Final Biomass Density Research Articles

Biomass, photosynthetic activity, and biomolecule composition in Chlorella fusca (Chlorophyta) cultured in a raceway pond operated under greenhouse conditions.

Raceways are widely used as microalgae culture systems due to their low cost, but they are not the best option for biomass yield. Understanding in situ photosynthetic performance can be a first step to increase their biomass productivity. This study aimed at comparing the real time photosynthetic activity in a greenhouse raceway culture (250L) with discrete measurements under laboratory conditions. We evaluated the photophysiology and biochemical composition of Chlorella fusca culture up to 120h. In situ photosynthetic activity was continuously monitored and compared to discrete ex situ measurements; biochemical compounds were measured daily. The results showed a final biomass density of 0.45gL-1 (5 days - 120h) and an increase of the electron transport rate (ETR) up to 48h but decreased thereafter. When the relative ETR was estimated considering the absorption coefficient (a) positive correlations of this parameter with photosynthetic capacity, cell density, biomass, biocompounds and antioxidant activity were obtained, whereas no correlation was detected without considering a. In situ photosynthesis monitoring showed higher absolute maximal ETR (10 - 160 μmol m-3s-1) than discrete ex situ measurements. We demonstrated the importance of considering the light absorption coefficient for expressing photosynthetic capacity and showed that C. fusca can produce, in the short-term, bioactive compounds that are correlated to photosynthetic conditions.

Optimization of nutrient utilization efficiency and productivity for algal cultures under light and dark cycles using genome-scale model process control

Algal cultivations are strongly influenced by light and dark cycles. In this study, genome-scale metabolic models were applied to optimize nutrient supply during alternating light and dark cycles of Chlorella vulgaris. This approach lowered the glucose requirement by 75% and nitrate requirement by 23%, respectively, while maintaining high final biomass densities that were more than 80% of glucose-fed heterotrophic culture. Furthermore, by strictly controlling glucose feeding during the alternating cycles based on model-input, yields of biomass, lutein, and fatty acids per gram of glucose were more than threefold higher with cycling compared to heterotrophic cultivation. Next, the model was incorporated into open-loop and closed-loop control systems and compared with traditional fed-batch systems. Closed-loop systems which incorporated a feed-optimizing algorithm increased biomass yield on glucose more than twofold compared to standard fed-batch cultures for cycling cultures. Finally, the performance was compared to conventional proportional-integral-derivative (PID) controllers. Both simulation and experimental results exhibited superior performance for genome-scale model process control (GMPC) compared to traditional PID systems, reducing the overall measured value and setpoint error by 80% over 8 h. Overall, this approach provides researchers with the capability to enhance nutrient utilization and productivity of cell factories systematically by combining genome-scale models and controllers into an integrated platform with superior performance to conventional fed-batch and PID methodologies.

High density cultivation and CO2 uptake by panel arrays of the macrophytic red alga Gracilaria vermiculophylla in a 100 L raceway pond

New approaches are needed for land-based cultivation of macrophytic red algae that reduce costly aeration requirements for biomass suspension and enable high-density cultivation. The goal of this study was to demonstrate the high-density cultivation of the carbohydrate-rich macrophytic red alga Gracilaria vermiculophylla on vertical arrays of panels deployed in an open channel raceway configuration similar to those developed for mass cultivation of microalgae. A clonal culture of G. vermiculophylla, consisting of branched, cylindrical thallus tissues of 8–10 cm length, was mechanically blended using a Waring blender into 2–3 cm fragments and then fluidically injected onto a 3 mm polypropylene mesh support. Immobilized G. vermiculophylla mesh panels were spaced 6.5 cm apart and aligned parallel to flowing seawater medium at nominal bulk velocity of 20 cm s−1 in a 100 L raceway pond of 20 cm liquid depth. This raceway was equipped with real-time measurement of CO2 concentration in the inlet and outlet gas for determination of CO2 uptake dynamics. Specific rates for CO2 uptake became saturated at 8000 ppm CO2. To match CO2 demand by the biomass under nutrient-replete conditions at 21 °C, the inlet gas CO2 was increased from 1000 to 4000 ppm (day 7–14), and then to 8000 ppm (day 14–23) at 0.010 L gas L−1 liquid min−1 gas flow. Over the 23 day cultivation, biomass on the panel increased by a factor of 48, with final biomass loading exceeding 10 kg FW m−2 panel area, and cumulative CO2 capture of 65%. The cumulative average areal productivity within the panel zone of the raceway exceeded 60 g AFDW m−2 day−1, and final biomass density nearing 7.2 g AFDW L−1 (47 g FW L−1) was achieved after 23 days. Overall, these outcomes demonstrate the potential for land-based raceway cultivation of clonal red macroalgae of present and future commercial significance.

Carbon supplementation promotes assimilation of aquaculture waste by the sea cucumber Holothuria scabra: Evidence from stable isotope analysis

Cultivating high-value deposit feeders such as sea cucumbers on solid waste from intensive aquaculture is an innovative approach to turn potential nutrient pollution into a resource. Carbon supplementation to increase the carbon to nitrogen ratio (C:N) of the nitrogen-rich aquaculture waste has been demonstrated to support higher deposit feeder biomass, but commercially viable carbon sources remain to be tested. This experiment investigated the performance of laboratory grade cellulose and bagasse, an agricultural waste product, to improve growth and nutrient utilization from milkfish aquaculture waste in juveniles of the sea cucumber Holothuria scabra. Supplementation with bagasse supported a significantly higher final biomass density (205.71 ± 11.08 g m−2, mean ± SE) than waste without carbon supplementation (p = 0.027). For the first time, a species-specific trophic enrichment factor (Δ13Corg) was applied in stable isotope analysis of feed sources by H. scabra (Δ13Corg of 2.56 ± 0.96‰ (mean ± SD) for the internal organs and 4.31 ± 0.96‰ for the body wall). Results indicated that sea cucumbers were able to assimilate carbon directly from the cellulose. Bagasse supported higher uptake of carbon from aquaculture waste, thus identifying it as a viable resource to improve bioremediation by deposit feeding sea cucumbers in integrated aquaculture. While illustrating the importance of nutrient balances for bioremediation, questions remain about the roles of direct feeding by deposit feeders vs. the decomposition by microbial communities.

Evaluation of Galdieria sulphuraria and Chlorella vulgaris for the Bioremediation of Produced Water

Produced water (PW) is the largest waste stream generated by the oil and gas industry. Traditional treatment of PW burdens the industry with significant expenses and environmental issues. Alternatively, microalgal-based bioremediation of PW is often viewed as an ecologically safe and sustainable platform for treating PW. Moreover, the nutrients in PW could support algal growth. However, significant dilution of PW is often required in algal-based systems due to the presence of complex chemical contaminants. In light of these facts, the current work has investigated the potential of cultivating Galdieria sulphuraria and Chlorella vulgaris in PW using multiple dilutions; 0% PW, 5% PW, 10% PW, 20% PW, 50% PW and 100% PW. While both algal strains can grow in PW, the current results indicated that G. sulphuraria has a higher potential of growth in up to 50% PW (total dissolved solids of up to 55 g L−1) with a growth rate of 0.72 ± 0.05 g L−1 d−1 and can achieve a final biomass density of 4.28 ± 0.16 g L−1 in seven days without the need for additional micronutrients. Additionally, the algae showed the potential of removing 99.6 ± 0.2% nitrogen and 74.2 ± 8.5% phosphorus from the PW.

Limits to biomass productivity during fed-batch cultivation of Laminaria saccharina female gametophyte cells in a stirred-tank photobioreactor

This study compared the growth of Laminaria saccharina female gametophyte filamentous cell suspension cultures in a stirred-tank photobioreactor under batch and fed-batch nutrient addition modes over a 48-day cultivation period. Cultures were grown on GP2 artificial seawater medium (0.75 mM nitrate, N:P = 16:1) at pH 8.3 without iron or copper. Total equivalent nutrient loadings ranged from 0.5X to 9.1X GP2 for batch cultivation and 1.3X to 10.4X GP2 for fed-batch cultivation at delivery rates of 0.0067–0.16 mmol N L−1 day−1 based on nitrate. The multicellular, L. saccharina filamentous clumps were dispersed to nominal size of 100 μm by mechanical blending (~ 16,000 rpm, 5 s) prior to inoculation. Fed-batch addition of all nutrients enhanced biomass productivity by a factor of two over a batch cultivation process at equivalent total nutrient loadings in a stirred-tank photobioreactor. Peak productivity through fed-batch cultivation was 57 mg DCW L−1 day−1, and average final biomass densities exceeded 1800 mg DCW L−1, vs. 30 mg DCW L−1 day−1 and 800–900 mg DCW L−1 for batch cultivation. However, there was a limit to biomass productivity enhancement at cumulative nutrient loadings greater than 3X GP2 that was not the result of insufficient CO2 or light delivery. It is suggested that the formation of large, multicellular clumps approaching 1-mm diameter during stirred-tank cultivation may have ultimately reduced biomass productivity during fed-batch cultivation under nutrient-replete conditions. Therefore, future bioreactor processing strategies might consider mechanical blending to disperse the filament clumps during the cultivation process.

Effects of inoculum size, light intensity, and dose of anaerobic digestion centrate on growth and productivity of Chlorella and Scenedesmus microalgae and their poly-culture in primary and secondary wastewater

Scale-up of microalgal biofuel technology is challenged by availability of nitrogen and phosphorus fertilizers and the potential negative impact vast increases in chemical fertilizer demand would have on conventional agriculture. The current study investigated replacement of chemical fertilizers with nutrients sourced from primary and secondary wastewater effluents and anaerobic digestion centrate (ADC). Although primary wastewater effluent possessed a high optical density (OD) and bacterial contamination, it was a superior growth medium for microalgal cultivation than nutrient-scarce secondary effluent. Chlorella sorokiniana and Scenedesmus acutus f. alternans showed higher growth rates, productivities, and robustness than other species or poly-cultures of five species. While supplementing with 5–10% nutrient-rich ADC increased wastewater OD, it also enhanced microalgal growth rates from 0.2–0.3d−1 to 0.7–0.9d−1 and biomass productivity from 10 to 20mgL−1d to 40–60mgL−1d with greater improvements for secondary effluents. Supplementation with ADC also increased nutrient concentrations (N, P, Mn, B, Zn, Co by >100% and S, Mg, Ca, Mo by 20–60%) and improved the nitrogen to phosphorus (N:P) ratio. Higher ADC dose of 20% inhibited microalgae growth potentially due to ammonia toxicity. Elevation of inoculum doses and light intensity increased final biomass density and productivity, with intensities <140μmolphotonm−2s−1 limiting algal growth rates. Inoculum doses of ≥2.5×105cellmL−1 were most favorable for cultivation of all tested microalgae and for FAME content and composition for a newly characterized strain of Chlorella sorokiniana. Overall, ADC represents an economical fertilizer substitute providing various nutrients needed for microalgal growth and enhancing biofuel sustainability.

Biomass production and nutrient assimilation by a novel microalga, Monoraphidium spp. SDEC-17, cultivated in a high-ammonia wastewater

To obtain suitable microalgae species for successful algal biomass production from low-cost wastewater, four axenic algae strains were isolated from a local lake. Through acclimation with the high-ammonia complex wastewater (CW) of a gourmet powder factory, one algae species showed good ability to yield biomass and endure high-ammonia conditions (>170mgL−1) in CW. This was verified as a Monoraphidium spp. by molecular identification, and named as SDEC-17. The algae were 27–60μm in length and 4–10μm in width, with relatively low specific surface area for withstanding ammonia ingress through the cell membrane. The final biomass densities of SDEC-17 in CW (1.29±0.09gL−1) and BG11 medium (1.31±0.08gL−1) did not show a statistically significant difference (p>0.05). Moreover, protein content was stimulated to 44% by CW, compared to 35% in BG11. Lipid accumulation of SDEC-17 was not significantly influenced by CW, and fatty acid profiles resembled those of palm oil. The algae would utilize ammonia first under conditions with various nitrogen sources present, and absorb large amounts of phosphorus from the wastewater. Thus, phosphorus and ammonia were removed with efficiencies of nearly 100%, satisfying the discharge standard of pollutants for municipal wastewater treatment plants. These results suggested that Monoraphidium spp. SDEC-17 is a promising candidate for algae biomass production and possibly chemical energy recovery from the complex wastewater.

&lt;em&gt;Saccharomyces pastorianus&lt;/em&gt; as cell factory to improve production of fructose 1,6-diphosphate using novel fermentation strategies

Enzymatic phosphorylation of glucose with inorganic phosphate, mediated by permeabilized yeast cells, is one of the methods commonly used to manufacture fructose 1,6-diphosphate, a compound of pharmaceutical interest. This process requires high concentrations of yeast active biomass, that is the catalyst of bioconversion of glucose and inorganic phosphate into fructose 1,6-diphosphate. In this study we firstly describe the high cell density production of a brewer's Saccharomyces strain (Saccharomyces pastorianus DSM 6581), focusing on the optimization of medium composition and exploiting fed-batch strategies and novel technologies based on membrane bioreactors. In fed-batch fermentation an appropriate exponential feed profile was set up to maintain the glucose concentration in the bioreactor below 0.9 g·L-1, thus yielding reproducibly 58 g dry weight biomass per liter in 80 h fermentation, improving eight-fold batch processes output. In addition a higher final biomass density was reached when implementing a microfiltration strategy (70 g dry weight biomass), that led to a productivity of 2.1 gcdw·L-1·h-1, 2.4-fold the fed-batch one. Successively, this biomass was opportunely permeabilized and proved capable of catalyzing the bioconversion of glucose into fructose 1,6-diphosphate. Acting on critical parameters of the bioconversion (substrates molar ratio, catalyst concentration and permeabilization agent), fructose 1,6-diphosphate was produced, after 3 h of process, at 56.3 ± 1 g·L-1 with a yield of 80% of the theoretical value.

Mineral and non-carbon nutrient utilization and recovery during sequential phototrophic-heterotrophic growth of lipid-rich algae.

A critical factor in implementing microalgal biofuels for mass production is the nutrient requirements. The current study investigated the fate of macro- and micronutrients and their availability in a sequential phototrophic-heterotrophic production process for the lipid rich microalga Auxenochlorella protothecoides. More than 99% (by weight) of overall process nutrients were supplied during the initial photoautotrophic stage reflecting its significantly larger volume. Under photoautotrophic growth conditions only 9-35% of supplied Mn, S, Fe, N, Mg, and Cu and less than 5% of P, Mo, Co, B, Zn, and Ca were consumed by the algae. The rest of these nutrients remain in the spent growth media during the culture concentration-down from an 800L phototrophic pond to a 5L heterotrophic fermenter. In contrast, Zn, Mo, Mn, Mg, Ca, and N were exhausted (90-99% removal) during the first 25h of the heterotrophic growth stage. The depletion of these key nutrients may have ultimately limited the final biomass density and/or lipid productivity achieved. Approximately 10-20% of the total supplied S, Mn, Fe, N, and Cu and 5% of Ca and Zn were assimilated into algal biomass. Several elements including N, P, Mn, B, Cu, Ca, Mg, S, and Fe were released back into the liquid phase by anaerobic digestion (AD) of the residual biomass after lipid extraction. The nutrients recovered from the AD effluent and remaining in the spent medium should be recycled or their initial concentration to the phototrophic stage decreased to enhance process economics and sustainability for future commercialization of algal-derived biofuels.

Analysis of iron ore sinter particles (IOSP) on the treatment of wastewater by a biological aerated filter

Iron ore sinter particles (IOSP) and clay ceramic particles (CCP) were applied in two lab-scale up-flow biological aerated filters (BAF) for wastewater treatment to investigate the availability of IOSP used as biofilm medium compared with CCP. It took about 16 days for IOSP reactor to reach the stable effluent and 4 days late for CCP reactor, according to the removal efficiencies of chemical oxygen demand (CODCr) and ammonia nitrogen (NH4+-N). Compared with CCP reactor, higher efficiencies of CODCr and NH4+-N were found in IOSP reactor in the whole experiment. And there was a great difference on the final biomass densities (39.12 mg/g for IOSP and 25.95 mg/g for CCP). Better efficiency on removing total phosphorus (TP) under aeration was found in IOSP reactor (about 70%), while less than 40% in CCP reactor. Moreover, better capabilities responding to low pH in IOSP reactor were found compared with CCP reactor. For dye wastewater with C.I. Reactive Blue 19, it was shown that IOSP reactor had greater removal efficiency than CCP reactor.

EFFECT OF PHOTOPERIODICITY ON CO2 FIXATION BY Chlorella vulgaris Buitenzorg IN BUBBLE COLUMN PHOTOBIOREACTOR FOR FOOD SUPPLEMENT PRODUCTION

To reduce the level of CO2 content in air, effort on converting CO2 to useful products is required. One of thealternatives includes CO2 fixation to produce biomass using Chlorella vulgaris Buitenzorg. Chlorella vulgarisBuitenzorg is applied for production of food supplement. Chlorella vulgaris Buitenzorg is also easy to handle due to itssuperior adaptation. Currently, Chlorella vulgaris Buitenzorg has been analyzed by some experts for its cellularcomposition, its ability to produce high quality biomass and the content of essential nutrition. A series of experimentswas conducted by culturing Chlorella vulgaris Buitenzorg using Beneck medium in bubbling column photobioreactor.The main variation in this experiment was photoperiodicity, where growth of Chlorella vulgaris Buitenzorg wasexamined during photoperiodicity condition. The difference between CO2 gas concentration of inlet and outlet of thereactor during operational period, was compared to the same experiment under continuous illumination. Underphotoperiodicity of 8 and 9 h/d, the culture cell densities (N) were approximately 40 % higher than under continuousillumination. Final biomass density of Chlorella vulgaris Buitenzorg at 9 h/d illumination was 1.43 g/dm3, around 46%higher than under continuous illumination. Specific carbon dioxide transfer rate (qCO2) in photoperiodicity was 50-80%higher than under continuous illumination. These experiments showed that photoperiodicity affects the growth ofChlorella vulgaris Buitenzorg The specific growth rate (μ) by photoperiodicity was higher than that by continuousilumination while the growth period was two times longer. Based on the experiments, it can be concluded thatphotoperiodicity might save light energy consumption. The prediction of kinetic model under continuous illuminationas well as under photoperiodicity illumination showed that Haldane model became the fitted kinetic model.

Converting crude glycerol derived from yellow grease to lipids through yeast fermentation

Cryptococcus curvatus, an oleaginous yeast was observed to grow on crude glycerol derived from yellow grease. When cultured in a one-stage fed-batch process wherein crude glycerol and nitrogen source were fed intermittently for 12 days, the final biomass density and lipid content were 31.2 g/l and 44.2%, respectively. When cultured in a two-stage fed-batch operation wherein crude glycerol was supplemented at different time points while nitrogen source addition was discontinued at the middle of the experiment, the biomass density was 32.9 g/l and the lipid content was 52% at the end of 12 days. Compared with other oil feedstocks for biodiesel production, lipid accumulated by C. curvatus grown on glycerol has high concentration of monounsaturated fatty acid, which makes it an excellent source for biodiesel use.

Insights from the eco-physiological book of records: Bewick's swans outperform the canonical intake-maximizing vertebrate

During periods of high energy demand an animal may be constrained by a physiological maximum to its energy intake rate. Predictions by allometric equations describing this maximum for endotherms were significantly surpassed during a few recent laboratory experiments on birds and mammals, being given access to food 24 h day−1. How relevant this is in the field remains to be assessed. We predicted that Bewick's swans Cygnus columbianus bewickii might surpass this maximum during stopover on their migration. We determined intake rate by measuring initial and final biomass density, and dividing the biomass difference by the feeding time required to reach this difference. This feeding time was given by the functional response. After conversion to daily energy intake rates, these exceeded the previously assumed maximum on two of the three stopover sites studied. The exception was a stopover site where daily foraging time was limited by the tidal cycle. Our study confirms that intake rates may exceed the formerly generally supposed maximum under natural conditions when foraging is possible day and night.

Growth and Feed Utilization of Captive Wild Black Sea Bass Centropristis striata at Four Different Densities in a Recirculating Tank System

AbstractA study to determine the effects of four stocking densities on growth and feed utilization of wild‐caught black sea bass Centropristis striata was conducted in a pilot‐scale recirculating tank system. The outdoor system consisted of 12 insulated fiberglass tanks (dia. = 1.85 m; vol. = 2.17 m3) supported by biological filters, UV sterilizers, and heat pumps. Subadults (N= 525; ×± SD = 249 ± 16.8 g) were stocked at densities of 4.6 fish/m3 (1.18 kg/m3), 16 fish/ m3 (3.91 kg/m3), 25.3 fish/m3 (6.83 kg/m3), and 36 fish/m3 (7.95 kg1m3), with three replicate tanks per treatment. Fish were grown under 35 ppt salinity, 21‐25 C, and under ambient photoperiod conditions. A commercial flounder diet containing 50% protein and 12% lipid was hand‐fed twice daily to satiation for 201 d.Mean (range) total ammonia‐nitrogen, 0.61 (0‐2.1) mg/L, nitrite‐nitrogen, 0.77 (0.04‐3.6) mg/L, and nitrate‐nitrogen 40.1 (0‐306) mg/L were significantly higher (P &lt; 0.0001) in the 25.3 and 36 fish/m3 treatments than in the 4.6 and 16 fish/m3 treatments [0.19 (0.05‐0.5), 0.1 (0.24‐0.63), and 11.9 (1.3‐82.2) mg/L, respectively]. However, there were no significant differences (P &gt; 0.05) in growth (RGR = 196.8‐243.1%; DWG = 2.55‐2.83 g/d; and SGR = 0.55‐0.61%/d), coefficient of variation of body weight (CwtV., = 0.24‐0.25), condition factor (K = 2.2‐2.4), feed consumption (FC = 1.45‐1.65%/d), and feed conversion ratio (FCR = 1.45‐1.52) among stocking densities. Final biomass densities on day 201 reached 3.48, 12.0, 21.1, and 27.2 kg/m3 at stocking densities of 4.6, 16, 25.3, and 36 fish/m3, respectively. Survival (83.8‐99.1%) did not differ among treatments. Apparent net protein retention (ANPR) was significantly higher (P &lt; 0.005) for fish stocked at the lower densities of 4.6 and 16 fish/m3 (22.5‐23.7%) than for those stocked at 25.3 and 36 fish/m3 (21‐20.1%). There were no significant differences (P &gt; 0.05) in apparent net energy retention (ANER = 55.9‐59.1 %) among stocking densities. Final whole body protein (15.3‐16.3%) and lipid (23.1‐26.4%) levels did not differ significantly (P &gt; 0.05) among treatments.The results demonstrated that growth, survival, and feed utilization were not impaired under stocking densities ranging from 4.6‐36 fish/m3 (3.48‐27.2 kg/m3), despite a slight reduction in water quality at the higher densities. In addition, growth variation and final whole body protein and lipid levels were not influenced by these densities. The results suggest that black sea bass are tolerant of crowding and moderate variations in water quality during intensive culture in recirculating tank systems and that higher stocking densities are possible.

Photolithotrophic cultivation of Laminaria saccharina gametophyte cells in a bubble-column bioreactor

The photolithotrophic cultivation of a novel cell suspension culture derived from the microscopic, filamentous gametophyte life phase of the complex brown alga Laminaria saccharina was feasible in an illuminated bubble-column bioreactor at 13°C using CO 2 in air as the sole carbon source for growth. Maximum cell densities exceeding 1,000 mg dry cell weight (dcw) l −1 and specific growth rates of 0.15 day −1 were attained within a 20-day cultivation period. Initial cell density had a significant effect on the final biomass density of the clumped cell suspension, but no significant effect on the specific growth rate. Although the optimum aeration rate for culture growth was 1.0 l air min −1 l −1 culture (vvm), the culture was not CO 2-transport limited at 0.17–2.0 vvm. Initial nitrate concentrations at or above 63.5 mg NaNO 3 l −1 in the GP2 artificial seawater medium had no significant effect on the specific growth rate or final biomass density. Both specific growth rate and final biomass density data were correlated to incident light intensity over the range of 1–91.2 μE m −2 s −1 using an exponential model for light-saturated growth where light-saturated growth was achieved within a low-incident light intensity of 20 μE m −2 s −1.

Effects of stocking density and dietary protein on green sunfish ( Lepomis cyanellus) × bluegill ( L. macrochirus) hybrids overwintered in ponds

Growth, survival, and feed conversion were evaluated in juvenile green sunfish ( L. cyanellus) × bluegill ( L. macrochirus) hybrids (mean wt. 40.6 g) stocked in twelve 0.04-ha ponds at densities of 12 350 and 24 700 fish·ha −1 and fed diets containing 25 or 35% protein for 183 days. Final mean weights were higher for fish stocked at 12 350 fish·ha −1 (53 g) than those stocked at 24 700 fish·ha −1 (48 g). There was no difference in weights of fish fed either dietary protein level. Final biomass densities increased with increasing stocking density (range=589–1245 kg·ha −1) but were not significantly affected ( P>0.05) by dietary protein level. Percentage increase in biomass density was significantly higher ( P<0.05) for fish stocked at 12 350 fish·ha −1 (26%) than for fish stocked at 24 700 (12%). Stocking rate and dietary protein had no significant effect on survival or feed conversion ratio which averaged 95% and 3.6, respectively. Results of this study indicate that stocking rate has a significant effect on winter growth of hybrid bluegill, possibly due to availability of natural foods. The refinement of feeding schedules and use of floating diets should be investigated.

Culture of Florida red tilapia in marine cages: the effect of stocking density and dietary protein on growth

Growth survival and feed conversion were studied in juvenile, monosex male Florida red tilapia (8.78 g average wt.) held in sea cages on Great Exuma, Bahamas. Twenty-four floating cages (1 m 3) were anchored in a sea pass and stocked at densities of 100, 200, and 300/m 3 and fed 84 days on commercially prepared diets containing 28 or 32% protein. Final mean weights were higher for fish fed the diet with 28% protein (average=176.8 g) than those fed at 32% protein (average=166.4 g), under all densities. Final biomass densities increased with increasing stocking density (range=16.1–52.2 kg/m 3) and were higher for fish fed the 28% protein diet than those fed the 32% protein diet under all densities. Daily weight gain (average=1.94 g/day), specific growth rate (average=3.54%/day), and survival (average=97.9%) were higher and feed conversion ratios (average=1.88) lower for fish fed the 28% protein diet than for those fed the 32% protein diet under all densities. No significant effects of stocking density on these parameters were observed. A significant effect of stocking density on final size variation was evident, with greater coefficients of variation of body weights and lengths among fish reared at a density of 100/m 3 (average=26.0%; 8.51%) than among those reared at higher densities (average=20.8%; 6.87%). In-cage dissolved oxygen fell to <3 ppm during the study due to declining ambient levels, suggesting that higher biomass densities are attainable, given higher ambient dissolved oxygen.