Effects of feeding rate and frequency on growth performance,digestion and nutrients balances of Atlantic salmon (Salmo salar) in recirculating aquaculture systems (RAS)

A 10‐week study was conducted to investigate the effects of feeding rate and frequency on growth performance, digestion and nutrients balances of Atlantic salmon (Salmo salar) in replicated recirculating aquaculture systems (RAS). Replicated groups of juvenile salmon weighing 90 ± 2.5 g (mean ± SD) were fed a commercial feed (21.63 MJ kg^?1 gross energy) to designed feeding rate (1.4%, 1.6% and 1.8% body weight day^?1, BW day^?1) and feeding frequency (2 and 4 meals day^?1) combinations. Specific growth ratio varied between 1.15 ± 0.02 and 1.37 ± 0.16% day^?1, and feed conversion ratio ranged from 0.96 ± 0.03 to 1.16 ± 0.02. The nitrogen and phosphorus retention rates were from 36.50 ± 1.94 to 47.08 ± 5.23% and from 20.42 ± 1.05 to 38.59 ± 2.80%. Apparent digestibility coefficients (ADC) in dry matter, protein, lipid and energy showed no significant differences for all groups. However, fish fed at 1.6% BW day^?1 and 4 meal day^?1 groups had relatively better growth and nutrient retention efficiency compared to other groups. In addition, concentrations of nitrogenous and phosphorous compounds were also detected in this study. These results suggested that salmon of 100–200 g in RAS could in practice be fed at 1.6% BW day^?1 and 4 meals day^?1, taking environmental impacts into account.     

High feeding and growth rates in common octopus (Octopus vulgaris) fed formulated feeds with an improved amino acid profile and mixture of binders

Four semi‐moist formulated feeds were supplied to Octopus vulgaris subadults (664 ± 70 g; 18.4 ± 0.7°C) in two different experiments. In the experiment #1, two diets were prepared with a new mixture of binders (gelatine 150 g kg^?1, starch 100 g kg^?1 and gum 50 g kg^?1). The GEL15‐Squid and GEL15‐Hake feeds included 100 g kg^?1 freeze‐dried squid (Todarodes sagittatus) or hake (Merluccius sp.) respectively. Both feeds showed low water disintegration rates at 24 h (13.6–15.0% dry weight). The specific feeding rate was higher in animals fed GEL15‐Hake (2.7%BW day^?1), but the growth and feed efficiency were significantly better in animals fed GEL15‐Squid (1.4%BW day^?1 and 61.2% respectively; P < 0.05). The proximate composition of the digestive gland, carcass and whole animals was similar. In the experiment #2, the GEL15‐Squid amino acid profile was improved by replacing 50 g kg^?1 gelatine by 50 g kg^?1 freeze‐dried squid (GEL10‐Squid) or freeze‐dried fish (GEL10‐Fish). These feeds showed higher water disintegration rates (31.7–36.3% dry weight). The feeding rates (2.2–2.3%BW day^?1), growth (1.5%BW day^?1) and feed efficiency were similar for both diets. Total lipids were higher in the digestive gland and whole animals fed GEL10‐Fish diet (P < 0.05). Future effort could be directed towards alternative binders that allow improve amino acid balance with a minimum gelatine content or even supplementation trials including essential amino acids.     

Reproductive performance,survival and development of nauplii and copepodites,sex ratio and adult life expectancy of the harpacticoid copepod,Euterpina acutifrons,fed different microalgal diets

A series of laboratory experiments were conducted on the harpacticoid copepod, Euterpina acutifrons, to assess the influence of 10 different microalgal diets (four monoalgal and six mixed algal diets) on several parameters related to its productivity in culture. The four monoalgal diets were the Tahitian strain of Isochrysis sp. (T‐Iso), Pavlova salina (Pav), Tetraselmis chuii (Tet) and the diatom Chaetoceros muelleri (Chaet), the five binary diets were T‐Iso+Tet, Pav+Tet, T‐Iso+Pav, Tet+Chaet and Pav+Chaet, while the tri‐algal diet was T‐Iso+Tet+Pav. All diets were fed to copepods at 1500 μ gC L^?1 and in the case of binary or trialgal diets, carbon concentration was divided equally between the two or three algae offered. Among monoalgal diets, the diatom Chaet was excellent for E. acutifrons. Out of the 10 diets tested, the binary diet Tet+Chaet, which contained the diatom Chaet, was the best for naupliar production of single pair E. acutifrons (19.5±1.7 nauplii female^?1 day^?1), significantly (P<0.05) higher than all other treatments except for the Chaet treatment (P>0.05). Similarly, in the group naupliar production trial (50 adult E. acutifrons per replicate), Tet+Chaet produced a significantly higher number of nauplii (405.8±18.6 nauplii day^?1) than the other treatments (P<0.05). Tet+Chaet further supported the highest naupliar survival (82.0±2.8%) and copepodite survival (89.0±2.8%), while the mono‐algal diet Chaet produced the second highest naupliar (76.7±2.6%) and copepodite survival (83.5±2.6%). In contrast, Pav produced the lowest overall survival at the naupliar stage (30.0±2.9%), significantly lower than all other treatments (P<0.05). While development from newly hatched nauplii to copepodites was not significantly affected by diets, mean development time from nauplius to adult was significantly different among treatments. Mean development time from hatching (naupliar I stage; NI) to the adult stage was the fastest with Tet+Chaet and Chaet (6.8±0.0 days for both treatments), which was significantly faster than that of Pav, T‐Iso Pav+Tet and T‐Iso+Pav+Te treatment (P<0.05). E. acutifrons sex ratio was significantly affected by diets, and always skewed in favour of males. Feeding on Pav resulted in the lowest proportion of females (23.7±1.2%), significantly lower than for six of the other treatments (P<0.05). Adult females had longer average life expectancy than males for all treatments, and were the longest when fed Tet+Chaet (9.5±0.4 days), which was more than twice as long as the shortest lifespan recorded for the Pav treatment (4.2±0.6 days) (P<0.05). In summary, among 10 diets tested, the binary diet Tet+Chaet appeared to support the highest culture productivity of E. acutifrons while the diatom Chaet also performed well as a monoalgal diet.     

Effects of dietary carbohydrate on weight gain and gonad production in small sea urchins,Lytechinus variegatus

In experiment 1, juvenile sea urchins (n = 80, 0.088 ± 0.001 g wet weight and 5.72 ± 0.04 mm diameter) were held individually and fed ad libitum one of three semi‐purified formulated diets (n = 16 individuals treatment^?1). In the diets, protein was held constant (310 g kg^?1 dry, as fed) and carbohydrate level varied (190, 260, or 380 g kg^?1 dry, as fed). Wet weights were measured every 2 weeks. Total wet weight gain was inversely proportional to dietary carbohydrate level and energy content of the respective diet. In experiment 2, sea urchins (5.60 ± 0.48 g wet weight, n = 40) fed 190 g kg^?1 carbohydrate consumed significantly more dry feed than those fed 260 g kg^?1, but not more than those fed 380 g kg^?1 carbohydrate. Based on differential feed intake rates, sea urchins that consumed more feed also consumed higher levels of protein and had the highest weight gain. Consequently, protein content and/or protein: energy ratio may be important in determining feed utilization and growth among sea urchins in this study. The average digestible energy intake was approximately 70 kcal kg^?1 body weight day^?1, suggesting daily caloric intake of juvenile Lytechinus variegatus is lower than in shrimp and fish.     

Effect of different dietary microalgae combinations on growth and survival of black‐lip pearl oyster (Pinctada margaritifera) larvae and the feasibility of replacing microalgae with a dietary lipid emulsion

A 10‐day experiment was performed to examine different mono, binary and ternary dietary combinations on survival and growth of D‐shaped and umbone black‐lip pearl oyster, Pinctada margaritifera, larvae. The three tropical microalgae species were the flagellate Isochrysis galbana clone T. Iso (CS‐177) and diatoms Chaetoceros calcitrans (CS‐178) and Chaetoceros muelleri (CS‐176) which were fed to D‐shaped and umbone larvae at a density of 7000 and 14 000 cells mL^?1, respectively. A second experiment was performed to investigate the feasibility of replacing T. Iso with a lipid emulsion for both D‐shaped and umbone larvae for 10 and 12 days, respectively. The treatments included only T. Iso, unfed and lipid emulsion to substitute T. Iso at levels of 10% (LIP10), 30% (LIP30) and 100% (LIP100). In the first experiment, results showed that a monospecific diet of T. Iso led to significantly higher (P < 0.05) survival and growth of D‐shaped larvae than all the other treatments. Meanwhile, D‐shaped larval survival was significantly lower when only fed C. calcitrans as well as growth for those fed C. calcitrans or in combination with C. muelleri. However, for umbone larvae, survival and growth were significantly higher when fed a binary combination of T. Iso and C. muelleri or the ternary combination of T. Iso, C. muelleri and C. calcitrans compared with all other treatments. For the second experiment, results showed that with increasing lipid emulsion replacement, survival of both D‐shaped and umbone larvae significantly decreased (P < 0.05); however, the LIP100 treatment was not significantly different (P > 0.05) from the unfed treatment. For D‐shaped larvae, no significant growth difference was detected (P > 0.05) between the T. Iso and LIP10 fed treatments while for umbone larvae, the T. Iso, LIP10 and LIP30 were not significantly different (P > 005). These results indicate that microalgae combinations appear more necessary for later staged P. margaritifera larvae. In addition, the use of a lipid emulsion appeared to provide some nutrition to the larvae, although more research should be conducted to improve the use of such replacements.     

Development of low‐lipid formulated feeds with different protein/energy ratios for Octopus vulgaris ongrowing

We studied the feeding and growth rates, feed efficiency and nutritional composition of subadult octopuses (689 ± 77 g) fed low‐lipid diets with two different protein/energy ratios (P/E): Medium P/E diet (30.5 g protein MJ^?1, 662 g kg^?1 protein dry weight (dw)) or High P/E diet (36.8 g protein MJ^?1, 843 g kg^?1 protein dw). Survival was 100% for the Medium P/E and 87.5% for the High P/E diet. The specific feeding rates were 1.91% and 1.67% body weight day^?1 for the Medium P/E and High P/E diet, respectively (P < 0.05). The specific growth rates (0.92% and 1.25% body weight day^?1), feed efficiency indices (47.3% and 72.7%), productive protein value (23.9% and 29.1%) and digestive gland index (5.6% and 6.4%) were significantly better in animals fed the High P/E than the Medium P/E diet (P < 0.05). The proximate composition of the digestive gland was similar for both diets, but the total lipid content of carcass was higher in animals fed the Medium P/E diet (P < 0.05). Our results suggest that the protein content of the feed could be a factor regulating feeding rates in octopus.     

Influence of feeding regime and temperature on development and settlement of oyster Ostrea edulis (Linnaeus, 1758) larvae

Under controlled conditions of food density and temperature, larval performances (ingestion, growth, survival and settlement success) of the flat oyster, Ostrea edulis, were investigated using a flow‐through rearing system. In the first experiment, oyster larvae were reared at five different phytoplankton densities (70, 500, 1500, 2500 and 3500 μm³ μL^?1: ≈1, 8, 25, 42 and 58 cells μL^?1 equivalent TCg), and in the second, larvae were grown at four different temperatures (15, 20, 25 and 30°C). Overall, larvae survived a wide range of food density and temperature, with high survival recorded at the end of the experiments. Microalgae concentration and temperature both impacted significantly larval development and settlement success. A mixed diet of Chaetoceros neogracile and Tisochrysis lutea (1:1 cell volume) maintained throughout the whole larval life at a concentration of 1500 μm³ μL^?1 allowed the best larval development of O. edulis at 25°C with high survival (98%), good growth (16 μm day^?1) and high settlement success (68%). In addition, optimum larval development (survival ≥97%; growth ≥17 μm day^?1) and settlement (≥78%) were achieved at 25 and 30°C, at microalgae concentrations of 1500 μm³ μL^?1. In contrast, temperature of 20°C led to lower development (≤10 μm day^?1) and weaker settlement (≤27%), whereas at 15°C, no settlement occurred. The design experiments allowed the estimation of the maximum surface‐area‐specific ingestion rate  = 120 ± 4 μm³ day^?1 μm^?2, the half saturation coefficient {X_K} = 537 ± 142 μm³ μL^?1 and the Arrhenius temperature T_A = 8355 K. This contribution put a tangible basis for a future O. edulis Dynamic Energy Budget (DEB) larval growth model.     

The effect of food type (formulated diet vs. natural) and fish size on feed utilization in common sole,Solea solea (L.)

This study compares the effect of food type (formulated diet vs. natural food) and fish size on protein and energy utilization efficiencies for growth in common sole, Solea solea (L.). Replicate groups of common sole (mean initial body weight ± SD was 45.7 g ± 2.1 and 111.2 g ± 4.2) received the diets at five (natural feed) or four (formulated diet) feeding levels. The protein utilization efficiency for growth (k_gCP) was higher (P > 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.40 and 0.31). Likewise, the energy utilization efficiency for growth (k_gGE) was higher (P = 0.001) in common sole fed ragworms than in common sole fed the formulated diet (respectively, 0.57 and 0.33). The protein maintenance requirement was not different between food types (P = 0.64) or fish size (P = 0.41) being on average 0.82 g kg^?0.8 day^?1. The energy maintenance requirement was not different between food type (P = 0.390) but differed between fish size (P = 0.036). The gross energy maintenance requirement of small common sole was 35 kJ g^?0.8 day^?1. The gross energy maintenance requirement of large common sole was 25 kJ g^?0.8 day^?1. In conclusion, the low growth of common sole fed formulated diets was related to reduced feed utilization.     

Dietary selenium requirement for on‐growing gibel carp (Carassius auratus gibelio var. CAS III)

A 12‐week growth trial was conducted in a flow‐through system to determine dietary selenium (Se) requirement for on‐growing gibel carp (initial body weight: 76.2 ± 0.05 g, mean ± SEM). Selenomethionine was supplemented to the basal diet to formulate seven semi‐purified diets containing 0.26, 0.58, 0.72, 1.14, 1.34, 1.73 and 2.09 mg Se kg^?1 diet. The results showed that plasma superoxide dismutase (SOD) activity significantly increased when fish were fed with 0.58 mg Se kg^?1 diet (P < 0.05) and then decreased at 2.09 mg Se kg^?1 diet (P < 0.05). Plasma T‐AOC activity was higher in fish fed with 0.72 mg Se kg^?1 diet (P < 0.05) and plasma malondialdehyde (MDA) was higher in fish fed with 0.26 mg Se kg^?1 diet (P < 0.05). When fish were fed 1.14 mg Se kg^?1 diet, hepatic GSH‐Px, T‐AOC, GSH and CAT activities were significantly higher than those fed with 0.26 mg Se kg^?1 diet (P < 0.05). Hepatic superoxide dismutase (SOD) activity was higher at 1.34 mg Se kg^?1 diet (P < 0.05). Fish liver Se concentrations were significantly higher when fed with 0.72 mg Se kg^?1 diet (P < 0.05) and then kept constant when Se ≥ 0.72 mg kg^?1 (P > 0.05). Whole‐body and muscle Se concentrations were higher when fed with 1.34 mg Se kg^?1 diet (P < 0.05) and kept a plateau when Se ≥ 1.34 mg kg^?1 (P > 0.05). In conclusion, based on broken‐line regression of hepatic Se concentrations, hepatic SOD activity and hepatic T‐AOC activity, dietary Se requirements for on‐growing gibel carp was 0.73 mg kg^?1, 1.12 mg kg^?1 and 1.19 mg kg^?1 diet respectively.     

Dietary myo‐inositol requirement for juvenile gibel carp (Carassius auratus gibelio)

An 11‐week growth trial was conducted to determine dietary myo‐inositol (MI) requirement for juvenile gibel carp (Carassius auratus gibelio). Myo‐inositol was supplemented to the basal diet to formulate six purified diets containing 1, 56, 107, 146, 194 and 247 mg MI kg^?1 diet, respectively. Each diet was fed to triplicate groups of juvenile gibel carp (initial body weight 3.38 ± 0.27 g, mean ± SD) in a flow‐through system. The diets were randomly assigned to different fish tanks. Fish fed ≥ 107 mg MI kg^?1 diet had significantly higher weight gain (WG), feed efficiency (FE) and protein efficiency ratio than those fed 1 mg MI kg^?1 diet. Fish fed ≥ 56 mg MI kg^?1 diet had higher feeding rate and survival compared with fish fed 1 mg MI kg^?1 diet. Dietary supplemental inositol did not affect fish liver inositol concentration. Fish fed ≥ 56 mg MI kg^?1 diet had higher body dry matter, crude protein and gross energy and lower hepatosomatic index than fish fed 1 mg MI kg^?1 diet. Dietary inositol supplementation decreased fish body ash. Quadratic regression of weight gain indicated that the myo‐inositol requirement to maximum growth for juvenile gibel carp was 165.3 mg MI kg^?1 diet.     

Use of Nannochloropsis sp. isolated from the East China Sea in larval rearing of sea cucumber (Apostichopus japonicus)

The supply of microalgae to hatcheries is a limiting factor for the mass larval production of sea cucumber (Apostichopus japonicus) in Fujian Province, China. In this study, Nannochloropsis sp. isolated from the East China Sea was tested as food for A. japonicus larvae. The first trial compared the effect of mono‐, bi‐ and trialgal diets comprising three microalgae (Chaetoceros muelleri, Dunaliella tertiolecta and Nannochloropsis sp.) on A. japonicus larval growth, survival, settlement and juvenile growth. The results showed that there were no significant differences in survival and settlement between larvae fed with Nannochloropsis sp. and other diets. All diet treatments yielded similar juvenile sea cucumber output. In the second trial, A. japonicus larvae were fed equally four times daily at three different rations (5000, 20 000 and 40 000 cells mL^?1 day^?1). Larvae fed 20 000 cells mL^?1 day^?1 were significantly larger than larvae in other groups and experienced the highest survival rate. In the third trial, A. japonicus larvae were fed 20 000 cells mL^?1 day^?1 in three different frequency (2, 3 and 4 meals day^?1). The greatest body length was observed in larvae that received 3 meals day^?1. Survival and settlement of larvae fed 2 meals day^?1 were significantly lower than other two groups. These results suggest that Nannochloropsis sp. can be used as a diet for the large‐scale production of A. japonicus seed, and larvae fed three times daily at a ration of 20 000 cell mL^?1 day^?1 are recommended for hatchery production of A. japonicus.     

Effects on growth,survival, body composition,processing traits and water quality when feeding a diet without vitamin and mineral supplements to Australian red claw crayfish (Cherax quadricarinatus) grown in ponds

To be profitable, producers must reduce diet costs, which can be as high as 80% of the variable costs of an aquaculture expense. As vitamin and mineral premixes represent a significant cost, eliminating addition of these premixes could reduce diet costs if no adverse effects were observed for growth and production parameters. A 105‐day feeding trial was conducted with juvenile Australian red claw crayfish (Cherax quadricarinatus) to evaluate the effects of growth, survival, body composition, processing traits and water quality when red claw were fed a supplemental diet containing 28% crude protein (CP) without vitamin and mineral premixes (and supplemented alfalfa hay) compared with red claw fed a diet (control diet) containing 42% CP, vitamin and mineral premixes, and with supplemented alfalfa hay, and compared with red claw only fed alfalfa hay when grown in ponds. Juvenile red claw (mean weight of 15.7 ± 1.0 g) were randomly stocked into nine 0.02‐ha ponds at a rate of 640 per pond (3.2 per m²), and each treatment was used in three ponds. There were two feedings per day, each consisting of one‐half of the total daily ration. At harvest, individual weight, percentage weight gain, specific growth rate, survival and total yield of red claw fed a control diet was significantly higher (P < 0.05) (83.0 g, 398%, 1.53% day^?1, 65.1%,and 1708 kg ha^?1 respectively) compared with red claw only fed alfalfa hay (44.9 g, 202%, 1.04% day^?1, 30.3% and 431 kg ha^?1, respectively), but not different (P > 0.05) from red claw fed the supplemental diet without vitamin and mineral premixes (76.2 g, 367%, 1.47% day^?1, 57.2% and 1378 kg ha^?1). There were no significant differences (P > 0.05) in feed conversion ratio (FCR) among treatments, which averaged 5.0 (based on prepared diet input). These results indicate that vitamin and mineral supplementation in a diet is not necessary when diet containing 28% CP and alfalfa hay are used in combination for pond grown red claw. These results may help reduce diet costs and possibly increase producers’ profits which might allow for industry expansion.     

Effect of dietary supplementation of calcium chloride on growth,survival, moulting frequency and body composition of narrow‐clawed crayfish,Astacus leptodactylus (Eschscholtz, 1823)

The effects of dietary calcium chloride (CaCl₂) concentration on the growth, survival, moulting and body composition of Astacus leptodactylus were studied. Diets were prepared using supplementation of 0 (control), 30, 60 and 120 g kg^?1 calcium chloride commercial trout larvae diet containing 50% protein and 12% lipid. Astacus leptodactylus larvae with an average total length of 22.0 ± 0.05 mm (TL) and weight of 0.53 ± 0.01 g obtained from eighteen ovigerous females collected from Seydisehir Sugla Dam lake in Konya, Turkey, were stocked in 0.2‐m² aquariums at a rate of 50 crayfish m^?2 and reared for 90 days. The experiments included four treatments (diets) with three replicates each. Calcium chloride exerted positive effects on growth, moulting frequency, feed efficiency and survival of narrow‐clawed crayfish. Crayfish fed with 60 g calcium kg^?1 calcium chloride‐supplemented diet exhibited the highest weight gain and specific growth rate (SGR) but the lowest survival rate (63.3%) (P < 0.05). There were no significant differences (P > 0.05) in mean moisture (803.5 g kg^?1) and protein content (177.0 g kg^?1) in crayfish tail meat. However, lipid values were between 3.8 and 11.6 g kg^?1 and significantly different among the diets (P < 0.05). Diet with 60 g kg^?1 calcium chloride is recommended for the best growth of freshwater crayfish.     

A comparison between marine and terrestrial invertebrate meals for mirror carp (Cyprinus carpio) diets: Impact on growth,haematology and health

Invertebrate meals (e.g. polychaetes and insects) present novel and sustainable high‐quality nutrient sources for use in fish feed formulations. To test this innovative source, an eleven‐week feeding trial was conducted evaluating the effects of replacing the fishmeal (FM) component as an example of a superior protein source (FM CTRL) with ragworm meal (RW, Nereis virens) and/or silkworm pupae (SWP, Bombyx mori) in mirror carp (Cyprinus carpio) diets. Three experimental diets with partial replacement of FM (diets: RW + FM, SWP + FM and RW + SWP + FM) were formulated. All diets were formulated to be iso‐nitrogenous, iso‐lipidic and iso‐energetic. Growth performance and feed utilization indices were assessed, and the feeding trial concluded with the analysis of haematological parameters to provide an indication of carp physiological and health status. Mean weight gain was greatest in mirror carp fed RW + FM (60.83 fish^?1 day^?1; P < 0.05 vs. all other diets) followed by SWP + FM (40.62 g fish^?1 day^?1; P < 0.05 vs. all other diets). The least weight gain was achieved in fish fed FM + SWP + RW+ and FM CTRL (34.34 and 33.96 g fish^?1 day^?1, respectively; not significantly different from each other). Fish fed on RW + FM diet had significantly lower plasma ammonia concentrations than any other dietary groups (P = 0.04). Mirror carp fed on SWP + FM diet (111.52 units mL^?1) were observed to have a marked enhancement in alternative complement activity than FM CTRL (79.21 units mL^?1, P = 0.041). Both ragworm and silkworm pupae meal present attractive sustainable functional feed component in carp diets, with benefits on enhancing growth performance and specific physiological parameters.     

Growth and survival of the freshwater clam,Galatea paradoxa (Born 1778) cultured on different substrata at the Volta estuary,Ghana

This study was conducted to assess the optimum clam size and substratum type for the culture of Galatea paradoxa. The experiment was conducted over a 90‐day period at the Volta Estuary, Ghana. Three size classes of G. paradoxa categorized as small (27.6 ± 0.4 mm), medium (36.8 ± 0.4 mm) and large (50.0 ± 0.6 mm), were used to ascertain the effect of a sandy and muddy substratum on growth performance and survival. Growth increased from the small‐sized clams to the large‐sized clams at 2.54, 3.03 and 3.43 g, respectively, over the experimental period. Growth was higher (P < 0.05) in the muddy substratum (3.58 g) compared with sandy (2.41 g). Similarly, the specific growth rate increased from 0.99% day^?1 in the small‐sized clams to 1.36% day^?1 in the large‐sized clams. Survival rates were significantly higher (99.4%) for the large‐sized clams compared with the medium (78.8%) and the small‐size clams (74.1%). There was significant interaction between the size class and the substratum type with a trend towards increasing survival rate from the small to the large size clams in both substrata. The survival rate was lower in the muddy substratum (71.4%) compared with the sandy substratum (96.7%). The yield was significantly higher in the muddy (2.01 kg m^?2 90 day^?1) compared with sandy substratum (1.87 kg m^?2 90 day^?1). The results of this study indicate that the culture of small‐sized clams is best practiced on sandy substratum due to their elevated survival rates, whereas the muddy substratum appears most suitable for the culture of larger clams (>40 mm) because of their relatively higher survivorship and better growth performance.     

Optimum feeding rates in juvenile olive flounder,Paralichthys olivaceus,at the optimum rearing temperature

Two feeding trials were carried out to determine the optimum feeding rates in juvenile olive flounder, Paralichthys olivaceus, at the optimum rearing temperature. Fish averaging 5.0 ± 0.11 g (mean ± SD) in experiment 1 and 20.2 ± 0.54 g (mean ± SD) in experiment 2 were fed a commercial diet at the feeding rates of 0%, 3.0%, 4.0%, 4.25%, 4.5% and 4.75% body weight (BW) day^?1 and satiation (5.52% BW day^?1) in experiment 1 and 0%, 1.0%, 2.0%, 3.0% and 3.5% BW day^?1 and satiation (4.12% BW day^?1) in experiment 2 at 20 ± 1 °C. Both feeding trials lasted for 2 weeks. Results from experiment 1 indicated that weight gain (WG) and specific growth rate (SGR) of fish fed to satiation were significantly higher than those of fish fed at other feeding rates while feed efficiency (FE) and protein efficiency ratio (PER) of fish fed at 4.25% BW day^?1 were significantly higher than those of fish fed to satiation and fish fed at 3.0% BW day^?1 (P < 0.05). In experiment 2 WG, SGR and PER leveled out after the feeding rate of 3.5% BW day^?1 whereas FE reached a plateau at 3.0% BW day^?1. anova of FE indicated that the optimum feeding rates in 5.0 and 20 g juvenile olive flounder could be 4.25% and 3.0% BW day^?1, respectively. Broken line analysis of WG suggested the optimum feeding rates of 5.17% and 3.47% BW day^?1 in 5.0 and 20 g fish, respectively. Therefore, these results indicated that the optimum feeding rates could be >4.25 but <5.17% BW day^?1 for 5.0 g, and it could be >3.0 but <3.47% BW day^?1 for 20 g size of juvenile olive flounder at the optimum rearing temperature.     

Effective use of glucose rather than starch in formulated semimoist diets of common octopus (Octopus vulgaris)

The aim of the present work was to test the capacity of Octopus vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg^?1 water, 200 g kg^?1 gelatine, 100 g kg^?1 egg yolk powder, 50 g kg^?1 freeze‐dried Sardinella aurita and 150 g kg^?1 freeze‐dried Todarodes sagittatus) and two obtained by substituting 50 g kg^?1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best‐accepted diet was STA50 (SFR 1.26%BW day^?1) although there were no significant differences in the growth rates obtained with the three diets: 10.12 g day^?1, 9.37 g day^?1 and 11.22 g day^?1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 71.88% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all the three diets (96–98% for proteins and 85–94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.     

Effect of shading colours on growth and pigment content of Gracilaria fisheri (Xia & Abbott) Abbott,Zhang & Xia (Gracilariales,Rhodophyta)

Sporeling and tissue propagation of agarophytic seaweed, Gracilaria fisheri, aimed to investigate the optimal shading colour for the preservation. This study was conducted under different shading colours indoor and outdoor experiments. The indoor experiment: tissues and sporelings of the seaweed were cultured in plastic chambers under fluorescent lights and were wrapped with white, green, blue and red colour PVC sheets of light intensity of 20 ± 1 μmol m^?2 s^?1. The outdoor tissues were cultured in the plastic tanks under different shadings of Saran sheets: white, green, blue and black covering the hoop‐houses with light intensity of 110 ± 10 μmol m^?2 s^?1. The results showed that different shading colours strongly influenced growth of G. fisheri sporelings and tissues but little effect on pigmentation. After 40 days, the highest growth rates of G. fisheri tissues and sporelings were found under red light with 1.44 and 1.89% day^?1 respectively. There was no significant difference (P > 0.05) on pigment content of tissues indoor, whereas it was found that chlorophyll concentration of the sporelings under green light with 416.8 μg g^?1 fresh weight was significantly higher (P < 0.05) than those in other treatments. After 8‐week culture, outdoor tissues showed the highest growth rate with 1.71% day^?1 in the green hoop‐house. The study has found that G. fisheri cultivation was less influenced by epiphytes in the back hoop‐house with 15%. This study showed the feasibility of successful cultivation of G. fisheri sporelings and tissues.     

Spat availability of commercial bivalve species recruited on artificial collectors from the northern Gulf of California. Seasonal changes in species composition

This study reports a year‐round recruitment of spat of four commercial bivalve species; Pteria sterna, Euvola vogdesi, Pinctada mazatlanica and Pinna rugosa collected in the region of Puerto Peñasco, north‐eastern coast of the Gulf of California. Bimonthly recruitment of commercial bivalve spat on netlon^® collectors was evaluated for six sites from June 2007 to August 2008. To describe spat recruitment abundances with environmental parameters, sea surface temperature (°C) and surface chlorophyll a concentration (mg m^?3) were characterized by means of monthly Aqua/MODIS satellite data. For each species a repeated measures anova was used to evaluate differences in the number of spat between months, sites and depths. Maximum sea surface temperature was recorded in August–September (~31.5°C) and the minimum in January–February (~15°C), while the minimum surface chlorophyll a was observed in June–September (mean range = 1.5–2 mg m^?3) and the maximum in January–March (mean range = 2–5 mg m^?3). Spat recruitment showed distinct patterns; P. sterna can be characterized as having a Winter–Spring pattern, E. vogdesi a winter pattern, while P. mazatlanica and P. rugosa a summer spat recruitment pattern. This information constitutes part of the fundamental data needed for the development of aquaculture and conservation initiatives in the region based on wild spat supply.     

Effective use of glucose rather than starch in formulated semimoist diets of common octopus (Octopus vulgaris)

The aim of the present work was to test the capacity of O. vulgaris to use carbohydrates supplied in three diets: a diet without added carbohydrates (diet C0: 500 g kg^?1 water, 200 g kg^?1 gelatine, 100 g kg^?1 egg yolk powder, 50 g kg^?1 freeze‐dried Sardinella aurita and 150 g kg^?1 freeze‐dried Todarodes sagittatus), and two obtained by substituting 50 g kg^?1 of T. sagittatus by glucose (diet GLU50) or by starch (diet STA50). The most stable and best accepted diet was STA50 (SFR 1.26%BW day^?1), although there were no significant differences in the growth rates obtained with the three diets: 10.1 g day^?1, 9.4 g day^?1 and 11.2 g day^?1 for C0, GLU50 and STA50, respectively (P > 0.05). The feed efficiency indices were better for GLU50, of particular note being the protein productive value of 72% and a feed conversion ratio lower than 1. Protein and lipid digestibility were similar in all three diets (96–98% for proteins and 85–94% for lipids), whereas carbohydrate digestibility was higher in GLU50 (98%) than in C0 (84%) and STA50 (0.33%). The content of carbohydrates increased in muscle and the digestive gland as a consequence of the increased carbohydrates intake.