J.H. Kluytmans

Seasonal variations in biochemical composition of mytilus edulis with reference to energy metabolism and gametogenesis

Abstract 1. 1. Seasonal changes in biochemical composition in relation to energy metabolism and to gametogenesis were studied in Mytilus edulis for nearly one and a half year. 2. 2. During the whole experimental period animals were selected from samples of the same musselbed in the Dutch Wadden Sea at intervals of about three weeks. 3. 3. The biochemical composition of total tissues and different organs was analyzed. In growing mussels a gradual increase of protein, glycogen and lipid contents was observed from spring to autumn. From November to next April the protein and glycogen content declined, whereas the lipid content remained rather constant until spawning. The observed changes are discussed in relation to environmental parameters as temperature, salinity and nutrient levels, as well as to energy production and gametogenesis. 4. 4. Hardly no seasonal variations were found in the total free amino acid concentrations from both the total tissues and different organs. However, the individual amino acids showed clear seasonal changes in all tissues investigated. The greatest fluctuations were found for taurine and glycine. These amino acids showed an inverse relation to each other. 5. 5. Seasonal changes in the accumulation of end products of anaerobic metabolism and in the composition of the free amino acid pool were found in groups of mussels exposed to air for 48 h. The observed variations in propionate and alanine accumulation as well as other compiunds involved in anaerobic metabolism are discussed in relation to temperature and salinity.

Tissue composition and reproduction of mytilus edulis in relation to food availability

Abstract Variations in the tissue composition of the sea mussel Mytilus edulis L. from culture beds in the western Dutch Wadden Sea were studied during the first half of 1978. Protein, glycogen and lipids were determined in the mantle tissue and non-mantle tissues of Mytilus . The content was found to fluctuate with the repeated release of gametes during the spawning season. Gamete emissions were observed in March and April. In May, however, low levels of nutrient reserves in the tissues were prolonged, in spite of high algae concentrations in the sea water. These high concentrations were caused by an algal bloom of Phaeocystis pouchetii . The glutinous colonies probably prevented food intake and digestion by Mytilus , and resulted in a delay in gonad recovery. Ultimately, at the beginning of June, glycogen content increased rapidly again, concomitant with a rapid rise in the sea water temperature.

Anaerobic production of volatile fatty acids in the sea musselMytilus edulis L.

Summary1.Mytilus edulis L. accumulates VFA during anaerobiosis.2.Propionic acid is formed in equal amounts as succinate (26 μmol g−1 dry weight), together with small amounts of acetate (2 μmol g−1 dry weight) during 72 h under N2.3.Under aerobic conditions acetate is the only free VFA present in appreciable amounts (12 μmol g−1 dry weight).4.About 8 μmol g−1 dry weight of esterified VFA are present in total lipid extracts.5.No significant increase in esterification to glycerol-3-phosphate takes place during 72h of anoxia.

Glycogen degradation and end products of anaerobic metabolism in the fresh water bivalveAnodonta cygnea

Summary1.Glycogen levels and the production of metabolic end products by the fresh water bivalveAnodonta cygena were determined under aerobic and anaerobic conditions.2.The glycogen content accounts for 5–14% of the dry weight. After 30 hours of aerobic or anaerobic incubation no significant glycogen breakdown could be observed.3.L-lactate and alanine seem to be only initial end products, whereas succinate increases continuously during the first 15 hours.4.Anodonta cygnea also accumulates volatile fatty acids during anaerobiosis. After 30 hours of anoxia 30.1 and 46.0 μmol g−1 dry weight of acetate and propionate respectively are formed. In fact the volatile fatty acids account together for about 75% of the total accumulated end products.

The Influence of Seasonal Changes on Energy Metabolism in Mytilus edulis (L.). I. Growth Rate and Biochemical Composition in relation to Environmental Parameters and Spawning

ABSTRACT The growth rate and biochemical composition of Mytilus edulis (L.) were studied during an annual cycle. Mussels were selected on shell length every three weeks from the same population of a sublittoral musselbed in the Dutch Wadden Sea. The increases in shell length, wet weight and dry weight of mantle and total tissues are given. Seasonal changes in biochemical composition, i.e. variations in glycogen, protein and total lipids are discussed in relation to environmental factors and the reproductive cycle.

Fatty acid synthesis in relation to gametogenesis in the mussel Mytilus edulis L.

1. 1. Seasonal fluctuations of the lipid level in Mytilus edulis are small compared to the changes in proteins and glycogen. 2. 2. In the later stages of gametogenesis (March–May) there is an increase of neutral lipids in the mantle, while there is no concomitant decrease elsewhere in the animal. 3. 3. Fatty acid analysis shows an increase of probably de novo synthesized fatty acids. 4. 4. Activity of acetyl-CoA carboxylase and fatty acid synthetase are virtually absent in mantle, muscle and digestive gland. 5. 5. These enzyme activities increase strongly in female mantle tissue in the period preceding the spawning, but only slightly in male mantles.

Production and excretion of volatile fatty acids in the sea musselMytilus edulis L.

Summary1.The accumulation of volatile fatty acids during anaerobic incubation ofMytilus edulis was studied in relation to incubation time and temperature.2.Propionate formation started after an initial lag period, the length of which was inversely related to the incubation temperature.3.Acetate accumulation took place at a lower rate and without a lag time.4.Under appropriate conditions excretion of volatile fatty acids was observed.5.Of all tissues studied the highest accumulation of acetate and especially propionate was found in the gills. The relation of these organs to volatile fatty acid excretion is discussed.

Time dependent changes and tissue specificities in the accumulation of anaerobic fermentation products in the sea mussel Mytilus edulis L.

Abstract 1. 1. Fermentation products accumulating in Mytilus edulis L. were determined after different periods of experimental anaerobiosis. 2. 2. Succinate levels increased continuously with time of anoxia in the animal as a whole as well as in most tissues studied separately. 3. 3. Propionate increased linearly after an initial lag period of 17 hr with very low levels. 4. 4. Alanine showed an initial increase with a maximum after 4 hr of anoxia. Possible changes during prolonged anaerobic incubation periods were obscured by widely varying concentrations of this component in the groups of animals studied. Very high alanine levels were observed in the mantle tissues. 5. 5. Acetate increased slowly with time, although this tendency is not always clear after short incubation periods due to the rather high initial level of this component. 6. 6. When groups of animals were not exposed to a N2 atmosphere but instead incubated in O2-free seawater, lowered tissue levels of succinate and propionate were observed. 7. 7. The composition of the free amino acid pool remained virtually unchanged during anaerobiosis except for small increases in glutamate and eventually alanine. 8. 8. Considerable variations were observed in initial level and accumulation of fermentation products in different tissues.

Organ specific changes in energy metabolism due to anaerobiosis in the sea mussel Mytilus edulis (L).

Abstract 1. 1. Anaerobic energy metabolism was investigated in different organs of Mytilus edulis and the whole animal. 2. 2. Succinate accumulates to high levels in most organs but remains low in the hemolymph. 3. 3. After 16 hours propionate accumulation is observed in all organs. Experimental evidence is not sufficient yet to point out organs that produce more propionate than others. 4. 4. Acetate is a minor end product. 5. 5. Acetate and propionate are found in the hemolymph in amounts equal to those in the organs. 6. 6. Animals incubated in oxygen-free seawater accumulate more end products than animals exposed to air, in the form of volatile fatty acids that are excreted into the incubation water. 7. 7. Alanine and glutamine increase in the posterior adductor muscle. Aspartate decreases in the total animal, posterior adductor muscle and gills, while in the hemolymph decrease in alanine, asparagine, serine, threonine and proline are observed.

The influence of seasonal changes on energy metabolism in Mytilus edulise (L.).—III. Anaerobic energy metabolism

Abstract 1. 1. Seasonal changes in the accumulation of end products after 48 hr of exposure to air and in the composition of the free amino acid pool were studied in Mytilus edulis. 2. 2. The accumulation levels of succinate and acetate showed only weak seasonal changes. 3. 3. Conversion of succinate to propionate was high in summer and virtually zero in winter 4. 4. Alanine and most other free amino acids were present in relatively high concentrations in summer and early autumn and reached minimal values in winter and early spring. 5. 5. Exceptions were glutamate, aspartate and taurine, which showed hardly an season related changes and glycine, which changed inversely to the majority of the free amino acids. 6. 6. The anaerobic formation of alanine was inversely proportional to the endogenous concentration. 7. 7. The only other free amino acids affected by anaerobiosis were glutamate and aspartate, which respectively increased and decreased under these conditions.