Days After Hatching Research Articles

Impact of Probiotic Bacillus sp. Dietary Supplementation on Pancreatic and Intestinal Activities in Seabream Sparus aurata.

The main objective of this study was to investigate the effects of commercial probiotic Bacillus sp. supplementation on seabream Sparus aurata larviculture under culture conditions. In this context, Bacillus was supplemented via rotifer feeding and water and its effects on pancreatic and intestinal enzyme activities as well as aquaculture parameters were evaluated during early life development. In the experimental group, as probiotic three Bacillus sp. spores was introduced via rotifer and larval culture tanks, while the larvae in control group did not feed any probiotic supplementation. At the end of the experiment on 40 days after hatching (DAH), the probiotic-supplemented group exhibited better growth performance and there were statistically differences between in groups of probiotic-treated and control regarding growth parameters (p<0,01), despite insignificant of survival rate (p>0.05). In terms of enzymatic expressions, S. aurata larvae receiving probiotic supplementation through rotifers demonstrated noteworthy (p<0.05) enhancements in specific activities of pancreatic and intestinal enzymes, except for amylase (p>0.05), when compared to the control group. It is concluded that the administration of Bacillus sp. as probiotic bacteria through rotifer supplementation and water intake demonstrates significant positive impacts on both growth parameters and specific activities of main pancreatic and intestinal enzymes of seabream larvae.

Association between Turbot (Scophthalmus maximus) Fish Phenotype and the Post-Larval Bacteriome.

Over the past decade, an increasing number of studies have emphasized the importance of the host microbiome in influencing organismal health and development. Aligned with this understanding, our study aimed to investigate the potential association between the turbot (Scophthalmus maximus) phenotypic traits and the post-larval bacteriome. Turbot post-larvae were sampled from twenty randomly selected production cycles thirty days after hatching (DAH) across multiple post-larval production batches over a three-month period (April to June). Fish were selectively sampled based on five phenotypic traits, namely, normal, large, small, malformed, and depigmented. Our results showed that small-sized post-larvae had significantly higher bacterial phylogenetic diversity in their bacterial communities than all other phenotypes. A more in-depth compositional analysis also revealed specific associations between certain bacterial taxa and fish phenotypes. For example, the genera Aliivibrio and Sulfitobacter were enriched in small-sized post-larvae, while the family Micrococcaceae were predominantly found in larger post-larvae. Furthermore, genus Exiguobacterium was linked to depigmented larvae, and genus Pantoea was more prevalent in normal post-larvae. These observations underscore the importance of further research to understand the roles of these bacterial taxa in larval growth and phenotypic differentiation. Such insights could contribute to developing microbiome modulation strategies, which may enhance turbot post-larval health and quality and improve larviculture production.

Sago palm weevil larvae: larval ontogeny and nutritional value assessed from enzymatic activity and in vitro digestibility

Abstract Sago palm weevil larvae (SPWL, Rhynchophorus vulneratus) have potential for use as food and feed. This study aimed to investigate their development, digestive enzyme activity, nutrient values, and digestible protein using an in vitro digestibility technique. Bioassays for SPWL at 21, 28, 35, 42, 49, and 56 days after hatching (DAH) were conducted in a completely randomized design (CRD). Analysis of variance (ANOVA) was performed, and means were compared at using Bonferroni (Dunn) t-tests and orthogonal polynomial contrasts. Trypsin activity significantly increased at 35 DAH (, quadratic effect ), with peak chymotrypsin activity at 28 DAH (). Lipase activity showed both linear and quadratic increases (), and cellulase activity also increased significantly (, linear and quadratic terms ). Meanwhile, the A:T ratio increased significantly (, quadratic effect ) with age-related rises in these digestive enzyme activities. The highest crude protein content in SPWL was observed at 42 DAH (), with peak carbohydrate at 28 DAH (). Phenylalanine and histidine levels increased linearly (), while lysine and total essential amino acids peaked at 42 DAH (, linear and quadratic terms ). Levels of linoleic acid, total polyunsaturated fatty acids, and the n-6:n-3 ratio peaked at 49 DAH (). In vitro protein digestibility assays were performed using enzymes extracted from quails, broilers, Thai native chickens, and ducks. Significant increases in digestibility were attributed to SPWL protein content and age, particularly beyond 42 DAH (, linear and quadratic terms ), except with duck enzymes. In conclusion, these findings suggest that SPWL cultivation, particularly between 42 and 56 DAH, provides a potential alternative protein source with substantial nutritional benefits for poultry feed. The promise of SPWL to contribute to more sustainable and efficient poultry feeding practices is evident, and further in vivo studies are warranted to validate these results.

REPRODUCCIÓN Y CULTIVO LARVARIO DEL PEZ PAYASO MARRÓN (Premnas biaculeatus) BAJO CONDICIONES CONTROLADAS

&lt;p&gt;&lt;strong&gt;Background:&lt;/strong&gt; Interest in ornamental marine fish, especially species associated with coral reefs, is rapidly growing. Most of the fish traded come from the wild, and collection methods harm coral reefs and cause massive mortalities in non-target species. To make the activity sustainable, it is necessary to develop aquaculture biotechnologies to reduce the collection of wild organisms and lessen the pressure on their natural environment. &lt;strong&gt;Objective:&lt;/strong&gt; To develop protocols for the reproduction and larval rearing of the maroon clownfish (&lt;em&gt;Premnas biaculeatus&lt;/em&gt;) for the sustained production of juveniles in captivity. &lt;strong&gt;Methodology:&lt;/strong&gt; Two pairs of &lt;em&gt;P. biaculeatus&lt;/em&gt; were placed in two aquariums of a recirculating system with filtered seawater. The obtained eggs were incubated in 100 L tanks. The larvae were fed with rotifers &lt;em&gt;Brachionus rotundiformis&lt;/em&gt;, &lt;em&gt;Artemia&lt;/em&gt; sp. nauplii, and weaned onto a commercial diet. The larvae were measured at hatching and every four days until weaning. &lt;strong&gt;Results:&lt;/strong&gt; The clownfish pairs began spawning 4-5 months after being placed in the recirculating system and continued spawning every 15-20 days. The eggs hatched 6-7 days after fertilization (DAF), and the hatched larvae measured 3.4±0.06 mm in total length (TL). At 19 days after hatching (DAH), after completing weaning, they measured between 9.8 to 11.5 mm in TL; at 26 DAH, they measured between 10.8 to 13.1 mm. After one month, between 800 to 1,000 juveniles were obtained for commercialization. &lt;strong&gt;Implications:&lt;/strong&gt; The reproduction and larval rearing protocols of the maroon clownfish &lt;em&gt;P. biaculeatus&lt;/em&gt; described in this work can be used to obtain juveniles in captivity for commercialization; additionally, they can serve as a basis for developing other protocols for obtaining juveniles of other ornamental marine fish species for commercialization, contributing to the protection of their natural environment. &lt;strong&gt;Conclusion:&lt;/strong&gt; The results obtained demonstrated the viability of maintaining &lt;em&gt;P. biaculeatus&lt;/em&gt; breeders in captivity and achieving their natural reproduction, larval rearing, and mass production of juveniles throughout the year.&lt;/p&gt;

Intra-cohort cannibalism and aggressive behavior in tropical gar (Atractosteus tropicus) larvae: Effects of stocking density and starvation

Cannibalism in early fish developmental stages is a biological phenomenon affecting aquaculture, so seeding density and feeding schemes play a fundamental role in its optimal control. The objective of this research was to evaluate two initial stocking densities, 0.7 larvae/L (D7) and 1.4 larvae/L (D14), which were fed (F) and not fed (NF) in tropical gar (Atractosteus tropicus) larvae on growth, attacks, survival, and digestive enzyme activity, digestive morphology, and oxidative enzymes and aggressiveness gene expression. A total of 420 larvae (0.022 ± 0.003 g; 1.52 ± 0.10 cm) were placed in 70 L tanks connected to a recirculation system. Treatment F larvae were fed a formulated food. D14F larvae had the highest final weight, total length, and specific growth rate (SGR) (p < 0.05). The highest survival percentage was in D7F larvae (46.19 ± 2.74) (p < 0.05). The highest frequency of attacks occurred in D14F larvae (26.66 ± 0.82) (p < 0.05). The coefficient of variation (CV) and size heterogeneity (SH) were higher in D7F larvae (13.56 ± 1.80; 0.81 ± 0.10) (p < 0.05). The F larvae started attacks at 8 days after hatching (DAH), while the NF larvae showed it at 10 DAH. The difference in weight between the attacker and the attacked was 16.44 ± 9.75% and in total length 12.28 ± 4.57% (p < 0.05). Acid and alkaline protease, trypsin, and lipase activities presented differences between both factors, as well as the interaction between them. D14F larvae presented the highest Glutathione peroxidase (GPX) activity (p < 0.05), while D7-NF larvae registered the highest catalase (CAT) activity (p < 0.05). Superoxide dismutase (SOD) activities only showed differences between F and NF larvae (p < 0.05). The liver presented the highest percentage of area with melanomacrophage centers (MMC) in D7-NF larvae, and hepatocytes with the highest area were recorded in D14F larvae (p < 0.05). In gut, the highest enterocytes were recorded in D14F larvae (p < 0.05). cat, cck, and gpx expression did not show difference between feeding regimes. The expression of sod1 and sod2 in D7F and D14F treatments presented the highest expressions (p < 0.05). D7F larvae presented higher expression of avp1, crh, htr1, sstr1, th and tph1 genes (p < 0.05). Our results show that A. tropicus larvae D14F presented the highest growth and morphometric parameters and decreased CV and SH, which shows a more homogeneous growth. Regarding cannibalism, fed larvae (D7F, D14F) presented cannibalism in a greater proportion than unfed larvae regardless of density, however, it is necessary to analyze other physiological and social factors that could be related to the aggressiveness and cannibalism of the species.

Changes in Digestive Enzyme Activities during Larval Development of Spotted Seatrout (Cynoscion nebulosus)

The spotted seatrout (Cynoscion nebulosus)—an important commercial species—has a high potential for aquaculture in the Gulf of Mexico. To optimize its feeding during larval rearing, this study aims to evaluate the primary gastric (pepsin), intestinal (leucine aminopeptidase and alkaline phosphatase), and pancreatic (alkaline protease, trypsin, chymotrypsin, amylase, and lipase) enzyme activities from hatching to day 30. A multivariate analysis identified three digestive enzyme development stages during the spotted seatrout larval transformation. The first stage occurred between 1 (mean ± standard error (SE) = 1.73 ± 0.14 millimeter (mm) standard length (SL)) and 3 (2.14 ± 0.07 mm SL) days after hatching (DAH); a period of digestive stability showed the highest activity in amylase and bile salt-dependent lipase. The second stage (from 4 (2.53 ± 0.09 mm SL) to 20 (10.92 ± 0.51 mm SL) DAH) was a period of digestive transition, during which leucine aminopeptidase, chymotrypsin, and alkaline proteases were identified as the predominant enzymes from 4 to 5 DAH. In the third stage—a period of digestive stability—pepsin was the major enzyme that occurred between 25 (16.51 ± 0.81 mm SL) and 30 (25.91 ± 0.82 mm SL) DAH. These results indicate that the spotted seatrout larvae have a digestive system adapted to lipids and carbohydrates at the onset of feeding, with an immediate transition to protein digestion when exogenous feeding begins. Additionally, the digestive system of the spotted seatrout may be considered mature at 25 DAH. Further research is needed to elucidate the mechanisms of digestive tract development in the spotted seatrout larvae.

Effects of selenium nanoparticles on larval development, ontogeny of antioxidant enzymes and fatty acid profile in Arabian yellowfin seabream (Acanthopagrus arabicus)

Selenium (Se) is an essential trace element that has vital effects on growth, antioxidant capacity and early development in marine fish larvae. However, traditional livefoods such as rotifer and artemia lack of Se. In this regard, a 50-day feeding experiment was conducted in order to examine the effects of Rotifer and Artemia enrichment with selenium nanoparticles (SeNPs) on growth, antioxidant capacity and fatty acid profile of Arabian yellowfin seabream (Acanthopagrus arabicus) larvae. Four levels of SeNPs were used to prepare the experimental emulsions,including control (0), 0.5, 1.0 and 5 mg SeNPs L−1. Larvae were stocked at density of 50 larvae L−1 into twelve 250-L cylindrical tanks. Tanks supplied with seawater (23 ± 1 ºC; 40.0 ± 1.0 g L−1). Green water was used from day first until 20 days after hatch (DAH). Rotifers (15 ml−1) were offered to larvae from day 2–21 DAH and Artemia metanauplii (1–3 Artemia ml−1) were offered to larvae from day 18–45 DAH. Fish were sampled at 0, 7, 10, 15, 22, 30, 40, 45, 50 DAH. The Se concentration in the livefoods and larval whole body linearly increased with the increment of SeNPs level in the experimental emulsions. Larvae wet weight showed quadratic response and increased with SeNPs up to 1 mg mg SeNPs/L, then decreased in SeNPs (5.0) group. The activity of antioxidant enzymes including catalase, superoxide dismutase glutathione peroxidase, and total antioxidant capacity increased but malondialdehyde level decreased in larvae fed the SeNPs-enriched livefoods and showed both linear and quadratic responses. Lysozyme activity in the whole body of larvae fed SeNPs-enriched livefoods had both linear and quadratic responses and in the most of the sampling times was higher than the control group. Docosahexaenoic acid (DHA) level in the livefoods and larval whole body increased with SeNPs. In conclusion, livefoods enrichment with SeNPs at 1 mg L−1 is recommended to elevate the antioxidant capacity and non-specific immune response in A. arabicus larvae.

The Use of Acartia tonsa Nauplii during the First Days of Feeding on the Ontogeny of the Digestive System of Greater Amberjack (Seriola dumerili Risso, 1810)

The effect of feeding greater amberjack with copepod nauplii (Acartia tonsa) on the ontogeny of the digestive system was observed until 40 days after hatching (DAH). Copepods are part of the diet of fish larvae in nature, and they are rich in highly unsaturated fatty acids and free amino acids that enhance the digestive capacity of the fish. In a marine hatchery, four cylindroconical tanks of 2,700 L were stocked with about 150 × 103 greater amberjack larvae (Seriola dumerili) in each. The larvae were initially fed from 3 to 17 DAH in two tanks with copepod nauplii and rotifers (Brachionus sp.; Copepods group), while in the other two tanks, they were fed only with rotifers (Control group) during the same period. All the tanks were fed with rotifers (3–27 DAH), Artemia nauplii (12–22 DAH), enriched Artemia metanauplii (20–30 DAH), and formulated diet (25–40 DAH). Fish samples were taken regularly (every 2 or 4 days) for histological analysis and every day for the measurement of total length (TL). The TL was 3.7, 4.5 ± 0.1, 6.1, 11, 17.3 ± 0.1 and 20.3 ± 2.3 mm at 4, 10, 16, 22, 30, and 40 DAH, respectively. Copepod-fed fish showed higher TL in the last 2 days of the trial (p &lt;0.05), while mortality rates were lower in the beginning of the trial 10–17 DAH, (p &lt;0.05). In addition, copepods-fed fish had less skeletal deformities (p &lt;0.05). Pyloric caeca appeared earlier in the Copepods group compared with the Control, while the length and surface of the villi, the abundance of goblet cells/100 μm of intestine length, and the area covered with lipid vacuoles in the liver were significantly higher in the Copepods group (p &lt;0.05). We can conclude that the use of copepods in the diet of the greater amberjack larvae can improve the ontogeny of the digestive system.

Early ontogeny of the African bony-tongue (Heterotis niloticus) and the effect of Artemia and rotifer live feeds on larval digestive enzyme activity and performance

High larval and fry mortality has been a major challenge to the commercial culture of the African bony-tongue (Heterotis niloticus). Research indicates inadequate feeding to be a possible cause of the high mortality rates of larvae/fry grown in captivity. An experiment was conducted to first describe the developmental stages of H. niloticus eggs and larvae until schooling, 6 days after hatching (DAH), at 26°C. The morphological development, survival, growth (weight gain and length), and swimming behavior of the larvae were monitored. A follow-up feeding trial was conducted with H. niloticus fry from 6 to 27 DAH involving four treatments: feeding with Artemia nauplii; a combined feed of 50% Artemia nauplii and 50% rotifers (w/w); feeding with rotifers; and no feeding. The activities of three digestive enzymes (trypsin, lipase, and amylase) were assessed in fry exposed to the live feed treatments. At hatching, the larvae had a large, vascularized yolk sac filled with yolk platelets, which occupied approximately one-third of the total body length of the abdominal cavity. Yolk platelet reabsorption started at 1 DAH and was complete at 6 DAH. Metamorphosis was completed at 6 DAH, and schooling behavior was observed. For the feeding trial, the fry that received Artemia nauplii underwent the fastest development until 27 DAH. Similarly, the survival rate was considerably higher in fry fed with Artemia nauplii than in those that received a combination of Artemia nauplii and rotifers or only rotifers. Overall, the survival rates for fry fed with Artemia nauplii and larvae co-fed were 72.7% ± 0.9% and 41.2% ± 3.3%, respectively. Fry did not survive until 27 DAH in the rotifer-fed and unfed treatment groups. Digestive enzyme activity differed significantly (p&amp;lt; 0.05) between treatments and sampling dates. All digestive enzymes were detectable at the onset of mouth opening (5 DAH) and fluctuated through the 7 and 9 DAH. Lower enzyme activity was observed when the fry were subjected to starvation or the rotifer treatment. Results indicate that Artemia nauplii is the best live feed organism for H. niloticus larviculture.

Tryptophan Reduces Intracohort Cannibalism Behavior in Tropical Gar (Atractosteus tropicus) Larvae

The intracohort cannibalism present in tropical gar larvae (A. tropicus) generates great problems in its culture, as in other fish species around the world. The addition of tryptophan (Trp) (10, 20, and 30 g/kg) and a control diet (CD) without Trp were evaluated in A. tropicus larvae regarding growth, survival, cannibalism, behavior, digestive enzymatic activity, and genes related to aggressiveness and/or cannibalism in two stages: 0–13 days after hatching (DAH); and only cannibals (14–24 DAH). In the first stage, no differences were observed in growth parameters; cannibalism was lower with the use of Trp, with the lowest percentage being the 10 g/kg Trp treatment (56.75 ± 2.47%) compared to CD (64.75 ± 1.76%). In the second stage, survival was greater in 10 g/kg Trp (75.00 ± 7.07%) than in CD (23.33 ± 5.77%). Thus, cannibalism was lower with 10 g/kg Trp (20.0 ± 10.0%) compared to CD (76.66 ± 5.77%). Cannibal larvae fed with 10 g/kg Trp had a greater enzymatic activity in acid and alkaline proteases and leucine aminopeptidase, as well as the overexpression of avpi1, crh, and htr1a and the subexpression of tph1, th, sstr1, and hdc (p &lt; 0.05). No aggressive behaviors were recorded in the larvae fed with the 10 g/kg Trp treatment, unlike those fed with CD. The use of 10 g/kg Trp improves survival and reduces cannibalism in A. tropicus larvae.

Performance Parameters of Paralarvae and Postparalarvae Rearing of Patagonian Red Octopus, Enteroctopus megalocyathus, under Experimental Conditions

Patagonian red octopus, Enteroctopus megalocyathus, an interesting species for Chilean aquaculture diversification, requires the improving of their experimental technology to obtain early juveniles. The first objective of the study was to enhance aspects of feeding and temperature management in broodstock, egg incubation, paralarvae rearing, and early juveniles’ growth. The results indicated that female weight decreases up to 46.0 ± 8.6% during the egg incubation. Test of 8, 14, and 18°C during egg incubation shows that at 18°C embryos do not survive. Paralarvae reared under four diet treatments: (1) unfed, (2) enriched Artemia (Nannochloropsis sp.), (3) copepod (Acartia spp.), and (4) juvenile crabs (Petrolisthes spp.) showed survival quadruplication when they fed copepods and crabs instead of Artemia. Juveniles reared at 11, 13, and 15°C improved feed conversion and protein efficiency ratios at 15°C. The second objective was to analyze batches of paralarvae and early juveniles of two different periods to obtain their performance indicators and to compare them between productive periods. The results of growth rates, the relative weight condition coefficient, and morphometric relationships are discussed in the context of paralarvae culture from 1 to 90 days after hatching (DAH) and early juveniles from 1 to 135 days postsettlement (DPS).

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius).

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

Development of Immersion and Oral Bivalent Nanovaccines for Streptococcosis and Columnaris Disease Prevention in Fry and Fingerling Asian Seabass (Lates calcarifer) Nursery Farms.

In the present study, chitosan-based bivalent nanovaccines of S. iniae and F. covae were administered by immersion vaccination at 30 and 40 days after hatching (DAH), and the third vaccination was orally administered by feeding at 50 DAH. ELISA revealed that the levels of total IgM and specific IgM to S. iniae and F. covae were significantly elevated in all vaccinated groups at 10, 20, and 30 days after vaccination (DAV). A qRT-PCR analysis of immune-related genes revealed significantly higher IgT expression in the vaccinated groups compared to the control group, as revealed by 44-100-fold changes in the vaccinated groups compared to the control (p < 0.001) at every tested time point after vaccination. All vaccinated groups expressed IgM, MHCIIα, and TCRα at significantly higher levels than the control group at 10 and/or 20 DAV (p < 0.05). In the S. iniae challenge tests, the survival of vaccinated groups ranged from 62.15 ± 2.11 to 75.70 ± 3.36%, which significantly differed from that of the control group (44.44 ± 1.92%). Similarly, all vaccinated groups showed higher survival rates of 68.89 ± 3.85 to 77.78 ± 5.09% during F. covae challenge than the control groups (50.00 ± 3.33%) (p < 0.05).

Live-food enriched with Chlorella vulgaris as a potential supplemental diet to enhance performance and immune response of Tor tambroides larvae (Bleeker 1854)

Tor tambroides is one of the Tor species identified in Southeast Asia with a promising aquaculture potential in Malaysia, fetching market price of up to USD 53 per kilogram. It is a slow grower that takes more than two years to reach marketable body weight (∼800 g) in captivity. This study was designed to establish the C. vulgaris enriched Artemia sp. and Moina sp. in enhancing the growth performance of T. tambroides larvae. The larvae were divided into five treatments, control (C) (commercial feed); unenriched Moina (UM); enriched Moina (EM); unenriched Artemia (UA); enriched Artemia (EA). The concentration of C. vulgaris used during enrichment was 1 × 107 algal cells/mL. On 14 to 29 days after hatching (DAH), the larvae were co-fed with the commercial feeds and each treatment four times daily. The highest body weight gained were observed in the larval group fed with EA (18.56 ± 1.02 mg), followed by UA (15.89 ± 2.08 mg) and were statistically different as compared to the UM (6.89 ± 0.51) and EM (6.11 ± 1.09) and C (3.56 ± 1.20) (p < 0.05). The final total length was also the highest in larvae fed with EA (17.8 ± 0.04 mm), followed by UA (17.2 ± 0.0 mm), EM (16.4 ± 0.02 mm), UM (16.0 ± 0.02 mm) and the lowest in C (15.4 ± 0.02 mm). The larvae fed with EA also displayed a significant increase in specific growth rate (4.66%), followed by UA (4.13%) and were statistically different to UM (2.10%), EM (1.88%) and C (1.14%) (p < 0.05). The relative growth rate of the larvae was the highest in EA (92.27%) and lowest in C (17.68%) (p < 0.05). The survival rate of the larvae was the highest in UM and EM with 89.4%, followed by EA (89.13%), UA (88.51%) and C (84.7%). The EA had high and positive upregulation of growth hormone genes (0.16 ± 0.13), myostatin gene (0.11 ± 0.10), MHCC1a gene (0.48 ± 0.12) and CC3 gene (0.28 ± 0.14) and were statistically different as compared to the control group. The enriched Artemia had enhancing effect on the growth performance and expression of the immune and growth genes of the larvae, potentially due to its nutritional contents and better ingestion by the larvae. The study suggests C. vulgaris enriched Artemia can be used in the hatcheries to improve the growth and survival of T. tambroides larvae, shorten its rearing period and increases its yield.

The effect of copepod Acartia tonsa during the first days of larval rearing in skeleton ontogeny and skeletal deformities in greater amberjack (Seriola dumeliri Risso, 1810)

The effect of feeding greater amberjack (Seriola dumerili) with copepod nauplii (Acartia tonsa) on osteological development was observed until 35 days after hatching (DAH). The skeletal deformities were observed at the end of the trial. Copepods are the natural food of marine fish larvae, and they are rich in highly unsaturated fatty acids and free amino acids. In a commercial marine fish hatchery in Greece (Galaxidi Marine Farm S.A.), four 2700 l cylindroconical tanks were stocked with amberjack yolk-sac larvae at a density of about 55 larvae/l. The larvae were initially fed from 3 to17 DAH in two tanks with copepod nauplii and rotifers (Brachionus sp.) (Copepods group), while in the other two tanks, only with rotifers (Control group). After 12 DAH, all the tanks were also fed with rotifers (3–27 DAH), Artemia nauplii (12–22 DAH), enriched Artemia metanauplii (20–30 DAH), and formulated diet (25–30 DAH). Fish samples were taken every three days, fixed in phosphate-buffered 5% formalin (pH = 7.2). Bone and cartilage were stained with alizarin red and alcian blue, respectively. Specific meristic characters were chosen to compare the first appearance and the completion of the formation of a structure as well as the completion of the calcification between the two rearing protocols (Copepods - Control), correlated with total length data. These meristic characters included replacement and membranous bones from the vertebral column and all the fins. The ontogeny of the meristic characters was observed earlier in fish larvae from the Copepods group compared with the Control, and for most of the meristic characters, these differences were significant (p < 0.05). TL50 data analysis was performed, and the results were similar. At the end of the trial, 35 DAH sixty fish from each tank were sampled for the analysis of skeletal deformities. A higher number and more significant deformities were observed in the Control group compared with the Copepods group (p < 0.05). In conclusion, the use of copepod nauplii during the first feeding period of greater amberjack had a positive effect on the osteological development and skeletal deformities of the larvae.

Artemia enrichment as modulator of gene expression patterns of Enteroctopus megalocyathus paralarvae at pre-settlement stage

Enteroctopus megalocyathus, the Patagonian red octopus, is the only octopus species for which a complete production cycle in captivity has been accomplished in Chile. The rearing of E. megalocyathus paralarvae from hatching to the settlement of juveniles lasts 90 days and it represents the bottleneck in the culture of this species. The paralarval stages from 1 to 60 days after hatching (DAH) are fed on enriched Artemia while, when pre-settlement behavior appears, from 60 DAH onwards, the feeding protocol is a mixed diet of enriched Artemia and juvenile marine crabs. Marine crustaceans represent a suitable diet to improve E. megalocyathus paralarvae survival, complementing the enriched Artemia to feed the pre-settling paralarvae. To determine the effect of Artemia enrichment on the response of E. megalocyathus at the pre-settling paralarval stage, paralarvae were fed two mixed diets containing juvenile marine crabs (Petrolisthes spp.) and differing only in Artemia enrichment: enriched (complete diet, CD), or unenriched (limited diet, LD). After 30 days of feeding trial, samples consisting of whole paralarvae were collected for transcriptomic analysis using high-quality total RNA to generate six mRNA libraries (two treatments x three biological replicates). A total of 270 genes were differentially expressed between paralarvae fed LD and those fed CD. When classifying the cellular processes in which the genes of LD and CD paralarvae differed significantly, it was observed that the downregulated/upregulated gene ratio was 2/1 in genes related to membrane organization and neuron differentiation. The genes of paralarvae fed a LD for which upregulation was equal to or >20 times compared with those fed a CD were related with increased rearrangement of tissues, molecular transport, energy production, improvement of sensory organs, cellular processes, transcription, and protein catabolic processes. The downregulated genes in paralarvae fed a LD were involved with reduced DNA repair and mRNA replication and elongation, molecular transport, cellular protein modification, cellular component organization, inflammatory cytokines, and biosynthetic processes. It was concluded that removing enrichment from Artemia, even under co-feeding with marine crustaceans, results in notable changes in the transcription that, while not generating a significant detriment to growth in 30 days of experimentation, could affect subsequent growth phases.

Co-supply with marine crustacean to enriched Artemia as food for the Patagonian red octopus (Enteroctopus megalocyathus) paralarvae

One of the most sensitive problems in the Patagonian red octopus (Enteroctopus megalocyathus) aquaculture is the high mortality of the paralarvae stage. Paralarvae are active hunters, and the enriched Artemia is the most traditional food for this species until 60 days after hatching (DAH). Then, the pre-settlement behavior appears, and co-feeding with juvenile sea crabs is initiated for another 30 days up to 90 DAH when settlement occurs and the paralarvae stage ends. Therefore, the present study aimed to investigate the effect of marine juvenile crabs on the Patagonian red octopus paralarva's feeding history before the pre-settlement stage. Early paralarvae (1 to 15 DAH) were fed two diets: only enriched Artemia (A) or enriched Artemia plus juvenile crab (AC). At 15 DAH, one-half of each group was exchanged with the opposite treatment during the following 35 days of the experimental period. An experimental design resulted in four combinations of early and late diets, A-A, A-AC, AC-A, and AC-AC. The overall performance and the expression of genes related to fatty acid biosynthesis, antioxidant defense system, and stress response were evaluated in paralarvae at 15 and 50 DAH. Besides, fatty acids and amino acids were compared between the four combinations at 50 DAH. At 15 DAH, the main differences were the highest length and growth rate in paralarvae-fed AC. At 50 DAH, after 35 days fed the four combinations of early-late diets, no differences were detected in SGR. In contrast, those paralarvae of AC-A and AC-AC triplicate their survival upon A-A and A-AC. Paralarvae from the A-A combination resulted in the lowest protein content, highest ash, and the highest expression of FADS5. In comparison, paralarvae from the A-AC combination resulted in the highest 18:3n-3 and PUFA n-6 and the lowest amount of free serine. Precisely the contrary to paralarvae fed AC-AC. Therefore, the relevance of the first feeding until 15 DAH upon further paralarvae development is discussed, and how co-feeding with juvenile crabs improves the overall performance compared to using only enriched Artemia.

Regulation of feed intake, digestive enzyme activity, and growth in response to live feed and prepared diet during early rearing of Labeo rohita

A 35 day feeding trial in a replicate of five was conducted to evaluate the impact of partial and total replacement of live feed (LF) with nanoparticulate-prepared diet (ND) on early rearing of rohu ( Labeo rohita (Hamilton, 1822)). Larvae 3 days after hatching (DAH) were evenly distributed into three groups; T1 was reared exclusively on LF, T2 was on ND, and T3 was co-fed both LF and ND (1:1). All groups showed a feed-dependent increase in growth and the expression of genes involved in feed intake and growth with age DAH. The T3 group showed significantly higher weight gain, specific growth rate, and expression of insulin-like growth factor-1 followed by the T2 group, while the highest expression of ghrelin and growth hormone secretagogue receptor was observed in T3 followed by T1. Furthermore, leptin showed the highest expression in the T2 followed by the T1 group. The intestinal enzymes showed variable trends, with the highest activity of cellulase, amylase, and protease in the T1, T2, and T3 groups, respectively. Moreover, in all groups, cellulase increased continuously with age DAH, while amylase and protease showed a positive correlation up to 30 DAH and then declined. The results of this study could be helpful in larval nutrition programming.

Addition of β-glucans in diets for tropical gar (Atractosteus tropicus) larvae: effects on growth, digestive enzymes and gene expression of intestinal epithelial integrity and immune system.

The effect of β-glucans 1,3/1,6 from Saccharomyces cerevisiae yeast at different inclusion percentages (0.0, 0.2, 0.4, 0.6, and 0.8%) in the diet for tropical gar (Atractosteus tropicus) larvae was evaluated on growth, digestive enzyme activity and, relative expression of the immune system genes. The bioassay started on the third day after hatching (DAH) and lasted 21days, using a total of 1500 larvae of 0.055 ± 0.008g and, a total length of 2.46 ± 0.26cm. Larviculture was carried out in a recirculation system with 15 tanks of 70 L using a density of 100 organisms per experimental unit. No significant differences in larval growth were observed by the inclusion of β-glucans (p > 0.05). Digestive enzymes showed changes in lipase and trypsin activities, presenting higher values in fish fed 0.6% and 0.8% β-glucans diets compared to the other treatments (p < 0.05). Leucine-aminopeptidase, chymotrypsin, acid phosphatase, and alkaline phosphatase activity showed higher activities in larvae fed with a 0.4% β-glucan diet compared to the control group. The relative expression of intestinal membrane integrity (mucin 2) muc-2, (occludins) occ, (nucleotide-binding oligomerization domain) nod-2, and immune system lys (lysosome) genes showed over-expression in larvae fed the 0.4% β-glucan diet to the rest of the treatments (p < 0.05). The inclusion of β-glucans at 0.4-0.6% in diets for A. tropicus larvae could improve larviculture, as effects on the increase in the activity of several digestive enzymes and the expression of genes of the immune system.

Determination of black soldier fly larvae performance for oil palm based waste reduction and biomass conversion

Oil palm biomass, such as empty fruit bunches and palm kernel meal, has low digestibility. Thus, a suitable bioreactor is urgently needed to efficiently convert oil palm biomass into high-value products. The polyphagous black soldier fly (BSF, Hermetia illucens) has gained global attention for its role in biomass conversion. However, there is scarce information on the ability of the BSF to sustainably manage highly lignocellulosic matter, such as oil palm empty fruit bunches (OPEFB). Therefore, this study aimed to investigate the performance of the black soldier fly larvae (BSFL) in oil palm biomass management. Several formulations were fed to the BSFL five days after hatching (DAH), and the effects on oil palm biomass-based substrate waste reduction and biomass conversion were analyzed. Furthermore, the resulting growth parameters correlating to the treatments were evaluated, including feed conversion rate (FCR), survival rates, and developmental rates. The most optimal results were obtained by mixing 50% of palm kernel meal (PKM) with 50% of coarse oil palm empty fruit bunches (OPEFB), resulting in an FCR of 3.98 ± 0.08 and a survival rate of 87% ± 4.16. Moreover, this treatment is a promising method for waste reduction (11.7% ± 6.76), with a bioconversion efficiency (corrected for residue) of 71.5% ± 1.12. In conclusion, the study findings indicate that incorporating PKM into OPEFB substrate can substantially alter BSFL growth, reduce oil palm waste, and optimize biomass conversion.