Benthic cages versus floating cages in Octopus vulgaris: Biological performance and biochemical composition feeding on Boops boops discarded from fish farms

Some benthic cephalopods are considered potential candidates to diversify marine aquaculture, as they show fast growth and high market price. Most research on cephalopod culture is currently focusing on the development of specific enrichments and compound feeds, while little research has been conducted in order to test new rearing systems for cephalopods. The rigid characteristic of the floating cages commonly used for the ongrowing of Octopus vulgaris has restricted their use to calm water conditions (estuaries and harbors). Such sites are scarce and highly demanded, especially by the tourism industry; therefore the development of O. vulgaris grow out at these locations competes with touristic interests. The present study was set to compare the biological performance of O. vulgaris reared in a benthic cage (2 m²) as opposed to the traditional floating cage (2.5 m²), during two ongrowing trials. Initial rearing density was 10 kg m⁻³ and octopuses (892 ± 125 g) were fed on bogue Boops boops, discarded from fish farms, for 60–67 days. High growth (1.8–1.9% day⁻¹) and high survival (91–97%) were observed, regardless of the rearing system, and led to best biomass increment (178–212%) and food conversion rates (2.3–2.6) ever recorded for O. vulgaris under industrial rearing conditions. These results underline the adequacy of the benthic cage for the ongrowing of this species, and also the potential of aquaculture discarded fishes, particularly bogue, as a single diet for this species. High growth rates obtained and the high lipid content of bogue (44% dry weight) suggest efficient lipid utilization in this species. Proximate composition and fatty acid profile in octopus muscle was not affected by the rearing system. High dietary lipid content was not reflected in muscle proximate composition, which showed high protein (87% dw) and low lipid content (5% dw) by the end of the experimental period. Farmed octopus showed high levels of n-3 HUFA (42%), which should enhance its value for the consumers.     

Efficient utilization of dietary lipids in Octopus vulgaris (Cuvier 1797) fed fresh and agglutinated moist diets based on aquaculture by‐products and low price trash species

The aim of this study was to evaluate growth, biochemical composition and dietary nutrients utilization in Octopus vulgaris fed on four diets based on bogue Boops boops, from different origin and in two presentations: fresh discarded bogue (aquaculture by‐product) (DB‐f), fresh wild bogue (low price trash species) (WB‐f), discarded bogue agglutinated moist diet (DB‐m) and wild bogue agglutinated moist diet (WB‐m). Diets based on DB showed higher lipid content (19–26% dw) than those based on WB (5–6% dw). Octopuses fed on DB‐based diets showed higher growth (1.5–1.9% day^?1) and higher protein efficiency ratio (0.64–0.69) than those fed on WB‐based diet (1.1–1.5% day^?1 and 0.36–0.37 respectively), which suggests good utilization of dietary lipids and also a possible protein sparing effect by lipids in O. vulgaris. Octopuses fed on diets presented fresh showed a higher growth (1.9–1.5% day^?1) and a higher feed efficiency (62–65%) than those fed on agglutinated diets (1.1–1.5% and 52–60% day^?1 respectively). Regarding fatty acids, the digestive gland clearly reflected dietary lipid and fatty acid profile, while muscle showed a more stable composition. Low dietary ARA content reflected in octopus tissues, especially in specimens fed on DB‐based diets, which did not seem to affect growth during the experimental period.     

Biological performance of Octopus vulgaris in ‘integrated aquaculture’ models: effect of two potential fresh diets,sex and sexual maturation during the grow‐out phase

Two fresh diets were tested on the biological performance of males and females of Octopus vulgaris under industrial rearing conditions in floating cages. The presence of females could potentially release paralarvae to the natural environment (‘integrated aquaculture’). Octopuses were fed on a single diet of bogue (aquaculture by‐product), and on a mixed diet (60–40% crab‐bogue), in two trials. In Trial 1 (918 ± 125 g), growth was higher in octopuses fed on the mixed diet (1.9–2.0%d^?1) than in those fed on the bogue diet (1.8–1.9%d^?1) irrespective of sex, and mortality was 3% regardless of sex and diet. In Trial 2 (1483 ± 269 g), growth was higher in males fed on the mixed diet (1.8%d^?1) than in males fed on the bogue diet (1.4%d^?1), both higher than females (1.1–1.3%d^?1), and mortality was 22–28% regardless of sex and diet. Best biological performance in trial 1 was related to the lack of functional maturation in females, evidence by the low average gonadosomatic index (2.0–3.6%) in comparison with trial 2 (8.8–11.4%), regardless of diet. No correlations between final weight and sexual maturity indices were found, so the length of the rearing period to maximize biomass increment or to release paralarvae depends on functional maturation in females.     

Growth,food intake,protein retention and fatty acid profile in Octopus vulgaris (Cuvier, 1797) fed agglutinated moist diets containing fresh and dry raw materials based on aquaculture by‐products

The lack of specific compound diets for cephalopods is limiting the industrial development of some species. In this study, four agglutinated moist diets were tested in individually reared Octopus vulgaris (979 ± 151 g) for 8 weeks. All diets were based on bogue Boops boops, accidentally reared in fish farms (aquaculture by‐product), and agglutinated with alginate and calcium. One diet was based exclusively on bogue fillets, two on bogue fillets complemented with meat from two crab species (Portunus pelagicus, Grapsus grapsus) and the last one on bogue and G. grapsus meals. As a control diet, bogue and P. pelagicus were supplied fresh on alternate days. All diets induced similar feed intake (2.1–2.6% day^?1). However, the meal‐based diet induced negative growth in comparison with the control and the other agglutinated diets (0.80–0.85% day^?1). Higher lipid content in agglutinated diets (28–30% dw) in comparison with the control diet (16% dw) led to higher protein retention in muscle. These results underline the inadequacy of traditional meals in diets for cephalopods and that the inclusion of crab meat did not increase feeding rates and growth in O. vulgaris. The dietary fatty acid, with high levels of oleic and linoleic acid and low levels of ARA, clearly reflected in digestive gland, while only decreasing ARA and increasing EPA levels were observed in muscle, with no apparent negative effect on growth.     

Effect of two extruded diets with different fish and squid meal ratio on growth,digestibility and body composition of Octopus vulgaris (Cuvier, 1797)

The present work studies the growth and body composition of 18 Octopus vulgaris (6 per treatment) fed two extruded diets, namely FMS and 3FMS, based on different fish and squid meal ratios (1:1, and 3:1 respectively). The diets are compared with a control diet based on crab (Carcinus mediterraneus) and bogue (Boops boops). The growing tests were conducted on animals placed in individual 300 L rectangular fibreglass tanks in an open seawater system, containing PVC tubes as shelters, resulting in 100% survival rate. The control group exhibited the highest specific growth rates (SGR = 2.14%BW day^?1), while values of around 0.69%BW day^?1 were achieved by octopuses fed the extruded diets. Even though the three groups of animals showed similar digestive gland indexes, the two extruded diets promoted significant differences in the muscle composition and fatness of the digestive gland. Digestibility of dry matter was not affected by the type of extruded diet, obtaining ADC values of around 88%. The results suggest that squid and fish meal can be both used in dry pelleted extruded diets, with moderate acceptance by the octopus, even though the formulation must be optimized with the aim of improving acceptability and achieve growths in the range of natural diets.     

Effect of two fresh diets and sexual maturation on the proximate and fatty acid profile of several tissues in Octopus vulgaris: specific retention of arachidonic acid in the gonads

Most nutritional studies on Octopus vulgaris were based on males to avoid interaction with reproductive processes, focusing on muscle and digestive gland tissues. This study intends to evaluate the effect of two fresh diets, a fish diet (bogue Boops boops) and a mixed diet (600 g kg^?1 crab Portunus pelagicus and 400 g kg^?1 bogue), on the biochemical composition of muscle, digestive gland and gonad in males and females of O. vulgaris. Six octopuses per diet were selected (n = 3 per sex) after 60 days of rearing in floating cages. Weight increase was higher in males (3–3.2 kg) than in females (0.9 kg) regardless of diet associated with sexual maturation. Gondosomatic Index in females was 11.3–13.4%. High‐lipid content in fish (440 g kg^?1 dw) was reflected in digestive gland regardless of the diet, while muscle and testis showed a relatively stable composition. The increase in protein content in the ovary was related to sexual maturation. The low arachidonic content in bogue was reflected in all tissues, with no apparent negative effect on growth and welfare. However, specific retention of arachidonic in the gonads, related to high arachidonic content in crab, underlined the importance of this fatty acid in for gonad development in O. vulgaris.     

Effects of two dietary protein levels on energy balance and digestive capacity of <Emphasis Type="Italic">Octopus maya</Emphasis>

Octopus maya is a carnivorous species and protein is the main energy source. During the present study, two different dietary protein levels (40 and 60% CP) were offered to octopuses as specifically designed artificial diets, to determine protein needs and the effects on metabolism. Frozen crab (Callinectes spp.) was used as control. Results obtained demonstrated that crab remains as one of the best diets for O. maya. The artificial diet with 60% CP produced a low but positive growth rate, and at times, a physiological response similar to that observed in octopuses fed crabs. The present results show the capacity of O. maya juveniles to adjust their digestive enzymes to different types of food and protein level, and this appears to be well correlated with octopus growth. General proteases and trypsin from the pancreas were well correlated with growth rates. A low activity was observed in octopuses fed 40% PC diet (negative growth rate), while a high activity was present in octopuses fed 60% CP diet and crabs (low and high growth rate, respectively). In contrast, these same enzymes were inducted in the salivary glands of octopuses fed with the diet that promoted weight loss (40% CP diet), while a reduced activity was observed in octopuses fed crabs. Energy budget indicates that the animals ingested more than 1,000 kJ week⁻¹ kg⁻¹; with such energy, octopuses should satisfy their physiological demands such as was observed when animals were fed crab (I = 1,300 kJ week⁻¹ kg⁻¹; P = 834 kJ week⁻¹ kg⁻¹). However, a very low digested energy was observed in octopuses the fed artificial diets, indicating that these could have a factor that limits digestibility.     

The effects of fish hydrolysate (CPSP) level on Octopus maya (Voss and Solis) diet: Digestive enzyme activity, blood metabolites, and energy balance

As has been demonstrated in previous studies, Octopus maya can be fed on artificial diets. In the present study six different diets were assayed. Five diets were designed to test the effect of percentage of inclusion of fish protein concentrate (CPSP: 0, 5, 10, 15, and 20%) and were offered to octopuses as a specifically designed artificial diet. The sixth diet consisted of frozen crab (Callinectes spp) and was used as control diet. Blood metabolites and energy budget of octopuses were evaluated to determine how CPSP levels modulate the digestive capacity and allow retaining energy for growth. Wild animals (316.4 ± 9.8 g) were used in the study. Results showed that CPSP produced a positive specific growth rate (SGR, % day^− 1) with high value in octopuses fed 15% CPSP level. A maximum growth rate of 0.86% day^− 1 was recorded in these animals, a value that is extremely low when compared with the SGR obtained when animals were fed fresh crab (3.7% day^− 1). In general, blood metabolites were affected by diet composition, indicating that some metabolites could reflect the nutritional and/or physiological status of octopus. Preliminary reference values for O. maya fed crab were found for glucose (0.09 ±0.02 mg/ml), lactate (0.004 ± 0.002 mg/ml), cholesterol (0.16 ± 0.02 mg/ml), acylglycerol (0.14 ± 0.01 mg/ml), protein (0.37 ± 0.04 mg/ml), hemocyanin (1.85 ± 0.04 mmol/l), and digestive gland glycogen (1.86 ± 0.3 mg/g). Total energy content can be used as an indicator of tissue metabolic reserves. In the present study, higher energy content in the digestive gland and muscle was observed in octopuses fed crab, followed by animals fed 15% CPSP. Results from the digestive gland indicated that the retained energy derived from glycogen, suggesting that lipids and protein were the main sources of variation linked with energy content. In general, digestive gland proteases activity and trypsin were induced in octopuses fed 15% CPSP. The capacity of O. maya juveniles to adjust their digestive enzymes to different types of food was evidenced. Essential amino acid content (EAA) of the diet was not a limiting factor. When dietary EAA profiles were compared with O. maya EAA profiles, all dietary EAA resulted in a higher concentration than whole body octopus composition. In the present study, all experimental groups ingested between 3300 and 4106 kJ wk^− 1 kg^− 1 without statistical differences among treatments, indicating that experimental diets were as attractive as crab. Differences were recorded in the proportion of absorbed energy (Ab, %) between CPSP-based and crab meat diets, suggesting digestion limitations associated with artificial diets. The present results indicate that the 15% CPSP diet had characteristics that stimulate digestive enzymes and reduce energetic costs associated with its digestion (HiE or SDA), channeling more biomass production than the other experimental diets.     

Replacing live feed with formulated diets in juvenile Patagonian red octopus (Enteroctopus megalocyathus)

Two formulated diets were evaluated to replace live crab (C) as feed for juveniles Enteroctopus megalocyathus. Formulated diets consisted of crab paste (CP) and a mixture of freeze‐dried meals of crab and squid (C&S). After 10 weeks of feeding, the effect of each diet was analysed on productive performance, nutritional and physiological condition and immune system. Both the crab and C&S diets produced the best values for specific growth rate, feed conversion ratio and protein efficiency ratio. The diet C&S proved to be the most digestible with greatest metabolized energy. The CP diet was similar to the C diet in terms of biological value and protein apparent digestibility; nevertheless, its performance was weaker for the other indicators. Furthermore, the highest α‐amylase, lipase and alkaline proteolytic activity values were observed in octopuses fed live crab, as opposed to those fed formulated feeds. The type of diet did not affect lysozyme activity in neither mucus nor haemolymph. The production of reactive oxygen species was highest in octopuses fed CP diet. It is proposed the use of C&S diet to study the nutritional requirements and to develop an optimal formulated diet for juvenile Patagonian red octopus.     

Effects of a dry pelleted diet on growth and survival of the Yucatan octopus, Octopus maya

The effect of a dry pelleted diet on growth of the Yucatan octopus (Octopus maya) was determined and compared with crab diet (Callinectes spp). Two groups of 15 wild collected animals were used. Octopuses were placed in isolation, in a flow‐through system composed of 30 circular tanks (80 L), with a bottom of 40 cm in diameter and a water depth of 80 cm. Experiment lasted 40 days, and octopuses were weighed every 10 days to determine growth rates. Octopuses were fed between 7% and 10% body weight (BW) per day, twice a day at 9:00 h and 17:00 h. Uneaten food was removed after 4 h in the tanks and weighed, to determine food ingestion and conversion. No mortality as a result of natural causes was observed. The 15 octopuses fed on frozen crabs and the 15 fed on the artificial diet had similar weights (P > 0.05) at the start of the experiment, of 486.2 ± 214.8 and 472.5 ± 228.3 g, respectively. At the end of the experiment, octopuses fed on frozen crabs weighed 1466.5 ± 484.0 g, and were significantly larger (P < 0.05), than octopuses fed on artificial diets (438.9 ± 202.6 g). Growth rates for the experiment were of 3.3 ± 0.2 and –0.0 ± 0.3% BW per day, for octopuses fed frozen crabs and the artificial diet, respectively. The artificial diet did not promote growth, but animals did not loose weight and more important, ate regularly all the food supplied, with feeding rates higher than reported in the literature for prepared diets. This makes O. maya a good research animal for the development of artificial diets for cephalopods.     

Growth,Mortality, and Biochemical Composition in Octopus vulgaris Reared Under Different Conditions of Sex Ratio

Octopus vulgaris is a potential candidate to diversify marine aquaculture. Even though mortality under rearing conditions has been related to reproductive processes, the benefit of sex segregation remains unclear. In order to clarify this, wild octopuses (862 ± 101 g) were reared in floating cages under three proportions of male : female sex ratio: 1:1, 1:0, and 4:1 (n = 30 per treatment). The experimental period lasted 2 mo and octopuses were fed on bogue, Boops boops (aquaculture by‐product). Higher growth rates were observed in octopuses reared under 1:1 and 1:0 (1.8%/d) in comparison with those reared under 4:1 conditions (1.6%/d). Regarding sexes, a lower growth was detected in females reared under 4:1 (1.1%/d) in comparison with females (1.8%/d) and males (1.7–1.9%/d) reared under 1:1 conditions. Survival was 97, 97, and 90% in sex ratio 1:1, 1:0, and 4:1, respectively. Sexual maturity data showed that males were all mature, while most females were still maturing (60–84%) at the end of the rearing period. High lipid content in bogue (44% dw) did not reflect on octopus muscle. This tissue showed a similar biochemical composition irrespective of the sex ratio condition, with a high protein (87% dw), a low lipid (5% dw), and a high n‐3 HUFA content (42%).     

Inclusion of citric acid and/or amino acid-chelated trace elements in alternate plant protein source diets affects growth and excretion of nitrogen and phosphorus in red sea bream Pagrus major

Nutrient dense diets not only challenge the physiological capabilities of fish but also result in discharge of excess amounts into the environment, causing eutrophication of the receiving water. This study investigated the effect of dietary levels of citric acid (CA) and/or amino acid-chelated trace element (AA-CTE) on growth and nutrient retention in red sea bream and loading of phosphorus (P) and nitrogen (N). Six practical diets were formulated, the control being a fish meal-based diet (F0) without addition of P, CA and AA-CTE. Diet F1 was supplemented with 1% mono calcium phosphate (0.25% P). In diets C1 and C2 fishmeal was replaced with alternate plant protein ingredients and supplemented with 1% and 2% CA, respectively. Diets A1 and A2 were akin to diets C1 and C2, respectively but contained AA-CTE instead of the inorganic trace element. Fish weighing around 12 g were offered the respective diets to satiation during the 12-week trial. Growth and feed performance were lowest for fish fed F0 diet, but significant improvement (P < 0.05) was noticed among those fed diets supplemented with P, CA or AA-CTE. The F1 group had the best growth (final body weight 85.02 g) while A1 group had the best FCR (1). Absorption of P was significantly higher (P < 0.01) for fish that received CA and/or AA-CTE (C1, C2, A1 and A2) compared to group that did not receive them (F0 and F1). The P and nitrogen (N) retention values in fish fed diets with CA and/or AA-CTE were significantly (P < 0.01) greater compared to the rest and this facilitated a reduction in excretion rates. The diet supplemented with 1% CA to an alternate plant protein sources diet without inorganic P supplementation had better performance compared to the diets supplemented with 2% CA, 1% CA + AA-CTE, and 2% CA + AA-CTE. Thus, without addition of inorganic P, 1% CA supplementation to alternate plant protein sources diets significantly improved fish growth, FCR and nutrient retention, besides lowering N and P loading. An efficient level of CA is suggested to be 1% or less in alternative plant protein source diets (containing 35% fish meal). These findings would contribute to the pursuit of environment-friendly feed for red sea bream.     

Octopus vulgaris (Mollusca: Cephalopoda) fishery management assessment in Asturias (north-west Spain)

Common octopus, Octopus vulgaris Cuvier, 1797, management in the west of Asturias has been carried out as a co-management experience since 2001. It includes the establishment of a closed season, a minimum capture weight of 1000 g and the limitation of traps as the only authorized fishing gear. An assessment of these management rules is made in the present study. The percentage of mature females weighing between 900 and 1900 g during the period of maximum reproductive development (February–June) is between 73% and 100% by 100 g size class. Consequently, a minimum capture weight of 1000 g can be considered adequate for the rational exploitation of this resource. Moreover, the constant monitoring of O. vulgaris landings (weight distribution and sex ratio) could be useful to find an indicator to permit the detection of changes in the spawning period, allowing managers to establish the closed season in the most suitable period in order to protect the recruitment of the next cohort.     

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.     

Variations on development and stress defences in Solea senegalensis larvae fed on live and microencapsulated diets

Growth, development, antioxidant enzymes, stress proteins (HSP70 and HSP60), lipid peroxidation (LP) and histology in Solea senegalensis larvae were followed from 8 to 30 days post hatching (dph). Larvae were fed on three different diets: (1) live Artemia nauplii, (2) microcapsules elaborated by internal gelation, (MA) and (3) these same microcapsules but 10-fold supplemented with vitamin A (MAV). The Artemia fed group showed higher growth and a faster metamorphosis than the ones fed with microencapsulated diets, although all had similarly high survival rates of 80%. Vitamin A (VA) supplementation improved growth and development from 15 dph in relation to the strictly inert diet (MA). Larvae fed with Artemia showed organs and tissues with a normal pattern of development, whereas histological alterations were seen in larvae fed with both inert diets. The antioxidant enzymes: catalase (KAT), superoxide dismutase (SOD), and total glutathione peroxidase (t-GPX) as well as LP levels and stress proteins (HSP70 but not HSP60), measured in whole larvae, showed diet and age dependence in their response. Larvae fed with both inert diets showed similar biomarker activities, but these activities were different (p < 0.05) from larvae fed with Artemia. That is, KAT and HSP70 were lower in larvae fed with live prey and t-GPX and LP levels were lower in larvae fed with the inert food. Among the factors responsible for increased antioxidant defenses were the initiation of metamorphosis and the use of inert food. This study suggests the usefulness of the biomarkers selected as tools to evaluate the effects of compound diets on larvae.     

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.     

Availability of essential amino acids,nutrient utilisation and growth in juvenile black tiger shrimp,Penaeus monodon,following fishmeal replacement by plant protein

Two trials with juvenile black tiger shrimp (Penaeus monodon) were undertaken to study the effects of replacing fishmeal by different levels of plant proteins on growth performances and nutrient utilisation of shrimp in semi-intensive conditions (Expt. 1) and on the availability of dietary nitrogen (N) and amino acids (Expt. 2). Five isoproteic diets (on crude protein basis) were formulated to contain 34, 24, 16, 8, or 0% fishmeal, with fishmeal being replaced by a mixture of plant protein (corn gluten meal, wheat gluten, and rapeseed meal). In Expt. 1, the shrimp (initial body weight, IBW 1.5 ± 0.1 g) were reared in earthen ponds for 144 days and fed one of the experimental diets. Apparent digestibility of nutrients and AA were assessed in Expt. 2, using 150 L tanks and shrimp of 12.8 ± 0.4 g IBW. After 144 days in grow-out ponds, shrimp fed the diet with 24% of fishmeal had similar growth as those fed the control diet containing 34% fishmeal (0% replacement). When 50% or more of the fishmeal were replaced, weight gain as well as N and energy gains significantly decreased. Digestibility of dry matter, protein and energy was also significantly lower in all fishmeal-replaced diets. In particular, leucine digestibility decreased by 26% at 100% replacement, which was significantly correlated to an increased incorporation of corn gluten meal. Our data confirm the need to improve our knowledge on AA availability and raw material quality in order to improve fishmeal replacement in P. monodon diets.     

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.     

Evaluation of levamisole as a feed additive for growth and health management of hybrid striped bass (Morone chrysops × Morone saxatilis)

Three separate experiments were conducted with juvenile hybrid striped bass to determine the effects of levamisole as a feed supplement on growth performance, innate immunity and specific antibody responses, as well as resistance to Streptococcus iniae and Aeromonas hydrophila infection. A basal diet was formulated to contain 40% protein, 10% lipid and an estimated digestible energy level of 3.5 kcal/g. Four levels (100, 250, 500 and 1000 mg/kg) of levamisole were added to the basal diet in place of cellulose. After the 3-week feeding period in feeding trial 1, enhanced weight gain was generally observed in fish fed the diets supplemented with a low level (< 500 mg/kg) of levamisole. Dietary supplementation of levamisole at 100 mg/kg significantly (P < 0.05) enhanced growth and feed efficiency, compared to fish fed the basal diet. Fish fed diet supplemented with 1000 mg levamisole/kg diet showed chronic toxicity signs of inferior growth, reduced feed intake and feed efficiency. Although the extracellular superoxide anion production of head kidney cells, hematocrit, serum lysozyme and peroxidase were not significantly affected by dietary treatments, intracellular superoxide anion production of head kidney macrophages of fish fed 250 mg levamisole/kg diet was significantly (P < 0.05) higher than that of fish fed the other four diets. The hypothesized benefits of dietary supplementation of levamisole in reducing mortality from infection of pathogenic bacteria including S. iniae and A. hydrophila were not proven after two separate 3-week feeding trials and disease challenges in the present study. Agglutinating antibody titers of individual fish were highly varied and not significantly influenced by dietary levamisole at the tested levels.     

Influence of natural diet on growth and biochemical composition of <Emphasis Type="Italic">Octopus vulgaris</Emphasis> Cuvier, 1797

The influence of diet on growth and biochemical composition of cultured Octopus vulgaris was investigated. Octopuses were reared in a open recirculation seawater system and during the experiment were kept apart in cages. Experiment lasted 30 days. Three experimental dietary groups were established: group I (mixed diet: Carcinus mediterraneus, Boops boops and Mytilus galloprovincialis), group II (monodiet on B. boops) and group III (monodiet on M. galloprovincialis). The best results were obtained with the monodiet based on bogue that gave a weight gain of 390.65 ± 37.54, an absolute growth rate of 13.02 g day⁻¹ and feed efficiency of 44.79 ± 0.96%. Regarding to biochemical composition, the mussel-fed and bogue-fed groups showed the highest protein content. Animals fed on bogue also showed the highest carbohydrate content, while the lowest value was observed in the mussels-fed group. The lipid content was found to be very low in all dietary groups. Saturated fatty acids were the most abundant fatty acid class, ranging from 58.22% in wild octopuses to 46.83% in bogues-fed octopuses. Polyunsaturated fatty acids (PUFAs) were the second most abundant fatty acids class in all dietary treatments (25.65–37.00% as a per cent of total FAs) except in octopuses fed with mussels. MUFAs ranged from 11.44 to 26.93% of total FAs. Although it is empirically known that a varied diet better covers the nutritional requirements than a monodiet, the results of this study reveal that a monodiet of B. boops may be used.