filamentous algae and different other algae species found at the bottom of ponds lead 

 us over to groups L, and 5 of submerged plants. 



In smaller ponds, the whole floor is often thickly carpeted mth filamentous algae, 

 especially during the month of June. And v/hile numerous aquatics give preference to this 

 algae carpet for their haunts, the felt-like toughness of it — on the other hand— does not 

 allov. even the smallest fish to enter into it. The hatch often becomes enmeshed in it, , 

 and these algae are therefore rather a nuisance than of use. 



Sessile plants 



»e have nentioned already — ^when dealing with aquatics — that sessile plants or algae, 

 i.e. algae which attach themselves to submerged plants of a higher species, together with 

 the algae "coating" of inanimate objects form the most Important nutriiaents of aquatics 

 that feed upon sessile plants . The remnants of these plants — as a valuable component of 

 detritus — fulfill still another important task in the productive chaiji . and are therefore 

 of decidedly positive value in fish culture. They are essentially THE productive factor, 

 chiefly responsible for production increase and will enormously multiply after fertili- 

 zation of the pond. 



It vfas V. Alten . who demonstrated that occurrence, form and size of cei-tain 

 diatomaceae are dependent upon the phosphoric acid contents of the water. 



The investigations of Tellers have confirmed that the pi^iductivity of sessile algae 

 of a pond is strongly influenced by the species and also by the nature of submerged plants, 

 since the possibilities for their existance vary, according to the different plants, 



Aracaig the most important of sessile filamentous algae are the Cladophera species 

 (as long as they are still young), and as most typical representatives of this kind of 

 vegetation, we have the Gomphonema (in gelatinous threads) and Cocconeis species of the 

 distomaceae group; the latter are to be found everyriiere. 



Plankton plants 



Plankton plants or "phytoplankton" performs a twofold as well as productive-biological 

 task* 



(1) Phytoplankton feeds the plankton fauna (in its fresh state as well as 

 after decay). 



(2) It creates most extensively the fertile, fine-colloidal slime at the 

 floor of a pond. 



Phytoplankton is detrimented to the metabolic cycle only in exceptional cases, for 

 instance, when through their enoxrooua development the water becomes turbid (formation of 

 "vQterbloom", "V.'asserbliite"), Really injurious to fishes is only the decaying waterbloon 

 (through its oxygen consuu^tion). 



The plankton flora is divided into two classes: Net-plankton, ie. plankton which 

 can be caught with the plankton net, and Dwarf-plankton (or nanno-plankton) which will 

 slip through a net of even finest meshes. The latter was unknown for a long time. It is 

 chiefly composed of small, autotrophic algae of a size up to 2/u (microns). It forms one 

 of the most important nutriments of plankton feeders and also of the otherwise non-plank- 

 tonic Daphnidae . 



Pauly found that phytoplankton is almost absent in the spring but increases in activity 

 in the height of summer, while in the fall, it even dominates the animal planktcxi. Fertili- 

 zer, especially the nitrogenous kind reacts strongly upon the propagation of phytoplankton 

 (especially upon Volvox) but without greatly influencing its specific composition. 



U 



