Rotifer Brachionus Research Articles

Prey Selection of Walleye Fry in an Experimental System

Abstract Five genera of invertebrates were fed to walleyes (Stizostedion vitreum vitreum) for 51 days after hatching to document the genera and sizes of invertebrates selected by the fish during their early development. The cladoceran Moina brachiata was selected for; the copepod Cyclops vernalis was initially eaten in the same proportion as available, but later selected for when M. brachiata was not available; and the cladocerans Daphnia magna and D. pulex and the rotifer Asplanchna sieboldi were selected against. The rotifer Brachionus sp. was not eaten. As the walleyes grew they selected for progressively larger cladocerans but not for progressively larger C. vernalis. Significantly more organisms were eaten by walleyes collected at 1100 hours than by those collected at 2300 hours initially, but significantly fewer after 15 days of feeding.

Spawning and Rearing Atlantic Menhaden

Abstract Two-year-old Atlantic menhaden (Brevoortia tyrannus) held in the laboratory at ambient temperatures and salinities for more than 1 year, were induced to spawn by injecting first human chorionic gonadotropin and then carp pituitary powder. Spawning took place at temperatures of 16 to 20°C in a 2,100-L indoor tank modified to recover the buoyant fertilized eggs. Larvae were reared to the juvenile stage on a diet of cultured rotifers (Brachionus plicatilus), sieved wild zooplankton (64 to 500 µm), brine shrimp (Artemia salina) nauplii, and powdered trout food.

FACTORS AFFECTING PHYTOPLANKTON DISTRIBUTION IN A DOUBLE-CELL SEWAGE LAGOON (1) (2).

The distribution of phyioplankton in a double-cell sewage lagoon at Hallam, Nebraska, was studied in relation to physical, chemical, and biological factors during the summer and fall of 1965. Sixteen species of algae were recorded in the first and more organically rich of the two physically similar ponds, with 28 species recorded in the second pond. Population sizes were always greater in the first pond due to reduced grazing during the summer and large quantities of ammonia-nitrogen during the fall. The dominant algal species in both ponds on nearly all sampling dates was Ankistrodesmus falcatus v. acicularis. Declines in this population occurred with high organic pollution and heavy grazing. Both ponds had severe reductions in algal numbers during late October due to heavy grazing by the rotifer Brachionus. The distribution of phytoplankton in the Hallam ponds is compared to that of other sewage ponds in the United States, and the general pattern which emerged is discussed.