Self-grading of larval pike-perch (Sander lucioperca), triggered by positive phototaxis

The phototactic behavior of pike-perch (Sander lucioperca) larvae from 1 to 50 days post hatch (dph) was evaluated using a channel system with 0 and 700 lx light treatment. The findings of this work show larval pike-perch to be highly positive phototactic during its larval stage with a peak of positive phototactic behavior between 10 and 22 dph. After 22 dph positive phototaxis decreased and pike-perch increasingly preferred the lower light treatment. In a second experiment observed positive phototaxis was used to evaluate the effectiveness of a light triggered self-grading mechanism for pike-perch larvae at 16, 22, 28 and 34 dph. The use of larvae’s positive phototaxis for a gentle self-grading was successful at 16 and 22 dph and decreased the length variability between 14 and 18% at 16 dph and between 18 and 28% at 22 dph. Whereas the grading at 28 and 34 dph led to an insufficient reduction in length heterogeneity. As a result the light triggered self-grading has the potential to be implemented in future rearing protocols and to be applied on pike-perch between 16 to 22 dph. Furthermore, it is suggested to consider a light triggered self-grading mechanism within upcoming tank designs for the rearing of larval pike-perch.     

Combined effects of feeding enriched rotifers and antibiotic addition on performance of striped trumpeter (Latris lineata) larvae

Striped trumpeter have a complex and extended larval phase and are difficult to culture. Two experiments were conducted in replicated, 300-l hemispherical tanks to determine if larval survival, growth, bacterial or fatty acid profile were improved by feeding non-enriched rotifers or rotifers enriched with algae or commercially available products, as well as the effect of an antibiotic, oxytetracycline (OTC). Larvae were stocked at 25 l^− 1 and 15 l^− 1 and reared until Day 16 and Day 19 in Experiments 1 and 2, respectively. In Experiment 1, the feeding treatments were non-enriched rotifers, or rotifers enriched on algae, DHA Selco (a fish oil based emulsion) or RotiMac (dried Schizochytrium). There were no significant differences in mean survival (± SD) across treatments, which were generally low at 14.6 ± 5.2%. Larvae reared on rotifers fed DHA Selco and RotiMac, had significantly higher proportions of incorporated DHA but no significant increase in growth. In Experiment 2, larvae were fed rotifers enriched on DHA Selco or AlgaMac 2000 and reared with or without the daily addition of 25 mg l^− 1 OTC. At Day 19, there was significantly higher survival for larvae reared on AlgaMac 2000 and OTC, (37.4 ± 5.6%), than DHA Selco and OTC, (16.0 ± 7.4%), AlgaMac 2000 without OTC (7.0 ± 8.0) and DHA Selco without OTC (3.3 ± 1.2). Larvae reared with OTC were larger (279 ± 58 μg and 7.4 ± 0.2 mm) than without OTC (177 ± 40 μg and 6.3 ± 0.2 mm). The addition of antibiotics did not significantly influence fatty acid profiles of larvae. There were no significant differences in the percentage of DHA, 27.6 ± 2.8%, EPA 4.6 ± 1.0% or ARA 4.9 ± 0.4%. Larvae reared with OTC had significantly less ‘grey gut’ (a measure of intestinal dysfunction). The results indicated that bacterial infection was a major source of mortality in striped trumpeter larvae and compromised larval growth. Assessment of the bacterial flora indicated that antibiotic use reduced the bacterial load, but did not eliminate potential pathogens. Our study suggests that microbial control has a greater influence than lipid nutrition on the survival and growth of larvae during the rotifer feeding stage.     

Performance of common carp,Cyprinus carpio L. and Nile tilapia,Oreochromis niloticus (L.) in integrated rice–fish culture in Bangladesh

Irrigated rice fields have enormous potential for expanding the aquaculture production in rice producing countries. Two field experiments were carried out at the Bangladesh Agricultural University, Mymensingh, to optimize the productivity of integrated rice–fish systems using Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. Both experiments were laid out in a randomized complete block design with three replicates per treatment and regular rice monoculture as control. In the first trial, carp and tilapia were tested in single culture and in mixed culture with supplementary feeding at 2× maintenance level. The highest fish yield was obtained in the carp/tilapia mixed culture (586 ± 125 kg ha^− 1), followed by tilapia alone (540 ± 65 kg ha^− 1), and carp alone (257 ± 95 kg ha^− 1). Carp had significantly lower yield than the other two fish groups (p < 0.05) due to high mortality and inefficient feed utilization. As the carp/tilapia combination performed the best in the first experiment, it was tested with different inputs in the second trial, i.e. regular urea fertilization and two different feeding levels. The feeding levels were: continuous feeding at 2× maintenance level (feed level I) and a declining feeding schedule from 4× to 2× maintenance level (feed level II). The highest fish yield was obtained in feed level II (935 ± 29 kg ha^− 1), followed by feed level I (776 ± 22 kg ha^− 1), and the non-fed group (515 ± 85 kg ha^− 1). Yield differences between the treatments were significant at p < 0.05. Rice yields showed controversial effects between the rice–fish treatments and were dependent on the inputs provided. The highest rice production (4.2 t ha^− 1) was obtained from rice–fish plots with regular urea fertilization. Various significant effects of fish on water quality parameters were observed. Fish decreased the dissolved oxygen (DO) and pH value compared to rice only, especially when supplementary feed was provided. Moreover, fish stimulated the growth of phytoplankton and increased chlorophyll-a concentration. In conclusion, carp/tilapia mixed culture with supplementary feeding was found to be optimal for maximizing the output from rice–fish culture.     

Effects of storage duration and storage media on initial and post-eyeing mortality of stored ova of rainbow trout Oncorhynchus mykiss

The effects of storage duration and storage media on the viability of unfertilized eggs of rainbow trout from fertilization to hatching stage was studied. The unfertilized eggs were stored in coelomic fluid and Cortland artificial media buffered with Tris–HCl (C₄H₁₁NO₃–HCl) and Hepes (C₈H₁₈N₂O₄S) at 2–3 °C. These eggs were fertilized after 0 (i.e. control eggs fertilized prior to storage), 2 and 9 days post-stripping using fresh, pooled sperm obtained from 4 to 5 males. According to the results of present study, after 2 days of storage, no significant (p > 0.05) change in survival to eyeing and hatching of eggs stored in coelomic fluid (85.5 ± 4.8%, 80.2 ± 6.3%) and Cortland medium buffered with Hepes (73.3 ± 4.1%,68.1 ± 4%) was observed in comparison to the control (82.6 ± 8%,78.7 ± 7.8%). However, eyeing and hatching survival rates of eggs stored for the same period in Cortland medium buffered with Tris–HCl (44.5 ± 7%,34.2 ± 8.2%) decreased significantly (p < 0.05) in comparison with the control. Also, eggs stored for 2 days in Cortland medium buffered with Tris–HCl (25 ± 6.7%) had significantly (p < 0.05) greater eyed egg mortality compared to the control (4.7 ± 0.6%), while no significant (p > 0.05) differences were observed between eyed egg mortality rates of eggs stored in coelomic fluid (6.7 ± 2.1%) and Cortland medium buffered with Hepes (7.3 ± 0.9%) compared to control. After 9 days of storage, the eggs that were stored in coelomic fluid showed no significant (p > 0.05) differences in eyeing (77.5 ± 7.2%) and hatching (67 ± 8.1%) rates in comparison with control, while both Cortland storage media exhibited significant (p < 0.05) loss in eyeing (44.4 ± 11.5%, 24.7 ± 13.8% for Hepes and Tris–HCl, respectively), and hatching (24.5 ± 5.9%, 19.2 ± 14.4% for Hepes and Tris–HCl, respectively) in comparison with control. Furthermore, eyed egg mortality increased significantly (p < 0.05) in coelomic fluid (14 ± 2.9%), media buffered with Hepes (43 ± 6.2%) and Tris–HCl (49.3 ± 26.9%) compared to control. Based on this study, unfertilized eggs of rainbow trout can be successfully stored in coelomic fluid for 9 days at (2–3 °C) without significant loss of fertility. However, storage within a similar period in artificial media showed lower fertilization rates and higher eyed egg mortality compared to coelomic fluid.     

The effect of high ortho-phosphate water levels on growth,feed intake,nutrient utilization and health status of juvenile turbot (Psetta maxima) reared in intensive recirculating aquaculture systems (RAS)

In intensive recirculating aquaculture systems (RAS) ortho-phosphate (ortho-P) is one of the main accumulating substances, but effects of chronically elevated concentrations on fish health and production performance are still unknown. Therefore 120 juvenile turbot (Psetta maxima) were exposed to ortho-P concentrations of 3 mg/L (control – C), 26 mg/L (low – LP), 52 mg/L (medium – MP) and 82 mg/L (high – HP) for 56 days and fed until satiation with a commercial diet. Health status and feed conversion ratio (FCR) were not significantly affected by treatment (p > 0.05). Specific growth rates (SGR) and daily feed intake (DFI) of C were not considered significantly different from LP, MP and HP treatments, however LP showed significant higher DFI and SGR than HP (p < 0.05). Using non-linear regression between SGR and ortho-P concentrations, 27 mg/L ortho-P was found as the optimum for turbot growth. Although not reflected in blood plasma P levels (p > 0.05) a potential aqueous P uptake might result in metabolic benefits leading to the observed growth enhancement in the LP treatment.In a second experiment 114 juvenile turbot were exposed to ortho-P concentrations of 2 mg/L (C2) and 25 mg/L (LP2) for 63 days and fed until satiation with a low P diet (4.6 g digestible-P/kg diet). Overall production performance was low due to low voluntary feed intake. Whereas the FCR was unaffected by treatment (p > 0.05), significantly higher feed intake and biomass gain were observed for LP2 compared to C2 (p < 0.05). LP2 treatment showed a trend for higher protein retention efficiency and lower whole body lipid content (p < 0.1). The dry matter, ash, Phosphorus, Calcium and protein content in whole body did not significantly vary between treatments (p > 0.05).In conclusion the accumulation of ortho-P in RAS does not negatively affect health of turbot. Elevated ortho-P seems to have slight positive effects on production performance of juvenile turbot. Further research to quantify dietary P requirements for turbot in general, as well as for turbot raised under elevated ortho-P conditions in RAS is strongly required.     

Feed and treat: What to expect from commercial diets

Basic data describing the physical characteristics of fish fecal waste are important in the design of effective solid waste management in aquaculture, especially in land-based facilities such as recirculating aquacultural systems (RAS).This study describes the physical properties of feces from rainbow trout fed eight different commercially available and widely used diets in Germany. Additional data from an earlier but unpublished study pertaining to feces derived from two rather extreme all-vegetarian diets are also presented for consideration of the settling properties. The diets were tested on duplicate groups of 50 rainbow trout in a flow-through aquaculture system. The effects of the diets on the physical properties of fecal particles such as particle size distribution (PSD), modeled settling velocity and rheological character were examined and the effects of each diet on fish health, growth and feed utilization were determined. Specific growth rate (SGR) and feed conversion ratio (FCR) for the different diets ranged from 0.98% d⁻¹ ± 0.012% d⁻¹ to 1.39% d⁻¹ ± 0.012% d⁻¹ and 0.97 ± 0.017 to 1.61 ± 0.017 (mean ± S.E.), respectively. The density of presoaked feces was significantly lower than that of intestinal feces and ranged from 1.01013 ± 0.00692 g cm⁻³ to 1.04547 ± 0.00692 g cm⁻³ (mean ± S.E.). Stability data were in the range from 390.12 ± 29.4 Pa to 1214.79 ± 29.0 Pa for elastic modulus and from 62.12 ± 6.1 Pa s to 232.68 ± 6.0 Pa s for dynamic viscosity. Based on the stability and PSD data theoretical efficiencies for removal of fecal waste using a drum filter showed remarkable variation, ranging from 82.5 to 95.9% (60 μm gauze). Based on the same data, theoretical removal by a sedimentation basin with routinely using overflow rates of 0.057 cm s⁻¹ to 0.394 cm s⁻¹ ranged from 62.8 to 93.8%. Both fecal density and PSD have an exponential impact on settling performance. Increasing fecal density improves the removal efficiency of a sedimentation basin by about 20%, however sedimentation was seen to be a less robust and efficient removal technique than drum filtration. Sedimentation systems also experience additional problems with respect to leaching. Turbulence that was mimicked in this study reflects to an optimal fish farm, which means disintegrating effects are mainly caused by fish motion. If disintegrating units e.g. pumps are used, which are known to promote further particle breakdown the effects would be amplified.The results demonstrate the central importance of density of suspended solids in defining removal efficiencies and suggest that manipulation of fecal density might offer a new and effective means of managing and optimizing waste output from aquaculture operations. This study describes the basic properties of fecal wastes generated by commercial diets and can be used as a basis for further research.     

The effects of food and the sum of effective temperature on the embryonic development of the seahorse,Hippocampus kuda Bleeker

The effect of different food (live Acetes spp., live Mysis spp., frozen Mysis spp., and mixed food of 50% live Acetes spp. and 50% frozen Mysis spp.) on gonad development of seahorses, Hippocampus kuda Bleeker, was evaluated in this experiment. The developmental durations of testes and ovary of seahorses were significantly different among the four experimental treatments. The live Acetes spp. treatment presented the shortest developmental durations to stage V, which were 87.6 ± 3.84 days and 89.2 ± 3.71 days, respectively, for ovary and testes. The frozen Mysis spp. treatment had the longest developmental durations (F_3,15 = 13.284, P < 0.05). The relationship between developmental duration of the ovary and gonad developmental stages could be formulated: Y₁ = 12.04x + 24.36 (r² = 0.9722, n = 16, P < 0.05). The gonadosomatic index (GSI) of parent seahorses among the four treatments differed significantly (F_3,15 = 18.364, P < 0.05). The standard GSI of seahorses fed live Acetes spp. was 15.64 ± 1.65%, which was the highest. Feeding live food had a significant effect on the fecundity and spawning of seahorses. The fecundity and spawning number of the live Acetes spp. treatment were 598 ± 45.49 and 552 ± 49.19 individuals, respectively, which were dramatically higher than those of frozen treatment (F_3,19 = 34.152, P < 0.05). Live food also had a similar effect on the fertilization and hatching rate during the embryonic development of seahorses (F_3,19 = 11.386, P < 0.05). Food treatment could also induce an indirect effect on survival rate of juveniles through gonadal and embryonic development of the parents (F_3,15 = 14.519, P < 0.05). In this experiment, the mortality within parent seahorses in the frozen Mysis spp. treatment was the highest (15.1 ± 6.55%), and the survival of juveniles was the highest in the live Acetes spp. treatment (90.4 ± 2.26% at 10 days). In conclusion, feeding live Acetes spp. significantly benefited the gonadal and embryonic development of H. kuda.The effect of temperature (22 °C, 24 °C, 26 °C, 28 °C, 30 °C and 32 °C) on the hatching time of H. kuda was also studied. We demonstrated that the higher the temperature, the shorter the hatching time, as well as the higher the hatching speed. The relationship between hatching time and temperature could be expressed: T = − 39.337 t + 677.75 (r² = 0.9755, n = 30, P < 0.05). In this finding, we provided the sum of effective temperature (SET) and threshold temperature of embryonic development of H. kuda (14066.9 °C h^− 1 and 13.7 °C, respectively). This new information on the effect of feeding type and culture temperature is beneficial for the commercial rearing and breeding industry of this species.     

Does orientation of raft helps in augmenting yield during lean period?: A case study of Gracilaria edulis cultivation in open sea by vertical raft alignment along the south-eastern coast of India

The food grade agar in India has been almost exclusively obtained from Gracilaria edulis, but the industrial production overwhelmingly relies on exploitation of natural resources. United Nations efforts through Food and Agriculture Organization under Bay of Bengal Program highlighted the necessity of undertaking commercial farming of this species along Indian coast for socio-economic benefits. The pilot-scale experiments established viability of large-scale cultivation by floating raft method. Nevertheless, drastic reduction in yield and quality during summer months due to enhanced sedimentation and severe epiphytism is found to be a major hindrance. Altering the positioning of rafts from horizontal to vertical alignment improved the growth and yield under open sea condition at two different locations along south east coast of India. The average yield in horizontal raft was found to be 3.08 ± 0.61 kg fr wt raft⁻¹ with corresponding DGR of 1.87 ± 0.63% day⁻¹ while same in case of vertical rafts was 13.76 ± 3.86 kg fr wt raft⁻¹ and 5.00 ± 0.5% day⁻¹ in Gulf of Mannar under 45 days growth cycle. The corresponding values along Palk Bay were 2.98 ± 0.52 g fr wt raft⁻¹ and 1.38 ± 0.42% day⁻¹ for horizontal raft and 13.02 ± 6.06 kg fr wt raft⁻¹ and 4.14 ± 1.18% day⁻¹ for vertical raft. ANOVA clearly indicated that raft position significantly influenced the biomass yield and DGR at Palk Bay (F = 75.77; F = 112.81) as well as Gulf of Mannar (F = 27.21; F = 59.16) at p = 0.001. The increment of 1.9–2.6% in fresh weight of individual frond was reported in vertically aligned rafts. The computational fluid dynamics (CFD) based unsteady numerical simulations have confirmed that vertical alignment of raft facilitates relatively free movement of water due to which sedimentation and epiphytism are either minimised or eliminated. Thus these studies can help us to deduce important conclusions pertaining to management of sustained commercial cultivation of this alga in Indian waters.     

Efficiency of producing bioflocs with aquaculture waste by using poly-β-hydroxybutyric acid as a carbon source in suspended growth bioreactors

With additional organic carbon, fish waste can be used as a substrate to produce bioflocs, a protein source for aquaculture animals. In choosing a carbon source, one should consider convenience, cost and biodegradability. This study investigates the efficiency of poly-β-hydroxybutyric acid (PHB), a biologically degradable polymer, as a carbon source to produce bioflocs in suspended growth bioreactors (SGRs), PHB-SGRs, compared with glucose (GLU-SGRs). The C:N ratio in PHB-SGRs could be maintained around 15:1. The volatile suspended solids (VSS) yield was 2.94 ± 0.72 gVSS/g fish waste for PHB-SGRS and 4.90 ± 0.23 gVSS/g fish waste for GLU-SGRs. The recycling rate of nitrogen in aquaculture solid waste was 56 ± 2% and 87 ± 7% for the PHB-SGRs and Glu-SGRs. No significant differences were found in the bioflocs produced and in the crude protein content of the produced bioflocs between PHB-SGRs and GLU-SGRs. PHB-SGRs and GLU-SGRs could remove dissolved inorganic nitrogen from aquaculture wastewater, with average values of 11.82 ± 8.95 and 16.27 ± 3.95 mg/g TSS/d. Because the calculation of the added amount of carbon and the multiple additions of carbon was avoided, PHB is considered to be a good choice as an organic carbon source for this process, even though not all parameters used for assessment were better than those of GLU-SGRs.     

Practical applications of low-pressure hydrocyclone (LPH) for feed waste and fecal solid removal in a recirculating aquaculture system

In this work, the practical application of a low-pressure hydrocyclone was examined for feed waste and fecal solid removal for common carp (27 ± 3.1 g, average ± SD) and Nile tilapia (33 ± 3.4 g, average ± SD) in a recirculating aquaculture system. The dimensions of the low-pressure hydrocyclone included an inflow diameter of 30 mm, a cylinder length of 575 mm, an overflow diameter of 60 mm, an underflow diameter of 50 mm, a cylinder diameter of 335 mm and a cone angle of 68°. The different operating conditions tested were inflow rates of 400, 600, 800 and 1000 ml s⁻¹, and underflow rates of 25%, 25%, 20% and 10% of the inflow rates, respectively. Feed waste totals of 4.1 to 4.8% and 3.6 to 4.0% of the feed intake were produced by the common carp and Nile tilapia, respectively. The maximum separation efficiency (Et) for the feed waste from the common carp was 71% at an inflow rate of 600 ml s⁻¹ with an underflow rate of 25% of the inflow rate. The maximum separation efficiency for the feed waste from the tilapia was 59% at an inflow rate of 400 ml s⁻¹ with an underflow rate of 25% of the inflow rate. The fecal solid production estimated from the digestibility was 37.9% and 35.7% of the feed intake for the common carp and Nile tilapia, respectively. The maximum separation efficiency for the feces from the common carp was 60% for an inflow rate of 600 ml s⁻¹ and an underflow rate of 25% of the inflow rate. The maximum separation efficiency for the tilapia feces was 63% at an inflow of 400 ml s⁻¹ with an underflow rate of 25% of the inflow rate. The low-pressure hydrocyclone can be adopted for prefiltration and/or post-filtration for the removal of various sized solids. Furthermore, the solids separated from the underflow can be easily removed for further processing.     

Production of Akoya pearls from the Southwest coast of India

The Indian pearl oyster Pinctada fucata (Gould) is typically capable of producing pearls of 3–5 mm diameter. The feasibility of production of pearls similar to Akoya pearls of 6–8 mm diameter was studied from the southwest coast of India. Along with this, mortality and retention rates of implanted oysters, rate of nacre production, thickness of nacre deposited, quality and type of pearls produced and effect of hydrographic variations on the mortality of implanted oysters were also studied. A total of 706 oysters were implanted, 311 with 5 mm, 395 with 6 mm nuclei and stocked in 30 cages for a period of 317 days. The mortality rates were highest, 0.173 ± 0.22 for the 6 mm nucleus implanted oysters followed by 5 mm nucleus implanted oysters at 0.107 ± 0.025 during the first 30 days after implantation. These rates were significantly different (P < 0.05) from the mortality rate of the control oysters (0.042 ± 0.04). The retention rates based on the surviving oysters, ranged from 33 to 61% (average 45.9 for 5 mm) and 31 to 60% (average 48.9% for 6 mm). The nacre deposition rates on the nuclei were found to be 4.0 ± 1.0 μm day^− 1 and 3.0 ± 1.0 μm day^− 1 for 6 and 5 mm nuclei respectively. Of the total 131 pearls obtained, 27.6% were A-grade, 31.3% B-grade, 19.8% C-grade, 7.6% baroques and 13.7% rejects or trash. The total suspended solids (TSS) in the water were found to be positively correlated (P < 0.05) with the monthly mortality rate of the implanted oysters. The study showed that it was possible to obtain relatively thick nacre within a short period of 10 months, the deposition rate being about 9 times higher than that observed in Japanese waters and 2.2 to 2.3 times more than that along the Indian southeast coast.     

Nutrient discharge,sludge quantity and characteristics in biofloc shrimp culture using two methods of carbohydrate fertilization

The aim of this study was to evaluate the effect of two methodologies of carbohydrate fertilization on the volume and characteristics of effluent from intensive biofloc shrimp cultivation. Six fiberglass circular tanks (50 m² each) were divided into two treatments. In the treatment called continuous (CONT), the tanks received daily molasses fertilization throughout the entire rearing period. In the treatment named initial (INI), molasses was used only in the early weeks of cultivation. Juvenile Litopenaeus vannamei (0.87 ± 0.10 g) were stocked at a density of 180 animals m⁻² and cultured during 12 weeks until they reached an average weight of 12 g. The tanks were operated with no water exchange and the total suspended solids concentration were kept between 300 and 400 mg L⁻¹ using settling chambers. The sludge produced and the wastewater at harvest were quantified and their characteristics were determined. The production of TSS in the CONT treatment was higher (0.25 kg of solids per kg of applied feed) than in the INI treatment (0.16 kg kg⁻¹) (P < 0.05). The analysis of the sludge revealed a high amount of volatile solids in both treatments, between 636 and 702 g kg⁻¹. However, due to the elevated sludge nitrogen content, the carbon to nitrogen (C:N) ratio was low, with values of 6.4 ± 1.4 and 7.5 ± 1.6 for INI and CONT respectively. The BOD:TSS ratio was also low in both treatments, but the INI showed lower values (10.3 ± 0.6%) than the CONT (14.9 ± 0.0%) (P < 0.05). Both fertilization strategies were able to modify the characteristics of sludge produced during cultivation. Moreover, the high nitrogen and sulfate content of the sludge in both treatments indicated that it may be difficult to use an anaerobic digestion process to treat sludge. In the INI treatment tanks, the sludge is partially stabilized, while in the CONT there was a greater need for stabilization.     

Nitrate removal effectiveness of fluidized sulfur-based autotrophic denitrification biofilters for recirculating aquaculture systems

There is a need to develop practical methods to reduce nitrate–nitrogen loads from recirculating aquaculture systems to facilitate increased food protein production simultaneously with attainment of water quality goals. The most common wastewater denitrification treatment systems utilize methanol-fueled heterotrophs, but sulfur-based autotrophic denitrification may allow a shift away from potentially expensive carbon sources. The objective of this work was to assess the nitrate-reduction potential of fluidized sulfur-based biofilters for treatment of aquaculture wastewater. Three fluidized biofilters (height 3.9 m, diameter 0.31 m; operational volume 0.206 m³) were filled with sulfur particles (0.30 mm effective particle size; static bed depth approximately 0.9 m) and operated in triplicate mode (Phase I: 37–39% expansion; 3.2–3.3 min hydraulic retention time; 860–888 L/(m² min) hydraulic loading rate) and independently to achieve a range of hydraulic retention times (Phase II: 42–13% expansion; 3.2–4.8 min hydraulic retention time). During Phase I, despite only removing 1.57 ± 0.15 and 1.82 ± 0.32 mg NO₃–N/L each pass through the biofilter, removal rates were the highest reported for sulfur-based denitrification systems (0.71 ± 0.07 and 0.80 ± 0.15 g N removed/(L bioreactor-d)). Lower than expected sulfate production and alkalinity consumption indicated some of the nitrate removal was due to heterotrophic denitrification, and thus denitrification was mixotrophic. Microbial analysis indicated the presence of Thiobacillus denitrificans, a widely known autotrophic denitrifier, in addition to several heterotrophic denitrifiers. Phase II showed that longer retention times tended to result in more nitrate removal and sulfate production, but increasing the retention time through flow rate manipulation may create fluidization challenges for these sulfur particles.     

Production performance of Labeo calbasu (Hamilton) in polyculture with three Indian major carps Catla catla (Hamilton), Labeo rohita (Hamilton) and Cirrhinus mrigala (Hamilton) with provision of fertilizers,feed and periphytic substrate as varied inputs

Inclusion of kalbasu, Labeo calbasu as a candidate species in the Indian major carps based polyculture system was evaluated through a six-month grow-out trial in earthen ponds of 0.08 ha each. Species performance was assessed through provision of varied inputs viz., fertilizers (T-1), fertilizers + supplementary feed (T-2) and fertilizers + supplementary feed + periphytic substrate (T-3) as the three treatments, which were evaluated in replicates. Catla (35%), rohu (35%), mrigal (15%) and kalbasu (15%) were stocked at combined density of 7500 fingerlings/ha. While ponds were fertilized with cowdung, urea and single super phosphate, mixture of groundnut oilcake and rice bran at 1:1 (w/w) was provided as supplementary feed. The periphytic substrate, comprised stripe bamboo mat, was provided at 10% of the pond surface area. Provision of each additional input caused significantly higher increase in overall mean survival, growth, SGR and net biomass yield of carps. Among the carp species, while only rohu and kalbasu showed significantly higher weight gain (234.4 g and 170.3 g, respectively) in T-3, no such increase was noticed either in catla or mrigal. The net production in T-3 (1516.1 ± 24.3 kg ha^− 1 6 months^− 1) was 13.0 and 73.2% higher than those of T-2 (1341.7 ± 15.5 kg ha^− 1 6 months^− 1) and T-1 (875.2 ± 15.6 kg ha^− 1 6 months^− 1), respectively. The study revealed the relative advantage of using periphytic substrates in carp polyculture systems with kalbasu as a component species.     

Use of artificial substrates in the culture of Litopenaeus vannamei (Biofloc System) at different stocking densities: Effects on microbial activity,water quality and production rates

Although the use of artificial substrates can favor shrimp culture, some studies indicate that their presence in growth tanks does not improve water quality or the performance of the animals. One objective of this study was to evaluate whether the presence of artificial substrates modifies the microbial activity and the water quality of the culture of Litopenaeus vannamei with bioflocs. The substrate effects on the shrimp performance and the relationship between these effects and the stocking density/biomass of shrimp were also evaluated. The experiment consisted of four treatments: D238: 238 shrimp m⁻³; D238 + S: 238 shrimp m⁻³ + substrates; D473: 473 shrimp m⁻³; D473 + S: 473 shrimp m⁻³ + substrates. Twelve experimental units of 850 L were stocked with juvenile L. vannamei (2.6 g) that were grown for 34 days. The substrates did not appear to affect water quality since the concentrations of orthophosphate, ammonia and nitrite were not significantly different in tanks with or without substrates. The periphyton biomass was low and the biological activity on the substrates was not significant, indicating that the water quality variables were mainly controlled by the microbial community associated with the suspended bioflocs. The shrimp grown in the presence of the substrate exhibited greater weight gain (D238 + S = 1.40 ± 0.05 and D473 + S = 1.20 ± 0.04 g week⁻¹) than those grown without substrates (D238 = 0.73 ± 0.04 and D473 = 0.44 ± 0.13 g week⁻¹). The final biomass was 314% greater in the tanks with substrates. The shrimp survival was significantly higher in the tanks with substrates (93.9 ± 2.4%) than in the tanks without substrates (42.5 ± 35.9%). The results indicate that the substrates served to increase the surface area of the tank and to reduce the relative stocking density, which appears to reduce the stress levels of shrimp, indicated by higher shrimp performance. In tanks with higher biomass, where the negative effects of intensification were most severe, the presence of the substrates had a positive effect on the production indices.     

Infrared reflection system for indoor 3D tracking of fish

Many fish rearing infrastructures are already equipped with human-operated camera systems for fish behavior monitoring, e.g. for stopping the feeding system when the fish is satiated or for monitoring of fish behavior abnormalities caused by poor water quality or diseases. The novel infrared reflection (IREF) system for indoor 3D tracking of fish demonstrated in the current study allows for automation of fish behavior monitoring, reducing the system running costs by eliminating the need for continuous human monitoring and increasing the behavioral analysis accuracy by excluding the human subjectivity factor.The operating principle of this system is based on the effect of strong absorption of near infrared (NIR) range light by water, thus allowing estimation of fish distance based on the corresponding fish object brightness on the camera image. The use of NIR illuminator as a part of the IREF system allows fish behavior monitoring in the dark so as not to affect fish circadian rhythm. A system evaluation under aquaculture facility conditions with Atlantic salmon (Salmo salar) using flow-through water in tanks, showed the mean depth estimation error was equal to 5.3 ± 4.0 (SD) cm. The physiological variations among conspecific individual fish introduced the mean depth estimation error of 1.6 ± 1.3 (SD) cm. The advantages of the IREF system over well-known stereo vision systems are lower hardware cost and less computationally intensive 3D coordinates estimation algorithm, while the disadvantage is lower accuracy that is nevertheless acceptable for most applications of aquaculture fish monitoring.     

Quantification by fluorescent in situ hybridization of bacteria associated with Litopenaeus vannamei larvae in Mexican shrimp hatchery

The bacterial composition in the hatchery at Unidad Experimental Peñasco (UEP) of the Sonora University, Mexico, was studied by using Fluorescent In Situ Hybridization (FISH) with rRNA-specific oligonucleotide probes. We applied fluorochrome-labeled polyribonucleotide probes to identify and enumerate marine shrimp culture hatchery related bacteria. Quantitative whole-cell hybridization experiments using α-, γ- and δ-Proteobacteria, and high and low G + C Gram-positive bacteria accounted for 20.8 ± 3.4% to 69.3 ± 3.3% of the total 4′,6-diamidino-2-phenylindole (DAPI)-stained cells in most samples. As predicted in a previous study, marine high G + C and γ-Proteobacteria predominated in different shrimp life sub-stages. The elevated percent of high G + C and γ-Proteobacteria, extending from nauplii to mysis stages, suggest that they represent a large and significant fraction of the total picoplankton biomass in Litopenaeus vannamei larval culture.     

Assessment of spat collector ropes in Galician mussel farming

The large amount of mussel seed required to support the present mussel farming production levels in Galicia (NW Spain) forces the development of new designs in artificial spat collectors for continual improvement of mussel seed gathering. In the present study, we have assessed both settlement and recruitment of Mytilus galloprovincialis on four different collector ropes in the Ría de Ares-Betanzos (Galicia). Besides the traditional collector ropes (lacing without loops and non-filamentous structure; NF-NL), three new rope designs with different lacing and structures were evaluated; ropes with a filamentous loop complement (F-L), ropes with a non-filamentous loop complement (NF-L) and filamentous ropes without loops (F-NL). Ropes with loops showed higher settlement densities (53,925 ± 4625 and 42,433 ± 5525 indiv./m for F-L and NF-L, respectively) than ropes without loops (26,475 ± 3875 and 13,033 ± 1136 indiv./m for F-NL and NF-NL, respectively). This may be explained by the increase in available surface area provided by the loops. Several studies recognized the importance of filamentous substrata for mussel spat settlement, which may help to explain greater settlement densities on filamentous structures between ropes with the same lacing. In recruitment evaluation, ropes with filamentous loops showed the highest densities expressed in indiv./m (5493 ± 587) as was the case of settlement. However, when density was expressed in kg/m, the ropes with non-filamentous loops had a higher yield (8.48 ± 0.22 kg/m), that could be a result of differences in adjusted shell length between ropes. Intra-specific competition and predation were identified as important factors affecting post-settlement mortality. The latter factors could also influence population length distribution. Ropes with rigid loops (NF-L) may supply refuges for spat from predators and therefore, enhance the recruitment of larger individuals, although other factors like size selective settlement could play a significant role in this result.     

The effect of nearly closed RAS on the feed intake and growth of Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus) and European eel (Anguilla anguilla)

One of the challenges that Recirculating Aquaculture Systems (RAS) are still facing is the risk that in RAS fish grow less than in flow-through systems due to the accumulation of substances originating from feed, fish or bacteria associated with the water re-use. The present study investigated whether RAS with high and low accumulation levels of these substances affect feed intake and growth of Nile tilapia Oreochromis niloticus, African catfish Clarias gariepinus, and European eel Anguilla Anguilla. One-hundred and twenty individuals of each species were used (start body weights: Nile tilapia 264.8 ± 8.3 g; African catfish 253.2 ± 2.1 g and European eel 66.6 ± 1.3 g). For a period of 39 days, growth and feed intake were compared between high and low accumulation RAS. HIGH accumulation RAS was designed for maximal accumulation of substances in the water by operating the system at nearly-closed conditions (30 L/kg feed/d), using mature biofilters and high feed loads; and (2) LOW accumulation RAS was designed to be a proxy for flow-through systems by operating at high water exchange rates (1500 L/kg feed/d), new biofilters and low feed load. HIGH accumulation RAS induced a reduction in feed intake (42%) and growth (83%) of Nile tilapia, as compared to systems that are a proxy for flow-through conditions. This effect was not observed in European eel and African catfish. The cause of this reduced feed intake and growth rate of Nile tilapia is still unclear and should be addressed in further studies.     

Effects of dietary palm oil source on growth,tissue fatty acid composition and nutrient digestibility of red hybrid tilapia,Oreochromis sp., raised from stocking to marketable size

A 20-week feeding trial was carried out to investigate the influence of three palm oil products as the principal dietary lipid source on the growth performance, proximate composition, tissue fatty acid composition and nutrient digestibility of red hybrid tilapia (Oreochromis sp.) fed these diets from stocking to marketable size. Four isonitrogenous (30% crude protein) and isoenergetic (16.5 kJ g^− 1) practical diets were formulated with 8% of added fish oil (FO), crude palm oil (CPO), palm fatty acid distillate (PFAD) or refined, bleached and deodorized palm olein (RBDPO), respectively. Each diet was fed to triplicate groups of 30 fish of 31.24 ± 0.05 g mean initial body weight. The tilapia were raised at 29 ± 1 °C in 12 round 1000 L fiberglass tanks with a continuous water flow rate of about 1.8 L/min.Results showed that the source of added lipid did not significantly influence (P > 0.05) final body weight, specific growth rate, feed conversion ratio, survival, body indices, hematocrit and production yield of tilapia. There was no significant difference in the fillet proximate composition of fish fed the various diets, except that fish fed the PFAD diet showed lower lipid deposition. The deposition of fatty acids in fish tissues was generally influenced by the fatty acid profile of the diets. Fillet fatty acid profiles of tilapia fed palm oil-based diets had significantly higher concentrations of saturated and monounsaturated fatty acids, but lower levels of polyunsaturated fatty acids (PUFA) compared to the fish fed the FO diet. Fillet of fish fed the FO diet had significantly higher concentrations of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) compared with fish fed palm oil-based diets. Dietary lipid source did not significantly affect dry matter and protein digestibility (62.1–64.8% and 83.5–85.0%, respectively). The inclusion of dietary palm-origin oils significantly reduced the total lipid digestibility of the diets due mainly to the decreased digestibility of the saturated fatty acids. In all treatments, the apparent digestibilities of both n − 3 and n − 6 PUFA were the highest, followed by monoenes, while the lowest were the saturated fatty acids. Despite the high free fatty acid content of PFAD (92.2%) compared to CPO (4.8%) and RBDPO (0.1%), the different free fatty acid content did not significantly affect the nutrient digestibility of the palm oil-based diets. Results obtained confirmed the feasibility of feeding tilapia with palm oil-based diets with a 100% substitution of added dietary fish oil throughout the grow-out cycle until marketable size.