Jean-Paul Blancheton

Populations of heterotrophic bacteria in an experimental recirculating aquaculture system.

Abstract The aim of this work was to identify the main viable heterotrophic bacteria in a marine fish farm with a recirculating water system and to study their growth dynamics. The experiments were performed with sea bass (Dicentrarchus labrax) in an experimental recirculating water system. The bacteria identified were typical of the marine environment: Pseudomonas, Oceanospirillum, Marinobacter, Paracoccus and Erythrobacter genus from Bergey’s group IV, two genus of Vibrionaceae, one strain of Vibrio and one strain of Aeromonas. These populations were stable when the ingested feed/replacement water ratio was kept constant. Fixed bacteria formed large biofilms, which released about 104 CFU ml−1 into the tank. The biological filter, with its large surface area, was the largest source of bacteria in the farm, but the UV disinfection unit kept the number of free bacteria stable. When properly managed, the majority of bacteria that grew on the biological filter were from Bergey’s group IV; no Vibrio were ever detected on it.

Bacteria and nutrients—nitrogen and carbon—in a recirculating system for sea bass production

In a recirculating rearing system, different chemical compounds (nitrate, phosphorus and dissolved organic carbon (DOC)) are accumulated depending on the quantity of replacement water added in the system. Some of them can also be used as bacterial nutrients. The aims of the present study were (1) to focus on the different forms of dissolved carbon; and (2) to establish if there was a relationship between the dissolved forms of the nutrients (N and C) and bacterial concentrations. We observed that the nature of DOC changed as the volume of replacement water was decreased, and that humic substances (HS) were accumulated. The concentration of fixed and free bacteria was constant at 3.13×105±2.6×105 CFU g−1 of packing and 3.29×103±2.09×103 CFU ml−1 (M±SD), respectively, regardless of the quantity of replacement water added in the system. This shows that the quantity of biodegradable DOC was not the limiting factor for heterotrophic bacterial growth. The quantity of replacement water was not the most important factor to control heterotrophic bacteria population. What appears to be vital is the quantity of feces reaching the biological filter, which can be reduced by a good mechanical filtration and a good feed conversion index.

Bacteria and particulate materials in recirculating seabass (Dicentrarchus labrax) production system

This study investigated the total aerobic bacteria and suspended matter concentrations in closed system seabass (Dicentrarchus labrax) rearing tanks. Higher concentrations were found during the larval rearing phase using live prey feeding than during fingerling production using pellet feeding. The biological filter appeared to be very efficient in controlling bacteria populations, both before the first feeding of the larvae and after weaning. The inflow water quality in the broodstock tanks was better in the closed system than in an open system, although the outlet water in the closed system contained more bacteria and suspended matter.

Separation efficiency of a vacuum gas lift for microalgae harvesting.

Low-energy and low-cost separation of microalgae from water is important to the economics of microalgae harvesting and processing. Flotation under vacuum using a vacuum gas lift for microalgae harvesting was investigated for different airflow rates, bubble sizes, salinities and harvest volumes. Harvesting efficiency (HE) and concentration factor (CF) of the vacuum gas lift increased by around 50% when the airflow rate was reduced from 20 to 10 L min(-1). Reduced bubble size multiplied HE and CF 10 times when specific microbubble diffusers were used or when the salinity of the water was increased from 0‰ to 40‰. The reduction in harvest volume from 100 to 1L increased the CF from 10 to 130. An optimized vacuum gas lift could allow partial microalgae harvesting using less than 0.2 kWh kg(-1) DW, thus reducing energy costs 10-100 times compared to complete harvesting processes, albeit at the expense of a less concentrated biomass harvest.

Effect of stocking density on performances of juvenile turbot (Scophthalmus maximus) in recirculating aquaculture systems

Limited information has been available about the influence of loading density on the performances of Scophthalmus maximus, especially in recirculating aquaculture systems (RAS). In this study, turbot (13.84±2.74 g; average weight±SD) were reared at four different initial densities (low 0.66, medium 1.26, sub-high 2.56, high 4.00 kg/m2) for 10 weeks in RAS at 23±1°C. Final densities were 4.67, 7.25, 14.16, and 17.47 kg/m2, respectively, which translate to 82, 108, 214, and 282 percent coverage of the tank bottom. Density had both negative and independent impacts on growth. The final mean weight, specific growth rate (SGR), and voluntary feed intake significantly decreased and the coefficient of variation (CV) of final body weight increased with increase in stocking density. The medium and sub-high density groups did not differ significantly in SGR, mean weight, CV, food conversion rate (FCR), feed intake, blood parameters, and digestive enzymes. The protease activities of the digestive tract at pH 7, 8.5, 9, and 10 were significantly higher for the highest density group, but tended to be lower (not significantly) at pH 4 and 8.5 for the lowest density group. The intensity of protease activity was inversely related to feed intake at the different densities. Catalase activity was higher (but not significantly) at the highest density, perhaps because high density started to induce an oxidative effect in turbot. In conclusion, turbot can be cultured in RAS at a density of less than 17.47 kg/m2. With good water quality and no feed limitation, initial density between 1.26 and 2.56 kg/m2 (final: 7.25 and 14.16 kg/m2) would not negatively affect the turbot cultured in RAS. For culture at higher density, multi-level feeding devices are suggested to ease feeding competition.

Development of an intensive culture system for sea bass (Dicentrarchus labrax) larvae in sea enclosures

A system for the intensive production of sea bass larvae (Dicentrarchus labrax) in sea structures was developed between 1987 and 1994. In 1994, this system was used successfully for two larval rearing cycles (with 400000 and 420000 2-day-old larvae) at a fish farm. One hundred days after hatching the survival rate was 11%, and the mean weight of fish was 2.5 g. The water temperature varied from 13.9 to 25.4 °C in the cylindro-conical enclosures (40 m3) which were set in the sea. The density of fish larvae at starting time was about 10 1−1. Larvae were fed initially with Artemia nauplii (hatched out on land). Digestive content observations showed that they also fed on natural plankton in the enclosure. Weaning onto microparticles started when the mean length of the larvae reached 12 mm. Temperature variations were largely dependent on the water surrounding the enclosure but the chemical parameters inside were quite different from those of the sea. Many problems solved during the preliminary experiments are discussed, including the control of fouling, but contamination by predators or competitors is still a risk. The natural food web which develops in the enclosure, with the fish larvae as the main predators, seems to be an advantage for larval rearing. The use of such an enclosure system, which is not expensive and is easy to set up at a farm, is discussed.

Evaluation of Aquaculture System Sustainability: A Methodology and Comparative Approaches

Over the last 30 years, aquaculture has experienced an unprecedented development in global animal production with an average yearly growth rate of over 10% between 1980 and 2000 (FAO, 2009). During the same period, capture fisheries saw their progression gradually grind to a standstill and growth stopped from 1995 (total catch fluctuating between 90 and 95 Mt/year according to the year). The growth of aquaculture, despite its benefits and the fact that it is the only way to meet the increase in demand for sea products, evaluated at 270Mt in 2050 (Chevassus au Louis et Lazard, 2009; Wijkstrom, 2003), raises a certain number of issues directly related to its sustainable development. Amongst these are issues related to feed for the farmed organisms, to their biological diversity, to the farms’ economic sustainability, to the impact of aquaculture development on social equity and to the set of arrangements constituting the sector’s governance. Feed, for example, is currently the subject of significant controversy as shown by the emblematic article of Naylor et al. (2000) that exposes the impact on catches of the massive use of fish meal and fish oil in fish and prawn aquaculture and advocates the return to sparser aquaculture systems, directly inspired by traditional Asian systems which use more extensive techniques based on polyculture and fertilisation and where artificial feed is only seen as a potential supplement. This diagnosis, although interesting as it generated much debate, was, however, incomplete and, in fact, inaccurate: by focusing on a single criterion and a single dimension (environmental) of sustainability, the authors were led to make proposals that had no chance of being adopted by the actors. De facto, farming systems have continued to intensify and this has led to a sustained increase in the use of

Bio-physiological response of biofilter algal candidate Ulva sp. to different nitrogen forms and fluxes

The present study was carried out to study the long term effect of different nitrogen forms and concentrations (14.3, 28.6 and 57.1 µM N-NH4 and 214, 2360 and 3700 µM N-NO3) on the photosynthesis and relative growth rate (RGR) of Ulva sp. for five weeks. Nutrient-enriched seawater was supplied at an exchange rate of between 12.6 and 14.4 volumes per day. Relative growth rate was determined weekly. Photosynthetic oxygen evolution response was measured using 20 - 25 mg fresh weight seaweed incubated in a DW3 measuring chamber for 56 min under different irradiances with light and dark periods alternating every seven minutes. Photosynthetic light-response curves were drawn using 15 photosynthetic oxygen evolution readings normalized to dry weight. Experimental data were fitted with a Haldane model to calculate photosynthetic rate (Pmax), saturation irradiance (Is) and compensation irradiance (Ic). At the experiment termination, the RGR following nitrate addition were higher, but not significantly, than those with the ammonium supplied. The highest RGR was determined at the medium nitrate concentration. The photosynthetic activity of Ulva sp. showed a positive relationship with nitrogen concentrations from both nitrogen forms. The highest significant Pmax was found at the highest nitrate concentration. The lowest ammonium concentration corresponded to the lowest significant Pmax value. No significant differences were found for Is and Ic irrespective of treatment, although, in general, ammonium treatments yielded higher Is values than nitrate treatments. The discrepancy between the growth rate results and photosynthetic oxygen evolution is discussed in light of the reproduction activity and temperature effect.