Onset Of Exogenous Feeding Research Articles

Concentrations of erythromycin and azithromycin in mature Chinook salmon Oncorhynchus tshawytscha after intraperitoneal injection, and in their progeny

A single dose (40 mg kg(-1)) of erythromycin or azithromycin dihydrate was injected intraperitoneally into maturing female fall Chinook salmon 12 to 32 d before spawning to observe the distribution, retention and clearance of the drugs in plasma, kidney, coelomic fluid and egg vitellin, and their persistence in alevins derived from these fish. Salmon administered prophylactic dosages of erythromycin as subadults were also included to investigate potential interactive effects of oral and injected treatments on reproductive performance and antibiotic clearance. Erythromycin was rapidly cleared from plasma and coelomic fluid, but was detected in the kidney (3.52 to 12.40 microg g(-1)) and egg vitellin (5.32 to 8.87 microg ml(-1)) of all fish at spawning. High, stable concentrations of azithromycin were detected in plasma (14.66 to 20.33 microg ml(-1)), kidney (43.16 to 59.96 microg g(-1)), coelomic fluid (2.52 to 5.50 microg ml(-1)) and egg vitellin (12.65 to 23.51 microg ml(-1)). Oral administration of erythromycin to subadult salmon did not significantly affect tissue concentrations of either erythromycin or azithromycin administered by prespawning injection. Reductions in the percentage of eggs that yielded live embryos at the eyed stage of development occurred among eggs derived from females that had received orally administered erythromycin as subadults. Erythromycin was not detected in unfed fry derived from adults injected with the drug prespawning, but azithromycin was present for more than 2 mo after the onset of exogenous feeding.

Histological study on the digestive system development ofTakifugu rubripes larvae and juvenile

The digestive tract ofTakifugu rubripes during early life stages was studied with light microscopy. At the beginning of hatching, the digestive tract is represented by a simple and undifferentiated straight tube and does not communicate with the exterior, as the mouth and anus are not open yet. At 2 d after hatching, a constriction between intestine and rectum that will become the intestino-rectal valve is visible. During the endogenous feeding phase, the yolk sac is resorbed and the digestive tract becomes functional and differentiated. The liver and pancreas also become apparent at this time. At onset of exogenous feeding (3 d after hatching), yolk sac resesves are not completely depleted, suggesting a period of mixed nutrition. The digestive tract differentiates fully into buccopharynx, esophagus, stomach, intestine and rectum. At 9 d after hatching, the yolk sac reserves are completely depleted. The most noticeable events occurring from 5 to 17 d after hatching are the transformation of the epithelia type, the differentiation of the pneumatic sac, the epithelial cell, gut convolution, mucosal fold increase, and the growth of liver and pancreas. From 18 to 27 d after hatching, the numbers of intestine folds and mucus cells increase progressively. From then on, morphological changes of digestive features are almost completed. At 27 d after hatching, the morphology and function of digestive system are similar to that of the adult.

Ingestion, assimilation and utilization of raw Spirulina by larval tilapia Oreochromis niloticus during larval development

Ingestion, assimilation and utilization of raw Spirulina by larval tilapia of varying sizes were examined to elucidate the effect of Spirulina on larval tilapia at different growing stages during the development. High initial concentration of 14C-labeled Spirulina was offered to larval tilapia from the onset of exogenous feeding to 3.8 cm SL to ensure ad lib feeding during 1 h feeding period. Ingestion efficiency (IE, %), assimilation efficiency (AE, %), utilization efficiency (UE, %), and metabolism efficiency (ME, %) were investigated by monitoring the fate of labeled food. IE increased with the development of larvae. Larval tilapia could ingest 2.6% to 90.0% of the available Spirulina biomass with larvae growing from the onset of exogenous feeding (0.8 cm SL) to 3.8 cm SL, and sharp increments of IE appeared at around 1.2 and 2.8 cm SL. However, the same pattern was not shown in AE and UE. Except for the rapid improvement in early stage larvae (0.8 to 1.2 cm SL), AE and UE did not show any significant increase with development of larvae. ME appeared independent of the larval development. These results demonstrate that ingestion rather than assimilation affected the acceptability of Spirulina in larval tilapia. Larval tilapia could efficiently assimilate and utilize the ingested Spirulina from onset of exogenous feeding. The so-called transition of feeding habit is the feeding strategy of the larval and early stage juvenile tilapia.

A histological study on the development of the digestive system of Pseudosciaena crocea larvae and juveniles

The ontogenetic development of the gut and accessory organs in large yellow croaker Pseudosciaena crocea was investigated using light microscopy from hatching up to the juvenile stage (40 days post hatch, dph). At 3 dph (mean ± s.d., 4·1 ± 0·1 mm total length, LT), coinciding with the buccopharynx opening, larvae started to feed exogenously, and the gut consisted of a well‐developed buccopharynx, a partially‐differentiated oesophagus and an intestine divided in three regions (anterior intestine, intermediate intestine and rectum). Yolk reserves were not completely depleted at the onset of exogenous feeding, and a period of mixed nutrition was observed up to 6 dph (4·3 ± 0·1 mm LT), when yolk was definitively exhausted. Important morphological changes occurred at the end of the larval period, coinciding with metamorphosis. At 17 dph (6·8 ± 0·6 mm LT), pyloric caeca differentiated at the junction of the pyloric stomach and the anterior intestine. Gastric glands were first observed at 21 dph (9·2 ± 1·2 mm LT), coinciding with the morphological development of the stomach in three different regions (cardiac, fundic and pyloric) according to the histological characteristics of their mucosa. At this age, large longitudinal folds appeared in the median and posterior oesophageal mucosa. These morphological and histological features suggested the achievement of a digestive system characteristic of large yellow croaker juveniles and adults.

Comparison of some live organisms and artificial diet as feed for Asian catfish Clarias macrocephalus (Gunther) larvae

Summary Experiments were conducted to evaluate the efficacy of five live organisms (Artemia, Brachionus calyciflorus, Chironomus plumosus, Moina macrocopa and Tubifex sp.) and an artificial diet (40% protein) in the larval rearing of Asian catfish Clarias macrocephalus. The larvae were fed three times daily starting at the onset of exogenous feeding. Results showed that the catfish larvae utilized the live organisms more efficiently than the artificial diet. The Tubifex-fed larvae consistently showed the highest growth rate. In trial 1, length increment (64.9 mm), weight gain (3192 mg) and specific growth rate (13.1%) after 8 weeks of feeding were significantly higher (P < 0.05) in catfish larvae given Tubifex than those in all other treatments. In trial 2, length increment after 4 weeks of feeding was highest in larvae fed Tubifex (22.9 mm) although it did not significantly differ from that of larvae given Moina (21.0 mm). However, weight gain of larvae fed Tubifex (253.0 mg) was significantly higher than that of larvae fed Moina (171.6 mg). The specific growth rate was highest for larvae fed Tubifex (15.0%) followed by larvae fed Artemia (14.5%), Moina (14.4%) and Chironomus (12.0%). Survival rates of the catfish larvae ranged from 9 to 39% after 8 weeks in trial 1 and from 26 to 83% after 4 weeks in trial 2. The present results suggest that Tubifex is an excellent food and a potential substitute for Artemia in the rearing of catfish larvae.

Dourado ( Salminus brasiliensis) larviculture: Weaning and ontogenetic development of digestive proteinases

This study examines the optimal weaning period in rearing larval dourado. This aim is achieved by comparing a series of differential weaning schedules, and by measuring the ontogeny of proteinase activities. Weaning from live food (curimba, Prochilodus lineatus, larvae) was carried out at the third, fifth or seventh day AH by gradual or total transition to formulated feed. Live food was either kept for two days after feeding the test diet (GW) or removed at the same day (TW). Acceptance of test diet started at the fifth day after hatching (AH) and larvae total length was higher ( P < 0.05) when feed transition occurred at the third (TW) (20.93 ± 1.33 mm, mean ± SEM) or seventh day (GW) AH (20.41 ± 0.80 mm); however, higher ( P < 0.05) wet weight was observed in larvae submitted to feed transition at the third (TW) (0.067 ± 0.014 g) or seventh day (GW) AH (0.078 ± 0.009 g). Total length and wet weight were not affected by the form of alimentary transition ( P > 0.05). Survival was significantly lower ( P < 0.05) when weaning occurred at the third or fifth day AH when compared to weaning at the seventh day AH. Additionally, survival was superior when transition to formulated feed was gradual. The ontogenetic development of proteinases was measured in the larval gut after hatching by sampling every 12 h AH, during seven days. Acid protease activity (0.0004 ± 0.0 U mg − 1 protein, mean ± SD) was detected at the third day AH and increased subsequently until the seventh day AH (7T), indicating stomach functionality at this time. Intestine proteinases activities (trypsin and chymotrypsin, 0.088 ± 0.0 and 0.018 ± 0.0 U mg − 1 protein, respectively) were detected as early as 12 h AH, before the onset of exogenous feeding. Digestive enzymatic contribution of live food was not clearly shown. Our findings corroborate the hypothesis that fish larvae will accept dry feed only when it is physiologically able to digest it, which happens when acid protease activity is detected, indicating stomach functionality. Our findings also demonstrate the importance of live food soon after hatching for dourado larvae and suggest that formulated feed could be offered, in a gradual form, as early as at the fifth day AH.

Dietary phospholipids are more efficient than neutral lipids for long‐chain polyunsaturated fatty acid supply in European sea bass Dicentrarchus labrax larval development

We evaluated the effects of dietary lipid class (phospholipid vs. neutral lipid) and level of n-3 long-chain PUFA (LC-PUFA) on the growth, digestive enzymatic activity, and histological organization of the intestine and liver in European sea bass larvae. Fish were fed from the onset of exogenous feeding at 7 to 37 d post-hatch with five isoproteic and isolipidic compound diets with different levels of EPA and DHA. Diet names indicated the percentage of EPA and DHA contained in the phospholipids (PL) and neutral lipids (NL), as follows: PL5, PL3, PL1, NL1, and NL3. Histological observations showed different patterns of lipid absorption and accumulation in the intestinal mucosa depending on the level and nature of the dietary lipid fraction. Fish fed high levels of neutral lipids (11%, NL3 diet: 2.6% of EPA + DHA in the NL fraction) showed large intracellular and intercellular lipid deposits in the anterior intestine, but no such lipid accumulation was detected when larvae were fed with low and moderate levels of EPA and DHA in the phospholipid and neutral lipid fractions of the diet (PL and NL1 diets). PL were preferentially absorbed in the postvalvular intestine, and the accumulation of marine PL was inversely correlated to their dietary level. The postvalvular intestinal mucosa and liver showed signs of steatosis; large lipid vacuoles were observed in this region of the intestine and in the liver and were inversely correlated with the level of dietary neutral lipids. The best results in terms of growth, survival, and development (maturation of the digestive system and histological organization of the liver and intestinal mucosa) were obtained in the group fed with 2.3% of EPA and DHA in the PL fraction of the diet (PL3 diet), revealing that European sea bass larvae use the LC-PUFA contained in the PL fraction more efficiently than those from the NL fraction of the diet.

Ingestion and assimilation of three species of freshwater algae by larval tilapia Oreochromis niloticus

Three species of freshwater algae ( Spirulina platensis, Euglena gracilis and Chlorella vulgaris) labeled with 14C were fed to larval tilapia ( Oreochromis niloticus) with a standard length (SL) from 0.8 to 3.4 cm. This was conducted to clarify the acceptability of the three species of algae to developing larval tilapia based on their ingestion and assimilation of the 14C-labeled algae. Ingestion rate (IR, μg C/fish/h) and assimilation rate (AR, μg C/fish/h), as well as ingestion efficiency (IE, %) and assimilation efficiency (AE, %) were investigated by monitoring the fate of the labeled food. Larval tilapia could ingest 2.6–85% of the available S. platensis biomass with larvae growing from an SL of 0.8–3.4 cm, and the relationship between IR and body weight (BW, mg) was expressed as IR=15.62BW 0.686 ( r 2=0.94). Larval tilapia ingested significantly less E. gracilis (1.6–26% of the available Euglena biomass) than Spirulina, and the relationship between IR and BW was IR=13.70BW 0.584 ( r 2=0.93). In contrast, a negligible amount (1.6–20% of the available C. vulgaris biomass) of Chlorella was ingested by larval tilapia over the range of sizes studied. For all three algae, a relatively lower assimilation efficiency (AE) was found in larvae right after the onset of exogenous feeding, but AE improved rapidly with increasing larval size from 0.8 to 1.2 cm SL. Spirulina was more readily assimilated (61.4–80%) than Euglena and Chlorella. Assimilated carbon from Euglena and Spirulina were about 1–2 and 3–6 times that of the resting carbon consumption requirement for respiration of the larval tilapia. It was concluded that Spirulina is more acceptable than Euglena and Chlorella as a diet for larval tilapia from the onset of exogenous feeding.

Family, induction methodology and interaction effects on the performance of diploid and triploid chinook salmon (Oncorhynchus tshawytscha)

The production of sterile triploid salmon for aquaculture is an effective strategy to minimize potential environmental risks and increase productivity. However, the efficacy of heat-versus pressure-based induction protocols and the effect of treatment and genotype on fitness related traits have rarely been examined in the same study. In this study, the effect of treatment, family and the treatment-by-family interaction on freshwater survival, growth and immune function was examined in full-sib groups of diploid and heat- and pressure-shock induced triploid chinook salmon (Oncorhynchus tshawytscha) from five families. Heat and pressure were equally effective at inducing triploidy, and few differences between the two treatment groups in survival, growth and antibody response to intraperitoneal Listonella anguillarum (formerly Vibrio) vaccination were observed. While triploids had lower survival and poorer performance than diploids, significant differences occurred mainly during the early stages of development. Survival was mainly influenced by treatment (heat-shock, pressure-shock) and family (genotype), while growth characteristics and the immune response to vaccination were mainly influenced by family. Significant treatment-by-family interaction effects were also found; however, they explained a relatively low proportion of the total variation in survival and growth, but a large proportion of the variation in immune response. An extended effect of heat-shock treatment on survival was present even after the onset of exogenous feeding. Despite the presence of significant interaction effects, consistent performance ranking among families was generally evident, regardless of ploidy or treatment. Since substantial family effects were observed for most of the performance variables, selection applied to diploid broodstock will be part of an effective strategy for improvement of triploid offspring performance.

Spawning and egg quality of the tilapia Oreochromis niloticus fed solely on raw Spirulina throughout three generations

In order to simplify the fish culture system in a Closed Ecological Recirculating Aquaculture System (CERAS), the feasibility of constructing a food chain of tilapia-Spirulina is being examined. This study investigated the reproductive performance of the tilapia Oreochromis niloticus fed solely on raw Spirulina platensis. The raw Spirulina (RS) was fed to the parent tilapia (SP) from 3.4 cm and to the progenies of the first generation (SF1) and second generation (SF2) from the onset of exogenous feeding, compared with the control parent fish (CP) and progenies (CF1, CF2) fed on commercial diets (CD). The parent fish (P) (n=6) in both groups of were cultured for 380 days, and the first generation progeny fish (F1) (n=6) for 575 days and the second generation progeny (F2) (n=6) for 380 days at 28±1 °C. The first spawning of brood stock of P, F1 and F2 in the groups of RS and CD occurred at almost the same age. There were no significant differences in the relative fecundities, spawning intervals, and egg sizes among SP, SF1, SF2, CP, CF1 and CF2. The fertilization rate and the hatching rate of the fertilized eggs, as well as the survival time of starved larvae from the parents fed the two types of diets were similar. The same results were also observed among the successive progenies (F1, F2). Significant differences in the fatty acid profile of eggs were observed between the RS and the CD groups, with RS group containing more linoleic acid, γ-linolenic acid, and Σn-6 highly unsaturated fatty acids (20:3n-6, 20:4n-6, 22:4n-6, 22:5n-6). It was concluded that tilapia fed solely on raw Spirulina could keep normal reproduction throughout three generations.

Ontogenetic development of the digestive system in California halibut ( Paralichthys californicus) with notes on feeding practices

The development of the digestive tract and accessory glands in California halibut ( Paralichthys californicus) is described from hatching to metamorphosis (42 days post-hatch, dph) at 18 °C. Differentiation of the alimentary canal into the buccopharynx, esophagus, pre- and postvalvular intestine, and rectum was complete by 3 dph (2.7±0.1 mm standard length, SL) coinciding with the time of first feeding. Zymogen granules (pancreatic enzyme precursors) were detected in the exocrine pancreas 1 day before the onset of exogenous feeding and their number increased after first feeding, confirming the importance of pancreatic secretions during the agastric period of larval development and their genetically rather than dietarily induced secretion. The stomach was morphologically differentiated at 27–30 dph (7.2–7.5 mm SL) coinciding with the onset of eye migration. At this stage, gastric glands were abundant in the fundic region and cardiac and pyloric regions were also clearly distinguishable. Supranuclear bodies were observed in the postvalvular intestine throughout the study period, although the number decreased as the stomach differentiated and extracellular digestion took place. The reduction of supranuclear bodies might be due to a change in the protein digestion mechanism. Histological observations showed that Artemia-fed larvae had almost intact nauplii in the postvalvular intestinal lumen and rectum, suggesting a fast intestinal transit in California halibut larvae, and a limited availability of nutrients from brine shrimp nauplii. Special attention might be required in rearing tanks during the first week of exogenous feeding, since the desquamation of the esophageal epithelium and the absence of mucous secretion due to the lack of functional goblet cells may promote bacterial infections under poor water quality conditions.

Lipid Nutrition and Feeding of Cobia Rachycentron canadum Larvae

AbstractThis study examined the fatty acid composition of cobia Rachycentron canadum eggs and yolksac larvae, as well as the ovaries of wild caught females as an initial guide to lipid nutritional requirements. A 2‐wk feeding study also was conducted to investigate the effectiveness of four dietary treatments on the growth and survival of cobia larvae. Cobia eggs in the tailbud stage contained 31.4 ± 1.3 μg lipid/egg. After hatching, the amount of lipid decreased significantly (P &lt; 0.05) from 28.3 ± 0.3 to 23.2 ± 0.1 μg lipid/larvae during the yolksac larval stage (days 1 to 3 after hatching). Ovaries from wild caught adults and captive spawned eggs and yolksac larvae contained high levels of PUFAs with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) accounting for approximately 80% of the total suggesting that cobia larvae may have a high dietary requirement for these fatty acids. For the feeding study, larvae were fed: 1) Artemia only; 2) enriched rotifers for 1 d only + microparticulate diet (day 313); 3) enriched rotifers for 3 d (day 3–5) + Artemia (day 3–13); and 4) enriched rotifers for 6 d (day 3–8) + Artemia (day 3–13). Cobia larvae began feeding on rotifers 3 d after hatching and on newly hatched Artemia nauplii by the fifth day following the onset of exogenous feeding (day 7). On day 7, no differences in larval growth were found among larvae fed rotifers for 3 versus 6 d, whereas larvae fed only Artemia or rotifers for I d followed by microparticulate diet were significantly smaller (P &lt; 0.05) and did not survive beyond day 9 and 13, respectively. The results of the feeding study indicate that cobia larvae require rotifers for a minimum of 4 d following the onset of exogenous feeding.

Amino acid requirements of fish larvae and post-larvae: new tools and recent findings

This paper reviews methodologies and recent findings in the study of the amino acid (AA) metabolism of fish larvae and post-larvae, in order to better understand the AA requirements. The larval indispensable AA (IAA) profile can be used as index of the IAA requirements. When turbot larvae and live food IAA profiles are compared, the profile of the latter seems to be deficient in some IAA. However, the larval IAA profile is only a rough indicator of AA requirements. A more precise estimate of the ideal dietary IAA profile implies the knowledge of the relative bioavailabilities of the individual AA, in particular, eventual differential rates of absorption and catabolism. Metabolic budgets (including unabsorbed AA, AA oxidation and AA retention) can be estimated using an in vivo method based on controlled tube-feeding of AA mixes containing a 14C-labelled AA. Results with fasted post-larval Senegal sole ( Solea senegalensis) and fasted herring ( Clupea harengus) larvae show a high retention of labelled doses of IAA (>60%) in the body, compared to catabolism as measured by liberated 14CO 2 (<25%). In contrast, dispensable AA (DAA) show a higher catabolism (>40%) and a lower retention (<57%). So, from the onset of exogenous feeding, fish larvae have high catabolic losses of AA, but use DAA preferentially to IAA as energy substrates. A new method combining the use of 13C-labelled live food and 13C-NMR spectroscopy can be used to study simultaneously the relative bioavailability of several individual AA in fish larvae. In larval gilthead seabream ( Sparus aurata) fed on rotifers, relative bioavailabilities (a combined measure of absorption efficiency and rate of catabolism) vary between AA being high for aspartate, glutamate and lysine and low for threonine. These estimates of relative biovailability of individual AA together with the IAA profiles of the larval seabream indicate that rotifers are deficient in threonine and leucine for larval seabream, threonine being the first limiting AA for protein synthesis. In order to define ideal IAA profiles for larval fish, further studies are needed on the factors affecting the relative bioavailability of IAA, such as species, age, developmental stage, temperature and the dietary nitrogen molecular form(s). Estimates of relative bioavailability of individual AA together with the IAA profile of the larval protein allow to determine the ideal dietary IAA profile for a given species.

Ontogeny of intestinal motility in correlation to neuronal development in zebrafish embryos and larvae

For the first time, spontaneous intestinal activity was demonstrated and quantified before the onset of exogenous feeding in zebrafish Danio rerio embryos and larvae in vivo, using digital motion analysis. At 3 days post fertilization (dpf), erratic and spontaneous contraction waves were observed in the gut. Later (4–7 dpf), more distinct contraction patterns were distinguished, and anterograde and retrograde contraction waves projecting anally and orally along the intestine, respectively, as well as local rectal contraction waves could be identified and quantified. The frequency of both anterograde intestinal and local rectal contractions increased significantly during the first days of development. There was a tendency towards shorter anterograde contraction waves in the first dpf stage investigated, but the velocity of the waves did not differ significantly between the different dpf stages. The presence of developing neurones in the gut of zebrafish was established using immunohistochemistry, staining for a suite of marker proteins (Hu C/D, HNK‐1 and acetylated tubulin). Structural neurones were present in the developing gut from the first dpf stage investigated (2 dpf). In conclusion, during the period (3–7 dpf) when erratic contraction waves turn into a more organized pattern of motility there is also a pronounced development of the innervation, suggesting a correlation in time of the development of gut motility and its neuronal control.

Behavioural variation in juvenile Arctic charr in relation to body size

Young Arctic charrSalvelinus alpinus, derived from one male and one female only from Lake Ölvesvatn in northern Iceland (a stock that has been popular in Icelandic aquaculture), showed large variance in body size, primarily as a consequence of variable egg size. Shortly after the onset of exogenous feeding, large fish (0·11–0·14 g) were more active and fed mainly from the water surface. Small fish (0·06–0·09 g) moved less and made fewer foraging attempts. They spent most of the time on the bottom, and foraged equally on the bottom and surface. These findings can be used to improve growth and performance of juveniles in rearing tanks.

Flesh quality of tilapia Oreochromis niloticus fed solely on raw Spirulina

ABSTRACT: In order to simplify the food chain in a closed ecological recirculating aquaculture system, raw Spirulina platensis cultivated in 50-L photobioreactors were fed to tilapia Oreochromis niloticus as a uni-feed from the onset of exogenous feeding. The feasibility of using tilapia grown on raw Spirulina (body weight: 155.4 ± 3.9 g, standard length: 16.2 ± 0.2 cm; n = 3) was investigated for 30 weeks for sashimi (sliced raw meat). Some of the rheological properties of the flesh were measured to clarify the obtained results of sensory evaluations of texture and fatness. The elastic modulus of flesh of the Spirulina-fed fish was significantly higher than that of the control fish (body weight: 168.9 ± 5.8 g, standard length: 17.8 ± 0.5 cm; n = 3) that were fed commercial diets. In addition, the viscosity of the flesh of the Spirulina-fed fish was significantly lower than that of the control fish. There was no significant difference in the rupture strength between the two treatments. The rheological parameters in the muscle were found to coincide with the results of the sensory assessment. These results suggest that tilapia fed solely on raw Spirulina have a high flesh quality that is suitable for sashimi. The muscle lipid of the raw Spirulina-fed fish had lower levels of non-polar lipids such as triglycerides and partial glycerides, but higher levels of polar lipids such as phosphatidylcholine and phosphatidylethanolamine. The fatty acid profile of the raw Spirulina-fed fish muscle, especially in the polar lipid fraction, was characterized by an abundance of Σn-6 highly unsaturated fatty acids (20:3n-6, 20:4n-6, 22:4n-6, 22:5n-6).

Histology of the developing digestive system and the effect of food deprivation in larval green sturgeon ( Acipenser medirostris)

The histological development of the digestive tract in hatchery-reared green sturgeon ( Acipenser medirostris) larvae and the effects of food deprivation on the digestive system organization were studied from hatching until 31 days post-hatching (dph). At hatching, the larval digestive system consisted of two rudiments: a large endodermal yolk sac and a primordial hind-gut. During the endogenous feeding phase, the wall of the yolk sac differentiated into the stomach (glandular and non-glandular regions) and the anterior and intermediate intestine, while the hind-gut primordium differentiated into the spiral valve and rectum. At the onset of exogenous feeding (15 dph at 16 °C), the organization and cytoarchitecture of the digestive system in green sturgeon larvae was generally similar to those of juveniles and adults. Larvae deprived of food exhibited a progressive deterioration, with subtle pathological changes observed after 5-d starvation: shrinkage of digestive epithelia, tissue degeneration, and necrosis were observed at 10–15 d of starvation (30 dph). No changes were observed in the mucous secretion of different regions of the digestive tract of food-deprived larvae. The histological analysis of the larval digestive system may be used to evaluate the nutritional condition of larval green sturgeon in their nursery habitats in spawning rivers, which are affected by dams and flow diversions.

The diet and growth of larval and juvenile pikeperch (Stizostedion lucioperca (L.)): A comparative study of fishponds and a reservoir

Diet of larval and juvenile pikeperch (Stizostedion lucioperca) reared in ponds wasinvestigated and compared with the diet ofpikeperch from a reservoir. The standard lengthof first feeding pikeperch larvae in ponds was6.1 mm, on average, and although rotifers werepresent in the diet, their numericalcontribution can be considered asinsubstantial. Rotifers were soon replaced bynauplii of cyclopoid copepods, which werehighly positively selected and contributedlargely to the diet up to a larval length of 10 mm.Daphnia spp. were consumed from the onsetof exogenous feeding, but were not positivelyselected until 15 mm. Anothersmaller cladoceran Bosmina longirostriswas highly negatively selected and did notcontribute significantly to the diet. A clearpositive selection for larger relatively tosmaller prey and a preference for Daphniafrom a body length of 15 mm onwards could beobserved. In the reservoir, rotifers were notfound in the diet of pikeperch larvae even inthe smallest individuals. Dominant food itemswere nauplii and 1st copepodite instar ofEudiaptomus gracilis and Cyclopsspp. Cladocerans – Daphnia galeata andto a lesser extent Diaphanosomabrachyurum appeared in the pikeperch diet at alength of about 10 mm. A shift from copepods toDaphnia spp. and especiallyLeptodora kindtii could be recognised inpikeperch at a length of 20 mm. When comparing ourdata from nursing ponds with the data fromŘimov reservoir, similar trends in dietcomposition were observed.

Expression of pancreatic enzyme genes during the early larval stage of Japanese eel Anguilla japonica

: To reveal the ontogeny of pancreatic exocrine function in the early larval stage of eel, cDNAs encoding major pancreatic enzymes, trypsinogen, amylase and lipase were identified from the Japanese eel Anguilla japonica and their expression pattern in larvae was analyzed. The cloned eel trypsinogen precursor consisted of 224 amino acids and showed 82.2% identity to trypsinogen-2 of winter flounder Pleuronectes americanus. The eel amylase precursor consisted of 512 amino acids and showed 77% identity to winter flounder amylase. Eel pancreatic lipase was composed of 470 amino acids and had 58.3% of identity to human pancreatic lipase. In the eel larvae, mRNA expression of trypsinogen and amylase was first detected at 6 days post-hatching (d.p.h.), and the expression level increased between 7 and 8 d.p.h. In contrast, mRNA expression of lipase was first detected at 8 d.p.h. Eel larvae start to feed actively at 8 d.p.h. Thus, it was indicated that eel pancreas starts to synthesize digestive enzymes at 6 d.p.h. and acquires full function by the onset of exogenous feeding at 8 d.p.h.

Acceptability of raw Spirulina platensis by larval tilapia Oreochromis niloticus

ABSTRACT: Thirteen-day-old tilapia larvae (mean weight: 0.01 g), at the onset of exogenous feeding, were stocked at five fish per liter in rearing tanks. They were fed unialgal cultures of Spirulina platensis from varying ages [0, 12, 17, 21, and 28 days after the onset of exogenous feeding with a standard length (SL) of 0.8 cm, 1.8 cm, 2.0 cm, 2.5 cm, and 3.0 cm, respectively]. Feeding experiments on larvae fed different amounts of raw Spirulina were also designed. Acceptability tended to improve with an increase in the initial SL of the experimental larvae, and larval tilapia from 2.0 cm SL showed significantly rapid growth when fed raw Spirulina. Larval tilapia that were fed solely raw Spirulina at a feeding rate of 30% (on a dry basis) of bodyweight in the first 3 weeks, 10% in weeks 4–6, and 3% in weeks 7–10, kept growing without any abnormality. Final weight and SL reached 3.2 ± 0.4 g and 4.5 ± 0.2 cm (n = 20), respectively, demonstrating that raw Spirulina was accepted by tilapia even just after the onset of exogenous feeding. Growth and survival rate of larvae fed Spirulina at different feeding rates in the first 3 weeks just after the onset of exogenous feeding showed a significant difference. Larval tilapia fed to satiation had the best growth performance throughout the 10-week rearing period, whereas those fed at a feeding rate of 10% stopped growing eventually and stunting was found. The availability of an abundant supply of Spirulina during the early stages seemed to be important for the normal growth and development of tilapia. Raw Spirulina appears to be an effective uni-feed for larval tilapia when developing a food chain of phytoplankton–fish for a closed ecological recirculating aquaculture system (CERAS).