In the laboratory, Asellus aquaticus .devoured intact green leaves from growing shoots of the aquatic macrophyte Elodea canadensis. in four collections of A. aquaticus on Elodea in a lake (Windermere), c. 20% of the specimens contained in their guts fragments of green Elodea leaves; this material and pieces of oak (Quercus) were identified from characteristic leaf hairs. Some specimens had also eaten the filamentous alga Oedogonium. Fluorescence microscopy is a useful aid for screening Invertebrates that may have eaten living plant tissues.Immature A. aquaticus, with an initial mean body length of c. 3 mm, wet weight c. 1 mg, were grown through sexual maturity over a 49-day period at 15°C in a series of twenty-two experiments (six to twelve isolated specimens in each experiment) comparing growth rates on different foods, including instances where no food was given. Animals were fed on a variety of items collected from the littoral of Windermere, plus some laboratory cultures of algae and bacteria. The highest mean specific growth rate (5.8% day"') was obtained on young Elodea leaves mechanically shaken to remove epiphytes. Other diets yielding fast growth rates (3.7-5.3%day"') were young growing leaves oi Elodea with few epiphytes and older green and brown living leaves covered with a thick growth of epiphytic algae, epiphytic algae removed from Elodea., plastic imitation Elodea immersed in the lake until covered with attached algae, epilithic algae on stones, Oedogonium, and decaying oak leaves. Slower growth (l.3-2.2%day"') and poorer survival was obtained on the following: a pure culture of the bacterium Sphaerotilus natans; cultured bacteria from lakewater; the filamentous algae Gadophora and Stigeoclonium both with and without epiphytes; faecal matter from Asellus; freshly killed Asellus; lake sediment. Some growth (mean = 0.7% day"') and 50% survival for 21 days occurred in 'starved' animals kept in filtered, sterilized lakewater. Better survival and slightly faster growth (1.0-1.5%day"') occurred in 'starved' animals kept in filtered and unfiltered lakewater.Growth of A. aquaticus was also experimentally determined from birth in animals fed on young green Elodea leaves and on decaying oak leaves. On both diets, growth was curvilinear and approximately exponential from birth to sexual maturity reached at c. 2mg wet weight in 46-60 days at \5°C. In older specimens the relative growth rate gradually fell over a period of 50 days, representing a more linear phase of growth during sexual maturity.

No abstract

No abstract

Asellus aquaticus was fed for 49 days at 15^C on aquatic actinomycetes in the laboratory. Specific growth rates (wet weight) of animals initially 2.5 mm in length ranged from 0.85 to 2.33% day"' on Micromonospora and Streptomyres S2 respectively. Asellus newly released from the brood-pouch ' (1.0 mm length) had a similar growth rate (2.74% day""') on Streptomyccs S2.The growth rates of animals fed on actinomycetes were lower than those of animals feeding on macroscopic foods such as Elodea and decaying oak leaves, regardless of the initial size of the animal. However, it was concluded that actinomycetes, and by inference bacteria also, could maintain a population, albeit a slow-growing one, in a situation where macroscopic foods are largely absent.The possible significance of hyphal diameter of micro-organisms in relation to assimilation from them is discussed. In this connection actinomycetes are considered as model filamentous bacteria.

No abstract