Aquacultural Engineering 51 (2012) 7–14 Contents lists available at SciVerse ScienceDirect Aquacultural Engineering journa l h omepa g e: www .elsevier.com/locate/aqua-online Use of laser scanning to evaluate turbot (Scophthalmus maximus) distribution in raceways with different water velocities C. Almansa, L. Reig, J. Oca ∗ Departament d’Enginyeria Agroalimentària i Biotecnologia, Universitat Politècnica de Catalunya, BarcelonaTech, C. Esteve Terrades 8, 08860 Castelldefels, Spain a r t i c l e i n f o Article history: Received 1 February 2012 Accepted 26 April 2012 Keywords: Water velocity Fish distribution Laser scanning Flatfish a b s t r a c t Fish distribution can be a reliable indicator of husbandry conditions but, as happens with other behav- ioral parameters, it is not easy to assess with objectivity and repeatability. Here, we used a laser scanning method to monitor the distribution variations of a turbot (Scophthalmus maximus) population in a tank under different water velocity treatments, using (1) two uniform water velocities throughout the rearing unit, by changing the water depth but keeping the water flow; (2) different water velocities inside the rearing unit, which allowed the fish to choose a preferred zone; and (3) baffles to create a higher velocity and turbulence above and below them. Preliminary results on water velocity preferences or tolerance for 22-cm turbot determined that velocities between 0.33 and 0.46 BL s -1 promoted a homogenous tur- bot distribution, but that when the fish could choose, they avoided swimming against water flows over 0.58 BL s -1 . With a velocity over 0.98 BL s -1 , turbot no longer appeared to be able to maintain their posi- tion. We also tested the viability of the method to estimate the total biomass of turbot in a high-density tank (from 280 to 320 percentage of coverage area [PCA]). The resulting coefficient of variation between samplings was lower than 10%. The laser scanning has proven to be a useful tool to monitor flatfish dis- tribution and to estimate the total biomass in flatfish culture, and it offers several advantages: (1) it is objective and non-intrusive, thus minimizing stress; (2) it can be used with a high stocking density; (3) it analyzes biomass population; and (4) it can be adapted to existing commercial facilities. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Tank hydrodynamics represent a vital part of the engineer- ing process in the rational use of resources, mainly of water and space. Aquaculture production units should be designed to use the minimum rearing volume necessary to keep fish under the best conditions for growth, thus ensuring fish welfare and minimizing resource consumption. This can be achieved when a tank provides uniform rearing conditions that favor a homogeneous fish distribu- tion, consequently guaranteeing optimal use of the entire rearing volume. While fish distribution could be a reliable indicator of husbandry conditions, it has the same problem as other behavioral parameters, namely, that it is difficult to guarantee its objectivity and repeatabil- ity. Frequently, fish behavior observation is not readily automated or objectively quantifiable (as exemplified by Almazán-Rueda et al., 2004; Griffiths and Armstrong, 2000; Ross et al., 1995; Wagner, 1993). Computer-imaging techniques provide a new approach to acquire and analyze animal behavioral data that could supply accu- rate, objective, and low labor-consuming information (see Cordero ∗ Corresponding author. Tel.: +34 935521223; fax: +34 935521001. E-mail address: joan.oca@upc.edu (J. Oca). et al., 1994; Duarte et al., 2009, 2011; Kato et al., 1996; Kristiansen et al., 2004; Stien et al., 2007). In order to non-invasively ana- lyze stress levels and welfare in farmed fish, a system is required that could automatically detect stress-related behavior (Stien et al., 2007). Previous studies have mainly used pelagic fish and techniques that are difficult to implement in flatfish culture due to the differ- ent physical and behavioral characteristics of flatfish. Nevertheless, the immobility and benthic behavior of these fish facilitate study- ing their distribution in two dimensions and even estimating their biomass. Based on this, Oca et al. (2007) proposed a laser scanning method based on image analysis that could be used in flatfish facil- ities, even those with high percentage of coverage area (PCA), by taking advantage of the relative immobility of flatfish to assess the biomass distribution in the tank. Laser scanning involves acquiring a multitude of XY or XYZ coordinates (2D or 3D analysis, respec- tively) from the surface of an object. This technique is widely used in civil engineering, archeology, prototyping, and the cinema and videogames industries (Bogue, 2010), and is increasingly in agricul- ture (Igathinathane et al., 2010; Rosell et al., 2009). It could also be an alternative to monitor fish biomass in flatfish aquaculture facili- ties, substituting traditional techniques based on fish sampling and weighing. It must be said that other innovative technologies used in pelagic species are based in acoustic methods (Conti et al., 2006) 0144-8609/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aquaeng.2012.04.002