Co-feeding Regime Research Articles

Nematodes Can Substitute Artemia in a Co-Feeding Regime for Pacific White Shrimp Post-Larvae Reared in a Biofloc Nursery System.

This study evaluated nematodes as an alternative to live Artemia when provided in a co-feeding regime to Pacific white shrimp (Penaeus vannamei) post-larvae (PL) reared in a biofloc nursery system. A 20-day experiment employing PL11 was performed for an evaluation of four dietary groups: control [C] (fed exclusively with a dry commercial feed); artificial Artemia [AA] (dry feed composed of extracted and processed Artemia cysts and dry commercial feed); live Artemia and dry commercial feed [LA]; and nematodes and dry commercial feed [N] (Panagrolaimus sp. dry nematodes). The diets were provided twice a day, with the remaining six feed provisions being a commercial dry feed for all experimental groups. A biofloc system was chosen as it offers a potentially sustainable approach to intensive shrimp farming. Alkalinity and pH in the [N] group were significantly higher in the last 5 days of the experiment (p < 0.05), likely causing the significantly lower nitrite levels observed in that same group (p < 0.05). Total and volatile suspended solids were significantly lower in the two live feed groups when compared with [C] and [AA] (p < 0.05). Although PL fed the dry diets exhibited higher growth rates (p < 0.05), the [N] and [LA] groups presented significantly higher final survivals (p < 0.05). No differences were found for survival after a salinity stress test (p ≥ 0.05). These results suggest that nematodes can successfully substitute Artemia in a co-feeding regime for P. vannamei PL reared in biofloc nursery systems.

Dietary protein complexity modulates growth, protein utilisation and the expression of protein digestion-related genes in Senegalese sole larvae

Given its complex metamorphosis and digestive system ontogeny, Senegalese sole larvae capacity to digest and utilize dietary protein is likely to change throughout development. In the present study, we hypothesized that the manipulation of dietary protein complexity may affect Senegalese sole larvae capacity to digest, absorb and retain protein during metamorphosis, as well as the mRNA expression of genes encoding for the precursors of proteolytic enzymes of the digestive tract and the enterocyte peptide transporter PepT1, which may have further impact on somatic growth. Three diets were formulated using approximately the same practical ingredients, except for the main protein source. The Intact diet protein content was mostly based on intact plant protein where the target peptide molecular weight (MW) would be >70kDa. The PartH diet protein fraction was mostly based on a protein hydrolysate with a high content of 5–70kDa peptides. The HighH diet protein fraction was mostly based on a protein hydrolysate with a high content of 5kDa peptides. A growth trial was performed with larvae reared at 19°C under a co-feeding regime from mouth opening. The transcription of pga, tryp1c, ialp, ampn and pepT1 (encoding respectively for PepsinogenA, Trypsinogen1C, Intestinal alkaline phosphatase, Aminopeptidase N and for the enterocyte peptide transporter 1) was quantified by qPCR, during the metamorphosis climax (16DAH) and after the metamorphosis was completed (28DAH). An in vivo method of controlled tube-feeding was used to assess the effect on the larvae capacity to utilize polypeptides with different MW (1.0 and 7.2kDa) representing a typical peptide MW of each of the hydrolysates included in the diets. The PartH diet stimulated growth in metamorphosing larvae (16DAH), whereas the Intact diet stimulated growth after 36DAH. The Intact diet stimulated the larvae absorption capacity for 1.0kDa peptides at 16DAH, which may have contributed for enhanced growth in later stages. The PartH diet stimulated the transcription of tryp1c and pept1 at 28DAH, which seemed to reflect on increased post-larvae capacity to retain dietary 7.2kDa polypeptides. That may indicate a possible strategy to optimize the digestion and utilisation of the PartH dietary protein, though it did not reflect into increased growth. The Intact diet promoted the transcription of pepsinogenA, which may reflect a reduced gastrointestinal transit time, which could have enhanced the dietary nutrients assimilation, ultimately improving growth. The present results suggest that, whereas pre-metamorphic sole larvae utilize better dietary protein with a moderate degree of hydrolysis, post-metamorphic sole make a greater use of intact protein.

Dietary indispensable amino acids profile affects protein utilization and growth of Senegalese sole larvae

In diet formulation for fish, it is critical to assure that all the indispensable amino acids (IAA) are available in the right quantities and ratios. This will allow minimizing dietary AA imbalances that will result in unavoidable AA losses for energy dissipation rather than for protein synthesis and growth. The supplementation with crystalline amino acids (CAA) is a possible solution to correct the dietary amino acid (AA) profile that has shown positive results for larvae of some fish species. This study tested the effect of supplementing a practical microdiet with encapsulated CAA as to balance the dietary IAA profile and to improve the capacity of Senegalese sole larvae to utilize AA and maximize growth potential. Larvae were reared at 19°C under a co-feeding regime from mouth opening. Two microdiets were formulated and processed as to have as much as possible the same ingredients and proximate composition. The control diet (CTRL) formulation was based on commonly used protein sources. A balanced diet (BAL) was formulated as to meet the ideal IAA profile defined for Senegalese sole: the dietary AA profile was corrected by replacing 4% of encapsulated protein hydrolysate by CAA. The in vivo method of controlled tube-feeding was used to assess the effect on the larvae capacity to utilize protein, during key developmental stages. Growth was monitored until 51 DAH. The supplementation of microdiets with CAA in order to balance the dietary AA had a positive short-term effect on the Senegalese sole larvae capacity to retain protein. However, that did not translate into increased growth. On the contrary, larvae fed a more imbalanced (CTRL group) diet attained a better performance. Further studies are needed to ascertain whether this was due to an effect on the voluntary feed intake as a compensatory response to the dietary IAA imbalance in the CTRL diet or due to the higher content of tryptophan in the BAL diet.

The supplementation of a microdiet with crystalline indispensable amino-acids affects muscle growth and the expression pattern of related genes in Senegalese sole (Solea senegalensis) larvae

The full expression of growth potential in fish larvae largely depends on an efficient protein utilization, which requires that all the indispensable amino acids (IAAs) are provided at an optimum ratio. The effect of supplementing a practical microdiet with encapsulated crystalline-AA to correct possible IAA deficiencies was evaluated in Senegalese sole larvae. Two isonitrogenous and isoenergetic microdiets were formulated and processed to have approximately the same ingredients and proximate composition. The control diet (CTRL) was based on protein sources commonly used in the aquafeed industry. In the supplemented diet (SUP) 8% of an encapsulated fish protein hydrolysate was replaced by crystalline-AA in order to increase the dietary IAA levels. The microdiets were delivered from mouth-opening upon a co-feeding regime until 51days after hatching (DAH). The larvae capacity to utilize protein was evaluated using an in vivo method of controlled tube-feeding during relevant stages throughout development: pre-metamorphosis (13DAH); metamorphosis climax (19DAH) and metamorphosis completion (25DAH). Somatic growth was monitored during the whole trial. A possible effect on the regulation of muscle growth was evaluated through muscle cellularity and the expression of related genes (myf5, myod2, myogenin, mrf4, myhc and mstn1) at metamorphosis climax (19DAH) and at a juvenile stage (51DAH). The SUP diet had a negative impact on larvae somatic growth after the metamorphosis, even though it had no effect on the development of Senegalese sole larvae capacity to retain protein. Instead, changes in somatic growth may reflect alterations on muscle growth regulation, since muscle cellularity suggested delayed muscle development in the SUP group at 51DAH. Transcript levels of key genes regulating myogenesis changed between groups, during the metamorphosis climax and at the 51DAH. The group fed the SUP diet had lower dnmt3b mRNA levels compared to the CTRL group. Further studies are needed to ascertain whether this would possibly lead to an overall DNA hypomethylation in skeletal muscle. Statement of relevanceIn farmed fish species, there has been a great effort over the years to provide the best conditions for successful development of embryos and small larvae, as early environmental conditions can strongly affect muscle growth during early stages and influence the subsequent growth potential at later life stages. In spite of increased efforts to understand the regulation of myogenesis by intrinsic factors like genotype and extrinsic factors such as photoperiod and temperature, studies evaluating the impact of nutritional factors on fish larvae muscle development are still very scarce.This work will raise interest to the discussion on whether a nutritional cue during an early developmental stage can impact on the regulation of muscle growth and on further growth potential in a metamorphosing farmed fish species, such as Senegalese sole. Supplementing microdiets with crystalline-AA in order to correct dietary IAA did not improve Senegalese sole larvae somatic growth and led to changes on the regulation of muscle growth associated with changes in expression patterns of muscle growth markers during the trial (secondary MRFs myogenin and mrf4, myhc and mstn1). Dietary IAA affected the expression of a DNA methyltransferase essential for de novo methylation, dnmt3b, suggesting that an epigenetic effect at the transcriptional regulation level may explain differences found in somatic growth as a response to a nutritional cue.This work may contribute to lay down basis for future studies on nutritional programming of muscle growth in fish larvae of important farmed species.

Benefits of probiotic administration on growth and performance along metamorphosis and weaning of Senegalese sole (Solea senegalensis)

Abstract Suitable nutrition at first feeding in marine fish larvae is an important factor for successful larval and juvenile rearing. In this way probiotic supplementation may contribute to better face the habitual stress of metamorphosis and weaning at early sole stages. The aim of this study was to optimize Shewanella putrefaciens Pdp11 administration to Senegalese sole (Solea senegalensis) at early stages of development. For this purpose, we studied the influence of a short pulse of S. putrefaciens Pdp11 (10–30 dah) on growth performance, gut microbiota modulation, digestive enzymes activities and body composition. These probiotic bacteria were incorporated using Artemia as live vector (2.5 × 107 cfu mL− 1) and supplied to sole specimens in a co-feeding regime (Gemma, Skretting) by triplicate. S. putrefaciens Pdp11 colonized larval gut being present from 23 to 119 dah. Probiotic supply significantly modulated larval and fry gut microbiota. A PCA analysis including all the parameters analyzed strongly associated S. putrefaciens Pdp11 presence with a higher fish growth, a higher digestive proteolytic activity level and a fish body composition modulation along S. senegalensis rearing. In addition less size variability was obtained from metamorphosis until the end of weaning. In conclusion a short pulse of S. putrefaciens Pdp11 (10–30 dah) seems sufficient to obtain a suitable microbial modulation involved in a better growth performance and body composition that suggests a great potential for sole aquaculture production.

Dietary probiotic supplementation (Shewanella putrefaciens Pdp11) modulates gut microbiota and promotes growth and condition in Senegalese sole larviculture

Probiotic supplementation in fish aquaculture has significantly increased in the last decade due to its beneficial effect on fish performance. Probiotic use at early stages of fish development may contribute to better face metamorphosis and weaning stress. In the present work, we studied the influence of Shewanella putrefaciens Pdp11 supplementation on growth, body composition and gut microbiota in Senegalese sole (Solea senegalensis) during larval and weaning development. S. putrefaciens Pdp11 was incorporated using Artemia as live vector (2.5 × 10⁷ cfu mL⁻¹) and supplied to sole specimens in a co-feeding regime (10-86 DAH) by triplicate. Probiotic addition promoted early metamorphosis and a significantly higher growth in length at 24 DAH larvae. S. putrefaciens Pdp11 also modulated gut microbiota and significantly increased protein content and DHA/EPA ratios in sole fry (90 DAH). This nutritional enhancement is considered especially important after weaning, where significantly higher growth in length and weight was observed in probiotic fish. Moreover, a less heterogeneous fish size in length was detected since metamorphosis till the end of weaning, being of interest for sole aquaculture production. After weaning, fish showed significantly higher growth (length and weight) and less variable lengths in fish when supplemented with probiotics. Both the enhancement of nutritional condition and the decrease in size variability associated with probiotic addition are highly interesting for sole aquaculture production.

Assessment of Nutrient Allocation and Metabolic Turnover Rate in Pacific White ShrimpLitopenaeus vannameiCo-Fed Live MacroalgaeUlva clathrataand Inert Feed: Dual Stable Isotope Analysis

The current study quantified the relative contribution of dietary carbon and nitrogen supplied by live biomass of the green macroalgae Ulva clathrata and a commercial inert feed to the growth of juvenile shrimp Litopenaeus vannamei. The stable isotope ratios of carbon and nitrogen (δ13C and δ15N) were analyzed in both food sources, whole bodies, and muscle tissue of shrimp reared on co-feeding regimes where 75%, 50%, and 25% of daily consumed macroalgal biomass was substituted by inert feed (regimes 75F/25U, 50F/50U, and 25F/75U, respectively). Higher growth rates were observed in shrimp fed regime 75F/ 25U (k = 0.062), followed by shrimp fed only inert feed (100F, k = 0.060). Animals reared only on U. clathrata (100U) showed minimal growth (k = 0.008) and very high metabolic turnover rates of carbon and nitrogen. Isotopic values measured in inert feed (δ13C = -23.0‰, δ15N = 9.1‰) and macroalgae (δ13C = -13.1‰, δ15N = -3.5‰) were highly contrasting and both had a rapid influence on the isotopic values of shrimp. Animals reached full isotopic equilibrium through growth and fast metabolic turnover in only 2 wk, except shrimp fed macroalgae only. At the end of the experiment, δ13C and δ15N values in shrimp reared on all cofeeding regimes were strongly biased toward the isotopic values of U. clathrata. Total dry matter contributions to growth were estimated using an isotope mixing model, and considered the elemental concentration of both nutritional sources. Results indicated that shrimp in the co-feeding regimes incorporated significantly higher amounts of dietary carbon and nitrogen from the macroalgal biomass. Shrimp in treatment 75F/25U incorporated 52% of carbon from the inert feed and 48% from the macroalgae. Animals under feeding regimes 50F/50U and 25F/75U incorporated higher amounts of dietary carbon from U. clathrata (65–89%) when compared with carbon proportions supplied by both co-feeding regimes (33-70%), and also incorporated the majority of nitrogen from the macroalgae. However, a high incorporation of nitrogen was not reflected in larger growth in the latter treatments because metabolic turnover rates were very high. Estimated turnover rates ranged from 0.049–0.191/day for carbon and from 0.013–0.100/day for nitrogen, and values followed an increasing trend as a function of macroalgae consumption. Nitrogen halftimes in tissue consistently decreased throughout the different treatments from 9.5 days (100F) to 6.4 days (100U). Proportions of incorporated nutrients in muscle tissue followed similar patterns as those observed in whole bodies.

Naturally-occurring stable isotopes as direct measures of larval feeding efficiency, nutrient incorporation and turnover

Stable isotopes are non-hazardous markers that have been widely-used in assessing energy flow within aquatic ecosystems. Hatchery systems are also highly amenable to this approach, as they represent controlled mesocosms with a limited number of food sources and short planktonic food chains with rapid and measurable bioaccumulation of the heavier stable isotopes of carbon and nitrogen at each trophic step. Differences in the natural isotopic composition of dietary components may be used to provide direct integrated measures of ingestion, nutrient incorporation and growth through development under normal feeding and environmental conditions, in either the laboratory or the hatchery. Simple isotopic mixing models allow estimation of relative utilisation of inert diets and live feeds, and individual components of compound feeds. Such experiments have investigated the effectiveness of co-feeding regimes, optimal timing of live food transitions (e.g. from rotifers to Artemia), presentation of inert diets, optimal size/age for weaning and incorporation of specific dietary components. Furthermore, time series measurement of changes in tissue isotopic signature ( δ 15N, δ 13C) enables modelling of growth dilution and tissue turnover components of isotopic change driven by nutritional sources. These measures need to take into account the difference in isotope values that is typically observed between the diet and consumer (isotopic discrimination factor, Δ). In marine larvae and early postlarvae, Δ 13C and Δ 15N have been found to range widely, from 0.4–4.1‰ and 0.1–5.3‰ respectively. The observation of such a high level of variation within species and life stages indicates a strong effect of diet quality on isotopic discrimination. Elucidating mechanisms underlying such observations, and much greater resolution in larval nutritional studies, can be achieved by application of rapidly-developing techniques for compound specific stable isotope analysis in tracing the transfer of dietary sources of carbon and nitrogen into tissue components. Fast growing aquatic larvae represent excellent model organisms exhibiting rapid transitions in isotopic composition in response to diet, rapidly-changing feeding behaviour and transitions in trophic level with ready ingestion of modifiable experimental diets in short and controlled food chains. Thus results of studies of the effects of diet composition, developmental stage, growth rates or environmental conditions on stable isotope incorporation will be of broad relevance not only in terms of larval nutrition but can also more broadly inform the design and interpretation of ecological studies.

Artemia replacement in co-feeding regimes for mysis and postlarval stages of Litopenaeus vannamei: Nutritional contribution of inert diets to tissue growth as indicated by natural carbon stable isotopes

The nutritional contribution from co-fed Artemia nauplii and inert diets to growth in mysis and early postlarval shrimp Litopenaeus vannamei was assessed by analyzing the carbon stable isotope ratios ( δ 13C) in diets and shrimp tissue. Artemia nauplii and inert diets showed significantly different δ 13C values but similar carbon contents and were supplied as single diets and also in three co-feeding regimes in which 25, 50 and 75% of the Artemia was replaced by inert diet on a dry weight basis, so that all feeding regimes provided similar amounts of dietary carbon. Shrimp δ 13C values were significantly influenced by the different feeding regimes and reached isotopic equilibrium with their respective diets as soon as 5 days. Survival was significantly higher in co-fed animals than in those fed either Artemia or inert diet alone. There was no significant difference in growth between shrimp fed on Artemia only and those co-fed Artemia with inert diet, although the variability was high. Growth and survival were very low in shrimp fed only inert diet. Results from an isotope mixing model suggest that observed nutrient contributions from Artemia nauplii were significantly higher than expected contributions indicated by proportions established in the co-feeding regimes. From mysis 3 to postlarvae 5, nutrient contributions to growth in the dietary regime providing equal carbon amounts of each diet type ranged from 73 to 87% for Artemia and from 13 to 27% for inert diet. Shrimp fed the 25% Artemia replacement regime exhibited a significantly higher retention of dietary carbon from the inert diet than those fed inert diet alone. This may have resulted from greater ingestion and/or assimilation of the inert diet in the presence of Artemia, combined with the higher growth rate supported by co-feeding. The results demonstrate the effectiveness of up to 50% replacement of Artemia with inert diet for L. vannamei mysis and early postlarval stages, indicating also that the inert diet may provide specific nutrients that promote higher survival, while digestibility may limit its contribution to tissue growth. The isotopic influence of maternal nutrients and dietary sources on earlier larval stages was also described.

Co-feeding of live feed and inert diet from first-feeding affects Artemia lipid digestibility and retention in Senegalese sole ( Solea senegalensis) larvae

The present study intended to evaluate the effects of early introduction of inert diet in lipid digestibility and metabolism of sole, while larval feed intake, growth and survival were also monitored. Solea senegalensis larvae were reared on a standard live feed regime (ST) and co-feeding regime with inert diet (Art R). Trials using sole larvae fed with Artemia enriched with two different lipid emulsions, containing glycerol tri [1- 14C] oleate (TAG) and L-3-phosphatidylcholine-1,2-di-[1- 14C] oleoyl (PL), were performed at 9 and 17 days after hatching (DAH) to study lipid utilization. Co-feeding did not affect sole survival rates (ST 59.1 ± 15.9%; Art R 69.56 ± 9.3%), but was reflected in significantly smaller final weight at 16 DAH (ST 0.71 ± 0.20; Art R 0.48 ± 0.14 mg). Higher feed intake was observed in sole larvae fed on Artemia enriched with labeled PL at 9 DAH but not at 17 DAH. At 17 DAH, the smaller larvae (Art R treatment) ingested proportionally more Artemia in weight percentage, independently of enrichment. At 9 DAH lipid digestibility was equal among treatments and higher than 90%, while at 17 DAH it was higher in ST treatment (around 73%) compared to the Art R group (around 66%). Lipid retention efficiency at 9 DAH was higher in the Art R treatment, reaching values of 50%, while these values almost duplicated at 17 DAH, ranging up to 80% in both treatments without significant differences. These results show that co-feeding of live feed and inert diet from first-feeding in Senegalese sole has a toll in terms of growth and lipid digestibility but does not seem to compromise lipid metabolic utilization.

Co-feeding in Senegalese sole larvae with inert diet from mouth opening promotes growth at weaning

The aim of this study was to determine if sole larvae co-fed with inert diet at mouth opening would perform better than larvae fed with live prey and if such a feeding regime would produce better quality juveniles. The experiment was separated in to two phases: pelagic and benthic. In the pelagic phase, treatments consisted of the standard feeding regime (rotifer and Artemia feeding), the standard feeding regime and inert diet, and rotifer for a longer period than the standard feeding regime until larvae reached 9 days after hatching (DAH). By the end of the pelagic phase, when the postlarvae were 20 DAH, sole that were co-fed with inert diet from mouth opening, were significantly smaller in weight than postlarvae fed exclusively with live prey. Sole digestive maturation was improved by co-feeding the inert diet. Survival rates, skeletal deformities and quality evaluation were not affected by the feeding regimes. In the benthic phase, the postlarvae from standard feeding regime (pelagic phase) were separated in to two treatments: standard live Artemia metanauplii until weaning and standard frozen Artemia metanauplii until weaning. Remaining treatments were the follow up of treatments from the pelagic phase. At the end of the experiment i.e. 68 DAH, the postlarvae co-fed with inert diet from mouth opening were significantly larger than all the postlarvae from remaining feeding regimes.The results of the present study demonstrate that it is possible to offer inert diet to sole at mouth opening in a co-feeding regime and to produce better quality postlarvae. Co-fed sole were larger and had a better tail condition at the end of the weaning.

Natural carbon stable isotope ratios as indicators of the relative contribution of live and inert diets to growth in larval Senegalese sole (Solea senegalensis)

The relative contributions of live Artemia metanauplii and an inert diet for growth of Senegalese sole larvae and postlarvae were assessed through the analysis of carbon stable isotopes ratios (δ13C) in both diets and whole larval tissue. Larvae were reared on four dietary regimes: 100% live prey (rotifers and Artemia), 100% inert formulated diet and two co-feeding regimes of 70:30 and 30:70 ratios of Artemia and inert diet, respectively. Larvae from the live food regime and both co-feeding regimes showed a steep increase in δ13C from 10 days after hatching (DAH) as a result of the onset and continuation of Artemia consumption. From 12 DAH fish larvae from all the regimes showed significant isotopic differences as their δ13C increased to final asymptotic values of −15.1, −15.6 and −16.3‰ in the live food, 70:30 and 30:70 regimes, respectively. Carbon turnover rates in larvae from both live food and co-feeding regimes were relatively high (0.071 to 0.116 d−1) but more than 90% of the observed change in fish tissue isotopic values was accounted for by the retention of carbon in new tissue growth. A two-source, one-isotope mixing model was applied to estimate the nutritional contribution of Artemia and inert diet to postlarvae growth in the co-feeding regimes. At 23 DAH, the relative contribution of live and inert diets to tissue growth in larvae was respectively, 88 and 12% for the 70:30 co-feeding regime and 73 and 27% for the 30:70 co-feeding regime. At 17 DAH, the estimated proportion of tissue carbon derived from the inert diet was higher at 23 and 38% for the 70:30 and 30:70 regimes, respectively. The results suggest that co-feeding regimes in Solea senegalensis larvae may be adjusted to meet ontogenetic changes in the capacity for larvae to utilise inert diets. The contrasting levels of carbon isotope discrimination between diet and tissue in larvae reared on either 100% live feed or 100% inert diet indicate relatively poor utilization of nutrients from the inert diet. The use of isotopic discrimination factors as potential indicators of the digestive physiological performance of a consuming organism in regards to its diet is discussed.

Dual Benefits of Whey Protein Concentrate in a Microencapsulated Diet for Larval White Shrimp, Litopenaeus vannamei

In this work a larval shrimp diet was spray-dried using a ratio of 75% whey protein concentrate and 25% mesquite gum as wall material, where the sole protein contribution to the diet was the whey protein concentrate. The microencapsulated diet exhibited the following physical properties: mean volumetric particle size of 49.3 µm, characteristic floatability time 225.3 min, and density of 606 g/l. Its outer morphology was characterized by a dimpled spherical shape with no evident surface pores or cracks. Inner microstructure showed a central void, with the feed components finely embedded in the wall matrix. Two bioassays were performed with zoea of white shrimp Litopenaeus vannamei. In the first study, microencapsulated diet, and microencapsulated diet plus a single dose of live algae, were compared with a live algae control diet; in the second study, three co-feeding regimes consisting of microencapsulated diet + 10, 30 and 60 C. muelleri cells/ µl, respectively, were compared with the live algae control diet. In overall terms, the co-feeding regime with 30 cells/ µl produced larvae with carapace length (0.74-mm Cl) and development index (4.5 DI) significantly superior to that of the live algae treatment (0.70- mm Cl, 4.1 DI; respectively), and yielded similar individual dry weight (34-µg DW) and survival rate (58%). These results indicate that microencapsulated diets supplemented with live algae can produce responses similar to those of live feed. These results further indicate that whey protein concentrate is a good protein source as well as a wall forming agent for microencapsulating shrimp larval diets.

Weaning of Senegalese sole (Solea senegalensis) postlarvae to an inert diet with a co-feeding regime

The objective of this study was to evaluate the weaning success of Senegalese sole, Solea senegalensis, postlarvae when cofed a compound diet, by means of the analysis of growth parameters (relative growth rate [RGR] and condition factor [K]), survival, protein and lipid content. Total ammonia in the rearing water was also measured. The experiment lasted for 46 days (36 to 82 days posthatching). One group was fed only with enriched Artemia sp. metanauplii (Artemia treatment), whereas in another group, the Artemia sp. metanauplii were gradually replaced by the International Council for the Exploration of the Sea (ICES) diet over a period of 39 days (ICES treatment). Postlarvae were sampled on rearing days 0, 9, 23, 30, 39 and 46 for growth and biochemical analysis. Water was sampled on rearing day 30 during a 24-h cycle in both treatments. Postlarvae from the ICES treatment were weaned, though by the end of the experiment the Artemia treatment exhibited significantly higher values for growth, RGR, K and survival rates (P &lt; 0.05). No significant differences were observed concerning total lipid content. Protein content was significantly higher for the Artemia treatment after 46 days of rearing (P &lt; 0.05). The total ammonia nitrogen concentration in the water increased after each meal and remained below a harmless level for postlarvae.

Limiting the use of rotifers to the first zoeal stage in mud crab ( Scylla serrata Forskål) larval rearing

Commercial mud crab ( Scylla spp.) aquaculture in many countries has been stifled to some degree by a lack of seed stock. A commercially viable larval rearing protocol for Scylla serrata has yet to be established. Two experiments were conducted to assess the requirement for rotifers in the larval feeding regime for S. serrata. These examined the timing of introduction and cessation of rotifers, and co-feeding protocols with Artemia. In the first experiment, it was shown that rotifers were necessary in the feeding regime for acceptable growth and survival, and when used as the only food source during the first zoeal stage (Z1), gave better survival than when co-fed with Artemia. It was also found that when rotifers were removed from the co-feeding regime at Z3, no detrimental effect on growth or survival occurred. Final survival to megalop of 58.67±7.35% was achieved when rotifers were fed singly up to zoea 2 and then co-fed with Artemia through to megalop. Crab larvae fed only Artemia throughout the rearing period took significantly longer to reach the megalop stage and suffered higher levels of mortality. The second experiment investigated the effects on survival, when rotifer feeding was discontinued at Z2, Z3, Z4, Z5 and when rotifers were fed up to the megalop stage (M). Artemia were offered to these treatments from Z2 onwards. A no-rotifer (NR) control that was fed Artemia-only from stocking, was also tested. It was again shown that rotifers, especially in the early stages, promoted acceptable levels of survival and growth. Without rotifers, moulting of crab larvae was delayed and survival was significantly lower during the first two zoeal stages. There was also a significant difference in survival to megalop, and a significant negative relationship between duration of rotifer feeding and survival to megalop. The best survival of 78.00±5.54% was achieved when rotifers were removed from the feeding regime at Z2. The NR treatment had the lowest survival of 32.00±7.51%. These trials established that while rotifers are a valuable inclusion in the feeding regime for larval S. serrata, their use should be limited to the first zoeal stage only to maximise growth and survival.

Effect of an experimental microparticulate diet on the growth, survival and fatty acid profile of gilthead seabream (Sparus aurataL.) larvae

In recent years, a great deal of interest has emerged in the development of microdiets as an economic alternative to live food, in the larval culture of marine fish species. The ability to grow Sparus aurata larvae on a prototype microparticulate diet was examined. To achieve this objective, four feeding regimes differing in the time when the microdiet was introduced (3, 7 or 12 days) and one based exclusively on an inert diet were tested, during the first 22 days of larval life. Significant differences in larval growth were found between the experimental feeding regimes and their corresponding controls (enriched rotifers during the whole experimental period); the larvae in the co-feeding regimes and with an exclusive microparticulate diet were always significantly smaller than larvae fed on rotifers alone. However, the difference was minimised by introducing the inert diet at a later date. A lower survival was found in larvae with a co-feeding regime, in comparison with the control treatments and the survival was significantly lower in larvae fed exclusively on a microparticulate diet. The fatty acid analysis revealed that the experimental microencapsulated diet and the rotifers enriched with Protein Selco® presented relatively similar fatty acid content. In spite of the slightly higher (n−3)/(n−6) and Docosahexaenoic acid (DHA)/Eicosapentaenoic acid (EPA) ratios and somewhat lower highly unsaturated fatty acid (HUFA) content found in the inert diet, the fatty acid composition of the diets cannot explain the differences found in larval performance. The results revealed that the complete replacement of live prey with the tested microparticulate diet is still not possible in S. aurata larval rearing. Nevertheless, better growth and survival results and a substantial reduction in the daily supply of live food can be achieved with a combination of microdiet and live prey.

Influence of co-feeding larvae with live and inert diets on weaning the sole Solea senegalensis onto commercial dry feeds

The senegal sole ( Solea senegalensis) is a potential culture species in salt water ponds in south Spain and Portugal. However, growth of an industry around this species is constrained by poor survival during weaning from live Artemia onto artificial diets. This paper describes the influence of larval conditioning with inert diets on weaning performance. Mixed diets of commercial formulated feed and live prey (rotifers and Artemia) allowed larvae to develop from first feeding to metamorphosis without significant differences ( P>0.05) in specific growth rate (SGR) (18.8%±1.2 and 18.1%±2.2) and survival (61.5%±10.6 and 61.1%±9.4) compared to larvae fed live feed alone (SGR of 18.4%±1.1 and survival of 71.6%±25.9). In metamorphosed fish, however, significant differences ( P<0.05) in survival after weaning onto commercial feeds occurred after 50 days of culture, according to previous co-feeding with live and inert feeds during the larval stages. There was no growth or survival in fish weaned without any previous larval co-feeding. Metamorphosed fish previously fed a 1:1 ratio of live–inert feed during larval stages, had a similar SGR (5.1%±0.1, P>0.05) after weaning (day 70) to that obtained for fish that remained all the time on Artemia (5.3%±0.1). The SGR after weaning significantly decreased (3.4%±0.3, P<0.05) when the larval co-feeding regime had a higher proportion (2:1) of live feed. Survival for the weaning period was significantly lower ( P<0.05) in weaned fish (39.0%±4.2 and 34.0%±11.3 for 2:1 and 1:1 live:inert larval co-feeding) compared to fish that remained on live feed (78.5%±5.0). This study demonstrates the feasibility of early weaning of S. senegalensis and that larval co-feeding enhances growth and survival after weaning.