In sole (Solea spp.) culture, like in other flatfish culture, it is likely that a vertical gradient of dissolved oxygen (DO) occurs with the lower concentrations being at the tank bottom. This lower concentration at the tank bottom is a consequence of fish oxygen consumption and of the presence of the boundary layer. This fact generates lower DO concentrations in the near-bottom zone where soles are lying most of the time. The aim of this work was to study the hydrodynamic conditions that determine the oxygen gradient that occurs in the layer of water adjacent to flatfish.; Three flow rates were tested in a circular tank and in a rectangular or raceway tank. For each flow rate, water velocities, boundary layer thickness and Reynolds number were calculated. Results showed that the vertical gradient of dissolved oxygen diminishes when water velocity and Reynolds numbers (Re) increase. At the fish density used in this work (11.6 kg m(-2)), when Re decreased under 6000, a large increase in the DO gradient was observed. Guidelines are presented to determine in which situations, as defined by hydraulic parameters, Re >6000 is achieved and DO stratification avoided.; The present work shows that in raceways, the flow rate required to avoid DO stratification is higher than that typically needed to maintain water quality (oxygen, ammonia-nitrogen, carbon dioxide and suspended solids). In circular tanks, it can be easier to achieve velocities that are high enough to avoid stratification with low water inlet flow rates, by adjusting the area of the water entry orifices. (C) 2014 Elsevier B.V. All rights reserved.
Oca, J.; Masaló, I.; Duarte, S.; Sanchez, P.; Almansa, C.; Reig, L. II Simposi d'Aqüicultura de Catalunya: Investigació, desenvolupament i transferència en aqüicultura des de Catalunya a Europa p. 33 Presentation's date: 2009-10-15 Presentation of work at congresses
Evaluating flatfish activity can be a useful tool for studying fish behavior and welfare. The aim of this
workwas to obtain a quantitative index for measuring flatfish activity using image analysis. Accordingly,
motor activity of a sole population was recorded by digital video for three nights, bearing in mind the
nocturnal lifestyle of the species. Subsequent image analysis was done by image subtraction of
consecutive frames. The result was a ‘‘difference frame’’ showing the changes in the image area due to
fish movement. Using these data, an image processing activity index (IPAI) was determined by
measuring the percentage of area altered due to fish movement and by taking this percentage as an
indicator of fish activity. Typical sole behavioral acts (take-off and surface swimming) were recorded by
direct observation during the same intervals in order to calibrate the IPAI. A direct observation activity
index (DOAI) was determined by weighting each kind of attitude according to its average duration.
Results obtained from image analysis (IPAI) were compared with results obtained by direct observation
(DOAI). A linear relationship between the two indexes was found with a correlation coefficient of
r2 = 0.80 for 92% of coverage area tank and r2 = 0.90 for 210% of coverage area tank. Thus, this digital
video-based index can be a highly reliable and accuratemethod for objectivelymeasuring activity levels
in sole with a low consumption of labor and time. Nevertheless, the application to farm conditions would
need further research and an accurate calibration for other species.