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Introduction THE River Stour, like many East Anglian rivers, is extensively managed for purposes of water supplies. Its flow to the sea is contained by a barrage scheme, water is abstracted from it along its length, and it receives water from the R. Ouse as part of the Ouse-Essex water transfer scheme. This management is bound to have some effects upon the fish of the river, and so in August, 1974, an intensive survey of the fish was carried out on the reach between Fiatford Mill and Cattawade. The survey was supported by the Suffolk Naturalists' Society, and was undertaken by the authors with the assistance of the Essex River Division of the Anglian Water Authority. Its particular aim was to investigate the distribution, growth, feeding and parasites of the fish present, with a view to providing base line data against which to measure any further changes in the fish due to water management, and to providing information on the fisheries for anglers and for courses held at Fiatford Mill Field Centre. The results of this survey are presented in the present paper. Sites and Methods Fishing was only carried out on the R. Stour between Fiatford Mill and Cattawade on the Northern branch of the river, and on the lowest reaches of the Southern branch (O.S. Map inches to 1 mile No. C6503). Fishing Operations were carried out by the bailiffs of the Anglian Water Authority using an A.C. electric fishing machine mounted on a boat, and supplemented by seine netting where necessary. The river was fished in stretches as follows: the Mill Pool below Fiatford Mill, Judas Gap, Judas Gap to Cattawade, Cattawade Pool, and the Stretch on the Southern branch referred to as Dedham Old Cut. All the fish caught in each Stretch were identified and their fork length recorded. The majority were then returned to the river, but samples of each species were retained for further examination. These were aged, using scales or opercula as appropriate, their stomach Contents were recorded and they were examined for the presence of parasites. All parasites found were identified, and their numbers and positions recorded. Distribution of fish The numbers of fish and the sites at which they were caught are shown in T A B L E 1 . In general the species found are those that


Suffolk Natural History, Vol. 17, Part I

would be expected from such a Stretch of a lowland river. The dominant group are the cyprinids, with roach Rutilus rutilus, dace Leuciscus leuciscus and gudgeon Gobio gobio as the most abundant species. In this river perch Perca fluviatilis appear to be rare, and the dominant percid is ruffe Gymnocephalus cernua. Both carp Cyprinus carpio and crucian carp Carassius carassius are very uncommon, and each was found on a single occasion only as a Single specimen. Notably no salmonid fish were found, nor any other migratory fish such as flounders Platichthys flesus, and the barrier at Cattawade appears to be hindering the entry of migratory salmonids such as sea trout Salmo trutta into the river. The distribution of fish within the river is clearly not uniform. The greatest number of species are found at Judas Gap, and the greatest numbers of individuals at Judas Gap and then at Cattawade. This distribution may, however, partly reflect the comparative fishing effort and different methods employed. At the time and conditions of the survey, the Dedham Cut showed the lowest number of species and individuals, but whilst this may in fact be a true reflection of the Situation, the overall numbers caught there were unexpectedly and inexplicably low. Individual species also exhibit preferences for particular stretches of the river. Roach are more abundant in the lowest Stretch of the river, between Judas Gap and Cattawade, whereas gudgeon appear to prefer the pool at Cattawade. Bream Abramis brama occur in other stretches, but are commonest in the region of Judas Gap, whereas ruffe are almost confined to this locality. Chub, Leuciscus cephalus are atypical in that they are scarce in the Northern branch of the river and are more common in the Dedham Old Cut. Eels Anguilta anguilla also appear to be commoner in the lower part of the river, whereas pike Esox lucius seem to prefer the Mill Pool and the Stretch between Judas Gap and Cattawade where there is an extensive development of marginal Vegetation. Dace by contrast occur throughout the river, but appear to prefer the upper stretches and in particular the Mill Pool, where they dominate the fish fauna. Size of fish caught The mean lengths and size ranges of the fish caught are shown in T A B L E 2. Carp, Crucian carp and perch are omitted in view of the small numbers found. The lengths of the carp and Crucian carp caught were, respectively, 19 cm. and 22.2 cm. The lengths of the perch were 6-5, 14-6 and 14-6 cm. Over the river as a whole, a wide ränge of sizes of all species of fish was encountered, and large individuals of most species, and in particular bream, pike and eels, were found. Apart from the very young fish therefore, most size classes are represented in the samples, and it



can be concluded that the river holds a stock of fish suitable both for anglers desiring large catches and for those desiring fewer but larger specimens. Growth rates of fish The growth rates of the prineipal angling species in the R. Stour are shown in T A B L E 3. Initially growth rates were calculated for each species for each Stretch of the river, but with one exception, these did not differ significantly and so data for all stretches have been combined. The one exception was the roach, the growth of which was significantly lower in the Dedham cut than in the main R. Stour. The growth rates in T A B L E 3 are also compared with growth rates in selected localities elsewhere in Britain, and wherever possible with other localities in East Anglia. It is clear that all species make very good growth in the River Stour, and the length of the majority of species at the maximum age they attain is greater than that in any of the localities with which they are compared. Only with dace is the growth rate in the River Stour exceeded elsewhere, in the River Cam. The size of the young fish in the River Stour in many cases is less than that of fish of the same age in other localities, but when they are two or three years old, the growth rate appears to increase until it overtakes those elsewhere. The River Stour therefore appears to be a particularly favourable site for coarse fish growth, and even the Dedham Old Cut, although less favourable for roach, produces chub with a better growth rate than in any other locality in the British Isles. Diet of fish The frequency of occurrence of food items in the fish caught is shown in T A B L E 4. These data must be interpreted with caution, since not all the fish were examined immediately, which probably accounts for the large proportion of empty stomachs, and this method of analysis is not quantitative and tends to be biased towards small animals, animals with hard parts and material that takes a long time to digest. The results must therefore be regarded only as an indication of the organisms on which the fish feed. The results do nevertheless appear to indicate preferences by particular species. Roach were feeding exclusively upon Vegetation, particularly filamentous algae. Chub also fed extensively upon algae, but in addition took insects and fish, including stickleback, Gasterosteus aculeatus. Bream were clearly feeding on the benthos principally, with a fairly varied diet, whereas ruffe concentrated upon benthic insects and especially upon chironomid larvae. Both eels and pike were piscivorous; the


Suffolk Natural History, Vol. 17, Part 1

latter species exclusively so. Amongst the fish identified in pike stomachs were dace and eels. Only the larger eels were piscivorous, gudgeon being identified positively in one stomach, and the smaller ones fed upon chironomid larvae. By contrast, gudgeon had a very wide and varied diet, and fed extensively upon the smaller crustaceans. It is interesting that maggots, from ground baiting by anglers, appeared in the diet of three species, and were a substantial item in the diet of bream. These results agree fairly well with those of Hartley (1947), who studied the food of coarse fish in East Anglia. He also found that roach fed predominantly upon vegetable matter, and that small crustaceans were a major item in the diet of bream. The results also agree in general with those of other authors. Roach are usually considered to be principally Vegetation feeders (CraggHine and Jones, 1969), pike to be piscivorous (Banks, 1970), bream to be benthic and crustacean feeders, raffe to prefer chironomids and chub and dace to be omnivorous (Hartley, 1947: Varley, 1967).

The parasites of fish A list of the parasites found, together with their hosts, site and incidence and intensity of infection is given in T A B L E 5. The list is on the whole very much as would be expected from such a fauna in such a river. There are no conspicuous absences from the list, with the exception possibly of cestodes of the genus Proteocephalus. These tapeworms are, however, nearly always seasonal in occurrence (Kennedy, 1970), and their absence from the River Stour may only be a reflection of the fact that samples were taken in mid-summer when proteocephalids are seldom present in fish. The parasites exhibit the specificity that would be expected of them. Some, such as Tetraonchus monenteron and Triaenophorus nodulosus are specific to a single species of fish, in this case pike. Others, such as Caryophyllaeus laticeps are found in more than one fish host, but clearly show a preference for one species, in this case bream. Others again, such as Diplostomum spathaceum, occur at a high incidence in virtually every species of fish, but occur only at high intensities in two or three species. In all cases, this specificity could be predicted on the basis of what is known of the parasite's biology and its occurrence in other localities. The most interesting species present is Ergasilus sieboldi. This crustacean is pathogenic, and at present has a very restricted distribution in Britain (Kennedy, 1974). It is however known to occur in the nearby River Blackwater, and it can be presumed



that it has been introduced into the Stour, probably with fish introduced for stocking or for angler's live bait. It is known to have been introduced into other localities in a similar way (Kennedy, in press a). The parasite fauna of the River Stour as a whole is interesting in that it is dominated by larval digeneans and by the crustacean Argulus foliaceus, the fish louse. This latter species is found in water bodies of all types, but prefers still water and slow flows. The dominance of a parasite fauna by larval digeneans indicates that the water body is frequented extensively by birds and that there is a high degree of predation of the fish by them, since these larvae reach maturity in birds and require their fish host to be eaten by them in order to complete their life cycle. The dominance by larval digeneans is also characteristic of eutrophic lacustrine conditions (Kennedy, in press b), and in the River Stour would seem to be associated with the slow flows and lacustrine conditions prevailing as a result of the management of the flow regime and water levels for water abstraction purposes. A similar parasite fauna is found in many of the fenland rivers and drains where water conditions approach those of a lake. Conclusions and Discussion This survey indicates that the River Stour is a very favourable river for coarse fish. It supports a wide variety of species, and these attain a large size and exhibit very favourable growth rates. This would seem to indicate that in the river as a whole the fish are not overcrowded and are not competing with each other, since this would be manifested by stunting and poor growth rates. The slower growth rate of the younger fish when compared with that in other localities could be held to be due to overcrowding amongst the smaller size classes in recent years, but a comparison of the growth rates at present with growth rates in previous years as computed from back calculations based on scale reading (TABLE 6) indicates that the growth rate of the younger fish has not declined during this period. More likely explanations for this Situation are that conditions in the river are less favourable for small fish than for large ones, and that many of the roach and bream found in the present survey are fish that were introduced into the river in 1972 from a crowded pond where their growth rate over the first few years of life was poor, but this improved with the more favourable conditions in the Stour. Both the feeding behaviour and parasite fauna of the fish are normal and to be expected. Only two of the parasites, namely A. foliaceus and E. sieboldi, are pathogenic, and only the latter species gives much cause for concern. Argulus foliaceus is a


Suffolk Natural History, Vol. 17, Part 1

common and widespread freshwater fish parasite, and only causes serious damage to young fish and under very overcrowded conditions. Ergasilus sieboldi can cause heavy mortalities, and lts introduction into the River Stour must be regarded as unfortunate as there is no practical way of eliminating it. This survey, by its nature, provides little evidence of the effects of recent changes in water regime in the River Stour upon the fish fauna. T h e absence of sea trout which, according to local anglers were sometimes found in the river, can be attributed directly to the barrage scheme at Cattawade. The good growth rates of the fish and the complete lack of evidence of any recent deterioration in them suggest that the changes have had no deleterious effects upon the fish. The parasites are also as would be predicted, and there is no indication that any of them have been introduced into the river as a result of the water transfers from the River Ouse. One of the main uses of this survey will be to provide a background against which the effects of these or any further changes can be assessed in the future. The authors wish to thank the Suffolk Naturalists' Society for financing the survey, Mr. F. J. Bingley and the staff of Fiatford Mill Field Centre for accommodating them and for putting up with an invasion of fish, and Mr. J. McManus and the bailiffs of the Essex River Division of the Anglian Water Authority for all their help and assistance in and out of the field.


Numbers of fish caught in the River Stour survey Fish

s te ' Judas Gap Cattawade Dedham to Cattawade

Mill Pool

" ' Judas Gap


Roach Dace Bream Chub Carp Crucian carp Gudgeon Pike Perch Ruffe Eels

3 86 8 0 0 0 0 8 0 1 0

97 71 37 1 0 1 84 0 2 76 16

32 35 0 0 1 0 16 7 0 0 7

115 41 5 0 0 0 125 2 1 0 7

8 0 0 4 0 0 0 0 0 0 0

255 233 50 5 1 1 225 17 3 77 30

Total fish Total no. of species
















Mean length (cm.) (and ränge) of the principal species caught Species Roach Dace Bream

Site Mill Pool 24-7 (23-9-26-0) 19-3 (10-5-23-5) 24-1 (13-7-46-2)

Judas Gap 11-7 (8-5-27-0) 15-3 (7-5-22-5) 11 -S (8-6-15-5) 24-3

Chub Pike

49-4 (16-2-72-0)

Eels Ruffe

44-12 (26-0-73-0) 9-26 (5-6-13-5) 9-08 (7-9-11-7)



Cattawade 10-7 (7-5-23-5) 15-0 (7-5-21-0) 15-1 (10-4-22-1)

Dedham 20-3 (18-8-22-8)

24-4 (21-7-29-2) 36-6 (11-1-62-0) 53-66 (40-8-61-0) 8-79 (5-0-11-8)


Growth rates of the principal angling species caught in the River Stour and in selected localities in the British Isles (lengths in cm.) Fish species and locality Roach R. Stour, Suffolk R. Stour, Dedham Cut Norfolk Broads R. Cam, Cambs Dace R. Stour, Suffolk R. Cam, Cambs R. Avon, Hants Willow Brook, Northants Bream R. Stour, Suffolk Norfolk Broads Chub R. Stour, Suffolk R. Avon, Hants R. Weiland, Lines Pike R. Stour, Suffolk R. Cam, Cambs Rostherne, Chesh Ruffe R. Stour, Suffolk Norfolk Broads

Age class 3+ 4 +





6 +

4 •7

9 •8 15 •1 20 3 22 •6 25-,

Present account

4 0 8' 1 11-•8 16' 2 18'•3 6 •9 9- 3 11 2 12 7 13'•6 15-: 6 9 10- 6 12' 9 16- 1 18 •2 21-:

Present account Hartley (1947) Hartley (1947)

6 •1 I i - 3 16 •4 19 2 i s 1 18 •4 20 1 11 •5 13- 7 16' 0 19' 1

Present account Hartley (1947) Hine & Kennedy (1974)

6 •0 10- 7 14'•5 16' 6

Cragg-Hine & Jones (1969)

5 •9 10 •6 16 •2 22 •8 29 •5 339 •9 13 •8 16 •3 18 •5 20 •3 22-

Present account Hartley (1947)

5 •3 12 6 20 •7 16- 8 17'•2

Present account Hine & Kennedy (1974) Leeming (1967)

6 •4 12 •6 15 •0 33 •1 42 • 1 53 •6 19 •0 28 •3 31 •1 34 •7 35 •7 43 •7 46 •1 7 •8 9 •9 11 •4 8 •7 10 •2 11 •3

Present account Hartley (1947) Banks (1970) Present account Hartley (1947)

Suffolk Natural History, Vol. 17, Part 1




% Frequency of occurrence of food items in fish of the River Stour Food

Item Dace

H i g h e r plants and algae Oligochaetes Cladocera Copepods Ostracods Dipteran larvae Maggots Fish

Fish Species Ruffe Bream






4 0 0 0 0

25 0 0 0 0

17 0 17 13 10

40 0 0 0 0

30 26 26 6 33

20 0 0 5 15

0 0 0 0 0

0 0 0 0 0

0 4 0

0 0 0

7 0 0

20 0 40

6 20 0

80 0 0

0 0 30

20 4 16


T h e parasite fauna of fish from the River Stour Species


PROTOZOA Myxobolus sp.

MONOGENEA Diplozoon paradoxum Tetraonchus


DIGENEA Diplostomum gasterostei (1)



sp. (1)

Infection %

Intensity Mean Max.

Ruffe Chub Pike

Gill branchiae Gill branchiae Gill branchiae

4-76 60 00 5-88

Bream Dace Pike

Gill branchiae Gill branchiae Gill branchiae

23 •81 11 •11 29 •63

7 •6 1 •0 2 •25

24 1 6


Vitreous h u m o u r of eye Vitreous h u m o u r of eye

4 •75

1 •0


2 •63

1 •0


Roach Diplostomum spathaceum

Site in host

Ruffe Bream Roach Dace Eel Pike Carp Perch Chub Gudgeon Dace

71 •44 Lens of eye 100 00 Lens of eye 94 •73 Lens of eye 100 •00 Lens of eye 26 •6 Lens of eye Lens of eye 11 •76 100 •00 Lens of eye Lens of eye 33 •33 80 •00 Lens of eye 80 •00 Lens of eye Vitreous h u m o u r of eye 3-•70

1 •0 6 •6 22 •0

3 •4 38 •57 34 •50 22 •68 1 •75 2 •25 2 •00 3 •00 2 •50 4 •95 1 0

1 17 22

9 144 247 57 3 4 2 3 3 15 1




Posthodiplostomum cuticola (1)

Sphaerostoma bramae Tetracotyle percafluviatilis (1) Tetracotyle A (Ichthyocotylurus) (1)

Tetracotyle B Tylodelphys clavata (1)

CESTODA Bo thriocephalus claviceps

Site in host


Infection Intensity % Mean Max.


Gill branchiae, fins Dace Gill branchiae Bream Gill branchiae Gudgeon Gill branchiae Dace Intestine Ruffe


7- 89 7' •40 9 •52 6 •66 11 •11

2' •33 1 •0 1 •5 1 •0 37 •66

4 •76

1 •0

Gudgeon Heart, body cavity, intestine ovary '30 00 Ruffe Heart, body cavity, gills 90 •48 Bream Heart 19 05 Dace Heart 7 •40 Ruffe Vitreous h u m o u r of eye 23 •80 Bream Vitreous h u m o u r of eye 13- 30 Roach Vitreous h u m o u r of eye 2< 31 Dace Vitreous h u m o u r of eye 29 •63 Chub Vitreous h u m o u r of eye 60 •00

3 1 2 1 77 1

5 •88


28' •78 3' •75 11 •5

86 8 17

1 •2


3 •5


5' 1




3 •33




33 •30

7 •9


Roach Dace Chub Gudgeon Bream Bream Roach Dace

Intestine Intestine Intestine Intestine Intestine Intestine Intestine Intestine

Triaenophorus nodulosus

2 •63 7 •40 20 00 20 •00 20 00 33 33 2 63 11 11

1 •0 1 •0 1 •0 3 •16 1 •66 3 •28 1 •0 1 •66

1 1 1 5 3 10 1 2




1 •66


NEMATODA Camallanus lacustris



4 •76

1 •0


Eel Eel Pike

Intestine Intestine Intestine

23' 33 3 •33 11 76

3 •57 1 •0 2 •25

11 1 5

Intestine Intestine Intestine

36 •6 5' •88 14 •28

3 •9 1 •0 9 •66

17 1 18

Caryophyllaeides fennica


Paraquimperia tenerrima Rhaphidascaris



ACANTHOCEPHALA Acanthocephalus clavula Eel Pike Bream




Speeles ARTHROPODA Argulus foliaceus

Ergasilus sieboldi



Vol. 17, Part 1

Site in host

Body surface, gills Bream Gills Body surface, Dace gills Body surface, Eel gills Body surface, Pike gills Gills Chub Gudgeon Body surface Gill branchiae Chub

Injection Intensity % Mean Max.


5-26 4-76

34' 0 1 •0

67 1


2 •0



1 •0


76-47 20 00 3-33 20 00

5 •07 1 •0 1 •0 1 •0

13 1 1 1


A comparison of grovvth rates of roach, dace and bream in the River Stour at present with that in previous years as revealed by back-calculation (lengths in cm.) Age elass 4 + 3 + 2 + 14Roach 20-3 15-1 9-8 4-7 From 1974 sample 20-3 14-9 9-7 4-1 From back-calculation



Dace From 1974 sample From back-calculation

6-1 5-3

11 -3 10-0

16-4 14-8

19-2 19-2

Bream F r o m 1974 sample F r o m back-calculation

5-9 4-7

10-6 10-5

16-2 16-2

22-8 22-8

References Banks, J. W. (1969). Observations on the fish population of Rostherne Mere, Cheshire. Fielet Studies 3, 357. Cragg-Hine, D. and Jones, J. W . (1969). T h e growth of dace Leuäscus leuciscus (L), roach, Rutilus rutilus (L) and chub, Squalius cephalus (L) in Willow Brook, Northamptonshire. J. Fish Biol. 1, 59. Hartley, P. H . T . (1947). T h e natural history of some British freshwater fishes. Proc. zool. Soc., Lond. 117, 129. Hine, P. M . and Kennedy, C. R. (1974). Observations on the distribution, specificity and pathogenicity of the acanthocephalan Pomphorhynchus laevis (Muller). J. Fish Biol. 6, 521. Kennedy, C. R. (1970). T h e population biology of helminths of British freshwäter fish. Symp. Brit. Soc. Parasit. 8, 145. Kennedy, C. R. (1974). A checklist of British and Irish freshwäter fish parasites with notes on their distribution. J. Fish Biol. 6, 613. Kennedy, C. R. (in press a). T h e distribution of some crustacean fish parasites in Britain in relation to the introduetion and movement of freshwäter fish. J. Inst. Fish Mgmt.



Kennedy, C. R. (in press b). T h e natural history of Slapton Ley N a t u r e Reserve: V I I I . T h e parasites of fish, with special reference to their use as a source of information about the aquatic Community. Field Studies. Leeming, J. B. (1967). The biology of some coarse fish of the River Weiland. P h . D . T h e s i s : University of Liverpool. Varley, M . E. (1967). British Freshwater Fishes. Fishing News (Books) Limited: London. C. R. Kennedy, R. Burrough, C. Aves, J. Landsberg, Department of Biological Sciences,, The University, Exeter.

The fish of the River Stour, Suffolk  
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