Techniques for the quantitative and qualitative analysis of the commensal bacterial flora of fish are reviewed. The literature concerning the commensal bacterial flora of fish indicates that teleost skin often features 10a-107 organisms per cm2 of skin, representing the following taxa, in descending numerical order, Achromobacter, Pseudomonas, Flavobacterium and Cytoghaga species also coryneform organisms. Actively feeding teleosts appear to have an alimentary canal bacterial flora similar to that of the skin and gills, often there are from 10s-108 organisms per 1.0 g, wet weight, of tissue. According to the limited data available for elasmobranchs Gram-positive bacteria are the predominant component of the bacterial flora on the skin of sharks, though the bacterial flora of North Sea skate (Raja spp.) is reported as being similar to that of teleosts. The commensal flora of fish, particularly of teleosts, is related t o their environment and is influenced by environmental changes that affect the quality of the water. Regular monitoring of the water of commercial fish ponds and aquaria for bacterial quality, temperature, dissolved oxygen concentration and pH, combined with a base-line knowledge of the water's quality, may provide an advanced indication of the presence of bacteria potentially able to produce diseased conditions, and factors that will enhance their growth.

SUMNARY. The aerobic flora of the skin of 56 Atlentic salmon from coastal, estuarine and river waters was analysed quantitatively; 50 skin and 33 gill samples were analysed qualitatively. The water at each sampling station w&s also analysed. The principal genera on the skin and gills were Moraxella. Plavobacterium, Cytophaga and Paeudmonaa; members of Acinetobacter, Bacillus, Aeromonas, Vibrio, the Entrobacteriaceae, Micrococcaceae and some coryneforms were also present. The gill flora was similar to that of the skin, which reflected that of the environment.

In the suninier of 1971 the village of Grasmere was converted from septic tank to mains drainage wilh sewage treatment at an activated sludge plant. The effluent was discharged into the River Rothay, the main inflow of a nearby small lake (Grasmere). This paper describes some of the effects on the lake. The mean areal hypohmnetic oxygen deficit increased from 274 to 434 mg O2 m'd ay"' with an accompanying marked increase in the degree of deoxygenation in the hypolimnion. Plate counts of bacteria in the surface water increased for 2 years but tliis increase was not sustained. The mean summer soluble reactive phosphorus concentration did, however, increase significantly (P = 0.05). but the same was not true of nitrate levels. This paper is particularly concerned with inorganic nitrogen transformations and analyses of (he main inflow have shown that 50-98% of the ammonia and 10-40% of the nitrate entering in this river was derived from the sewage effluent. The concentrations In the main body of the lake were usually lower, possibly due to assimilation and denitriflcation in the shallower reaches of the lake. Seasonal changes in the inorganic nitrogen species in the hypohmnion showed three distinct phases of activity, ammonificatlon, nitrification and denitrification. Nitrification accounted for approximately a quarter of the oxygen uptake in the hypolimnion. Correspondence: J. G. Jones. Kreshwaler !Mo-^^*"' ^^'^ P^P^^ ''^^^^ largely concerned with logical .\ssocialion, Windermere Laboratory, The ^^^ effect of the effluent on the deoxygcna-Ferry House, AmbiesitiL". Cumbria LA22 OLP. tion and inorganic nitrogen chemistry of the 0046-5070/78/0400-0165 $02.00

During summer stratification ammonia is released from the profundal sediments of Blelham Tarn (English Lake District). The quantity of ammonia released exceeds the consumption of nitrate in the hypolimnion. Nitrate dissimilation may be a component in the generation of ammonia, but only during early summer when nitrate is still available. The remainder of the ammonia arises largely from the deamination of proteins, amino acids and urea. Population estimates of bacteria which produced ammonia from nitrate, amino acids and urea were of the same order of magnitude. Numbers of bacteria which produced ammonia from nitrate increased with sediment depth, and urea decomposers were more numerous in the profundal (deep water) sediments. While nitrate was available in the water column, surface sediments converted nitrate almost exclusively to nitrogen gas. After depletion of the nitrate, the release of ammonia from washed sediment particles was largely microbiological, whereas there was a significant chemical component to the release from intact sediment cores. Chemical binding of ammonia by the sediments was demonstrated and this hindered calculations of inorganic nitrogen metabolism based on changes in water chemistry. Trace additions of l4C-labe1led protein, amino acids and urea to sediments showed that urea was turned over the most rapidly, but more reliable estimates of available protein in the sediments are required before decomposition rates can be treated with confidence.

During 1976 the temperature, dissolved oxygen and nitrate content of Grasmere water at 6 m and 20 m depth were determined on a seasonal basis and the isolated heterotrophic, nitrate‐reducing bacterial flora analysed both quantitatively and qualitatively under aerobic and anaerobic conditions. Throughout the year 8 population cycles of nitrate‐reducing heterotrophs were observed to occur simultaneously at both horizons which related to changes in the nitrate and dissolved oxygen content of the water. Nitrite producers were most numerous during the isothermal and early thermally stratified periods of the lake water, particularly when the nitrate content was rising. The qualitative analyses indicated seasonal variation in the bacterial populations isolated on the culture media and the dominant taxonomic groups could be related to the nitrate and dissolved oxygen content of the lake water. Pseudomonas. Moraxella/Acinetobacter, Flavobacterium/Cytophaga, Aeromonas and Enterobacteriaceae were the principal taxonomic groups in the Grasmere heterotrophic, nitrate‐reducing flora. Aeromonas with, possibly, Pseudomonas and Enterobacteriaceae are implicated in lowering the nitrate content of Grasmere water at 20 m depth when it becomes anoxic.