Dietary Macrogard reduces <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis> mortality in tench (<Emphasis Type="Italic">Tinca tinca</Emphasis>) through the activation of cellular and humoral defence mechanisms

Influence of beta-1.3/1.6-glucan (Macrogard) on the innate immunity and protection against Aeromonas hydrophila in tench (Tinca tinca (L.)) was assessed. Macrogard was fed at doses of 0, 0.5, 1 and 2 g kg⁻¹ of pellets for 1 month. The blood, spleen and head kidney from 10 fish of each group were separated and analysed for immunity parameters. Twenty tench from each group were infected with A. hydrophila. Macrogard at doses 1 and 2 g kg⁻¹ of feed significantly (P < 0.05) increased the phagocytic activity of macrophages and proliferative response of mitogens stimulated lymphocytes. The same doses significantly (P < 0.05) increased lysozyme activity and Ig level in serum, compared to the control and dose 0.5 g kg⁻¹ of feed. The challenge test showed that Macrogard reduced mortality of tench after experimental infection (5–35%).     

Compensatory growth in sub‐yearling Siberian sturgeon,Acipenser baerii Brandt, 1869: Effects of starvation and refeeding on growth,feed utilization and body composition

The capacity of sub‐yearling Siberian sturgeon (Acipenser baerii Brandt, 1869) (19.7 ± 0.8 g) to show compensatory growth was assessed for a 40‐day period for the effects of short‐term starvation and refeeding on growth, feeding performance and body composition. After acclimation, 25 experimental fish were randomly distributed among twelve 500‐L cylindrical fiberglass tanks with a flow‐through system. The fish were subjected to four different feeding regimes: control, which was fed four times daily to apparent satiation; T₁: four periods of 2 days starvation alternating with 8 days re‐feeding; T₂: two periods of 4 days starvation alternating with 16 days refeeding; T₃: an 8 days starvation period followed by 32 days refeeding. At the end of the experiment, the deprived fish attained body weights comparable to those attained by the control fish. There were no differences in growth and feeding performances between the deprived and the control fish. Total protein and lipid contents of the control fish were significantly higher than that of T₁ and T₂ fish at the end of the experiment (P < 0.05). A significant difference in the energy content was observed between T₂ and the control. Siberian sturgeon exhibited complete compensation, indicating a high ability of the deprived fish to grow sufficiently to fully compensate for weight loss during starvation. The results suggested that the feeding schedule involving starvation–refeeding cycles could be a promising feed management option for the culture of this species.     

Effect of supplementation of a dry feed with natural food on growth, condition and size distribution of juvenile tench Tinca tinca (L.)

In a 120‐day experiment, tench Tinca tinca juveniles [initially, 135 days post‐hatch, 37.4 mm total length (TL), 0.51 g body weight (BW)] maintained at 28°C received commercial starter alone (control group) or together with a supplement of frozen fly or chironomid larvae, in single or double quantities. Final survival rates were 100% in all treatment groups. Double additives significantly (P ≤ 0.05) improved fish growth in TL (final growth 62.0 or 62.5 mm, respectively) as compared with those fed single quantities (both 60.8 mm) or starter alone (59.1 mm). Significant differences in BW were found only between groups fed double additives and starter alone (final growth 2.96–3.07 and 2.71 g, respectively). Significantly highest Fulton's coefficient values were found in the control group and in the group fed single supplement of fly larvae (both K = 1.22), and lowest in both groups receiving chironomid larvae (K = 1.15–1.17). BW distribution was positively asymmetric in all groups, and the distribution of TL only in the control group and in the group fed with the single supplement of chironomid larvae. From a practical point of view, supplementation of a commercial starter with insect larvae has a minor effect on the results of T. tinca rearing under controlled conditions.     

Food‐related dominance between two carcharhinid shark species,the Caribbean reef shark,Carcharhinus perezi,and the blacktip shark,Carcharhinus limbatus

Although tench (Tinca tinca Linnaeus 1758) has been cultured traditionally in Eurasia, Central and Southern Europe mostly by low intensity methods, investigations of the optimum intensive culture conditions for the species have recently been initiated. This work was aimed to investigate the effect of food ration level on growth and survival of sub-adult tench, under intensive culture conditions. One hundred and twenty individuals (24.55?g?±?3.28) were fed for 102 days at three feeding levels: 0.5%, 1%, 2% b.w.d^?1. Higher body weights (b.w.) have been achieved with the 2% ration level in all experimental phases. However, by the end of the experiment (up to the b.w. of 34?g), fish fed with the ration level of 1% b.w.d^?1 resulted in better indices (FCR, SGR, % weight gain). These findings conform to the ones previously observed for tench juveniles and indicate that the 1% b.w.d^?1 ration level (below satiation) could be advantageous for tench sub-adults as well.     

Breeding,production and marketing of golden tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> (L.)) in Gan Shmuel Fish Breeding Center,Israel

A first attempt to introduce tench (Tinca tinca (L.)) to Israel, followed by comparative growth experiments, was carried out in 1947. A batch of 200 fingerlings, which were supposed to serve later as brood fish, was imported from Switzerland to Fish Culture Experimental Station at Sdeh Nahum. However, after 2 years tench were considered unsuitable for culturing in Israel and the trials were abandoned. Two factors affected negatively these historically early trials: (1) Tench was just second exotic species introduced to Israel some years after introduction of the common carp, and the Israeli fish farming expertise at that time was low. (2) The Independence War temporarily delayed advancement of aquaculture. A second introduction of tench was performed in 1992, when a golden mutant of tench was imported to Gan Shmuel Fish Breeding Center (GS-FBC) from the Research Institute of Fish Culture and Hydrobiology at Vodňany, Czech Republic. Currently, GS-FBC is the only Israeli fish hatchery that maintains golden tench as a part of breeding program as well as a number of other varieties of ornamental fish and species, all of them produced mostly for export. Tench (800–1,000 g) females are maintained separately from males, in order to prevent uncontrolled reproduction. Routinely, in April, the fish are transferred indoors and induced to spawn artificially with a single injection of GnRH synthetic analog—DAGIN. Dry method of stripping is used to obtain eggs and sperm. After fertilization the sticky eggs are spread in a single layer on walls of 230 dm³ cylindrical incubators provided with conical bottom, or they are degummed using a solution of milk/water. At a water temperature of 24°C, hatching (70% hatching rate) occurs 36–40 h after fertilization. The larvae absorb their yolk sac 2–3 days after fertilization and they start feeding on small size (200 μm) Artemia nauplii. At the age of 7–10 days, if fry are retained indoors, they are fed with regular size Artemia and starter feed, or are released into a nursing 0.5–1.0 ha pond. Usually, the fish are grown to the marketing size (5–15 cm) and exported abroad, mainly to Europe. About 100,000 golden tench fingerlings, with a total value of € 40,000 are produced and marketed annually.     

Response of juvenile tench Tinca tinca (L.) to the anaesthetic 2-phenoxyethanol

The response of tench Tinca tinca aged 40–171 days post‐hatch (22–49 mm TL) to the anaesthetic 2‐phenoxyethanol was studied at 25°C. The lowest effective concentration of 2‐phenoxyethanol increased with age, while the highest safe concentration decreased. The fish aged 40 days post‐hatch required a significantly (P ≤ 0.05) shorter time to become anaesthetized than did older fish. The recovery time after 15 min of exposure to 2‐phenoxyethanol at 0.45 g dm^?3 was significantly shorter in the 40‐day‐old fish than in older fish. In juveniles of the same age, induction time or recovery time did not depend on their size or condition (Fulton's coefficient). At 25°C, 2‐phenoxyethanol at 0.5 g dm^?3 may be used to efficiently and safely anaesthetize T. tinca juveniles.     

Effects of different dietary fatty acids profiles on the growth performance and body composition of juvenile tench (<Emphasis Type="Italic">Tinca tinca</Emphasis> (L.))

Juvenile tench (initial weight of about 57 g) were fed feed supplemented with fish oil (group FO), linseed oil (group LO), peanut oil (group PO), or rapeseed oil (group RO) containing 47% protein and 12% fat for 55 days. The inclusion of the tested oils was 50 g kg⁻¹ (42% total crude lipids in diets). No significant differences were noted in the fish growth performance. The proximate composition of the whole fish bodies and the viscera (water, protein, fat, ash) was similar in all the dietary treatments (P > 0.05). Differences were noted only with regard to the ash content of the fillets (P < 0.05). The analysis of the fatty acids profiles of tench (whole fish) indicated there were significant differences in the total content of monoenoic and polyenoic (PUFA) acids. Significant differences were also noted with regard to n-3 PUFA and n-6 PUFA. Consequently, the ratio of n-3/n-6 acids ranged from 1.6 (group PO) to 2.08 (group LO; P < 0.05). The feed applied was not confirmed to have had an impact on the fatty acids profile of the tench fillets. There was a statistically significant intergroup difference in the content of saturated fatty acids (SFA) in tench viscera. In the fish fed vegetable oils supplemented diets, the level of SFA was lower (P < 0.05).     

Toxicity of Diazinon 60 EC for embryos and larvae of tench, <Emphasis Type="Italic">Tinca tinca</Emphasis> (L.)

The effects of Diazinon 60 EC (organophosphate insecticide, active substance diazinon) on mortality, growth rate, early ontogenetic rate, and occurrence of malformations was studied in embryos and larvae of tench, Tinca tinca (L.). The exposure of fish to 0, 10, 100, 1,000, and 3,000 μg dm⁻³ of Diazinon 60 EC was initiated 24 h after fertilization of eggs and concluded 32 days later. At the highest concentration tested (3,000 μg dm⁻³), total mortality was observed within the first 15 days of exposure. A concentration of 1,000 μg dm⁻³ caused high incidence of malformations, decrease in growth rate and ontogenetic development slowed down. A concentration of 100 μg dm⁻³ mildly decreased growth rate, but at 10 μg dm⁻³ no changes compared to the control were observed. Thus, Diazion 60 EC at the concentration of 10 μg dm⁻³ is not dangerous for the embryos and larvae of tench.     

Comparison of compensatory growth responses of juvenile three-spined stickleback and minnow following similar food deprivation protocols

The compensatory growth responses of individual juveniles of two co- existing species were compared after identical periods of starvation to determine inter-specific similarities and differences. The carnivorous stickleback Gasterosteus aculeatus was compared with the omnivorous minnow Phoxinus phoxinus. Both species experienced 1 or 2 weeks of starvation before being re-fed ad libitum. The two species differed in their response to the starvation periods, with minnows showing a lower weight-specific loss. Both species showed compensatory responses in appetite, growth and to a lesser extent, growth efficiency. Minnows wholly compensated for 1 and 2 weeks of starvation. At the end of the experiment, sticklebacks starved for 2 weeks were still showing a compensatory response and had not achieved full compensation. The compensatory responses of the sticklebacks showed a lag of a week before developing in the re-feeding phase, whereas the response of the minnows was immediate. Analysis of lipid and dry matter concentrations suggested that the compensatory response restored reserve lipids while also bringing the fish back to the growth trajectory of continuously fed fish.     

Survival, growth and condition of tench Tinca tinca (L.) larvae fed live food for 12, 18 or 24 h a day under controlled conditions

The present 20‐day trial was performed in order to improve growth of tench Tinca tinca (L.) larvae reared intensively in a controlled environment. Larvae of 4.53 mm initial length, 45 per dm³, were fed each day with live Artemia nauplii for 12, 18 or 24 h at 28°C. Final survival rates were very high in all treatment groups, ranging from 88.9 to 91.8%. Duration of daily feeding significantly affected growth and final condition, expressed by Fulton's coefficient (K) (P ≤ 0.05, Duncan's test). The fastest larval growth (17.6 mm total length, TL; 88.8 mg body weight, BW) and the best condition (K = 1.54) were recorded in the group fed 24 h each day. The second best results were attained with the larvae fed 18 h a day (16.5 mm TL, 67.9 mg BW, K = 1.40) whereas those fed 12 h daily grew the slowest (13.5 mm TL, 31.7 mg BW) and showed the worst condition (K = 1.19). Thus, to maximize growth and condition of tench larvae being reared at the optimal growth temperature, intensive 24 h feeding is necessary.     

The effects of different cycles of starvation and re‐feeding on growth and body composition in rainbow trout (Oncorhynchus mykiss,Walbaum, 1792)

This study was designed to investigate the effects of starvation and re‐feeding cycles on the growth performance and body chemical composition of Oncorhynchus mykiss juveniles. A total of 360 juveniles with initial mean weights (IW) of 8.46 ± 0.07 g (n = 360) were stocked into 400‐L tanks in triplicate for each group, with 30 juveniles per tanks. The control group received regular feed, as is the common practice. The three other groups were periodically starved: 1 day starvation followed by 6 days re‐feeding (S1), 2 days starvation followed by 5 days re‐feeding (S2) and 3 days starvation followed by 4 days re‐feeding (S3). The experiment lasted for 10 weeks, over the course of which the water flow rate was 4 L min^?1 and the water quality parameters determined as: temperature 14.4 ± 1.1°C, oxygen 8.2 ± 0.4 mg L^?1 and pH 7.5 ± 0.2. At the end of the study, S1 had the best growth performance (final weight, specific growth rate, average daily growth) of all test groups (P < 0.05). The lowest daily feed intake (DFI) and growth performance parameters were observed in S3 (P < 0.05), while protein efficiency ratio (PER), net protein utilization (NPU) and lipid efficiency ratio (LER) were higher in the S3 fish group than in the other groups (P < 0.05). Whole body protein and lipid contents were highest in S1 fish. The hepatosomatic index (HSI) and viscerosomatic index (VSI) were significantly different among groups (P < 0.05). Feed conversion ratio (FCR) was significantly lower in starvation groups S1, S2 and S3 than in the control (P < 0.05). Compensation coefficient (CC) values were higher than 1 in all starvation groups. The concluding indicate that rainbow trout exposed to 1 and 2 days of starvation in week cycles could achieve over compensation compared to the control. Additionally, partial growth compensation and improved feed utilization could be achieved in a starvation group within 3 days in a week, by beginning with the juvenile size over a 10‐week experimental period.     

A performance test with five different strains of tench (Tinca tinca L.) under controlled warm water conditions

Growth performance tests were carried out with a total of five different strains of tench (Tinca tinca L.) originating from the Czech Republic (4) and Germany (1). Tench larvae and juveniles were reared in closed recirculating systems for 446 to 452 days, respectively. At the end of each test, the tench strains showed differences in performance, e.g. specific growth rates (SGR) from 2.13 to 2.52, feed conversion ratios (FCR) from 1.75 to 3.65 kg feed per kg weight gain, and survival rates from 64.4 to 81.0%. Thus, appropriate strain selection appears to have the potential to remarkably increase productivity of the species. The highest SGR was observed in the Vodnany 96 strain in the first trial and the best FCR in the Tabor strain in the second trial. However, the rearing conditions in the recirculating systems were not optimal for tench; many fish with deformed bones (head, fins, spine) were observed in all strains, particularly in the faster‐growing strains.     

Effects of feed restriction on growth performance,lipid mobilization,and gene expression in rose spotted snapper (Lutjanus guttatus)

The effects of feed deprivation were evaluated for 1 week and 2 weeks in Lutjanus guttatus juveniles. A significant reduction in body mass was observed in both feed deprivation schemes, as well as in hepatosomatic, viscerosomatic and mesenteric fat indexes. The composition of fasted fish was characterized by a decrease in lipid content; the liver displayed an intense reduction of lipid reserves in both fasted groups, and increased expression of the lysosomal acid lipase. 1 week after re-feeding, both experimental groups showed an increase in specific growth rate, feed intake and feed conversion ratio. A recovery in hepatic lipid reserves was observed, and the expression of the lysosomal acid lipase decreased, although lipid content in both groups was still significantly lower than in control groups. Hepatic expression of the growth hormone receptor decreased after fasting, and remained low even after the fish were fed, whereas the expression of insulin-like growth factor 1 and 2 increased after fasting and decreased in both groups when fish were fed again. Altogether, these results showed a partial compensatory growth response in L. guttatus juveniles after fasting, with enhanced growth rates and improved feed efficiency. Fish used stored lipid reserves as the main energy source, and the expression of growth-related and lipid mobilization marker genes in the liver showed similar patterns in both fasting schemes. Based on the results, we suggest as much as 1-week fasting intervals during grow-out programmes to reduce visceral fat and increase growth rate in this species.

     

Effect of starvation and re‐feeding on growth performance and content of plasma lipids,glucose and insulin in cultured juvenile Persian sturgeon (Acipenser persicus Borodin, 1897)

The effect of starvation and subsequent re‐feeding to satiation on compensatory growth performance, insulin and blood serum values were investigated in juvenile Persian sturgeon (Acipencer persicus) with an average weight 108.04 ± 0.28 g (mean ± SEM) and in the same rearing condition over an 8‐week period. Sturgeons were allocated to one of five feeding treatments: controls (C, continuous feeding), W1 (1 week starvation), W2 (2 weeks starvation), W3 (3 weeks starvation) and W4 (4 weeks starvation), followed by a single 4 weeks of re‐feeding to satiation. Changes in growth performance and blood serum indices were examined at the end of weeks 4 and 8. Body weight, specific growth rate (SGR), condition factor (CF) and weight gain were determined to have significantly decreased during starvation. Fish starved for 1 week reached the same weight as the control fish after re‐feeding for 4 weeks, indicating that complete compensatory growth occurred. Although the specific growth rate in W2, W3 and W4 fish was greater than that in the control fish after re‐feeding, W2, W3 and W4 fish did not reach the same body weight as control fish at the end of re‐feeding period, and showed partial compensation only. Blood plasma, glucose and insulin concentrations did not change significantly during starvation and re‐feeding (P > 0.05). This suggests that sturgeon are able to maintain glycaemia during starvation, probably due to their non‐carbohydrate dietary source. Plasma total lipid and triglyceride levels increased in starvation treatments, whereas the increases were significant only in W3 treatment (P < 0.05). After a 4‐week re‐feeding period, their levels decreased in comparison to the starvation periods. Increases in plasma total lipid and triglyceride levels appear to be due to their roles as preferred nutrients for mobilization in Persian sturgeon and the magnitude and duration of compensatory growth depended on the length of food deprivation.     

Fish induced macrophyte loss in shallow lakes: top–down and bottom–up processes in mesocosm experiments

SUMMARY 1. Macrophyte loss from Sites of Special Scientific Interest in England has become widespread over the last 20 years. One reason for this may be changing trends in angling, a multimillion pound industry that has an enormous impact on aquatic ecosystems. Stocking with cyprinid fish is a common angling management practice but the particular fish species and distribution of their biomass may be crucial to the ecosystem. 2. Carp (Cyprinus carpio), roach (Rutilus rutilus), bream (Abramis brama) and tench (Tinca tinca) at biomasses ranging from 0 to 800 kg ha^?1 and at various sizes were placed into experimental mesocosms in Little Mere, a shallow, fertile lake in Cheshire, U.K. The effects these treatments had on the aquatic ecosystem were studied over two summers. Specifically the effects of the treatments on macrophyte growth, benthic and macrophytic macro‐invertebrate populations, water chemistry, epiphyton production and plankton survival were investigated. 3. Carp had a greater detrimental effect on the macrophytes than bream, tench and in particular roach. A biomass of fish > 200 kg ha^?1 adversely affected the extent of macrophyte growth. 4. The decline in macrophyte growth was most likely as a result of increased epiphyton growth that probably reduced the amount of light and carbon dioxide available to the plant. There were no observed direct fish impacts on macrophytes. 5. The chemical data suggested that inorganic nitrogen levels were low and it is possible that release of nitrogen, from fish excreta, followed by immediate uptake, could have been a major factor stimulating epiphyton growth and subsequently macrophyte loss. Phosphorus concentrations increased even in the controls and substantial amounts were available. Phosphorus stimulation can therefore be discounted. Macrophyte‐associated macro‐invertebrates were positively correlated with epiphyton load but had no impact on the extent of epiphytic growth. Shading from disturbed sediment or phytoplankton was also unimportant.     

Koi herpesvirus infection in experimentally infected common carp Cyprinus carpio (Linnaeus, 1758) and three potential carrier fish species Carassius carassius (Linnaeus, 1758); Rutilus rutilus (Linnaeus, 1758); and Tinca tinca (Linnaeus, 1758) by quantitative real‐time PCR and in‐situ hybridization

Only single cells in the carrier fish species Carassius carassius (Linnaeus, 1758) for koi herpesvirus (KHV) are infected in contrast to large numbers in the susceptible species common carp Cyprinus carpio (Linnaeus 1758). Several species of the family Cyprinidae have been described as virus carrier species, showing no clinical signs of a KHV disease but able to transmit the virus to other susceptible fish. In this study, 72 common carp Cyprinus carpio (Linnaeus, 1758), 36 tench Tinca tinca (Linnaeus, 1758), 36 crucian carp Carassius carassius (Linnaeus, 1758) and 36 common roach Rutilus rutilus (Linnaeus, 1758) were experimentally infected with KHV (isolate “Israel”) by immersion and kept at 20°C. The fish were euthanized at 12 timepoints over a period of 90 days and virus DNA was quantified in tissues by a real‐time TaqMan PCR. Whereas KHV‐DNA was found in Cyprinus carpio for up to 90 days, the virus DNA was detectable only in single individuals of Rutilus rutilus, Tinca tinca and Carassius carassius for up to 25 days after experimental virus exposure. Tissue samples of Cyprinus carpio and Carassius carassius were screened by in‐situ hybridization. Positive signals were found in various organs of the common carp tested crucian carp. In the latter species a much smaller number of virus‐positive stained cells was detected compared to the infected carp.     

Assessing the capacity for compensatory growth in growth‐hormone transgenic coho salmon Oncorhynchus kisutch

The effect of feed cycling (consisting of periods of starvation followed by periods of refeeding to satiation) on compensatory growth was evaluated in growth hormone transgenic and non‐transgenic wild‐type coho salmon Oncorhynchus kisutch. The specific growth rate (G_SR) of feed‐restricted non‐transgenic O. kisutch was not significantly different from the G_SR of fully‐fed non‐transgenic O. kisutch during two refeeding periods, whereas the G_SR of feed‐restricted transgenic O. kisutch was significantly higher in relation to the G_SR of fully‐fed transgenic O. kisutch during the second refeeding period, but not during the first, indicating that growth compensation mechanisms are different between non‐transgenic and growth‐hormone (GH)‐transgenic O. kisutch and may depend on life history (i.e. previous starvation). Despite the non‐significant growth rate compensation in non‐transgenic O. kisutch, these fish showed a level of body mass catch‐up growth not displayed by transgenic O. kisutch.     

The energetics of starvation and growth after refeeding in juveniles of three cyprinid species

Synopsis Experiments were conducted to monitor changes in body mass and metabolic energy expenditure before, during, and after periods of starvation in juveniles of three species of cyprinids: Leuciscus cephalus, Chalcalburnus chalcoides mento, and Scardinius erythrophthalmus. During the starvation period all fish lost weight at about the same rate and the total amount of oxygen consumed during an experimental period of 20 h was about 40% lower in the starved than in the fed groups. Upon refeeding, both mass specific maintenance; and routine rates of metabolism as well as relative growth rates increased rapidly, the peaks of these increases being directly proportional to the length of the starvation period. Maximum compensatory growth was observed after four weeks of starvation in C. chalcoides and S. erythrophthalmus, with relative growth rates reaching 30% d^-1 during the first measuring interval after refeeding. The pattern of time-dependent compensatory growth displayed by these fish is similar to the responses of a colonial hydroid in which the rate of catch-up growth increased with the amount of stress to which the animals had been exposed. The exact cost of compensatory growth cannot be calculated because oxygen consumption and growth were not measured simultaneously. However, on the basis of data and calculations reported by Wieser & Medgyesy (1990) it appears that compensatory growth, if fuelled by the metabolic power indicated by our measurements of oxygen consumption, would have to be about twice as efficient as normal growth in the related species Rutilus rutilus.     

Effects of waterfowl, large fish and periphyton on the spring growth of Potamogeton pectinatus L. in Lake Mogan, Turkey

It has been argued that waterfowl and fish may threaten growth of submerged macrophytes, especially in spring during the early growth phase when plant biomass is low. A small reduction of biomass at that time might delay growth or decrease subsequent productivity. We investigated the impact of waterfowl and large fish on the spring growth of fennel pondweed (Potamogeton pectinatusL.) by employing an exclosure experiment in the macrophyte-dominated clear-water Lake Mogan, Turkey. Birds and large fish were excluded from eight plots and both in situvegetation and macrophytes kept in pots were compared to eight open plots. Also, to investigate the effect of periphyton on plant growth it was removed from half of the pot plants. Exclusion of waterfowl and fish may decrease predation on macroinvertebrates, which in turn may affect periphyton, and macrophyte growth, why macroinvertebrates also were sampled. Waterfowl density was high (15–70 ind. of coot, Fulica atraL. ha^–1), abundance of submerged plants was also high with a surface coverage of 70–80%, and benthivorous fish were present, mainly tench, (Tinca tincaL.) and carp, (Cyprinus carpioL.). Exclusion of waterfowl and large fish did not significantly affect the spring growth of pondweed; neither plants growing in situnor kept in pots. Removal of periphyton from the plants in the pots did not favour growth. The density of macroinvertebrates was not affected by the exclusion of waterfowl and large fish, but it was positively related to aboveground biomass of fennel pondweed. We suggest that even if waterfowl and large fish are in high densities, their effect on fennel pondweed spring growth in lakes with abundant submerged vegetation, such as Lake Mogan, is low.