Effect of increasing docosahexaenoic acid content in weaning diets on survival,growth and skeletal anomalies of longfin yellowtail (Seriola rivoliana,Valenciennes 1833)

Five isoproteic (54.8%) and isolipidic (24.1%) microdiets, which varied in their docosahexaenoic acid (DHA) content (0.25%, 0.75%, 1.64%, 1.99% and 3.17%; dw), were manufactured to determine its effects on longfin yellowtail Seriola rivoliana larvae in terms of fish biological performance, whole body fatty acid profile and incidence of skeletal anomalies from 30 dah (11.31 ± 1.79 Total Length, TL) to 50 dah (19.80 ± 0.58 mm TL). The inclusion of dietary DHA up to 3.17% (dw) improved larval resistance to air exposure, although DHA did not significantly affect fish final growth or final survival. Indeed, high levels of dietary DHA (1.99% and 3.17%, dw) tended to increase the incidence of skeletal anomalies in S. rivoliana larvae, albeit no significant differences were observed. Furthermore, the occurrence of severe anomalies such as kyphosis and lordosis, was mainly associated to the larvae fed the highest levels of dietary DHA. In terms of survival, increasing dietary DHA levels did not significantly affect longfin yellowtail survival rate, despite a tendency for enhanced survival. The results of the present study proved that the inclusion of dietary DHA in inert diets up to a 3.17% (dw) and a DHA/EPA ratio above 3.1 increased the final survival and stress resistance in S. rivoliana larvae.     

Effect of Two Novel Experimental Microdiet Types on Growth,Survival, and Pigmentation during the Weaning Period of the Fine Flounder,Paralichthys adspersus,Larvae

The aim of this study was to evaluate two new types of experimental weaning microdiets for fish larvae, using the same formulation, but with different manufacturing processes, microextrusion marumerization (MEM) and particle‐assisted rotational agglomeration (PARA). Both microdiets were compared to a commercial microdiet, Otohime? (OTO), during the weaning of the fine flounder, Paralichthys adspersus . Weaning was achieved by cofeeding with live food from 40 to 50 d after hatch (d.a.h.). Thereafter, only the microdiets were fed to the end of the study (60 d.a.h.), where the total length, dry weight, and survival rates were 15.9 ± 3.20, 14.3 ± 1.72, and 14.4 ± 2.28 mm; 8.83 ± 3.40, 5.53 ± 2.85, and 7.10 ± 3.56 mg; 18.1, 16.3, and 15.2%, for OTO, MEM, and PARA, respectively. The dry weight and total length were significantly higher (P < 0.05) for larvae fed OTO compared with those fed MEM. There were no differences between the other comparisons. Based on these results, any of the two experimental microdiets can be used for future investigations. However, we recommend the PARA microdiets because the manufacturing process produces less‐dense and smaller particle size diets, reducing sinking rates and increasing the probability of the larvae in detecting and ingesting the diet.     

Potential of three new krill products for seabream larval production

The objective of this study was to evaluate three products derived from krill as sources of essential fatty acids, protein and, particularly, phospholipids in microdiets for larval gilthead seabream (Sparus aurata). Their effect on larval performance, biochemical composition and histological development was investigated. The addition of krill phospholipids, rich in highly unsaturated fatty acids, improved larval sea bream growth in terms of weight and length, enhanced hepatic utilization of dietary lipids and reduced the incidence of enterocyte injuries. These results confirm the higher nutritional value of marine phospholipids for the early development of marine fish larvae in comparison with soybean phospholipids.     

Growth performance,survival and body composition of southern flounder Paralichthys lethostigma larvae fed different formulated microdiets

Three experiments were conducted to evaluate the effects of micro‐bound diets (MBD) on southern flounder larvae. In experiment 1, four MBDs were formulated with different protein sources as follows: MBD 1: herring meal, MBD 2: menhaden meal, MBD 3: menhaden and squid meal; MBD 4: menhaden, squid and herring meal. In experiment 2, four MBDs were formulated as follows: MBD 5: menhaden, squid and herring meal; MBD 6: menhaden, squid, herring and attractants; MBD 7: menhaden, squid, herring and casein, and MBD 8: menhaden, squid, herring, casein and attractants. In experiment 3, three groups were maintained as follows: Group 1: live feed; Group 2: co‐fed with MBD 6; and Group 3: MBD 6. In experiment 1 on 35 dph, survival and body weight (BW) of the fish fed MBD 4 was significantly higher than the MBDs 1 and 2. In experiment 2 on 34 dph, fish fed MBD 6 had significantly higher BW than the commercial microdiets. In experiment 3 on 21 dph, fish receiving only MBD had significantly lower survival than the other groups. Growth, survival and larval fatty acid composition suggested that co‐feeding MBD 6, a mixture of marine protein sources plus attractants was more effective than the other MBDs.     

Peptide molecular weight distribution of soluble protein fraction affects growth performance and quality in European sea bass (Dicentrarchus labrax) larvae

Dicentrarchus labrax were fed from 10 to 40 days posthatching with six microdiets differing in the inclusion level (60 g kg^‐1 and 120 g kg^‐1) and type of protein hydrolysate (PH; yeast, YPH; pig blood, PBPH; pig red blood cells, PRBCPH). A microdiet containing 120 g kg^‐1 fish PH (FPH) was used as a control. PH differed in their amino acid (AA) profile and molecular weight distribution and therefore the tested microdiets too. The estimated content in FAA and di‐ and tripeptides in the FPH microdiet was 2 g kg^‐1 and 44 g kg^‐1, respectively. FAA estimated levels in YPH and PBPH microdiets were 26 g kg^‐1 and 53 g kg^‐1, whereas levels of di‐ and tripeptides were 30 g kg^‐1 and 60 g kg^‐1, respectively. The estimated levels of FAA in PRBCPH microdiets were 8 g kg^‐1 and 17 g kg^‐1, whereas estimated levels of di‐ and tripeptides were 11 g kg^‐1 and 22 g kg^‐1, respectively. Results revealed that FPH may be replaced by alternative PH from yeast and pig blood products, as fish fed those diets performed, in terms of growth, survival, digestive function and incidence of skeletal deformities, as well as those fed the FPH microdiet. Using YPH, PBPH and PRBCPH, the inclusion level of PH in microdiets might be reduced to a half with respect to current practices using FPH.     

Fish oil replacement by different microalgal products in microdiets for early weaning of gilthead sea bream (Sparus aurata,L.)

The aim of this study was to determine if algal products rich in DHA or ARA are able to completely replace fish oil in microdiets for marine fish larvae, gilthead seabream and if extra supplementation with EPA may further enhance larval performance. For that purpose, 20 day‐old gilthead seabream larvae of 5.97 ± 0.4 mm mean total length and 0.12 ± 0.001 mg mean dry body weight were fed with five microdiets tested by triplicate: a control diet based on sardine oil; a diet containing AquaGrow^® DHA (diet DHA) to completely substitute the sardine oil; a diet containing AquaGrow^® ARA (diet ARA); a diet containing both products, AquaGrow^® DHA and AquaGrow^® ARA to completely substitute the fish oil; and, a diet containing both products, AquaGrow^® DHA and AquaGrow^® ARA, together with an EPA source. Temperature, air and salinity activity tests were also performed to detect larval resistance to stress. At the end of the experiment, final survivals did not differ among groups. The microorganism produced DHA was able to completely replace fish oil in weaning diets for gilthead seabream without affecting survival, growth or stress resistance, whereas the inclusion of microorganism produced ARA did not improve larval performance. Moreover, addition of EPA to diets with total replacement of fish oil by microorganism produced DHA and ARA, significantly improved growth in terms of body weight and total length. The results of this study denoted the good nutritional value of microorganisms produced DHA as a replacement of fish oil in weaning diets for gilthead seabream, without a complementary addition of ARA. However, dietary supplementation of EPA seems to be necessary to further promote larval performance.     

Growth,survival and fatty acid composition of Rhamdia quelen (Quoy and Gaimard, 1824) larvae fed on artificial diet alone or in combination with Artemia nauplii

Black catfish (Rhamdia quelen) is a species of interest for aquaculture in Brazil, Argentina and Uruguay. A feeding trial was conducted to evaluate the effect of feeding R. quelen larvae on either only an artificial diet or in combination with Artemia nauplii (AN) on larval performance and fatty acid composition. For 12 days, larvae were fed from first feeding (3 days after hatching, TL = 5.88 ± 0.23 mm) with artificial food only or a combination of artificial food and AN (co‐feeding). At the end of the trial, total length of co‐fed larvae was significantly higher than that of larvae fed solely artificial food (P < 0.001). No significant differences were found in survival rates. Co‐feeding microdiet with a small amount of AN significantly affected larval fatty acid composition. Lipid and fatty acid composition of food and larvae revealed the importance of n‐3 fatty acids for growth of black catfish larvae and that, as most freshwater fish, R. quelen larvae can elongate and desaturate linolenic acid to n‐3 highly unsaturated fatty acids. Results suggest that R. quelen larvae can be fed from first feeding on microdiets as unique food source, although better larval performances are obtained by co‐feeding with a small amount of AN.     

Influence of dietary polar lipids' quantity and quality on ingestion and assimilation of labelled fatty acids by larval gilthead seabream

Dietary supplementation of phospholipids seems to be extremely important to promote growth and survival in fish larvae. Several studies also suggest the importance of n-3 highly unsaturated fatty acids (HUFA) rich phospholipids to further enhance larval performance. In the present study, four different diets were formulated in order to compare the effect of total dietary polar lipid contents, of soya bean lecithin supplementation and of feeding n-3 HUFA in the form of neutral or polar lipids on ingestion and incorporation of labelled fatty acids in gilthead seabream larvae. These diets were prepared including radiolabelled fatty acids from palmitoyl phosphatidylcholine, glycerol trioleate, free oleic acid (FOA) and free eicosapentaenoic acid (FEPA) and were fed to 25 day-old larvae. The results of these experiments showed that the elevation of the dietary polar lipid levels significantly improved microdiet ingestion, regardless of the origins of the polar lipids. This effect caused an improved incorporation of phosphatidylcholine fatty acids to the larval polar and total lipids (TL) as the dietary polar lipids increased. Nevertheless, a better incorporation of fatty acids from dietary polar lipids in comparison with that of fatty acids from dietary triglycerides into larval lipids was found in gilthead seabream, whereas a better utilization of dietary triglycerides fatty acids than dietary free fatty acids could also be observed. Besides, the presence of n-3 HUFA rich neutral lipids (NL) significanlty increased the absorption efficiency of labelled oleic acid from dietary triglycerides, but the presence of n-3 HUFA rich polar lipids, particularly improved the incorporation of FEPA. This fatty acid was preferentially incorporated into larval polar lipids in comparison with FOA.