Scavenger-driven fish carcass decomposition and phosphorus recycling: Laboratory experiments with freshwater fish and crayfish

1. Fish carcass decomposition can generate fluxes of nutrients to the water column at levels comparable to other major nutrient sources. However, relatively little is known about the biological processes modulating fish decay or the rates at which carcass-bound nutrients are made available to the biota.
2. This study focused on quantifying scavenger-mediated phosphorus (P) recycling, because the availability of this essential element can regulate the trophic state of aquatic ecosystems.
3. To explore the role of some important macroscopic aquatic scavengers in P recycling, laboratory experiments were conducted where carcasses of two fish species (common bleak Alburnus alburnus; pumpkinseed Lepomis gibbosus) were offered to two size classes of black bullhead (Ameiurus melas) and two crustacean species (spiny-cheek crayfish Faxonius limosus; narrow-clawed crayfish Astacus leptodactylus).
4. Our results show that the black bullhead and the two crayfish species are highly efficient macroscopic decomposers as the P contents of scavenged carcasses were reduced at significantly higher rates compared to those of microbially decomposed (control) carcasses.
5. Pumpkinseed carcasses proved to be more resistant to rapid decomposition, as they typically lost lower proportions of their P content than bleak carcasses during the course of the experiments.
6. Scavengers sequestered a relatively large fraction (up to 33% in black bullhead and 36% in crayfish) of total carcass P in their bodies. This suggests that the consumer species used in this study can transfer/return considerable quantities of carcass-derived nutrients directly to higher trophic levels incorporated into their own tissues, and may serve as an additional, short-term sink of these nutrients.

     

Changes of gastric mucosal biochemistry in ethanol-treated rats with and without acute surgical vagotomy

The biochemical background of ethanol-(ETOH) induced gastric mucosal damage was studied in rats with intact vagus and after acute surgical vagotomy. Observations were carried out on Sprague-Dawley (CFY) strain rats of both sexes. Gastric mucosal lesions were produced by intragastric administration of 1 ml 96% ethanol. Bilateral truncal surgical vagotomy was carried out 30 min before ETOH administration. The number and severity of gastric mucosal lesions was noted 1 h after ETOH administration. Biochemical measurements (gastric mucosal level of ATP, ADP, AMP, cAMP and lactate) were carried out from the total homogenized gastric mucosa. The adenylate pool (ATP + ADP + AMP), energy charge ((ATP + 0.5 ADP)/(ATP + ADP + AMP)) and ratio of ATP/ADP were calculated. It was found that: 1) ATP transformation into ADP increased, while ATP transformation in cAMP decreased in ethanol-treated animals with intact vagus nerve, while these transformations were quite the opposite in vagotomized animals; 2) no significant changes were found in the tissue level of lactate: and 3) the extent of biochemical changes was significantly less after surgical vagotomy. It is concluded that an intact vagus is basically necessary for the metabolic adaptation of gastric mucosa.     

Is acute surgical vagotomy an aggressor to gastric mucosa in pylorus ligated rats with and without indomethacin treatment?

Previously it was proved that intact vagal nerve is basically necessary for the development of gastric cytoprotection. The aims of this study were to receive further data about the role of vagal nerve in the development of gastric mucosal damage. The observations were carried out on Sprague-Dawley rats. Acute bilateral surgical vagotomy was done with pylorus ligation and/or indomethacin (IND) treatment (20 mg/kg, sc.) at the time of operation. The animals were sacrificed 4 h after the operation. The number, the severity (semiquantitative method), the mean size and summed surface (computer assisted quantitative method) of gastric mucosal damage, the H+ output and the mucosal PGE2 level were determined. It has been found that 1) the ASV itself (without IND or pylorus ligation) provoked gastric mucosal damage, which was more severe than in the pylorus ligated animals at 4 h; 2) IND was able to reduce the summed surface of mucosal damage after ASV; 3) ASV aggravated the gastric mucosal damage in pylorus ligated animals in spite of the decreased H+ output; 4) the PGE2 level was lower in vagotomized and vagotomized+pylorus ligated animals then in the control group, and the IND did not cause further decrease in its level after ASV. It has been concluded that the balance between aggressive and defensive factors of gastric mucosa was shifted to the aggressive side in surgically vagotomized animals.     

Use of desmids to assess the natural conservation value of a Hungarian oxbow (Malom-Tisza,NE-Hungary)

A method recently proposed by Coesel that uses the desmid flora to assess the conservation value of aquatic habitats was applied to an alkaline and hypertrophic oxbow of the Upper Tisza river (NE Hungary). According to the macrophyte community the oxbow contains two distinct habitats, both of which provide suitable conditions for the development of a rich desmid flora. High temporal and spatial differences in the algal flora were observed in periphyton and plankton samples taken in June and August 2004. The sample of Utricularia vulgaris periphyton collected in August was characterised by the most species-rich desmid flora. The conservation value of this sample was the maximum according to Coesel’s method. The latter also proved to be useful for the assessment of the conservation value of plankton net samples taken from among the macrophytes. The use of modified rarity value calculations as recently proposed by Fehér did not significantly affect the conservation value, but different enumeration methods to quantify the floristic diversity did result in different conservation values. We found that Coesel’s desmid based method is a useful tool for assessing the conservation value of the studied oxbow. Based our results the Coesel method’s applicability and usefulness depended on (i) the sampling location (open water or macrophytic region) samples were taken from open water or from macrophytic region; and (ii) species enumeration procedures (up to 400 specimens counted, or whole droplets counted). Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.