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Leiden, Netherlands

Burgerhout E.,Leiden University | Burgerhout E.,NewCatch BV | Tudorache C.,Leiden University | Brittijn S.A.,NewCatch BV | And 4 more authors.
Journal of Experimental Marine Biology and Ecology | Year: 2013

During migration, swimming in schools provides fish with a number of behavioural and ecological advantages, including increased food supply and reduced predation risk. Previous work shows that carangiform and tunniform swimming result in energetic advantages for individuals using a diamond swimming formation. However, little is known about the potential energetic advantage associated with schooling for anguilliform fish, such as European eel. European eels migrate over a long distance to their spawning area in the Sargasso Sea and may experience energetic advantages when swimming in schools. In this study the effect of group-wise swimming on the cost of transport was tested. In addition, the swimming pattern of eels swimming in groups was studied.Male silver eels were individually subjected to an increased velocity test (0.4-0.9ms-1) with increments of 0.1ms-1 every 2h. Groups comprising of seven males were swum following the same protocol. Video recordings were obtained to analyse tail beat frequency at the various water speeds.At all swimming speeds the oxygen consumption was significantly lower in group-wise vs. individually swimming males. The cost of transport at the optimal swimming speed of group-wise swimming males was significantly lower than that of the individually swimming males (21.3±3.2 vs. 32.0±0.6mgO2kg-1h-1, respectively). The optimal swimming speeds, however, were not significantly different (0.57±0.02 and 0.52±0.04ms-1 respectively). At speeds of 0.50ms-1 and above, tail beat frequency was lower in males swimming in groups than in males swimming individually (2.6±0.1 and 3.8±0.1, respectively). In contrast to the 'diamond' shape pattern of many group-wise swimming fish, eels tend to swim in a synchronized fashion parallel to each other, possibly reducing swimming costs by Karman gaiting. Although not an evidence, the present study provides support for the assumption of group migration in European eels. © 2013 Elsevier B.V.

Palstra A.P.,Wageningen University | Blok M.C.,Wageningen University | Kals J.,Wageningen University | Blom E.,Wageningen University | And 4 more authors.
General and Comparative Endocrinology | Year: 2015

Reproduction of many temperate fishes is seasonal and maturation and spawning of gametes are under photothermal control. Reproductive success of first generation (G1) common sole Solea solea in captivity has been low. In this study, the sexual maturation status has been assessed during the prespawning months in G1 sole that were housed (a) outdoor under the natural photoperiod and temperature, or (b) indoor under artificial photothermal induction. Maturation was assessed in male and female G1 broodstock in November as controls, after which the remaining population was divided over two outdoor flow-through tanks placed in a pond and two indoor recirculating aquaculture system (RAS) tanks. Subsequently, maturation status (gonadosomatic index GSI and plasma levels of testosterone T and 17β-estradiol E2) was assessed in one tank for each condition in January, February and during spawning in early April, while fish in the other tank were not disturbed in achieving reproductive success. Quantitative real-time PCR was performed to determine species-specific gonadotropin mRNA expression in females. Successful G1 spawning and egg fertilisation occurred in all experimental tanks. Gonadal development was similar under both conditions. Higher E2 and T levels were found in indoor housed females. Gonadotropin expression revealed similar profiles between outdoor and indoor housed females. G1 sole could be reproduced in the outdoor tanks under the natural photoperiod and in the indoor tanks under artificial simulation of this regime that includes a potentially crucial chilling period of 2-3months at 5-7°C. © 2015 Elsevier Inc.

Tudorache C.,Leiden University | Burgerhout E.,Leiden University | Burgerhout E.,NewCatch BV | Brittijn S.,NewCatch BV | van den Thillart G.,NewCatch BV
Frontiers in Physiology | Year: 2015

The spawning migration of the European eel (Anguilla anguilla) can cover more than 6000 km, while that of the New Zealand short-finned eel (A. australis) is assumed to be approximately 3000 km. Since these species are expected to show adaptive traits to such an important lifetime event, we hypothesized differences in swimming capacity and energetics as a response to this adaptation. In an experimental swimming respirometer set-up, critical swimming speed (Ucrit), optimal swimming speed (Uopt), mass specific oxygen consumption rate (M˙O2), standard metabolic rate (SMR), active metabolic rate at Ucrit (AMRcrit) and at Uopt (AMRopt), the minimum cost of transport at Uopt (COTmin), and the scope for activity, were assessed and compared between the species. With a similar body length and mass, European eels showed ca. 25% higher values for both Ucrit and Uopt, and 23% lower values for COTmin, compared to New Zealand short-finned eels. However, SMR, AMRcrit, AMRopt, and scope for activity did not differ between the species, indicating very similar swimming physiology traits. This study discusses physiological aspects of long distance migration and provides recommendations for (a) swimming respirometry in anguilliform fish, and (b) telemetry research using externally attached pop-up tags. © 2015 Tudorache, Burgerhout, Brittijn and van den Thillart.

Tudorache C.,Leiden University | Burgerhout E.,Leiden University | Burgerhout E.,NewCatch BV | Brittijn S.,NewCatch BV | Van Den Thillart G.,NewCatch BV
PLoS ONE | Year: 2014

Telemetry studies on aquatic animals often use external tags to monitor migration patterns and help to inform conservation effort. However, external tags are known to impair swimming energetics dramatically in a variety of species, including the endangered European eel. Due to their high swimming efficiency, anguilliform swimmers are very susceptibility for added drag. Using an integration of swimming physiology, behaviour and kinematics, we investigated the effect of additional drag and site of externally attached tags on swimming mode and costs. The results show a significant effect of a) attachment site and b) drag on multiple energetic parameters, such as Cost Of Transport (COT), critical swimming speed (Ucrit) and optimal swimming speed (Uopt), possibly due to changes in swimming kinematics. Attachment at 0.125 bl from the tip of the snout is a better choice than at the Centre Of Mass (0.35 bl), as it is the case in current telemetry studies. Quantification of added drag effect on COT and Ucrit show a (limited) correlation, suggesting that the Ucrit test can be used for evaluating external tags for telemetry studies until a certain threshold value. Uopt is not affected by added drag, validating previous findings of telemetry studies. The integrative methodology and the evaluation tool presented here can be used for the design of new studies using external telemetry tags, and the (re-) evaluation of relevant studies on anguilliform swimmers. Copyright: © 2014 Tudorache et al.

Burgerhout E.,Leiden University | Burgerhout E.,NewCatch BV | Brittijn S.A.,NewCatch BV | Tudorache C.,Leiden University | And 5 more authors.
Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology | Year: 2013

European eels (Anguilla anguilla) migrate ~. 6000. km towards their spawning area in the Sargasso Sea. Based on the recent discovery that males swim even more efficiently than females, it was predicted that males also would be able to swim ~. 6000. km within six months. Additionally, eels do not mature naturally in captivity due to strong neural inhibition. Earlier, it was hypothesized that swimming exercise is a natural trigger to induce sexual maturation and may even result in full maturation. In the present study two groups of farmed male silver eels were subjected to either endurance swimming or resting for up to 6. months. It was found that male eels were able to swim continuously for a total distance of 6670. km within 6. months. The body weight decrease in swimming and resting males after 6. months was similar (<. 30. g) underlining the extreme low energy cost of swimming. In contrast to our expectation long-term swimming did not induce sexual maturation in farmed silver eels, suggesting that swimming alone is not sufficient as a trigger for sexual maturation. In conclusion, male eels are efficient long distance swimmers and likely able to cover the distance to the Sargasso Sea within the expected time span of 6. months. © 2013 Elsevier Inc.

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