Onset Of First Feeding Research Articles

Light conditions during Atlantic salmon embryogenesis affect key neuropeptides in the melanocortin system during transition from endogenous to exogenous feeding.

During the first feeding period, fish will adapt to exogenous feeding as their endogenous source of nutrients is depleted. This requires the development of a functional physiological system to control active search for food, appetite, and food intake. The Atlantic salmon (Salmo salar) melanocortin system, a key player in appetite control, includes neuronal circuits expressing neuropeptide y (npya), agouti-related peptide (agrp1), cocaine- and amphetamine-regulated transcript (cart), and proopiomelanocortin (pomca). Little is known about the ontogeny and function of the melanocortin system during early developmental stages. Atlantic salmon [0-730 day degrees (dd)] were reared under three different light conditions (DD, continuous darkness; LD, 14:10 Light: Dark; LL, continuous light) before the light was switched to LD and the fish fed twice a day. We examined the effects of different light conditions (DD LD , LD LD , and LL LD ) on salmon growth, yolk utilization, and periprandial responses of the neuropeptides npya1, npya2, agrp1, cart2a, cart2b, cart4, pomca1, and pomca2. Fish were collected 1 week (alevins, 830 dd, still containing yolk sac) and 3 weeks (fry, 991 dd, yolk sac fully consumed) into the first feeding period and sampled before (-1 h) and after (0.5, 1.5, 3, and 6 h) the first meal of the day. Atlantic salmon reared under DD LD , LD LD , and LL LD had similar standard lengths and myotome heights at the onset of first feeding. However, salmon kept under a constant light condition during endogenous feeding (DD LD and LL LD ) had less yolk at first feeding. At 830 dd none of the neuropeptides analyzed displayed a periprandial response. But 2 weeks later, and with no yolk remaining, significant periprandial changes were observed for npya1, pomca1, and pomca2, but only in the LD LD fish. This suggests that these key neuropeptides serve an important role in controlling feeding once Atlantic salmon need to rely entirely on active search and ingestion of exogenous food. Moreover, light conditions during early development did not affect the size of salmon at first feeding but did affect the mRNA levels of npya1, pomca1, and pomca2 in the brain indicating that mimicking natural light conditions (LD LD ) better stimulates appetite control.

Growth Performance and Nutritional Condition of Marble Goby (Oxyeleotris marmoratus) Larvae Fed under Different Onsets of First Feeding

The marble goby (Oxyeleotris marmoratus) is a valuable food fish, but its aquaculture production is often hampered by poor growth performance associated with starvation at an early stage. The objective of this study was to investigate the effects of delayed initial feeding on the growth performance and nutritional condition of the marble goby. Six different first feeding times were examined: 0, 12, 24, 36, 48, and 60 hours after the first feeding (HAFF), and their impacts on growth performances were evaluated based on larval final total length (mm) and survival (%), while nutritional condition was evaluated based on body morphometric changes, gut epithelium height (μm), and gut condition. The experiment was conducted for 15 days. All parameters were measured after larvae were collected at different sampling times, except survival and growth, which were measured at the end of the experiment. The results showed that the onset of the first feeding was 36 h after hatching (hAh) and that a short delay in the first feeding by 12, 24, 36, 48, and 60 HAFF significantly reduced the growth performance of the larvae and severely affected the larval nutrition condition with noticeable shrinkage in body morphometry and gut epithelium height. This study concluded that the onset of first feeding in marble goby occurs at 36 hAH and that first feeding beyond 36 hAH significantly worsens the nutritional condition and growth performance of the larvae.

Effects of duration and timing of immersion in 17α-methyltestosterone on sex reversal of female rainbow trout

Sex reversal of female rainbow trout (Oncorhynchus mykiss) by oral administration of 17α-methyltestosterone (17MT) is well established for production of XX males. Drawbacks to this protocol include a high proportion of males fail to develop fully functional sperm ducts and must be euthanized to harvest sperm, and difficulty in preventing the steroid from reaching the environment. Recent experiments demonstrate immersion of female rainbow trout in 17MT at 400 µg/L for 2 h at one week post hatching, and six weekly immersions starting at the onset of first feeding, was also effective for inducing sex reversal and should increase efficiency of hatchery operations by reducing harvesting of immature males and allowing reuse of functional males, as well as simplifying steroid containment. This experimental protocol was evaluated in a broodstock population of 501 treated animals and shown to deliver similar results with 95% developing testes and a minimum of 45% able to release milt. Treatment was uniformly effective for fish first immersed at 4–7 days post hatching. The effects of reducing the duration of the immersions and the timing of the second immersion were evaluated. Immersion for 1 h was as effective as 2 h. The treatment was consistently effective when the second immersion was applied by 21 days post hatching. Furthermore, there was an apparent family effect on fish that failed to develop gonads independent of treatment, that can impact interpretations of efficacy. Administering the first immersion at 4–7 days post hatching and the second immersion by three weeks post hatching achieves a reliably high rate of sex reversal and a reduction in the duration of the immersions to 1 h is a significant decrease in time required for the procedure and lessens risk by reducing how long the larvae or fry are maintained in static water.

Sex reversal of female rainbow trout by immersion in 17α-methyltestosterone

The use of oral administration of 17α-methyltestosterone (17MT) at 3 mg 17MT/kg of feed for 60 days following the onset of feeding to sex reverse female rainbow trout (Oncorhynchus mykiss) to produce XX males is well established. The treatment has shown to consistently result in nearly 100% of the treated animals being males. A primary drawback to this protocol is a high proportion of males are non-functional, in that milt is not released when pressure is applied to the abdomen, and therefore the males must be euthanized to harvest sperm from the testes. A second drawback to the protocol is the difficulty in preventing the steroid from reaching the environment when used as a feed additive. A protocol using immersion to administer 17MT for sex reversal was developed to address these issues. Immersion of female rainbow trout in 17MT at 400 μg/L for 2 h at one week post hatching, and weekly for five weeks starting at the onset of first feeding, for a total of seven immersions, resulted in nearly 100% sex reversal to male and about half the males being functional. The technique should increase efficiency of hatchery operations by allowing greater flexibility inherent in functional males, reduce the accidental harvesting of immature males, and simplify the capture of the steroid before reaching the environment.

Transcriptional regulation of lipid metabolism when salmon fry switches from endogenous to exogenous feeding

The onset of first feeding is a critical period for Atlantic salmon (Salmo salar). The fish goes through a dramatic transition, from using the yolk sac as an energy and nutrient resource to rely on exogenous food. However, the digestive system of salmon is not fully developed at start feeding. This is especially true for digestion and absorption of dietary lipids. To optimize lipid composition of the initial feed for better growth and development of salmon, it is important to have a systemic understanding of lipid metabolism. The present study combines transcriptomics and lipid composition data to obtain an overview of how lipid metabolism pathways change when salmon switch from endogenous to exogenous feed. Transition to exogenous feeding had higher influence on gene expression and fatty acids composition in pyloric caeca relative to liver, suggesting metabolism is more responsive in pyloric caeca when diet switches. The pathways of phospholipid and lipoprotein synthesis were both up-regulated in pyloric caeca, while phospholipid content unchanged. Because phospholipids are a major component of intestinal lipoproteins, it suggests that a higher level of dietary phospholipids is required for optimal lipid transport at first feeding stages. De-novo cholesterol synthesis pathway was up-regulated in pyloric caeca after exogenous feeding, while a down-regulation of bile acid synthesis pathway was found in liver. This suggests a higher requirement of cholesterol in salmon fry after switching to exogenous feeding. The present study has provided new insights on the systemic changes of lipid synthesis and transport pathways in salmon fry when switching from endogenous to exogenous feeding.

Microbial interference and potential control in culture of European eel (Anguilla anguilla) embryos and larvae

Abstract Recent experimental research applying hormonally induced maturation in European eel has resulted in production of viable eggs and yolk-sac larvae. However, present incubation and larval rearing conditions are suboptimal and few larvae survive until onset of first feeding. The aim of this work was to investigate if high mortality during egg incubation and larval culture resulted from microbial interference. By suppressing microbial coverage and activity on fertilised eel eggs using antibiotic and disinfection treatment, egg hatching success and larval longevity were significantly improved. A new approach based on scanning electron microscopy was developed to quantify microbial coverage of eggs. Measurements of microbial coverage in combination with growth curves of egg-associated bacteria indicated that microbial activity rather than physical coverage led to reduced hatch success. In addition, an inverse relationship between microbial coverage of eggs and larval survival indicated that attachment of micro-organisms on the egg surface during the last 24 h of incubation affected later larval survival. These results suggest that microbial control through application of egg surface disinfection in combination with microbial management will be fundamental for improved post-hatch larval survival.

Ontogenetic development of digestive functionality in golden pompano Trachinotus ovatus (Linnaeus 1758)

Ontogenetic development of the digestive system in golden pompano (Trachinotus ovatus, Linnaeus 1758) larvae was histologically and enzymatically studied from hatch to 32day post-hatch (DPH). The development of digestive system in golden pompano can be divided into three phases: phase I starting from hatching and ending at the onset of exogenous feeding; phase II starting from first feeding (3 DPH) and finishing at the formation of gastric glands; and phase III starting from the appearance of gastric glands on 15 DPH and continuing onward. The specific activities of trypsin, amylase, and lipase increased sharply from the onset of first feeding to 5-7 DPH, followed by irregular fluctuations. Toward the end of this study, the specific activities of trypsin and amylase showed a declining trend, while the lipase activity remained at similar levels as it was at 5 DPH. The specific activity of pepsin was first detected on 15 DPH and increased with fish age. The dynamics of digestive enzymes corresponded to the structural development of the digestive system. The enzyme activities tend to be stable after the formation of the gastric glands in fish stomach on 15 DPH. The composition of digestive enzymes in larval pompano indicates that fish are able to digest protein, lipid and carbohydrate at early developmental stages. Weaning of larval pompano is recommended from 15 DPH onward. Results of the present study lead to a better understanding of the ontogeny of golden pompano during the larval stage and provide a guide to feeding and weaning of this economically important fish in hatcheries.

Functional modifications associated with gastrointestinal tract organogenesis during metamorphosis in Atlantic halibut (Hippoglossus hippoglossus)

BackgroundFlatfish metamorphosis is a hormone regulated post-embryonic developmental event that transforms a symmetric larva into an asymmetric juvenile. In altricial-gastric teleost fish, differentiation of the stomach takes place after the onset of first feeding, and during metamorphosis dramatic molecular and morphological modifications of the gastrointestinal (GI-) tract occur. Here we present the functional ontogeny of the developing GI-tract from an integrative perspective in the pleuronectiforme Atlantic halibut, and test the hypothesis that the multiple functions of the teleost stomach develop synchronously during metamorphosis.ResultsOnset of gastric function was determined with several approaches (anatomical, biochemical, molecular and in vivo observations). In vivo pH analysis in the GI-tract lumen combined with quantitative PCR (qPCR) of α and β subunits of the gastric proton pump (H+/K+-ATPase) and pepsinogen A2 indicated that gastric proteolytic capacity is established during the climax of metamorphosis. Transcript abundance of ghrelin, a putative orexigenic signalling molecule produced in the developing stomach, correlated (p < 0.05) with the emergence of gastric proteolytic activity, suggesting that the stomach’s role in appetite regulation occurs simultaneously with the establishment of proteolytic function. A 3D models series of the GI-tract development indicated a functional pyloric sphincter prior to first feeding. Observations of fed larvae in vivo confirmed that stomach reservoir function was established before metamorphosis, and was thus independent of this event. Mechanical breakdown of food and transportation of chyme through the GI-tract was observed in vivo and resulted from phasic and propagating contractions established well before metamorphosis. The number of contractions in the midgut decreased at metamorphic climax synchronously with establishment of the stomach’s proteolytic capacity and its increased peristaltic activity. Putative osmoregulatory competence of the GI-tract, inferred by abundance of Na+/K+-ATPase α transcripts, was already established at the onset of exogenous feeding and was unmodified by metamorphosis.ConclusionsThe functional specialization of the GI-tract was not exclusive to metamorphosis, and its osmoregulatory capacity and reservoir function were established before first feeding. Nonetheless, acid production and the proteolytic capacity of the stomach coincided with metamorphic climax, and also marked the onset of the stomach’s involvement in appetite regulation via ghrelin.

First feeding and subsequent growth performances in piscivorous larvae of Chinese perch Siniperca chuatsi (Perciforms: Sinipercidae)

The success of first feeding is influenced by many factors, such as prey availability, and is critical to subsequent larval growth performances. To test the advantages of prey exposure before complete yolk absorption in piscivorous larvae, feeding incidence and specific growth rate were longitudinally measured in Chinese perch Siniperca chuatsi larvae first fed at different ages. The results showed that Chinese perch larvae were able to capture live piscine prey at 4 DAH (days after hatching), 1 day before complete yolk absorption. The feeding incidence and specific growth rate were higher in larvae first fed at 4 DAH than in larvae first fed at 5 or 6 DAH. These results indicate that prey exposure experience can facilitate the onset of first feeding, and that successful exogenous feeding, even before complete yolk absorption, is important for growth performances of piscivorous fish larvae.

Temperature and dissolved oxygen requirements for survival of yellowfin tuna, Thunnus albacares, larvae

We determined the optimal water temperature and oxygen ranges for survival, development, and growth of yellowfin tuna ( Thunnus albacares) eggs and yolk-sac and first-feeding larvae by conducting a series of experiments between 2004 and 2006 at the Achotines Laboratory on the Pacific coast of the Republic of Panama. Based on the results of our experiments, yolk sac and first-feeding yellowfin larvae exhibited lethal limits for their survival at temperatures less than 21 °C and greater than 33 °C. Embryos hatched alive at all temperatures tested except 36 °C; however, larvae were malformed after hatching at temperatures < 20 °C and ≥ 34 °C. Egg and larval development were significantly slower at mean incubation temperatures < 23 °C. Mean egg diameters were significantly greater at mean incubation temperatures < 26 °C compared with those incubated at temperatures > 27 °C. Within the temperature range for survival and normal development, mean specific growth rates in weight for larvae after 2 days of feeding maintained at mean temperatures of 21.3 °C, 26.6 °C, 27.5 °C, and 31.5 °C were 1.8%, 20.9%, 27.2%, and 45.0%, respectively. The optimal range of temperatures for rapid growth and moderate to high survival in first-feeding larvae was from about 26° to 31 °C. Lethal conditions (100% mortality) for larvae after hatching and shortly after the onset of first feeding occurred at dissolved oxygen concentrations of < 2.2 mg O 2 L −1 (< 34% oxygen saturation) at temperatures between 26° and 29 °C. Significantly lower survival first occurred for first-feeding larvae when the larvae were exposed to dissolved oxygen concentrations of 2.65 mg O 2 L −1 (40.4% oxygen saturation). Based on our experimental results, critical depths for survival of yolk-sac and first-feeding yellowfin larvae within the Panama Bight of the Pacific Ocean would occur at depths less than 30 m during the upwelling season and at depths less than 50 m during the reduced upwelling season, based on temperature alone. Limiting oxygen levels may occur at depths greater than 30 m during the upwelling season and greater than 50 m during the reduced upwelling season.

Role of heterotrophic protists in first feeding by cod (Gadus morhua) larvae

The present study evaluated whether the presence of autotrophic phytoplankton and/or heterotrophic dinoflagellates (Oxyrrhis marina) influenced first-feeding success and early larval growth and development of Baltic cod Gadus morhua L. Newly hatched cod larvae were maintained in salt water ('clear water', CW), greened water using Nannochloropsis sp. (NA) or a combination of Nannochloropsis sp. and O. marina (NO) from 2 to 11 d post-hatch. On each day, larvae from each group were placed into feeding tanks and provided potential prey (nauplii of the calanoid copepod Acartia tonsa). Feeding performance was measured both as the percentage incidence of feeding and gut fullness index. The onset of first feeding, point of no return and the magnitude of feeding were derived from the feeding incidence. The study clearly demonstrated precocious, exogenous feeding by cod larvae in the presence of Nannochloropsis sp. and O. marina by 1.2 and 2.2 d (10°C), respec- tively. Gut fullness was also significantly improved in the presence of both phytoplankton and pro- tists over the entire window of opportunity (defined as the period between onset of first feeding and point of no return). However, the nutritional capacity of these unicellular organisms was not sufficient to alter the somatic growth characteristics in NA and NO groups relative to starving yolk-sac larvae maintained in only salt water (CW group). These findings expand the current understanding of the degree of interaction between fish larvae and unicellular plankton communities and indicate a lack of nutritional benefits from feeding on components of the pelagic microbial loop but a clear benefit in terms of 'priming' first-feeding capabilities.

Distribution of cholecystokinin‐immunoreactive cells in the gut of developing Atlantic cod Gadus morhua L. larvae fed zooplankton or rotifers

One of the main gastrointestinal hormones, cholecystokinin (CCK), was studied in order to advance understanding of the control of the digestive process in Atlantic cod Gadus morhua larvae after onset of first feeding. Larvae were fed either natural zooplankton or enriched rotifers in similar rearing systems and sampled from hatching to 22 days post-hatch (dph). CCK was visualized by immunohistochemistry and the first CCK-immunoreactive (IR) cells were detected at 8 dph corresponding to 6 days after first feeding. The CCK-IR cells were mostly found in the anterior midgut, and the number of CCK-IR cells was lower in the posterior midgut. They were also present in the hindgut of some of the larvae, but not in the foregut. No clear differences were found in the ontogenetic appearance and the distribution pattern of CCK-IR cells between the two dietary treatments. This indicates that the onset of CCK production in the gut as well as the spatial distribution of the CCK-IR cells is not differentially affected by these diets. To what extent the hormone production itself is influenced by dietary factors needs to be studied by more sensitive methods.

Analysis of effects induced by a pollock protein hydrolysate on early development, innate immunity and the bacterial community structure of first feeding of Atlantic halibut ( Hippoglossus hippoglossus L.) larvae

A pollock protein hydrolysate was used for enrichment of the live feed offered to halibut larvae from the onset of exogenous feeding and the effects of treatment on selected innate immune parameters studied. The effects of treatment on the bacterial community structure of larvae were furthermore studied using the PCR–DGGE method. C3 and lysozyme were identified in larvae already at the onset of first feeding and low concentrations of IgM detected at this stage indicate maternal origin. Endogenous production of IgM was validated in the gastrointestinal tract of larvae from 29 days post onset of first feeding, with similar concentrations found in both groups. Feeding the peptide-enriched live feed stimulated production of lysozyme and affected the distribution of C3 in larval tissue but survival and normal development of halibut larvae were not affected by the treatment. Vibrio sp. and Pseudoalteromonas sp. dominated the bacterial community of larvae from both groups and peptide enrichment of the live feed was not found to affect the bacterial community structure associated with surface sterilized larvae.

Reproductive behaviour and early development in yellowtail kingfish ( Seriola lalandi Valenciennes 1833)

The spawning behaviour of wild caught brood stock as well as early egg and larval development were studied in yellowtail kingfish ( Seriola lalandi). Spawning occurred naturally in the austral spring/summer (November–February) when the seawater temperature was above 17 °C. Courtship behaviour involved one male and female, and consisted of a high-speed pursuit punctuated by stalling, nipping and touching. This lasted for approximately 0.5–1.5 h until, immediately prior to spawning, the male would nip at the female gonoduct, presumably to induce spawning. At this stage, in 50% of spawns, a second male would become involved. The release of gametes involved frenzied circling behaviour near the bottom of the tank and lasted approximately 22 s. Spawning occurred in the early daylight hours at the start of the spawning season, but shifted to around dusk in the latter part. Spawned eggs were positively buoyant, had a high fertilisation rate (> 99%), ranged 1.33–1.50 mm in diameter with a single oil droplet 0.30–0.33 mm diameter, and developed in a similar manner to that described in congenerics. Egg viability within the floating fraction was visually determined to be 74% ± 17% over the entire reproductive season. Indistinct cell margins and asymmetrical cleavage were the most common blastomere deformities observed. Egg and oil droplet volume were found to decrease by 15–20% over the spawning season, though no relationship was found between visually assessed egg viability and date. Egg incubation trials between 16 and 24 °C indicated that temperature accelerated the time to hatch by a Q 10 of 5.0. While larvae were found to hatch at a smaller length with a larger yolk sac and oil droplet at warmer incubation temperatures, there was little difference in the maximum larval length reached at the onset of first feeding among the rearing temperatures used. It is proposed that the reason for this was that higher incubation temperatures accelerated the hatching process faster than the rate of tissue deposition. The findings from this study are discussed in terms of the biological significance and implications for the larviculture of this species.

Ontogenetic development of the digestive tract in reared spotted sand bass Paralabrax maculatofasciatus larvae

Histological and histochemical methods were used to describe the development of the digestive tract in spotted sand bass larvae reared under culture conditions. The larvae were kept in six 100-l tanks for 30 days. They were fed with Brachionus plicatilis from day 2 after hatching to day 13; Artemia nauplii from day 12 to day 17; Artemia juveniles and adults from day 14 to day 26; and a semi-dry artificial diet from day 20 onwards. Development of the digestive tract in spotted sand bass followed the general pattern described for other species. At hatching, it consisted of an undifferentiated straight tube laying over the yolk sac. At first feeding (day 2), the yolk sac was partially depleted and the mouth and anus were open. On day 5, the digestive tract was fully differentiated into buccopharynx, esophagus, stomach, anterior intestine, posterior intestine, and rectum. A few days after the onset of first feeding, a PAS-positive reaction was observed in both intestinal mucosae. The liver showed a constant glycogen accumulation after day 4. Formation of several supranuclear ninhydrin-Schiff (NS) positive vacuoles was observed in the enterocytes of the posterior intestine. Large supranuclear vacuoles were present in the enterocytes of the anterior intestine. The gastric glands and pyloric caeca appeared on day 16. Vacuoles of both intestines decreased in size and number with the appearance of gastric glands. A probable modification of the actual feeding schedule of spotted sand bass larvae is proposed.

Diet breadth variability in larval blue whiting as a response to plankton size structure

Diet breadth (measured as the S.D. of the log of prey size per larvae; SLH) of blue whiting micromesistius poutassou larvae followed a quadratic equation with larval size. In small larvae, diet breadth in terms of size (SLH), the mean and the maximum of the log of prey size per larvae (MLH and XLH, respectively) increased with larval size as prey size selection shifted to larger prey. In contrast, large larvae tended to reduce diet breadth of prey sizes ingested, focusing on the larger prey that were abundant, instead of raising the upper limit of prey sizes because of the low abundance of larger prey. Except for larvae at the onset of first feeding, number of prey stayed constant or decreased in relation to larval size. Both patterns (in small and large larvae) maintained a constant rate of increase of gut carbon content with increase in larval size. Large larvae appear to maintain the increase in gut carbon content during ontogenetic development by reducing diet breadth (SLH) and increasing selection towards the larger prey that are abundant.

Swim bladder malformation in hatchery-reared striped trumpeter Latris lineata (Latridae)

Swim bladder malformation is common in both larvae and later life stages of cultured striped trumpeter Latris lineata. This study used histology and gross morphology of whole larvae to describe the progression of abnormal development that proceeded initial liquid dilation of the primordial swim bladder. In addition, radiography was used to compare swim bladder morphology of cultured juveniles with wild-caught specimens. The histomorphology of the swim bladder prior to lumenal dilation was typical of transient physostome larvae reported in the literature. A distinct swim bladder lumen present in larvae between 5.2–5.7 mm standard length (SL) was assumed to be liquid dilated and coincided with mouth opening. Initial gaseous inflation was first apparent when larvae attained 5.7–6.2 mm SL, after the resorption of the yolk sac and oil globule and the onset of first feeding (<5.5 mm SL). Successful gaseous inflation ranged between 0% and 75% in the cohorts of larvae examined. When gaseous inflation failed to occur, abnormal development proceeded in which the liquid dilated swim bladder collapsed, occluding the lumen. Hypertrophy of the swim bladder epithelium and hyperplasia of the rete mirable ensued. Radiography revealed that wild-caught striped trumpeter had a euphysoclist (dual-chambered) swim bladder, in which the chambers are separated by a diaphragm. In comparison, cultured juveniles and sub-adults displayed highly varied swim bladder morphologies, including apparently normal, malformed, and non-functional swim bladders in which a gaseous lumen was entirely absent. Kyphosis was inflicted in extreme cases of swim bladder malformation in which a distended single chamber both displaced the viscera and pushed the spine upwards. It was concluded that striped trumpeter larvae can be afflicted with swim bladder malformations consistent with cultured larvae of other transient physostomes; however, swim bladder malformation of later life stages of striped trumpeter is atypical in comparison to other literature reports and may be unrelated to the larval malformation described.

Development of bile salt‐dependent lipase in larval turbot

Pancreatic bile salt‐dependent lipase (BSDL) was present with 0·5 μg BSDL larva−1 from hatching in turbot larvae. The enzyme content increased during the yolk sac phase to 1·1 μg BSDL larva−1. This suggests that larval turbot are able to digest lipids from the start of exogenous feeding. The BSDL synthesis was stimulated first by food about 5 days after the onset of first feeding. The content per larva increased exponentially in fed larvae to 20 μg BSDL larva−1 on day 23 after hatching and decreased in starved larvae. In contrast, the specific content decreased during the first feeding phase, meaning that smaller larvae had a higher content of enzyme related to their biomass than did bigger larvae.

Muscle growth and development in Atlantic cod larvae (Gadus morhua L.), related to different somatic growth rates.

The present study describes the development of the axial musculature in first-feeding larvae of Atlantic cod (Gadus morhua L.) with different somatic growth rates achieved by using different nutritional conditions. Muscle growth was assessed by determining the number of muscle fibres (hyperplasia) and the growth of existing fibres (hypertrophy). Larvae were fed rotifers containing a high (1. 4; treatment 1) or low (0.2; treatment 2) ratio of docosahexaenoic acid to eicosapentaenoic acid from day 5 after hatching. From day 17, the larvae were fed Artemia nauplii with the same enrichment in both treatments. Treatment 1 gave the highest somatic growth rate and hence the highest dry mass at the end of the experiment, but no difference in larval standard length was found between treatments. In slow-growing larvae, higher priority was thus put into reaching a certain length than into increasing muscle mass. The largest fibres, which were present from hatching, increased in cross-sectional area during larval development, but no differences were found between treatments in the cross-sectional area of individual fibres or the total cross-sectional area of these fibres at the end of the experiment. The first white recruitment fibres were observed at the dorsal and ventral apices of the myotome at approximately the onset of first feeding (larval length 4.5 mm). In larvae 8.5 mm long, the total cross-sectional area of white muscle fibres in the treatment 2 group was 75 % of that in the treatment 1 group. The highest somatic growth rate was associated with an increased contribution of hyperplasia to axial white muscle growth. In the faster-growing larval group, the relative contribution of hyperplasia to the total white muscle cross-sectional area was 50 %, whereas it was 41 % in the slower-growing larval group. The subsequent growth potential may thus be negatively affected by inadequate larval feeding.

Fish larval nutrition: a review of recent advances in the roles of amino acids

Marine pelagic fish eggs from various latitudes contain up to 50% of the total amino acid pool as free amino acids (FAAs). The FAA pool is established during final oocyte maturation and seems to derive from the hydrolysis of a yolk protein. During yolk resorption, the FAA pool is depleted and reaches low levels at first feeding. The FAA are predominantly used as metabolic fuel, but they are also utilized for body protein synthesis. Amino acids are also important catabolic substrates after the onset of first feeding and may account for 60% or higher of the energy dissipation. Since growth is primarily an increase in body muscle mass by protein synthesis and accretion and fish larvae have very high growth rates, they have a high dietary requirement for amino acids. Fish larvae that develop stomachs late in development have a low proteolytic and absorptive capacities of the digestive systems at first feeding. In vivo studies have shown higher absorption of FAA than peptides and protein bound amino acids from the larval gut in the early stages of marine fish larvae. In the ocean, marine fish larvae obtain a large supply of FAA by consuming plankton after first feeding. The FAA composition of live feed used in aquaculture may to some extent be manipulated within rearing conditions and species and strain selection. While microdiets are a promising feed for larval fish, no satisfactory techniques have at present been developed that allows delivery of high contents of FAA. New techniques using liposomes have the potential to alleviate this problem.