconcentration factor of 144 was measured at 8 degrees C. Data show that P. amnicum accumulates BPA so that the bioconcentration factor rises over 100 at each temperature tested. Further, the data demonstrate the importance of temperature on the processes that control both the uptake and elimination of this compound.

Temperature- and parasite-induced changes in toxicity and lethal body burdens of pentachlorophenol in the freshwater clam Pisidium amnicum.

Seasonal variation in abiotic and biotic environments may modify the toxicity of organic chemicals for aquatic organisms. In present study, survival of the freshwater clam Pisidium amnicum was studied in laboratory exposures to pentachlorophenol (PCP) in April (at 5 degress C) and July (at 19 degress C). Behavioral responses, mean survival times (MSTs), and the lethal body burdens (LBBs) of PCP for uninfected clams and for clams infected by digenean trematodes were determined separately in two PCP concentrations, 100 and 300 microgram/L. Analysis of data revealed reduced behavioral activity of the clams in the PCP exposure compared to that in the control. The time needed for toxic responses was greatly affected by temperature; MSTs were 5 to 15 times longer in winter than at summer temperatures. Unexpectedly, the infected clams in summer were more tolerant to PCP than the uninfected clams. Despite the differences in survival times, the LBBs between the seasons were constant. However, in summer, the infected clams had significantly higher LBBs than the uninfected clams. The differences in survival and LBBs between the infected and uninfected clams are suggested to be caused by the high lipid contents found in parasites, which may change the internal distribution of PCP.

Toxicokinetics of 2,4,5-trichlorophenol and benzo(a)pyrene in the clam Pisidium amnicum: effects of seasonal temperatures and trematode parasites.

Several biotic and abiotic stress factors may affect aquatic organisms simultaneously. However, not much is known about the effects of, e.g., low temperatures and parasite infections on the toxicokinetics of organic hydrophobic chemicals. Here we studied the accumulation and depuration of [(14)C]2,4,5-trichlorophenol (TCP) and [(3)H]benzo(a)pyrene (BaP) in the sediment-dwelling freshwater clam Pisidium amnicum. Experiments were made in October (+15 degrees C), April (+4 degrees C), and July (+15 degrees C) both with uninfected clams and clams infected with Bunodera luciopercae (Trematoda). The accumulation rate for both chemicals was slower at 4 degrees C than at 15 degrees C. The depuration of TCP was biphasic, and the slowest depuration occurred at 4 degrees C. For BaP, the depuration was very slow and monophasic at all temperatures. The highest BCFs for both chemicals were found in July at 15 degrees C. Surprisingly, the BCFs for TCP were higher in April at 4 degrees C than in October at 15 degrees C. For BaP, no steady-state was reached in April. Differences in chemical toxicokinetics between the infected and uninfected clams were only minor. However, for both chemicals a trend of slightly lower BCFs in the infected clams was found. In conclusion, low temperatures modify the toxicokinetics of organic chemicals in P. amnicum and the effects depend on hydrophobicity of the chemical. The effects of parasites on toxicokinetics seem to be small.

Digenean parasites of the bivalve mollusc Pisidium amnicum in a small river in eastern Finland.

The host-parasite relationship between digeneans and a semelparous population of the mollusc. Pisidium amnicum Müller in a small river in eastern Finland was studied during 1992/1993. The parasite prevalence of the population was high. The total prevalence was 45.6% in 1992 (n = 790) and 47.5% in 1993 (n = 160). The dominant digenean, Bunodera luciopercae (34.2% in 1992, 35.0% in 1993), had highest prevalences in July/August and in winter. Two other species, Palaeorchis crassus (7.8% in 1992, 7.5% in 1993) and Phyllodistomum elongatum (4.7% and 5.0%), were rare during the winter. The prevalence of B. luciopercae increased as clams aged, while the other species were most common in middle-sized clams. Apparently B. luciopercae rediae dominate over P. elongatum, which has only sporocyst stages, while P. crassus, which has large rediae, is more deleterious to the clam and induces host mortality. Double infections were significantly less common (1.2%) than might be expected by chance. All parasites castrated their hosts; no clam containing both parasites and embryos was found. Semelparity of the population is apparently caused by parasitic castration.

Effects of hypoxia on valve-closure time and bioaccumulation of 2,4,5-trichlorophenol by the freshwater clam Sphaerium corneum [L].

The effects of hypoxia and 2,4,5-trichlorophenol (TCP) on the behavior of the freshwater clam Sphaerium corneum (L.) and the accumulation and elimination rates of 2,4,5-trichlorophenol were studied in the laboratory at 20 degrees C. After an initial high activity period, the shell valves were held closed for significantly longer periods in hypoxia than in normoxia. At the end of the 36-hr exposure period, the number of individuals with closed valves increased under normoxic conditions as well. The accumulation of TCP into clam tissues in normoxia was rapid and an uptake rate constant of 27.97 (+/-6.64) ml/g/hr was measured. An apparent steady state was achieved within 12 to 24 hr and the bioconcentration factors varied between 115 and 139. The depuration rate constant (kd) based on the accumulation data was 0.2717 (+/-0.07) hr-1. However, the much lower kd of 0.0137 (+/-0.0019) hr-1 measured over the depuration period from 24 to 120 hr suggests biphasic depuration kinetics. After a 6-hr exposure to TCP in both hypoxia and normoxia, the highest body burdens were found in clams exposed under normoxic conditions. A significant correlation was found between body burden and length of time the valves were open during the exposure. Results suggest that in short-term experiments, S. corneum can reduce the bioaccumulation of TCP by closing their shell valves.

Normoxic and anoxic heat output of the freshwater bivalves Pisidium and Sphaerium : I. Rhythms of spontaneous quiescence and behaviour.

In fasting Pisidium amnicum and Sphaerium corneum, regular periods of behavioural and metabolic quiescence were shown to occur in the normoxic, constant environment of the flow-through chamber of a heat-flow microcalorimeter. The metabolic rate was suppressed to 7.5% of normal at 10° C and to 8.5-9.7% at 20° C for periods exceeding the period of active metabolism by a factor of 3.5 at 10° C and 8.3 at 20° C. The rate of heat output during normoxic quiescence was equal to that during environmental anoxia, suggesting spontaneous achievement of body anoxia by complete shell closure. The mass-specific integrated heat output during closure periods was independent of size. Parallel observations on clam behaviour suggested that metabolic quiescence coincided with shell closure, and bursts of heat flow with active ventilation. Shell closure was accompanied by pronounced bradycardia, down to 20% of the active rate. In a constant environment, the rhythmic quiescence is regulated by shell closure which is probably triggered by lack of food. Regular quiescence of fasting bivalves may conserve energy reserves considerably, the amount depending on the possible excretion rate of the end products, and the post-quiescence recovery costs, which were not measured. Heat output during the active period was close to the average metabolic rate found earlier for Sphaeriidae. However, all the values determined so far are likely to be underestimates of the natural metabolism because the effects of digestion and growth are not included.

Anaerobic wintering of crucian carp (Carassius carassius L.)--II. Metabolic products.

In long-term experimental anoxia (up to 140 days) crucian carp excreted ethanol and acetic acid. The maximum concentration of ethanol found in fish blood was ca 0.1%. The excretion rate of ethanol at temperatures from -0.5 to +5 degrees C was ca 25 micrograms/g fish wet wt/hr, but increased rapidly with increasing temperature. At 2 and 5 degrees C the ethanol excretion rate was independent of fish size, but at 12 and 18 degrees C a higher rate was observed in smaller fish. The decrease of water pH below 5 in the experimental vial during long anoxia was assumed to be due to excretion of acid compounds by the fish.

Carbon dioxide output in the respiration of three Pisidium species (Bivalvia, Sphaeriidae).

The carbon dioxide output in respiration of Pisidium casertanum, P. henslowanum and P. conventus was studied in the laboratory. A closedbottle method was used, and the amount of dissolved inorganic carbon was measured with an infrared gas analyser. The mean value of the constant b in equation R=aW b, where R is the respiration rate and W the ash-free dry weight of the animal, was ca. 0.75 in both the eurytherm P. casertanum and the cold-stenotherm P. conventus at five temperatures, but the temperature dependence of b was opposite in these species. The temperature dependence of metabolism increased with increasing size in P. casertanum and P. henslowanum but decreased in P. conventus. A 'reversed acclimatization pattern' was found, where the metabolism rate and its temperature dependence was lower in the cold-adapted stenotherm species.