Abstract
Commercial farming of turbot (Scophthalmus maximus) at high stocking densities may lead to growth depression and increasing production costs. Moreover, the high levels of accumulated waste in an intensive system may cause rapid deterioration of water quality, which may undermine the production. L-carnitine is known as a growth-enhancer which shows promise as mitigator of crowding effects. The effects of stocking densities (4, 8, 11 and 14 kg m²) on growth performance, feed utilization and body composition were evaluated during 75 days on turbot (75.6 ± 2.8 g) fed two dietary L-carnitine levels (40 or 240 mg kg¹). At the end of the feeding trial, total ammonia excretion (TAN) was measured postprandially for 24h. Specific growth rate and weight gain decreased with increasing stocking density. Fish held at 4 kg m² had higher final body weight (94-96 g) than fish held at higher densities (80-87 g). Protein efficiency ratio was higher in fish held at 4 kg m² (1.33-1.36), in comparison to fish stocked at 8 kg m² (0.98) or 14 kg m² (0.45). Voluntary feed intake decreased from 0.70 to 0.56% BW with increasing stocking density. Dietary L-carnitine supplementation did not affect growth performance and body composition, except for body L-carnitine content which increased from 75 to 128 mg kg¹ BW with supplementation. Fish fed 240 mg L-carnitine supplements had lower TAN that the ones fed 40 mg L-carnitine (p < 0.05).
Highlights
The turbot, (Scophthalmus maximus) is recognized by European consumers as one of the most valued species
This study hypothesizes that the addition of carnitine to aquafeeds may promote wellbeing of turbot, decreasing stress-related pitfalls induced by intensive aquaculture practices, and investigates interaction effects of dietary L-carnitine and stocking density on growth performance, body composition and nitrogen excretion of juvenile turbot
Mortality rates were below 5%, occurred with no systematic trend and did not differ among experimental groups
Summary
The turbot, (Scophthalmus maximus) is recognized by European consumers as one of the most valued species. Environmental factors influencing fish growth have been significantly studied, little attention has been devoted to rearing conditions (e.g. stocking density, culture system, husbandry) leading to the establishment of social interactions in confined stocks. Social interactions, such as development of hierarchical groups through competition for food and/or space, can negatively affect biomass accumulation (Irwin et al, 1999; Aksungur et al, 2007). The intensive production of turbot generates size disparities during the grow-out phase that could be partly attributed to poor husbandry practices and stocking density conditions In many cases, this may lead to the development of slow growing individuals, increasing production costs. This study hypothesizes that the addition of carnitine to aquafeeds may promote wellbeing of turbot, decreasing stress-related pitfalls induced by intensive aquaculture practices, and investigates interaction effects of dietary L-carnitine and stocking density on growth performance, body composition and nitrogen excretion of juvenile turbot
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