Hatchery cultivation of the common cockle (Cerastoderma edule L.): from conditioning to grow‐out

This study describes for the first time the cultivation of Cerastoderma edule on a commercial scale. A protocol to grow F₂ generation cockles was developed, which led to fine‐tuning experiments for broodstock conditioning and spat growth. Broodstock animals were conditioned with diets of Isochrysis galbana (T‐Iso) or Tetraselmis suecica, whereas a third group was not fed. The best diet, T. suecica, induced 12 females out of 100 animals to spawn a total of 3 380 000 eggs. The non‐fed group did not spawn. Cockle spat (4.9 ± 1.0 mm) grew best when given a mixed diet of C. muelleri, T‐Iso and Sceletonema costatum, or a mixture of P. tricornutum and S. costatum at a concentration of 240 cells μl^?1 day^?1, resulting in a tripling of their wet weight after 14 days. The impact of density, burrowing substrate and food availability on cockle spat growth (41 days old, 5.6 ± 1.2 mm) was studied for 11 weeks. Best results were obtained by culturing spat at ad libitum food conditions at 500 ind m^?2, resulting in an average growth rate of 168 μm day^?1, an average final size of 19.0 ± 1.9 mm and a total final biomass of 1040 g m^?2.     

Growth,survival rate and fatty acid composition of sterlet (Acipenser ruthenus) larvae fed fatty acid‐enriched Artemia nauplii

We evaluated the growth and survival rate of sterlet (Acipenser ruthenus) larvae fed Artemia nauplii enriched with Olioω3 or Red Pepper commercial emulsions (BernAqua NV, Belgium). Sterlet larvae, 0.022 ± 0.002 g body weight, were randomly assigned to one of three feeding regimes with two different feeding durations. After administering live feed for 7 or 14 days, larvae were weaned onto commercial food and reared to 36 days posthatching (28 days of feeding). There were no significant differences in body weight among groups at the end of the trial. A significantly higher survival rate (p < 0.05) was observed in larvae fed Artemia enriched with Red Pepper for 14 days compared to other feeding regimes. Based on the analysis of growth parameters, we can conclude that 7 days of live feeding to be sufficient for efficient rearing of sterlet larvae. And longer duration of live feeding with use of special enrichment can be recommended for a higher survival rate.     

饲料中花生四烯酸水平对凡纳滨对虾免疫相关基因表达及抗菌能力的影响

为探讨饲料多不饱和脂肪酸n-3 PUFA/n-6 PUFA比值对罗氏沼虾幼虾生长性能、虾体肌肉组成、抗氧化能力、血清生理指标以及消化能力的影响,实验设计了n-3 PUFA/n-6 PUFA比值分别为0.37 (D1)、0.59 (D2)、0.93 (D3)、1.51 (D4)和4.38 (D5)的5种等氮等脂饲料饲喂罗氏沼虾幼虾8周,每组设4重复,每个重复40尾虾 。结果显示,饲料n-3 PUFA/n-6 PUFA比值对罗氏沼虾幼虾存活率 (SR)无显著影响;实验虾终末体重 (FW)、增重率 (WGR)和特定生长率 (SGR)随饲料n-3 PUFA/n-6 PUFA比值增加先升后降,均在D3组最高;且D3组虾有最大的肝胰腺蛋白酶活性及脂肪酸合成酶活性。虾体肌肉粗蛋白质、水分和灰分含量不受饲料n-3 PUFA/n-6 PUFA比值影响,但总脂肪含量在D3组显著高于其他组;各组虾体肌肉的n-3 PUFA/n-6 PUFA比值的变化趋势与饲料的n-3 PUFA/n-6 PUFA比值变化趋势呈正相关。随饲料n-3 PUFA/n-6 PUFA比值增加,实验虾血清和肝胰腺中超氧化物歧化酶 (SOD)活性、总抗氧化能力 (T-AOC)和血清铜蓝蛋白 (CP)含量均呈现先升后降趋势,并在n-3 PUFA/n-6 PUFA比值为0.93~1.51时达到最大,但丙二醛 (MDA)含量持续上升;D1组血清总胆固醇 (T-CHO)和甘油三酯 (TG)含量显著高于其他组;血清谷草转氨酶 (AST)和谷丙转氨酶 (ALT)活性先降后升,且D3组最低。研究表明,饲料适宜的n-3 PUFA/n-6 PUFA可显著提升罗氏沼虾生长性能和抗氧化能力,对增重率和特定生长率进行折线回归,建议罗氏沼虾幼虾饲料中最适n-3 PUFA/n-6 PUFA比值为0.86~0.94。

     

Improving the fitness of Holothuria arguinensis larvae through different microalgae diets

Development and design of adequate feeding protocols on sea cucumber larvae are necessary for improvements on larvae growth, survival and production of competent juveniles. This work assessed the Holothuria arguinensis larvae growth and survival, fed with three different single microalgae diets of Chaetoceros calcitrans, Isochrysis galbana and Tetraselmis chui, and two microalgae diets based on a combination of C. calcitrans and T. chuii (C:T; 1:1) and C. calcitrans, T. chuii and I. galbana (C:T:I; 1:1:1) during 2 months. Holothuria arguinensis larvae fed with T:C:I, showed higher survival and larger larval and stomach sizes than the ones fed with the other diets. Comparing the results obtained from the single diets, H. arguinensis larvae fed with I. galbana grew and survived better during the first 5 days. However, higher growth was obtained on the larvae fed with C. calcitrans from day 5 to day 12; since this day, larvae fed with T. chuii showed the largest size. These results could be related to the different microalgae size and morphology, in addition to the nutritional value of the different microalgae used. However, no competent larvae that metamorphosed into doliolaria were obtained during this experiment. The tanks used were transparent, which could be causing light stress to the larvae, since competent larvae were obtained in opaque production tanks in our aquaculture installations during the same time period. The combined diet of C. calcitrans, T. chuii and I. galbana (C:T:I) could improve the growth and larvae competency of H. arguinensis.     

Assessment of the fecundity,population growth and fatty acid composition of Apocyclops royi (Cyclopoida,Copepoda) fed on different microalgal diets

The brackish cyclopoid copepod Apocyclops royi is used in Taiwanese aquaculture industry as a prey for fish larvae. This study investigated the effects of seven microalgal diets, namely single‐species diets of Isochrysis galbana (ISO), Nannochloropsis oculata (NAN), and Tetraselmis chui (TET), two‐species diets (ISO+NAN, ISO+TET and TET+NAN), and a three‐species diet (ISO+NAN+TET), on the population growth, female fecundity and fatty acid composition of A. royi. For reproductive traits, the combination ISO+NAN was found to be the most supportive diet for both population growth and female fecundity. For nutritional value, copepods fed ISO and ISO+NAN were detected to have the highest content of docosahexaenoic acid (DHA) (18.99% and 10.73% total fatty acid, respectively) and, more importantly, a high DHA/EPA ratio (6.09 and 4.09, respectively). Additionally, a comparison of fatty acid composition between copepods and microalgae gives a tentative indication that A. royi may have the ability to synthesize long‐chain polyunsaturated fatty acids (PUFA) from short‐chain PUFA. Our findings illustrate that ISO+NAN is the most suitable microalgal diet for mass culturing A. royi because it increases productivity and enhances the nutritional value of the copepods for use as fish larvae prey.     

Effects of different dietary lipid sources on tissue fatty acid composition,serum biochemical parameters and fatty acid synthase of juvenile mud crab Scylla paramamosain (Estampador 1949)

A 6‐week study was conducted to determine the effects of different lipid sources in pelleted diets on juvenile mud crab Scylla paramamosain. Five isonitrogenous and isolipidic diets containing 8% level of fish oil (FO), lard (LD), safflower oil (SO), perilla seed oil (PO) or mixture oil (MO; V_FO:V_SO:V_PO = 1:1:1), and a live food of marine bivalve Potamocorbula rubromuscula as the control diet (CF), were fed to groups of 25 juvenile crabs (average initial weight 7.4 g, carapace width 3.5 cm) in triplicate. The results showed that crabs fed MO had the highest survival (P < 0.05). The moisture content was significantly higher in crabs fed LD, SO and PO (P < 0.05). Crabs fed SO exhibited the lowest crude protein and lipid (P < 0.05). Ash contents were obviously lower in LD group (P < 0.05). Highest total lipid in the hepatopancreas and muscle was in LD and FO group respectively. Glucose, total cholesterol and low‐density lipoprotein were higher while high‐density lipoprotein was lower (P < 0.05) in LD group. Tissue fatty acid compositions were consistent with those in diets. FO and MO diets had the same depression effect like CF on fatty acid synthase activity and mRNA expression in the hepatopancreas. The results of this study indicated that FO and mixed oil are suitable for preparation of pelleted diets with better effects for juvenile S. paramamosain compared with live food, and the ratio of n‐6/n‐3 fatty acids in pelleted diets must be <1.     

Growth,immune response and resistance to Aeromonas hydrophila of darkbarbel catfish Pelteobagrus vachelli fed diets with different linolenic acids,vitamins C and E levels

The role of dietary linolenic acid (LN), vitamin E (E) and vitamin C (C) in regulating fish growth and immune response was tested on juvenile darkbarbel catfish Pelteobagrus vachelli. Five dietary combinations were used (?E?LN, +E?LN, ?E+LN, +E+LN and ?C+E+LN; ‘+’ with addition and ‘?’ without addition) in triplicate. Weight gain was highest in the ?E+LN feeding group. Red blood cell in fish fed the +E+LN diet was highest. The haematocrit and haemoglobin of fish fed the ?E+LN diet was lowest. Superoxide dismutase, catalase, glutathione peroxidase and glucose‐6‐phosphate dehydrogenase activities in fish fed the ?E+LN diet were higher than those in fish fed other diets. Malondialdehyde in fish fed the ?C+E+LN diet was highest. Fish fed the +E+LN diet had higher levels of lysozyme activity, serum protein, complements C3 and C4, and immunoglobulin contents than fish fed other diets. Fish fed the +E+LN diet showed lower mortality and higher antibody titre than fish fed other diets after the fish were challenged with Aeromonas hydrophila for 14 day. This study suggests that the growth of darkbabel catfish is improved by increasing dietary linolenic acids. The diets with high linolenic acid, vitamin E and vitamin C can enhance the immune response and resistance in darkbarbel catfish challenged with A. hydrophila.     

Effect of diets containing laurel seed oil on growth and fatty acid composition of rainbow trout,Oncorhynchus mykiss

The aim of this study was to determine the effects of replacing fish oil (FO) with laurel seed oil (LSO), as an alternative plant lipid source in diets on the growth and fatty acid composition of rainbow trout (Oncorhynchus mykiss; 111.47 ± 0.2 g mean individual weight). At the end of the feeding trial, survival was 100% in all treatments. No significant differences were seen in growth between the dietary groups (P > 0.05). The protein, lipid and ash contents were not significantly different among the groups (P > 0.05); however, there was a significant difference in protein and ash content between the treatment groups and the initial, and between the 50LSO group and the initial group, respectively (P < 0.05). The viscerosomatic index (VSI) and hepatosomatic index (HSI) values were not affected by increasing LSO percentages in the diets. The n‐6 polyunsaturated fatty acid (PUFA) concentration increased with increasing LSO levels in the diets. In contrast, the n‐3 PUFA levels decreased with increasing LSO levels in the diets. The liver and muscle were used for the analysis of fatty acids. The highest level of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations was recorded in fillet of fish fed the FO diet and the lowest in those fed the 50LSO diet. However, EPA and DHA ratios in the liver of fish fed the 75LSO diet were higher than those in fillet of fish fed the FO and 50LSO diets. No significant differences were seen in fatty acid composition between the dietary groups (P > 0.05). Based on the results of growth performance and fatty acid composition of the experimental fish in this study, it can be concluded that the 75% concentration of laurel seed oil performed best among the diets tested in the experiment.     

Response of juvenile tench (Tinca tinca L.) fed practical diets with different protein contents and substitution levels of fish meal by soybean meal

A basal practical diet for juvenile tench (Tinca tinca) was formulated and elaborated to test several protein contents and substitution possibilities of fish meal (FM) by soybean meal (SBM) in a 90‐day trial with 5‐month‐old juveniles (30.54 mm TL, 0.30 g W). A factorial design included nine feeding treatments: three protein contents (50%, 40% or 30%) and three levels of replacement (0%, 25% or 45%) of FM protein by SBM protein. In addition, a commercial carp feed was used as reference. Final survival ranged from 98.2% to 99.4%. The 50% dietary protein with 0% or 25% replacement and 40% dietary protein with 25% replacement diets enabled higher growth (P < 0.05) and lower FCR (P < 0.05) than the rest of practical diets. Fish fed 50% dietary protein had similar growth than those fed carp feed (63.8% protein). Deformed fish averaged 1% for the practical diets and 87.6% for the carp feed. The basal practical diet has showed to be feasible and levels of 40–50% dietary protein with 25% replacement of FM protein by SBM protein can be recommended for juvenile tench aged 5–8 months.     

Growth response and fatty acid composition of juvenile red claw crayfish (Cherax quadricarinatus) fed different sources of dietary lipid

A study was conducted to determine the effects of different sources of dietary lipid that differ in fatty acid (FA) composition on growth, feed conversion ratio (FCR), survival, and whole‐body proximate and FA composition of juvenile red claw. Juvenile red claw (0.55 ± 0.02 g) were reared over a 12‐week period. Five practical diets were supplemented with 70 g kg^?1 oil (by weight) from either linseed oil (LO), canola oil (CAO), corn oil (CO), beef tallow (BT) or menhaden oil (MO) and formulated to contain 400 g kg^?1 crude protein. Red claw were fed three times daily (800, 1200 and 1600) to controlled excess. At the conclusion of the experimental period, there were no significant differences (P > 0.05) found in percentage survival and FCR among dietary treatments and values averaged 85.4% and 3.4, respectively. However, final mean weight and specific growth rate of red claw fed Diet 1 (LO) was significantly higher (16.44 g and 3.95% day^?1, respectively) compared with that of red claw fed Diet 4 (BT; 12.24 g and 3.43% day^?1, respectively), but not different from red claw fed the other three diets. Likewise, red claw fed Diets 1 (LO) and 2 (CAO) had significantly higher percentage weight gain (2990 and 2880%, respectively) compared with the BT diet (2124%), but not different from red claw fed Diets 3 (CO) and 5 (MO). Whole‐body fat and ash composition was significantly affected (P < 0.05) by source of added lipid, but no differences were found in whole‐body moisture and protein. Moreover, whole‐body FA composition showed differences among the varying oil sources and primarily reflected the FA in the diets. Results of the present study indicate that plant oils LO, CAO and CO rich in linolenic acid (18:3n‐3), linoleic acid (18:2n‐6) and oleic acid (18:1n‐9) perform as well as MO containing high levels of n‐3 highly unsaturated fatty acids eicosapentanoic acid (20:5n‐3) and docosahexaenoic acid (22:6n‐3) for juvenile red claw crayfish grown indoors lacking natural food items. Further, red claw fed a diet containing BT, which has a high percentage of saturated FA, performed poorly compared with LO and CO in regards to weight gain. It appears that juvenile red claw can be fed diets containing less expensive plant‐based oils with high levels of 18‐carbon unsaturated fatty acids. This could reduce diet costs for producers and allow for profitability.     

Influence of different diets on the growth,survival, fecundity and proximate composition of brine shrimp Artemia franciscana (Kellog, 1906)

Artemia franciscana was studied under in vitro conditions, and fed with five different microalgae species, two organic diets and one mixed diet to evaluate the nutritional profile and growth performance. The A. franciscana instar‐I nauplii were stocked at a density of 100 per litre of ground borewell water with a salinity of 70 ppt in a plastic container and the culture continued for 12 days. The A. franciscana was fed with five microalgal species, such as Tetraselmis sp., Chaetoceros sp., Isochrysis sp., Thalassiosira sp. and Nannochloropsis sp., and organic diets of rice bran, soybean meal, and a mixture of Tetraselmis sp. and Chaetoceros sp. with rice bran, giving a total of eight experiments. The growth of A. franciscana was measured by length, and was observed to be the greatest (10,850 μm) in the group that was fed the mixed algae combination, and the lowest (7,290 μm) in the group that was fed Nannochloropsis sp. Among the different treatments, the highest survival value of 76% was seen in the group that was fed Chaetoceros sp. The fecundity was higher in A. franciscana that were fed with algae Chaetoceros sp., while the lower rate was observed with the group that was fed Nannochloropsis sp. Analysis of proximate composition showed increased levels in the animals fed with Chaetoceros sp. (lipid, 19.40%; eicosapentaenoic acid, 6.70 mg; docosahexaenoic acid, 10.20 mg; amino acids: proline, 2.06 μg; histidine, 0.77 μg, arginine, 0.65 μg, glycine, 0.80 μg, glutamic acid, 1.75 μg; threonine, 1.42 μg) and the mixed diet (protein, 58.59%; carbohydrate, 21.30%; amino acids: asparagine, 0.90 μg; serine, 1.65 μg; tryptophan, 1.66 μg; leucine, 1.50 μg; phenylalanine, 1.14 μg; valine, 0.66 μg). All components showed the lowest level in the diet fed with Tetraselmis species. These A. franciscana populations showed better survival, higher fecundity and biochemical profiles when cultured with microalgae Chaetoceros sp. These data are useful to improve A. franciscana culture in aquaculture to produce quality cysts and biomass, especially in feeding larvae of marine species.     

Effects of dietary fish oil replacement by microalgae raw materials on growth performance,body composition and fatty acid profile of juvenile olive flounder,Paralichthys olivaceus

Replacing dietary fish oil with DHA‐rich microalgae Schizochytrium sp. and EPA‐rich microalgae Nannochloropsis sp. for olive flounder (Paralichthys olivaceus) was examined. Three experimental isonitrogenous and isolipidic diets with lipid source provided by 50% fish oil (F50S50), 50% (M50F25S25) and 100% microalgae raw material (M100) respectively were compared with a soybean oil (S100) diet as control. Triplicate groups of olive flounder juveniles (16.5 ± 0.91 g) were fed the experimental diets, and a group was fed the control diets for 8 weeks in a recirculation system. Results showed feed efficiency and growth performance were not significantly changed when fish oil (FO) was totally substituted by soybean oil (SO) or microalgae raw material (MRM). The whole‐body composition, lipid content of liver and muscle, and lipid composition of plasma were not significantly influenced by the total substitution of FO by MRM. The polyunsaturated fatty acids (PUFA) content of muscle and liver declined in fish fed S100 diet, whereas it was not significantly reduced in fish fed M50F25S25 and M100 diets. The total substitution of FO by MRM not only maintained the levels of arachidonic acid, EPA or DHA but also increased n‐3/n‐6 ratio. In conclusion, MRM as the sole lipid source is sufficient to obtain good feed efficiency, growth performance and human health value in olive flounder juveniles.     

Growth performance of juvenile kuruma shrimp,Marsupenaeus japonicus (Bate) fed diets replacing fishmeal with soybean meal

A feeding trail was conducted to evaluate the effect of lowering dietary fishmeal (FM) levels while increasing levels of dehulled soybean meal (SBM) on growth, nutrient utilization and body composition of juvenile kuruma shrimp, Marsupenaeus japonicas. Five experimental diets were formulated to be isoenergetic, isolipidic and isonitrogenous with decreasing FM levels from 40 to 16% while increasing SBM from 0 to 33% respectively. Quadruplicate groups of shrimp (initial wt = 1.5 g) were fed the test diets for 56 days under the flow‐through system. There were no significant differences in final weight (g) and specific growth rate (SGR, % day) among shrimp fed FM40, FM34, FM28 and FM22 diets respectively. Growth parameters significantly decreased in shrimp when fed FM16 diet, which was the lowest level of FM. Feed intake was positively correlated with the SGR of shrimp, and the lowest one was found in shrimp fed FM16 diet. Protein gain and retention, whole body lipid, arginine and methionine significantly decreased in FM16 fed group. Thus, it is concluded that dietary FM could be reduced down to 22% with SBM without compromising growth, nutrient utilization and retention, and whole body composition of kuruma shrimp.     

Effect of replacing dietary fish oil with soybean oil on growth performance,fatty acid composition and haematological parameters of juvenile meagre,Argyrosomus regius

A nutrition trial with meagre, Argyrosomus regius was assessed to determine the effect of dietary replacement of fish oil (FO) by soybean oil (SO) on the growth, feed utilization, body composition, fatty acid composition and basic haematological parameters. Six isonitrogenous (47% crude protein) and isoenergetic (gross energy 22 kJ/g) experimental diets were formulated by replacing 0 (FO), 20 (S20), 40 (S40), 60 (S60), 80 (S80) and 100 (S100) % of the FO with SO. Fish were fed three times daily to near satiation for 14 weeks. The specific growth rate (SGR) of fish fed S100 diet was significantly lower than the other treatments, except SO80 diet. The fish fed SO100 diet displayed significantly higher feed conversion ratio than that of other diets (P < 0.05). It was observed that fish fed the SO100 and SO80 diets displayed haemoglobin (HGB) levels significantly lower (P < 0.05) than fish fed the SO20 diet. Packed cell volume (PCV) of fish fed SO20 diet was significantly higher compared to SO100. The white blood cell (WBC) and red blood cell (RBC) remained unaffected by dietary treatment. The docosahexaenoic acid (22:6n‐3, DHA) and eicosapentaenoic acid (20:5n‐3, EPA) levels of meagre were significantly reduced by the substituting of dietary SO by FO at the end of the feeding period. The level of linoleic acid (18:2n‐6, LA) and linolenic acid (18:3n‐3, LNA) significantly raised in fish fed with SO diets (P < 0.05). The results of this study showed that SO could be replaced FO up to 80% in meagre diet without negative effect on growth performance and basic haematological parameters. Furthermore, the maximum level of FO replacement with SO determined by second order polynomial regression analysis, was 30.1% on the basis of maximum SGR.     

Growth,antioxidant capacity,intestine histology and lipid metabolism of juvenile red claw crayfish,Cherax quadricarinatus,fed different lipid sources

Five dietary lipid sources (fish oil, soybean oil, palm oil, rapeseed oil and linseed oil) were evaluated in juvenile red claw crayfish, Cherax quadricarinatus, based on the response of growth, antioxidant capacity, intestine histology, whole‐body composition, fatty acid nutrition and lipid metabolism. Crayfish were fed in quadruplicate net cages for 8 weeks. Crayfish fed diets with fish oil, soybean oil and linseed oil obtained significantly higher weight gain and specific growth rate than those fed the other two diets. Survival, condition factor and hepatosomatic index were not significantly affected by lipid sources. Lipid sources also do not affect the whole‐body composition of crayfish. Serum SOD, T‐AOC and GSH‐PX activities of crayfish fed the palm oil and rapeseed oil diets had a significantly lower value than those fed other diets. The minimum concentrations of MDA have been observed in crayfish fed the soybean oil diet. The activity of ACC in the hepatopancreas of crayfish fed the linseed oil diet showed the highest value, and the CPT‐1 activity was not significantly affected by different lipid sources. Crayfish fed the soybean oil diet showed significantly higher TC and TG contents in hepatopancreas than those fed other diets. Crayfish fed linseed oil diet had a significantly higher percentage of EPA, C18:3n?3 and Σn?3 PUFA in muscle than those fed other treatments. Most of the fatty acid compositions in the hepatopancreas had a close correlation to fatty acid compositions in diets. All findings in this study indicate that soybean oil is the advantageous lipid source for juvenile C. quadricarinatus which can reflect in satisfactory growth performance, antioxidant capacity and fatty acid nutrition of edible tissues.     

Gonadic conditioning and maturation of the queen conch (Dosinia ponderosa) fed three microalgae at three temperatures

Gonadic conditioning and maturation of queen clam Dosinia ponderosa fed three microalgae (Isochrysis galbana, Tetraselmis suecica and Chaetoceros calcitrans) at three temperatures (20, 25 and 30°C) were assessed. Histological analysis showed six gonadic stages, indicators of maturity. The evaluation included sex proportion, oocyte diameter and frequency of gonadic stages after 22 (middle of trial) and 44 days (end of trial). At day 22, around 60% of females conditioned at 20°C, reached stage III (advances grade of maturation) when fed T. suecica. At day 44, around 50% of females were on stage III, conditioned at 20 and 25°C and fed T. suecica and C. calcitrans. For males, the best combination was C. calcitrans at 20 and 25°C. The temperature of 30°C resulted inadequate for maturation, especially when fed the diatom Isochrysis galbana. High mortalities occurred at that temperature with the three microalgal diets, especially in females. The results permits conclude that T. suecica and C. calcitrans are good sources of feed for D. ponderosa and that the best range of temperature for gonadic development is 22–25°C. These results may be basic for a best management and culture of this clam.     

Essential fatty acid enrichment of cultured rotifers (Brachionus plicatilis, Müller) using frozen-concentrated microalgae

There is a growing interest in preserving microalgal preparations to maintain constant properties over a long period. The aim is to ensure sufficient delivery of essential fatty acids (and other key nutrients) to mollusc and crustacean larvae and to zooplankton used as live prey in the first feeding of fish larvae. For example, the rotifer Brachionus plicatilis has to be enriched with polyunsaturated fatty acids (PUFA) prior to fish feeding. We used four microalgal species [ Isochrysis galbana (T-ISO), Chaetoceros muelleri (CHGRA), Pavlova lutheri (MONO), and Nannochloropsis sp.] both as fresh culture or in a frozen-concentrated form to enrich rotifers. Overall, rotifers had similar relative fatty acid levels when fed the frozen-concentrated or fresh microalgal diets. The levels of 20:4n-6, 22:6n-3, and 20:5n-3 between B. plicatilis and the microalgal diets were linearly correlated. The fatty acid 20:4n-6 was the most readily assimilated: the content found in rotifers reached half the level measured in the microalgal diets. Our results indicate that both the fresh and frozen-concentrated forms of the four microalgal species can be used to enrich PUFA levels in rotifers. Further experiments should be conducted to test if assimilation differs when rotifers are enriched with mono- or multispecific microalgal preparations.     

Growth, survival, lipid and fatty acid profile of juvenile monaco shrimp Lysmata seticaudata fed on different diets

The present work evaluated the effect of three inexpensive diets (frozen minced mussel and edible cockle (MMC), frozen minced squid (MS) and gilthead seabream feed (GSF)) on growth, survival, sex reversal, lipid classes and fatty acid (FA) profile of juvenile ornamental shrimp Lysmata seticaudata. Shrimp fed GSF displayed the highest survival rate (±SD) (85.2±1.8%) and the highest percentage (±SD) of shrimp changing from male to simultaneous hermaphrodite (SH) phase (25.2±2.2%). All diets promoted growth rates superior to those reported in the wild, with SH shrimp displaying higher total lengths (TL). Shrimp in SH phase fed GSF displayed the highest TL (±SD) (40.6±1.2 mm). Cultured shrimp reflected the lipid content of experimental diets, with shrimp fed GSF displaying the highest triacylglycerols and sterols (ST) contents. The higher rearing density induced by lower mortality rates of shrimp fed GSF, and the high ST levels present in the diet, may explain the higher proportion of shrimp in SH phase. The higher levels of highly unsaturated fatty acids (HUFA) displayed by MS did not promote higher survival or growth rates. The low polyunsaturated fatty acids and HUFA content of MMC was not reflected in cultured shrimp, probably because of a selective retention of these FA.     

Growth,immune response and resistance to Aeromonas hydrophila of darkbarbel catfish,Pelteobagrus vachelli (Richardson), fed diets with different linolenic acid levels

Experimental diets were formulated containing six levels of linolenic acid (0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%) and each diet was fed to darkbarbel catfish Pelteobagrus vachelli in triplicate for 84 days. Weight gain, specific growth rate and feed efficiency increased with the increasing levels of dietary linolenic acid, but were not significantly different among diets containing 1.0%, 1.5%, 2.0% and 2.5% linolenic acid. Red blood cell count and haemoglobin were significantly higher in fish fed the 1.0% linolenic acid than other diets. Lysozyme activity and immunoglobulin M content in fish fed 1.0% of linolenic acid were significantly higher compared with the other diets. Antibody titre in fish fed 1.0–2.5% linolenic acids was significantly higher than in fish fed 0 or 0.5% linolenic acid 14 days after Aeromonas hydrophila challenge. This study indicates that linolenic acid is essential to darkbarbel catfish. Two‐straight broken‐line analysis with SGR showed that a dietary level of 1.29% linolenic acid is the minimum required for adequate growth of darkbarbel catfish. Considering other measured indicators of fish performance, a level of 1.0–1.5% linolenic acid in the diet is recommended for the darkbarbel catfish.