Rodlet Cells in the Head and Trunk Kidney of the Domestic Carp (Cyprinus carpio): Enigmatic Gland Cells or Coccidian Parasites?

 Rodlet cells have been found in the head and trunk kidneys of the common carp (Cyprinus carpio L.). From an experimental sample of 50 carps of various ages, we detected these cells in only seven fishes, contradicting the hypothesis that they constitute a normal component of the fish epithelia. The rodlet cells have a typical structure: 12–16 μm in diameter, with a basal nucleus various in form, and an encasing layer of fibrillar structure. The cells contain rodlets, composed of elongated, opaque sacs featuring dark rods in the center, which strongly elongate in ripening cells. Remarkable pseudopodia-like extensions from the apical parts of the rodlet cells penetrate into the delicate blood vessels and sinusoids of the organs. The encasing layer at the cell apex then opens to release the rodlets into the bloodstream. No junctions were found between the rodlet cells and neighboring cells. It is suggested that these cells comprise some kind of "symbiosis" between leukocyte, possible granulocyte cells, and the parasitic rodlets. The cells serve the rodlets as an incubation chamber, as well as a means of transportation into the bloodstream after ripening. Received: 29 December 1998 / Accepted in revised form: 3 March 1999     

Hatching failure in common terns (Sterna hirundo) in relation to environmental chemicals

The hatching success of two Common Tern colonies, a highly contaminated one at the Elbe estuary (Hullen) and a less contaminated one at the Jade (Augustgroden, southern North Sea coast, Germany), was similar in 1988; 69% at Hullen and 73% at Augustgroden. Most egg loss was due to predators. The number of eggs failing to hatch from unknown causes was 6.3% higher at Hullen than at Augustgroden. Egg-shell thickness and strength were not correlated with the chemicals' concentrations. At Hullen unhatched eggs were compared with randomly collected fresh eggs; the former containing a significantly higher amount (20%) of PCBs (134 microg) than the eggs collected at random (112 microg). Seven out of 45 PCB-congeners were found in significantly higher amounts in the failed eggs, among them the toxic congener PCB 138. The two samples showed no difference in mercury concentration, which was 6.2 mg kg(-1), nor difference in shell strength. Eggs of Common Terns breeding at the Elbe estuary had concentrations of some contaminants reaching levels endangering breeding success.