This paper describes an industrial research approach to fish farming and illustrates where appropriate how it differs from the research strategy employed by universities and governmental bodies. To illustrate this the Unilever experience of the establishment of salmon farming from a research concept to a production and marketing operation is discussed in detail. Three separate phases in the process of establishing industrial fish farming were undertaken and were entitled ‘Biological, Technological and Commercial’. The research programme involved in each of these phases is described in detail.

The salmon farming cycle which was arrived at after the biological phase is described in detail. The technological phase involved the translation of this biological phase into a viable farming operation. This enabled a computerised cost model of the salmon farming process to be built. This identified the six or seven crucial areas which had to be improved if the enterprise was to be profitable—the commercial phase.

To demonstrate the way the nature of the research programme has changed during the period 1968–76 a graph is given showing the main discipline involved in each year and how these have changed over that period.

The hydrology of the 6000 sq km basins of the rivers Tay and Earn is examined from the special point of view as the source of freshwater for the middle and lower parts of the Tay estuary. Discharge frequency curves and average inflow figures are presented and analysed. Using these flow figures and chemical analyses obtained since the completion of the Hydro-Electric schemes estimates of the dissolved oxygen, Biological Oxygen Demand and suspended solids load transported into the estuary have been prepared.

A range of small, long-life ultrasonic fish tags is described and their use illustrated with an improved system of fixed hydrophone tracking stations. A boat-mounted hydrophone system giving bearing and range estimations for use in open-water fish tracking is described together with a portable handheld unit for simple location of tagged fish in rivers, etc. Typical results based on intensive use of these systems are given.

Life histories and production of the five common species of Tanypodinae (Pentaneura monilis, Procladius simplicistilus, P. crassinervis, P. choreus and Psilotanypus rufovittatus) in the mud at Loch Leven were measured from March 1971 to March 1972. The methods used to identify each species of larva are described. All were univoltine except Pentaneura monilis which had two generations per year, but the seasonal patterns of the life cycles were different. The average density of third and fourth instar Tanypodinae was 3100/m2 and densities of individual species exceeded 2500/m2 for short periods in Procladius crassinervis and P. choreus. Net annual dry weight production by this subfamily was 2·6 g/m2(57 kJ/m2), with individual species ranging from 1·1 g/m2 (P. crassinervis) to 0·16 g/m2 (Pentaneura monilis). These results are discussed briefly and compared with production estimates for other zoobenthos.

An understanding of the movement of a body of water can be considered a prerequisite to any other study whether it be physical or biological. This is particularly so in the case of an estuary where the water movements are complex. The movement of water in an estuary is primarily governed by the tidal and freshwater inputs, the resulting flow being modified by bed and channel configurations, salinity, and siltload variations. The tidal and freshwater inputs are themselves variables, the tidal range varying with the lunar cycle, and the freshwater input varying with the season or rainfall. The salinity variations within an estuary are interlinked with the tidal and freshwater fluctuating inputs. In addition the local and regional weather can modify the tidal response.

The distributions of the four variables—temperature, salinity, currents and dissolved oxygen—are discussed with particular reference to the Scottish west coast. In fjords, the distributions are related to the sources of change—tides, freshwater runoff, winds and, in the case of currents, to friction, which makes currents very variable over small areas. Current speed in floating cages has been found less than that outside. A model of the oxygen concentration in such a cage has been used to examine the conditions of current and fish stocking density under which the cage can be operated without reaching dangerously low oxygen concentrations.

The micro-organisms in rumen samples from Red deer, hill sheep and reindeer grazing their natural pastures in the Scottish Highlands were examined at different seasons over a number of years. The total counts of bacteria and protozoa varied with the season, and were lowest in winter when fermentative activity was also at its lowest.

As is usual in roughage-fed ruminants, viable counts were only a very small proportion of the total counts. The reindeer rumens had the highest concentrations of bacteria.

There were no consistent differences in the types of bacteria between seasons, but although there were no bacteria peculiar to any animal species the balance of predominant types varied between the species. The principal types of bacteria were similar to those found in domesticated ruminants. The numbers of protozoa in the Red deer were higher than those in the sheep, and the concentrations in reindeer were higher than those generally reported for domesticated cattle or sheep. A number of species of protozoa were found in each animal and the predominant species differed in the different animals.

A 3-year survey of wild fish in Loch Awe and the surrounding watershed has shown a restricted distribution and low prevalence of infection with infectious pancreatic necrosis virus. No signs of clinical disease were observed in infected fish. The restricted distribution close to a rainbow trout farm is consistent with the virus originating from this farm, where virus infected stocks have been found each year since 1971. The continuing low prevalence is also consistent with virus in wild fish resulting from the spread of infection from the farm. If infection is spreading between wild fish, it is slow within the time scale of the survey. The possible mechanisms of transmission of infection from the farm to wild fish are discussed.

Salinity distribution in the Tay estuary measured during the years 1969–70 is influenced by freshwater flow and tidal range. Between Pool and Flisk, tidal-depth-mean salinity is a strong function of river flow but is much less influenced by tidal range. The relationship between salinity range (difference between maximum and minimum depth-mean salinities) and tidal range can be approximated by a linear function. The observed vertical salinity distribution varies with tidal state. The net non-tidal circulation has been estimated at Pool, Broughty Ferry, Newport, Balmerino and Flisk, and found to be dependent on river flow and position.

Red deer, sheep and reindeer grazing on their normal hill ranges were examined at intervals over a period of four years. Samples from the digestive tract were taken at different seasons and processed in the field. The Red deer and reindeer were killed before samples were taken; rumen samples from the sheep were taken by stomach tube, but a number of animals were also killed at different seasons to correlate stomach tube and whole rumen samples. The animals sampled were representative of the general condition of the herds. Examinations were made for parasites and any pathological conditions. In most instances parasitic infections were slight. Apparent seasonal changes were found in the compositions of the diets. The Red deer and sheep ate principally heather and grass, the proportion of heather increasing in the winter. The reindeer ate mainly grass in the summer, with lichens and grass forming the winter diet, and these animals seemed to have a higher nutritional status in the winter than did the other two species. The weights of the animals and of their rumen contents, the concentrations of rumen ammonia and volatile fatty acid, and the rates at which different dietary components were fermented are recorded. Rumen fermentation was low in winter and the diets were generally inadequate for the animals. A lack of nitrogen seemed to be a major factor.

Some data on caecal contents are also given.

Two behavioural responses were considered. In the first, rainbow trout were trained to press a trigger to obtain food, and in the second they were conditioned to respond to a sound signal in anticipation of food delivery. The trigger pressing, demand feeding, response was quickly learned and the pattern of feeding analysed. There was a dusk peak of feeding as well as appreciable nocturnal trigger pressing. Feeds were highly aggregated into bouts, more so in the case of groups of trout than with individuals. This suggests two behavioural mechanisms, one operating within individuals and a second social effect. The preferred time between trigger presses was 8–16 min. Total daily food intake could be controlled by adjusting the reward level per trigger press so that demand feeding was not necessarily ad lib feeding. Rainbow trout would respond to a sound signal of 100 Hz played for 30 seconds prior to a food delivery by showing a feeding type of behaviour in response to the sound only. Experiments are planned to try and use this sort of response to recall fish from a relatively free-swimming environment to a central point for feeding and eventual recapture.

A lack of modern river-borne sediment and a steady supply of marine materials have led to the hypothesis that the upper Tay estuary is undergoing an erosive phase counterbalanced by a headward moving sheet of largely marine-derived sand presently occupying the upper-middle estuary. This primal division (based on sediment budget criteria) is also reflected in the bathymetry, distribution of sediment types, and sedimentary structures. The situation of two contrasting ‘phase zones’ juxtaposed within a relatively small area is ideal for an empirical and indirect analysis of the response of a wide variety of sediment types to the gross physical processes acting on them. The analysis takes the form of standard grain-size characterisations using conventional sedimentary statistics, supplemented by adaptations of C-M and QDa-Md diagrams transformed for display on distribution maps.

During periods of sustained moderate river discharge and quiescent marine conditions little external suspended sediment enters the estuarine circulation of the Tay. That material which is in suspension is largely derived from the estuary margins where tidal currents superimposed by wind-induced waves are competent to resuspend fine material from the surface of the ‘mud’ flats and erode bedded silts from the incised banks of minor channels and runnels draining them. The quantities of this sediment entering the system are largely determined by tidal state and amplitude, as well as wind velocity.

On spring tides the flats are entirely covered at high water, and dry out completely at low water. The volume of water and its areal coverage at high tide ensures that, during the ebb, water charged with high concentrations of suspended sediment is directed from the fiats into the surface and middepth waters of the main channel. This process acting along the 20 km length of the channel flanking the ‘mud’ flats, combined with the low tide ‘ponding effect’ caused by the tide flooding from the sea while the upper estuarine water is still ebbing, results in the cumulative formation of a zone of high suspended sediment concentrations (turbidity maximum). As the flood tide becomes fully established the zone is diluted and dispersed. During neap tides the same processes operate, but because a smaller area of the flats is covered at high water and uncovered at low water, and because neap tidal current speeds are lower than those for spring tides, two proportionally weaker zones are recognised.

Following periods of sustained moderate river discharge, quiet sea conditions and calm weather, suspended sediment concentrations in the Tay are negligible irrespective of tidal state or amplitude.

Administration, by dietary supplement, of ethylestrenol to rainbow trout and to salmon parr results in significant increases in growth rate; further treatment of smolts retained in fresh water reduces the growth rate. Treated parr develop into 1 + smolts in significantly lower proportion than controls, but have a higher condition factor.

Stress induces in rainbow trout long-lasting reductions in plasma thyroxine levels and increases in serum cortisol concentrations. The origin and significance of these changes is discussed.

The administration of 17β-oestradiol at 20 mg/kg of food for the first 30 days of feeding causes sex-reversal of male salmonids. Treatment with 17α-methyltestosterone at 3 mg/kg food for 90 days following first-feeding causes sex-reversal of female salmonids.

The southern entrance shores to the Tay estuary form an area of extensive inter-tidal sedimentation. Tidal currents of varying strengths characterise the area and the situation is modified by both wind and wave. The net result is a series of seven sub-environments of sedimentation. The textural characteristics of the sediment and the distribution of major and minor sedimentary structures in each subenvironment is closely linked to stability and changing physical processes. The distribution of organisms, live and dead, provides a good indication of these patterns of sediment and stability.

There is considerable interest in the cultivation of salmonids in several countries. In Norway it is now a question of rate of expansion rather than a question of whether this industry will develop or not. Interest is turning more and more towards sea farming based on Atlantic salmon rather than on rainbow trout.

One of the most important economic factors in fish fanning is the producing ability of the fish. It is essential for the future expansion of fish farming that one develops a more productive animal which is better adapted to captivity.

Progress in the development of marine flatfish farming suggests that, for two species, commercial viability is becoming a real possibility.

Dover sole can be reared in tanks on shore supplied with warmed water from the cooling of coastal power stations. Turbot can be reared likewise, or in cages floating in the sea.

The main area in which problems remain is in the controlled production of juveniles in hatcheries on shore, but recent progress has been good.

There is a good potential in the UK for marine fish farming, with probable sites available for an annual output of all species of up to around 50,000 tonnes p.a. At this level, or even at 25% of this level, the requirement for the catching of fish as farm fodder would become significant to the fishing industry.

This paper describes only those aspects of progress or outstanding problems which, in the author's opinion, are of major significance in economic terms.

The distributions of benthic macroflora and macrofauna in the Tay estuary were investigated qualitatively and quantitatively during the spring and summer months of 1973 and the results compared with the study by Alexander et al. (1935). Sublittoral areas were sampled using SCUBA diving techniques. The overall distribution of flora and fauna is determined primarily by salinity variation and substrate texture, a large part of the sublittoral area being found to have little or no infaunal component due to the instability of the coarse sediments found widely in this region. The most prominent sublittoral populations are those of Mytilus edulis found in the middle and outer estuary. The northern shore of the inner estuary is composed entirely of mud and sand flats bounded by large areas of Phragmites communis. The predominant organisms in this area are euryhaline annelid and crustacean species. The southern shore is comparatively narrow and is composed of a variety of substrates from bedrock to mud. The flora and fauna of this shore varies with substrate type but it is here that macroalgal species are found to penetrate the inner estuary. Some euryhaline organisms penetrate the estuary as far as Newburgh, the point where freshwater and estuarine populations overlap. No evidence of gross pollution was detectable in this study except in the immediate vicinity of sewage outfalls.