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- Steroids accumulate in the rearing water of commercial recirculating aquaculture systemsPublication . Mota, Vasco; Martins, Catarina I. M.; Eding, Ep; Canario, Adelino V. M.; Verreth, JohanLittle information is available on steroid concentrations in the rearing water of aquaculture systemsand whether they accumulate in recirculating aquaculture systems (RAS). Therefore this study aimedat determining (1) the concentrations and variation of cortisol and sex steroids in RAS, (2) the con-tribution of fish rearing conditions to steroid concentrations in seven commercial RAS. Each RAS wassampled twice at three different points: (1) make-up water; (2) influent and (3) effluent of the rear-ing unit. The results showed significant higher steroid concentrations in the influent and effluent whencompared with the make-up water. On average cortisol concentration was 15.7% higher in the efflu-ent when compared with the influent. Mean steroid concentrations in the rearing unit effluent variedbetween: 3.8–217.0 ng/L for cortisol, 3–12.5 ng/L for testosterone, 0.9–7.1 ng/L for 11-ketoteststerone and1.8–12.8 ng/L for 17,20 -dihydroxypregn-4-en-3-one. Stocking density, Total Ammonia-Nitrogen con-centration and orthophosphate-P concentration (a measure of make-up water usage) showed a positivecorrelation with sex steroids in the water. The steroid concentrations from the present study were ordersof magnitude lower than initial estimations indicating a water treatment efficiency of >99%. The resultssuggest that an intensification of fish production through decrease of make-up water use and increaseof stocking density will lead to a build-up of steroids in the water. Although intensification is critical forthe economical success of RAS, this ultimately could affect fish performance as steroids accumulates inthe water of RAS at levels that can potentially be detected by some fish species.
- Chemical communication in tilapia: a comparison of Oreochromis mossambicus with O. niloticusPublication . Hubbard, Peter; Mota, Vasco; Keller-Costa, Tina; Silva, José P. da; Canario, Adelino V. M.In allopatric speciation species differentiation generally results from different selective pressures in different environments, and identifying the traits responsible helps to understand the isolation mechanism(s) involved. Male Mozambique tilapia (Oreochromis mossambicus) use urine to signal dominance; furthermore, 5-pregnane-3,17,20-triol-3-glucuronide (and its -epimer, 5-pregnane-3,17,20-triol-3-glucuronide), in their urine is a potent pheromone, the concentration of which is correlated with social status. The Nile tilapia (O. niloticus) is a close relative; species divergence probably resulted from geographical separation around 6 million years ago. This raises the question of whether the two species use similar urinary chemical cues during reproduction. The olfactory potency of urine, and crude extracts, from either species was assessed by the electro-olfactogram and the presence of the steroid glucuronides in urine from the Nile tilapia by liquid-chromatography/mass spectrometry. Both species showed similar olfactory sensitivity to urine and respective extracts from either species, and similar sensitivity to the steroid glucuronides. 5-pregnan-3,17,20-triol-3-glucuronide was present at high concentrations (approaching 0.5 mM) in urine from Nile tilapia, with 5-pregnan-3,17,20-triol-3-glucuronide present at lower concentrations, similar to the Mozambique tilapia. Both species also had similar olfactory sensitivity to estradiol-3-glucuronide, a putative urinary cue from females. Together, these results support the idea that reproductive chemical cues have not been subjected to differing selective pressure. Whether these chemical cues have the same physiological and behavioural roles in O. niloticus as O. mossambicus remains to be investigated.
- Cortisol and testosterone accumulation in a low pH recirculating aquaculture system for rainbow trout (Oncorhynchus mykiss)Publication . Mota, Vasco; Martins, Catarina I. M.; Eding, Ep H.; Canario, Adelino V. M.; Verreth, Johan A. J.Steroids accumulate in recirculating aquaculture system (RAS), although explanatory factors for such accumulation are still poorly explored. This study investigated the effect of water exchange rate and pH in six replicated RAS on the concentration of the stress hormone cortisol in rainbow trout blood plasma and in the holding water and of the sex steroids testosterone, 11-ketotestosterone (11-KT) and 17,20-dihydroxypregn-4-en-3-one (17,20-P) over a 70-day experimental period. Three combinations of water exchange rate and pH were used each treatment, with two replications: (i) high water exchange rate (+/- 1700Lkg(-1) feed) and neutral pH (+/- 7.3), (ii) low water exchange rate (+/- 500Lkg(-1) feed) and neutral pH (+/- 7.3) and (iii) low water exchange rate (+/- 500Lkg(-1) feed) and low pH (+/- 5.8). Plasma cortisol concentrations at day 70 were higher (24.4 +/- 9.5ngmL(-1)) for fish kept at low pH when compared to fish kept at neutral pH (12.0 +/- 0.1 and 8.7 +/- 0.2ngmL(-1)). Water cortisol and testosterone concentrations at day 35 were higher at low pH than at neutral pH, whereas water 11-KT and 17,20-P did not differ among treatments. At day 70, there were no significant differences between low and high pH. These results demonstrate that low pH contributes to increased plasma cortisol concentrations and to its accumulation in water, possibly indicating a stress response to low pH. The higher concentration of testosterone but not of the other sex hormones point to unspecified reproductive effects that need further investigation.