Organization for the Improvement of Inland Fisheries
Nieuwegein, The Netherlands
In the Netherlands every year more than 200 000 kg of roach (15–25 cm) caught by seine netting, are stocked in sport-fishery waters.
From 1973 to 1980 experiments were carried out in drainable ponds to quantify the survival of these roach.
Experimental ponds (0.05 and 0.1 ha) were stocked in November to March and drained in July of the same year. Survival of roach varied from 0.8 to 67.3 percent with a mean value of 23 percent.
Induced stress seems to be the most critical factor in the overall handling procedure (catch, storage, transport, stocking). Suppressing stress with a tranquillizer (benzocaine) added to the transport medium improved survival up to five times.
Aux Pays-Bas, on capture chaque année à la seine plus de 200 000 kg de gardons (15–25 cm) pour repeupler les eaux où se pratique la pêche sportive.
La survie de ces gardons a été étudiée dans des étangs vidangeables de 0,1 ha à la station expérimentale de l'Organisation pour l'amélioration des pêches continentales. Les gardons ont été mis à l'eau de décembre à mars et les étangs ont été vidés en juillet de la même année.
Durant la période 1973–81, le taux de survie des gardons a varié entre 0,8 et 67,3 pour cent, le taux moyen étant de 23 pour cent. Le stress occasionné par les manipulations (capture, stockage, transport) semble être le facteur le plus important. On a constaté qu'en versant un tranquillisant (benzocaïne) dans l'eau des bacs de transport, on pouvait réduire la mortalité de près de 30 pour cent.
Every year more than 200 000 kg of roach (Rutilus rutilus (L.)), caught by commercial fishermen by seine netting, are stocked into waters generally managed by sport fishery associations. A greater part of this quantity (nearly 150 000 kg) is stocked into water of managers registered at the Organization for the Improvement of Inland Fisheries (OVB). If stocked into such waters, roach stockings can be subsidized at a maximum of 40 percent of the costs.
At first, quality of roach was evaluated on the basis of injuries and scale losses at stocking and/or the visible mortality immediately after stocking. When the majority of the roach showed no sign of either of these, the quality of roach was assumed to be good, with a corresponding high survival rate. Later, quality of roach was quantified more objectively by determining the post stocking survival in drainable ponds. In view of the low survival rates demonstrated in these, the OVB started an investigation in 1975 to study the possibility of lowering post stocking mortality. The results of this study are reported here.
During the winter period between 1 November and 31 March, roach for stocking into sport fishing waters of managers registered at the OVB are seined by commercial fishermen in two main areas of the Netherlands. More than 60 percent of the 150 000 kg of roach needed each year, are caught in the lower reaches of the Maas and Waal Rivers (The Biesbosch) situated in the southwestern region of the country. Approximately 35 percent of the roach are caught in the lower reaches of the River IJssel near Lake IJssel (Lake IJssel region) in the eastern part of the country.
After seining, roach (15–30 cm) are usually transported in aluminium tanks to the holding units of fish dealers. During transport, fish density does not exceed 300 kg/m3. The holding units used by the fish dealers are mainly large keep nets (5–15 m3). Roach are kept at a density of 60–120 kg/m3 in these for a 2–7 days period during which quantities large enough for stocking are collected and dead, injured or lethargic individuals are sorted out. Finally, roach are transported (300 kg/m3) and are stocked into sport fishery waters all over the country.
Survival experiments were carried out in drainable ponds at the OVB Experimental Station, situated in the centre of the Netherlands near Beesd. These experimental ponds (0.05 and 1.0 ha) were of a similar (rectangular) shape with a mean depth of 1.0 m and a bottom consisting of alluvial clay. Ponds were stocked exclusively with roach in order to determine a conditional survival value for the species.
Ponds were stocked between 1 November and 31 March at the same time as the period of normal stocking of sport fishing waters.
Stocking density was standardized at 2 000 roach/ha. In practice, roach are stocked to increase catches or to guarantee angling success in the summer following the closed season (15 March–1 June). Experimental ponds were drained in the first weeks of July to gain an impression of the proportion of stocked roach left from the stocking in the previous winter. At draining, surviving fish were counted and the numbers of fish injured, wounded or ulcerated were determined. Survival was calculated as the percentage of living fish relative to the total number stocked into the ponds. The injury ratio was calculated as a percentage of the number of fish harvested.
2.2.2 Determination of survival of roach provided for stocking in sport fishery waters
Ponds were stocked with roach taken from samples from different batches of roach just prior to being stocked into sport fishing waters. From 1972 to 1980 samples of 70–100 kg of roach were taken each year between 1 November and 31 March from roach deliveries without prior notice to the fish dealers. Only batches of roach originating from the most important fish dealer of the “Biesbosch region” and that of the “Lake IJssel region” were sampled. These two fish dealers were handling nearly 80 percent of the total catch of roach. The samples were transported to the Experimental Station in oxygenated water in glass-fibre tanks. Depending on the place of sampling, transport to the Experimental Station took between two and three hours.
2.2.3 Experiments to determine causes of mortality
In these experiments, started in 1975, three kinds of roach were tested for conditional survival rate:
roach, sampled as described in 2.2.2;
roach, harvested by draining experimental ponds in which the fish were hatched and reared. These were subjected to simulated transport and storage at a density of 150 kg/m3, as practised by the fish dealers.
roach, sampled as soon as possible after seining by the fishermen (with exclusion of the storage at the fish dealers) and kept in simulated storage. Some of these samples were treated with the tranquillizer benzocaine (10 ppm) during transport from fishing site to Experimental Station and during the simulated transport before stocking.
The survival of different batches of roach, sampled from the deliveries from fish dealers are summarized in Table 1.
Independent of the region of origin, the survival of roach varied from 0.8±67.3 percent with a mean value of 23.0 percent. Mean survival of roach from the Lake IJssel region was 24.4 and 22.0 percent of roach from the Biesbosch survived.
As is shown in Fig. 1, the survival of roach originating from both regions appeared to be negatively correlated to the injury ratio.
Roach, sampled directly at the fishing sites and stocked into the experimental ponds without storage, showed considerably better survival than roach sampled from the deliveries from fish dealers, at about the same time (Table 2).
With no storage by the dealer, the survival of roach reached values of more than 90 percent, suggesting that seining and transporting can be done without being harmful to roach. However, low survivals (36.9 percent) were also recorded in batches of roach which were not exposed to storage.
Experiments carried out with artificially reared roach subjected to simulated transport without storage revealed a survival of 93.0 and 96.9 percent. When subjected to storage as well as transport the survival of these roach decreased to 43.5 percent.
The results of experiments with batches of roach sampled at the fishing sites and the same batches kept at the holding units of the fish dealers are shown in Table 3.
This demonstrates that survival decreased sharply from 47.0 to 7.6 percent and from 23.9 to 0.8 percent, respectively. The negative effect of keeping roach seemed most pronounced during the first 24 h of storage. Survival decreased with longer storage but less drastically.
The results of treatment with benzocaine administered to the water during the transport of roach before as well as after simulated storage at the Experimental Station is shown in Table 4.
In all samples, the survival after 72 h storage was increased by treatment with benzocaine. The mean survival rate increased from 19.0 to 43.3 percent and when survival of untreated roach was low (11.0 and 20.0 percent respectively) treatment with benzocaine increased survival above these values.
The results of a seven-year study of the survival of roach after stocking, reveals a generally low survival of about 22.0 to 24.4 percent (mean values) independent of the region of origin of the stocked fish.
If the same situation applies in practice, i.e., when roach are stocked into sport fishing waters, only a small part of the roach stocked just prior to the beginning of the closed season for angling is available at the opening of the season in the beginning of June.
It is apparent that handling, and especially storage, of roach as practised by the fish dealers decreases survival drastically. Similar results are reported for other species, especially salmonids (Hosmer, 1980; Johnson and Metcalf, 1982; Strange and Schreck, 1978). When storage is avoided by taking roach directly from the fishermen, survival can be increased up to 97.3 percent. However, the exclusion of storage by the fish dealers does not always guarantee a high survival of roach. As may be seen from Tables 2, 3 and 4 survival of roach obtained immediately from the fishing sites varies considerably from 97.3 to 11.0 percent and it is supposed that the low survival is connected with storage as practised by the fishermen themselves. If only small quantities of roach are caught, the fishermen keep them in their tanks until sufficiently large quantities are available which are saleable to fish dealers. There is no doubt that the avoidance of storage would be a good way to improve the survival of roach. However, in practice, such a measure seems hard to realize. In general, the batches of roach caught by fishermen are brought to the fish dealer in the afternoon. As a consequence, transport and stocking are not possible during the same day as seining. Furthermore, storage is often necessary to give fish dealers the opportunity to sort the fish and to accumulate small batches until deliverable amounts are obtained. In view of the practical impossibility of avoiding storage, improvement of post stocking survival seems only possible by reducing the metabolic processes (stress) which are induced by handling and keeping the fish, and which affect the survival.
Applying the stress-reducing tranquillizer benzocaine (Laird and Oswald, 1975) during the transport of fish, survival rate has been shown to improve up to and even over five times. Comparable effects are reported for other species, using different tranquillizers or salt (Collins and Hulsey, 1963; Long et al, 1977; Taylor and Solomon, 1979).
The treatment of roach with tranquillizer, however, is restricted to the transport of fish, in view of the impossibility of applying these chemicals through the flowing water systems as used in storage.
Collins, J.L. and A.H. Hulsey, 1963 Hauling mortality of threadfin shad reduced with MS 222 and salt. Prog.Fish-Cult., 25:105–6
Hosmer, M.J., 1980 Handling as a factor in mortality of trout with or without furunculosis. Prog.Fish-Cult., 42(3):157–9
Johnson, D.L. and M.T. Metcalf, 1982 Causes and controls of freshwater drum mortality during transportation. Trans.Am.Fish.Soc., 111:58–62
Laird, L.M. and R.L. Oswald, 1975 A note on the use of benzocaine (Ethyl-P-Aminobenzoate) as a fish anaesthetic. Fish.Manage., 6(4):92–4
Long, C.W., J.R. McComas and B.H. Monk, 1977 Use of salt (NaCl) water to reduce mortality of chinook salmon smolts, Oncorhynchus tshawytscha, during handling and hauling. Mar.Fish.Rev., 39(7):6–9
Strange, R.J. and C.B. Schreck, 1978 Anaesthetic and handling stress on survival and cortisol concentration in yearling chinook salmon (Oncorhynchus tshawytscha). J.Fish.Res.Board Can., 35(3):345–9
Taylor, A.L. and D.J. Solomon 1979 Critical factors in the transport of living freshwater fish. 1. General considerations and atmospheric gases. Fish.Manage., 10(1):27–32
Table 1 Percentage survival of different samples of roach originating from the Biesbosch region or the Lake IJssel region
(1 Nov.–31 March)
|1975/76||32.5; 15.5; 66.8; 34.5||67.3; 24.5|
|1979/80||7.0; 10.0; 10.0||-|
Table 2 Percentage survival of different batches of roach caught by seine net sampled at fishing sites and fish from dealers
|Roach from fishermen||Roach from fish dealers|
Table 3 Percentage survival of roach sampled at the fishing sites and kept at the fish dealers
|Duration of storage|
|0 h||24 h||49 h||120 h|
Table 4 Effect of benzocaine (10 ppm) on the percentage survival after stocking of four different batches of roach, sampled at the fishing site and stored for 72 hours before stocking
|Untreated||Storage (72 h)||Storage (72 h) benzocaine during transport|
Fig. 1 Relationship between percentage survival and injury ratio