No abstract

Summary Proximate analyses and determinations of mean lipid unsaturation have been performed on monthly samples of Scomber scombrus (L) caught off the Cornish coast throughout a period of one year (December 1968‐November 1969). Maximum and minimum total‐lipid levels were recorded in December and June respectively. The highest mean lipid unsaturation levels were recorded in November and the lowest in May. An inverse linear relationship between lipid and water content with protein level remaining substantially constant was observed. Biometric data were collected on samples of June and December fish and detailed lipid analysis performed on the flesh, liver and gonad. Prominent features of the data are discussed and some comment made on the nature and functions of lipids in fish.

It has long been known that an excess of nutrients can degrade freshwater ecosystems and fish habitat. However, in some situations human activities can reduce nutrients below natural levels and negatively affect fish production. Nutrient restoration or augmentation may therefore be required for effective habitat management. In this study, we restored nutrients in the form of adult Atlantic salmon carcasses to streams in the Conon river system in northeastern Scotland. We monitored colonisation of the carcasses by aquatic macroinvertebrates, assessed incorporation of carcass-derived nutrients into aquatic food webs and compared invertebrate abundance (IA) in carcass-addition and reference sites. The isotopic signatures of periphyton, macroinvertebrates and juvenile salmon were all enriched after carcass addition, indicating incorporation of marine-derived nutrients. Atlantic salmon carcasses were rapidly and intensively colonised by a wide range of macroinvertebrates, some of which were found on carcasses nearly exclusively. Larval blackflies (Simuliidae) were the most abundant colonists in early samples. By late May and June, when carcasses were in an advanced state of decomposition (<20% of initial mass), larval chironomid (non-biting) midges, which appeared to use carcasses largely as a food source, were the dominant invertebrates. In the multiple-stream study, carcass-addition sections had significantly higher total invertebrate biomass than reference sections. Incorporation of marine-derived nutrients by all major food web components, extensive invertebrate colonisation of Atlantic salmon carcasses and increased IA suggest that nutrient restoration may be an important part of habitat management, and may partly be accomplished by ensuring the availability of marine-derived nutrients from migratory Atlantic salmon. Salmonid Fisheries: Freshwater Habitat Management Paul Kemp

Sulphate a t concentrations of less than 30 mg 1-l of sulphur is determined on the AutoAnalyzer by reduction to hydrogen sulphide, distillation of the latter and its subsequent colorimetric determination.The method has been found to be suitable for aqueous solutions of sulphate, digests of leaf samples and animal faeces, and extracts of soils; it is applicable to a wide range of agricultural, biological and industrial materials.

Gas chromatography on an alkaline Dowfax 9N9 column has been found to be suitable for the qualitative and quantitative analysis of alkylamines in dilute aqueous solution. The method has been applied to the analysis of trimethylamine (TMA) and dimethylamine (DMA) in fish and has been used to throw further light on uncertainties concerning the use of the "picrate" procedure for TMA determination. IntroductionAs a first step in dealing systematically with the analysis of flavour extracts from fish the extracts can be separated into neutral, basic and acidic fractions; such a preliminary separation will facilitate the execution and interpretation of the subsequent detailed analysis. For the analysis of volatile compounds within one of these groups their low concentration and the probable complexity of the mixtures indicate gas chromatography (g.c.) as the method of choice. In the case of the basic and acidic fractions, however, the polar nature of the solutes together with the desirability of analysing them in dilute aqueous solution make gas-liquid chromatography (g.1.c.) analysis difficult. Numerous workers have reported severe peak "tailing" and the appearance of "ghost" or "memory" peaks when attempting to chromatograph such solutions.In accordance with the general strategy outlined above it was necessary to find a g.1.c. column system which was capable of separating and quantifying mixtures of aliphatic amines in dilute aqueous solution; these compounds can form an important part of the basic fraction of flavour extracts from fish. A literature search indicated that a number of column packing materials were useful, to varying degrees, for this purpose and were experimented with.It was found that the Dowfax 9N9-NaOH column reported by O'Donnell and Mann' met our requirements to a high degree. The original system has been modified slightly by us and under these conditions direct quantitative analysis of amine hydrochlorides is possible, the free bases being liberated in situ on the column. This quantitative procedure has been exploited for the analysis of trimethylamine (TMA) and dimethylamine (DMA) in fish and results compared with those obtained by purely chemical techniques.