justification of the larval husbandry work planned in diversify
The successful larval husbandry of any fish species determines the number of juveniles that will be available for grow out to market weight, but also the quality of these fry, in terms of future growth performance, metamorphic success, incidence of morphological deformities and disease resistance (Koven, 2003; Georgakopoulou et al., 2007; Sandel et al., 2010). In order to improve juvenile quality, research must be carried out on environmental (e.g.. salinity, temperature, light, microalgae type and concentration) and husbandry (type and concentration of zooplankton prey) requirements that can pose bottlenecks to a successful industry. The results of these studies form the basis for species- specific protocols for enhanced production of high quality juveniles.
Meagre has the biological characteristics to be an excellent candidate for commercial aquaculture and has adapted well to modified gilthead sea bream and European sea bass culture protocols (FAO, 2005-2011), particularly those based on rotifer and Artemia feeding methodologies. This has lead to meagre production, which increased 7 fold since 1997. Although the precise requirements for essential amino and fatty acids are not completely known, the larvae show very good growth and survival rates using commercially available enrichment products for live prey. Therefore, producers do not consider larval rearing in general to be a major bottleneck for the expansion of meagre culture, although cannibalism and variable size distribution in larvae and juveniles are causing increasing concern. This may be due to a protracted dependence on feeding on Artemia, which have lower protein levels and are less dense in nutrients than dry feeds, possibly resulting in asynchronous growth. Consequently, advancing the early weaning of larvae on dry feeds is a priority and the major focus of the larval work on meagre.
Early larval rearing techniques applied for greater amberjack based on a variety of semi-intensive approaches (Papandroulakis et al., 2005) have shown promising results. Nevertheless, substantial gaps remain in these protocols as inadequate live food quality and quantity continue to cause significant mortality. Growth performance during early life is rapid, with 40 dph individuals reaching 0.5 g and having completed weaning to artificial diets. However, survival is about 3%, while it is argued that modifying the feeding regime and developing specific diets could improve survival to 20% during the first month (Anonymous, 2008; Hamasaki et al., 2009; Roo et al., 2012). Further studies are essential for the definition of nutritionally sensitive periods during larval rearing and the development of appropriate feeding regimes adapted to the development of the digestive system of the larvae (Papadakis et al., 2009). Furthermore, environmental factors such as the intensity and duration of light, as well as rearing tank volume and hydrodynamics may have a significant effect on larval performance (Carton, 2005; Stuart & Drawbridge, 2011). In the proposed research, these factors will be studied, to develop intensive rearing protocols that will improve fry production and quality.
In percids such as pikeperch, survival is 5-20% during larval rearing while cannibalism represents 30-50% of all mortality (Babiak et al., 2004; Mandiki et al., 2007; Ledoré et al., 2010) and it is caused primarily by size heterogeneity (Kestemont et al., 2003; Mandiki et al., 2007). Cannibalistic behaviour is observed first around 7 dph (Babiak et al., 2004) and progresses to become very severe from 18 to 39 dph representing up to 80% of all mortality at weaning time (19 to 23 dph) in pikeperch (Kestemont et al., 2007; Szkudlarek and Zakeś, 2011). Presently, there is no effective larval rearing protocol to reduce this very high mortality during larval rearing. One approach to reduce cannibalism is to sort out the larger larvae from their slower growing cohorts. However, this method is weakly effective as a new group of faster growing individuals emerges shortly afterwards (Kestemont et al., 2003, 2007; Mandiki et al., 2007), suggesting a social interaction factor may be involved. Consequently, successful culture of pikeperch requires development of effective larval rearing and weaning protocols that reduce cannibalism and mortality while improving growth. These protocols will be based on knowledge gathered from multifactorial experiments that integrate the combined effects of numerous environmental, social, genetic and nutritional factors, as well as their many interactions (Folkvord and Otterå, 1993; Baras et al., 2003, 2011; Kestemont et al., 2003; Teletchea et al., 2011; Trabelsi et al., 2011). Moreover, practical protocols can also be evaluated by their effect on the ontogeny of the digestive and sensory systems, larval behaviour and sensitivity to stress (Kestemont et al., 2003, Ostaszewska et al. 2005; Sabate et al., 2009; Baras et al., 2010; Trabelsi et al., 2011).
Commercial production of Atlantic halibut fry currently is carried out in FTS. However, there is growing agreement that RAS would offer more stable environmental and chemical water conditions that would lead to improved larval performance. Larval feeding is based on the intensive use of Artemia nauplii and metanauplii as the sole food, which is provided during a long photo-phase (17L:7D) until weaning (60 days or more after first feeding) onto a dry feed (Hamre & Harboe, 2008a,b). However, the protracted use of feeding Artemia nauplii and metanauplii in discrete meals until weaning (Harboe et al., 2009) appears to reduce prey intake and digestion efficiency. Antibiotics have been found to ease this situation (Roiha Sunde et al., 2011) although larval growth still decreases during the second half of the live prey period. A practice that is currently in use in order to reduce bacterial load as well as production costs is the addition of clay instead of algae to the rearing tank, which creates the necessary turbidity (Harboe & Reitan, 2005). Having this in mind, the objectives in the proposed project are to (1) compare the use of antibiotics in RAS with FTS during yolk sac and early feeding on larval performance, (2) optimise use of probiotics during early development and (3) develop a production protocol for on-growing Artemia and compare the effects of this live food with Artemia nauplii on larval performance, development and behaviour at different developmental stages.
Embryonic development and early stages of larval life until yolk sac consumption have been described in wreckfish (Papandroulakis et al., 2008, Peleteiro et al., 2011). These studies show that larvae at mouth opening are large (5 mm) and, therefore, are expected to adapt easily to commonly cultured live food such as rotifers and Artemia. Nevertheless, there is a need to investigate the factors influencing the larval rearing environment of the species such as light, temperature and hydrodynamics of larval rearing tanks, as well as the type and concentration of zooplankton prey to be fed to the larvae. To accomplish these aims, it is essential to identify nutritionally sensitive periods by relating the type and concentration of live prey with the development of the larval digestive tract (Papadakis et al., 2009). In addition, it is expected that the application of knowledge from the rearing of related species such as Polyprion oxygenius in New Zealand (Anderson et al., 2012) and dusky grouper (Epinephelus marginatus) (Bruzón, 2007) will facilitate the domestication of wreckfish. In the proposed project the objective is to evaluate larvae in terms of growth, survival as well as biochemical and biometric analyses from three culture systems --mesocosm, RAS and flow-through-- in order to develop a larval rearing protocol for this species.
There is a general consensus that a major factor limiting the commercial rearing of grey mullet is the high mortality occurring during early larval development (Murashige et al., 1991; Yoshimatsu et al., 1995; Harel et al., 1998). Harel et al. (1998) found that the “greening” of the rearing tanks with Isochrysis galbana, which has characteristically high levels of DHA (22:6n-3), contributed significantly more to larval survival than adding Nannochloropsis oculata, a microalgae relatively rich in EPA (20:5n-3). On the other hand, a number of researchers have claimed that ceramic clay is a viable alternative to adding microalgae to the rearing tanks (Attramadal et al., 2012), suggesting that the role of “greening” in rearing tanks is mostly to provide turbidity and background lighting to facilitate the larval hunting of zooplankton prey. Taken one step further, this suggests that adding concentrated algal pastes, frozen or freeze-dried, might be an economical alternative. On the other hand, the addition of live algae to the larval rearing tanks may be imparting other biochemical and stimulatory benefits to the larvae that would outweigh the advantage of freeze dried or concentrated algal pastes. Therefore, studies are necessary to compare the effect of microalgae species and concentration on larval rotifer ingestion, biochemical composition, digestive enzyme ontogeny and metamorphic synchrony. In addition, there is a need to investigate if the benefit of algal addition is due to its effect on facilitating larval hunting. Finally the effectiveness and cost-benefit of using dried or frozen algal pastes must be examined.
Meagre has the biological characteristics to be an excellent candidate for commercial aquaculture and has adapted well to modified gilthead sea bream and European sea bass culture protocols (FAO, 2005-2011), particularly those based on rotifer and Artemia feeding methodologies. This has lead to meagre production, which increased 7 fold since 1997. Although the precise requirements for essential amino and fatty acids are not completely known, the larvae show very good growth and survival rates using commercially available enrichment products for live prey. Therefore, producers do not consider larval rearing in general to be a major bottleneck for the expansion of meagre culture, although cannibalism and variable size distribution in larvae and juveniles are causing increasing concern. This may be due to a protracted dependence on feeding on Artemia, which have lower protein levels and are less dense in nutrients than dry feeds, possibly resulting in asynchronous growth. Consequently, advancing the early weaning of larvae on dry feeds is a priority and the major focus of the larval work on meagre.
Early larval rearing techniques applied for greater amberjack based on a variety of semi-intensive approaches (Papandroulakis et al., 2005) have shown promising results. Nevertheless, substantial gaps remain in these protocols as inadequate live food quality and quantity continue to cause significant mortality. Growth performance during early life is rapid, with 40 dph individuals reaching 0.5 g and having completed weaning to artificial diets. However, survival is about 3%, while it is argued that modifying the feeding regime and developing specific diets could improve survival to 20% during the first month (Anonymous, 2008; Hamasaki et al., 2009; Roo et al., 2012). Further studies are essential for the definition of nutritionally sensitive periods during larval rearing and the development of appropriate feeding regimes adapted to the development of the digestive system of the larvae (Papadakis et al., 2009). Furthermore, environmental factors such as the intensity and duration of light, as well as rearing tank volume and hydrodynamics may have a significant effect on larval performance (Carton, 2005; Stuart & Drawbridge, 2011). In the proposed research, these factors will be studied, to develop intensive rearing protocols that will improve fry production and quality.
In percids such as pikeperch, survival is 5-20% during larval rearing while cannibalism represents 30-50% of all mortality (Babiak et al., 2004; Mandiki et al., 2007; Ledoré et al., 2010) and it is caused primarily by size heterogeneity (Kestemont et al., 2003; Mandiki et al., 2007). Cannibalistic behaviour is observed first around 7 dph (Babiak et al., 2004) and progresses to become very severe from 18 to 39 dph representing up to 80% of all mortality at weaning time (19 to 23 dph) in pikeperch (Kestemont et al., 2007; Szkudlarek and Zakeś, 2011). Presently, there is no effective larval rearing protocol to reduce this very high mortality during larval rearing. One approach to reduce cannibalism is to sort out the larger larvae from their slower growing cohorts. However, this method is weakly effective as a new group of faster growing individuals emerges shortly afterwards (Kestemont et al., 2003, 2007; Mandiki et al., 2007), suggesting a social interaction factor may be involved. Consequently, successful culture of pikeperch requires development of effective larval rearing and weaning protocols that reduce cannibalism and mortality while improving growth. These protocols will be based on knowledge gathered from multifactorial experiments that integrate the combined effects of numerous environmental, social, genetic and nutritional factors, as well as their many interactions (Folkvord and Otterå, 1993; Baras et al., 2003, 2011; Kestemont et al., 2003; Teletchea et al., 2011; Trabelsi et al., 2011). Moreover, practical protocols can also be evaluated by their effect on the ontogeny of the digestive and sensory systems, larval behaviour and sensitivity to stress (Kestemont et al., 2003, Ostaszewska et al. 2005; Sabate et al., 2009; Baras et al., 2010; Trabelsi et al., 2011).
Commercial production of Atlantic halibut fry currently is carried out in FTS. However, there is growing agreement that RAS would offer more stable environmental and chemical water conditions that would lead to improved larval performance. Larval feeding is based on the intensive use of Artemia nauplii and metanauplii as the sole food, which is provided during a long photo-phase (17L:7D) until weaning (60 days or more after first feeding) onto a dry feed (Hamre & Harboe, 2008a,b). However, the protracted use of feeding Artemia nauplii and metanauplii in discrete meals until weaning (Harboe et al., 2009) appears to reduce prey intake and digestion efficiency. Antibiotics have been found to ease this situation (Roiha Sunde et al., 2011) although larval growth still decreases during the second half of the live prey period. A practice that is currently in use in order to reduce bacterial load as well as production costs is the addition of clay instead of algae to the rearing tank, which creates the necessary turbidity (Harboe & Reitan, 2005). Having this in mind, the objectives in the proposed project are to (1) compare the use of antibiotics in RAS with FTS during yolk sac and early feeding on larval performance, (2) optimise use of probiotics during early development and (3) develop a production protocol for on-growing Artemia and compare the effects of this live food with Artemia nauplii on larval performance, development and behaviour at different developmental stages.
Embryonic development and early stages of larval life until yolk sac consumption have been described in wreckfish (Papandroulakis et al., 2008, Peleteiro et al., 2011). These studies show that larvae at mouth opening are large (5 mm) and, therefore, are expected to adapt easily to commonly cultured live food such as rotifers and Artemia. Nevertheless, there is a need to investigate the factors influencing the larval rearing environment of the species such as light, temperature and hydrodynamics of larval rearing tanks, as well as the type and concentration of zooplankton prey to be fed to the larvae. To accomplish these aims, it is essential to identify nutritionally sensitive periods by relating the type and concentration of live prey with the development of the larval digestive tract (Papadakis et al., 2009). In addition, it is expected that the application of knowledge from the rearing of related species such as Polyprion oxygenius in New Zealand (Anderson et al., 2012) and dusky grouper (Epinephelus marginatus) (Bruzón, 2007) will facilitate the domestication of wreckfish. In the proposed project the objective is to evaluate larvae in terms of growth, survival as well as biochemical and biometric analyses from three culture systems --mesocosm, RAS and flow-through-- in order to develop a larval rearing protocol for this species.
There is a general consensus that a major factor limiting the commercial rearing of grey mullet is the high mortality occurring during early larval development (Murashige et al., 1991; Yoshimatsu et al., 1995; Harel et al., 1998). Harel et al. (1998) found that the “greening” of the rearing tanks with Isochrysis galbana, which has characteristically high levels of DHA (22:6n-3), contributed significantly more to larval survival than adding Nannochloropsis oculata, a microalgae relatively rich in EPA (20:5n-3). On the other hand, a number of researchers have claimed that ceramic clay is a viable alternative to adding microalgae to the rearing tanks (Attramadal et al., 2012), suggesting that the role of “greening” in rearing tanks is mostly to provide turbidity and background lighting to facilitate the larval hunting of zooplankton prey. Taken one step further, this suggests that adding concentrated algal pastes, frozen or freeze-dried, might be an economical alternative. On the other hand, the addition of live algae to the larval rearing tanks may be imparting other biochemical and stimulatory benefits to the larvae that would outweigh the advantage of freeze dried or concentrated algal pastes. Therefore, studies are necessary to compare the effect of microalgae species and concentration on larval rotifer ingestion, biochemical composition, digestive enzyme ontogeny and metamorphic synchrony. In addition, there is a need to investigate if the benefit of algal addition is due to its effect on facilitating larval hunting. Finally the effectiveness and cost-benefit of using dried or frozen algal pastes must be examined.
