The importance of free amino acids to the energy metabolism of eggs and larvae of turbot (Scophthalmus maximus)

A study was undertaken to establish the role of free amino acids (FAA) in aerobic energy dissipation in embryos of turbot (Scophthalmus maximus) which contain an oil globule in the egg. Laboratory-reared developing eggs and larvae (15°C, 34 salinity) were measured for oxygen uptake, ammonia excretion, contents of FAA, protein, and ammonium, and volumes of yolksac and oil globule. Newly spawned eggs from different batches contained 55 to 90 nmol egg^–1 of FAA. Resorption of FAA occurred in parallel with the consumption of yolk. Resorption of the oil globule, however, occurred predominantly after hatching and mainly after yolk resorption. The combined data suggest that approximately 70% of the FAA are utilized as an energy substrate, while the rest are polymerized into body proteins. FAA become a significant energy substrate in the early egg stage and account for 100% of the aerobic energy dissipation 2 d after Fertilization then decrease to ca. 60% at the time of hatching. Lipids derived from the oil globule seem to be the main fuel after hatching and account for ca. 90% of the energy dissipation at the onset of first-feeding. Thus, the energetics of fish embryos which contain an oil globule seems to be different from those that depend exclusively on the nutritional reserves of the yolk.     

Compartmental distribution of free amino acids and protein in developing yolk-sac larvae of Atlantic halibut (Hippoglossus hippoglossus)

Free amino acids (FAA) and protein have been measured in whole laboratory-readed halibut larvae and on dissected individuals separated into yolk and body compartments. At hatching both FAA and protein are mainly located in the yolk compartment. During the first 12 d of the yolk-sac stage more than 70% of the FAA pool disappeared from the yolk without any significant changes in the yolk protein pool. This suggests different uptake mechanisms for FAA and protein from the yolk, and a sequential utilisation of the endogeneous reservoirs of free and protein amino acids in Atlantic halibut larvae. The data suggest that in the early yolk-sac stage FAA enter the embryo from the yolk and are utilised both for energy and protein synthesis. Later on when the free pool cannot fulfil the nutritional requirements, additional amino acids are recruited from yolk protein. Of the total amino acids (free + protein amino acids) present at hatching ca. 60% will be used as precursors for body protein synthesis while the remaining 40% are used as fuel in the larval energy metabolism.     

Sequential utilization of free amino acids, yolk proteins and lipids in developing eggs and yolk-sac larvae of barfin flounder Verasper moseri

Changes in the contents of free amino acids (FAA), M_r 170,000 lipovitellin (oLv B), that is the major yolk protein in ovulated eggs, and lipids were measured in developing eggs and yolk-sac larvae of barfin flounder (Verasper moseri) to elucidate the sequential utilization of these nutrient stocks before the first feed. Hatching takes place on the 10th day after fertilization at a water temperature of 8°C, and the hatched larvae absorb almost all of their yolk masses within 21 days after fertilization. The total FAA content showed no change during the first 4 days, then decreased to about 13% of the initial level by the 13th day after fertilization. During the consumption of FAA, non-essential amino acids tend to decrease earlier than essential amino acids. The native molecular weight and immunoreactivity of M_r 170,000 oLv B did not show any change during the first 16 days after fertilization, though the sodium dodecyl sulphate-polyacrylamide gel electrophoresis patterns of oLv B showed a serial change. The oLv B contents, measured by quantitative immunodiffusion using antiserum against oLv B of ovulated eggs, were approximately stable during the 13 days after fertilization, then decreased rapidly until the end of yolk-sac absorption. Phospholipids (PL), which seem mostly to bind with lipovitellin-proteins, decreased gradually after hatching coincident with the decrease in oLv B and M_r 330,000 lipoprotein. From these results, we conclude that there are three periods for sequential nutrient utilization in barfin flounder embryos and larvae: (1) pre-FAA utilization period, 0-4th day; (2) FAA utilization period, 4th-13th day; (3) oLv B and PL utilization period, 16th-21st day post-fertilization.     

Free amino acids and energy metabolism in eggs and larvae of seabass, Lates calcarifer

Contents of free amino acids (FAA), protein and ammonium ions together with rates of ammonia excretion and oxygen consumption were measured in order to study the role of FAA as an energy substrate in developing eggs and larvae of seabass (Lates calcarifer) maintained in seawater (30 ppt) at 28 °C without feeding. Initially eggs contained 25.3 nmol ind⁻¹ of FAA of which 21.5 nmol was rapidly utilised by the developing eggs and larvae during the period up to 40 h post spawning (PS) when nearly all the yolk had been resorbed. During the same period, a net increase in protein content of 1.7 μg ind⁻¹ was observed, indicating that the major part of the amino acids lost from the free pool had been polymerised into body proteins. Assuming that the balance of the FAA after protein synthesis was used entirely for energy metabolism, FAA appeared to be an important energy substrate during the embryonic stages (2 to 16 h PS); after hatching, the contribution of FAA to energy metabolism was less significant. From 50 h PS until the end of the study period at 100 h PS, amino acids derived from somatic protein were used for energy metabolism. For the overall period from just after spawning up to 100 h PS, the data indicate that ca. 14% of the total aerobic energy metabolism was derived from amino acid catabolism. Received: 26 September 1997 / Accepted: 1 April 1998     

Changes in metabolic substrates during early development in anchoveta Engraulis ringens (Jenyns 1842) in the Humboldt Current

We assessed the ontogenetic changes in protein content and free amino acids (FAA) in eggs and early larvae of Engraulis ringens (anchoveta) off central Chile on different dates during the spawning season. On all sampling dates, a reduction in embryonic yolk-sac volume, proteins and FAA concentrations occurred during development. Protein electrophoresis (SDS–PAGE) of eggs and larvae showed at least 22 protein bands: 11 were consumed early and not detected after hatching. The proportion of essential FAA (EFAA) was higher than the proportion of non-essential FAA (NEFAA) in early eggs and in 7 day-old larvae (82.5-73% EFAA respectively). During egg development, the FAA pool was dominated by leucine, alanine and lysine, three amino acids contributing 35–44% of the total FAA in eggs. During larval development, histidine was the most abundant FAA. In July, total FAA constituted 13–18% of the egg dry weight. A similar proportion (45–51%) occurred in July between protein plus FAA and total lipids. The differences in egg size during the spawning season along with variability in batch composition suggests that the female spawning condition is a major factor determining egg quality and early offspring success.     

Free amino acids as energy substrate in developing eggs and larvae of the cod Gadus morhua

The content of free amino acids (FAA) in the cod (Gadus morhua L.) egg is about 200 nmol at spawning, decreasing by about 100 nmol/egg during the egg stage and about 75 nmol/larva during the yolksac larval stage. Together, alanine, leucine, serine, isoleucine, lysine, and valine account for about 75% of the decrease. Ammonium accumulates gradually during the egg stage and is quickly excreted after hatching. The body protein content is maintained during the egg and yolksac larval stages. The measured oxygen uptake of the cod embryo during the egg and yolksac larval stages accounts for about 85% of the oxygen necessary to catabolize the FAA disappearing during this period. Ammonia excretion of the cod embryo, as taken from literature data, is similar to the expected ammonia production from catabolism of the FAA. Our data suggest that FAA are a major substrate for aerobic energy production in cod eggs and yolksac larvae. The implication of this finding for the production of a favourable first-feed for cod and other cultivated marine fish larvae, and for the selection of high quality eggs of marine fishes, is stressed.     

Fatty-acid composition of ovulated eggs from wild and cultured turbot (Scophthalmus maximus) in relation to yolk and oil globule lipids

The fatty-acid composition of lipids from ovulated eggs of wild and cultured turbot was investigated in order to estimate the nutritional requirements during embryonic and early larval development. Lipid comprised 13.8±0.5% (n=5) and 13.2±0.7% (n=7) of the egg dry weight in wild and cultured turbot, respectively. Polyunsaturated fatty acids (PUFA) of the (n-3) series accounted for 39% of total fatty acids in total lipid of both wild and cultured fish. The predominant (n-3) FUFA was docosahexaenoic acid (22:6 n-3), which also was the most abundant fatty acid in turbot eggs and comprised 24 and 23% of the total egg fatty acids in wild and cultured fish, respectively. Phospholipids, triacylglycerols and cholesterol-wax esters of turbot eggs all exhibited a specific fatty-acid profile distinctly different from that of total lipid. The general pattern of the fatty-acid distribution in lipids of eggs from wild and cultured turbot was similar, but the relative amount of 18:2(n-6) was considerably higher and 20:1(n-9) slightly higher in cultured fish. These differences were extended to all lipid classes and probably reflect the dietary intake of certain vegetable and marine fish oils. Calculations based on light microscopical studies showed that 55 to 60% of the total lipids in cultured turbot eggs are confined to the oil globule. The size of the oil globule remained constant during embryogenesis, and a reduction in size occurred first after hatching and mainly after yolk depletion. This implies that the total amount of lipids utilised during the embryonic development is considerably less than the total lipids present in ovulated turbot eggs. Comparison of the fatty-acid composition of total lipids from eggs and vitellogenin of wild turbot reveals that egg lipids contained a lower level of saturated and a higher level of monounsaturated fatty acids. Eggs also contained wax esters, which were not detected in vitellogenin, suggesting that vitellogenin is not the only source of lipids for turbot eggs.     

Physiological energetics of developing embryos and yolk-sac larvae of Atlantic cod (Gadus morhua). II. Lipid metabolism and enthalpy balance

This paper presents quantitative data for the changes in the contents of total lipids, lipid classes and their associated fatty acids, together with the changes in caloric contents of developing eggs and yolk-sac larvae of Atlantic cod (Gadus morhua L.). During development between Day 0 to 28 post fertilisation, 32% of catabolic metabolism was fuelled by lipids. On a mass-specific basis, polar lipids (mainly phosphatidyl choline) contributed 60%, and neutral lipids (mainly triacyl-glycerol) contributed 40% to this catabolic component, with each class supplying similar amounts of fatty acids as fuel. The fatty acids supplied by phosphatidyl choline were catabolised non-selectively (i.e. in proportion to their presence in the egg), with about half of them being polyunsaturated. However, of the fatty acids esterified in triacylglycerol, the larvae showed an apparent oxidation preference for monoenes over polyunsaturates or saturates. Routine rates of oxygen consumption and ammonia production were related to the caloric contents of the eggs and larvae in order to derive an enthalpy balance equation (of the form P=C+R+E) for an Atlantic cod larva during its period of endogenous nutrition. For the interval of Day 0 to 25 post fertilisation (the period of yolk dependence), integration of the physiological and caloric data revealed that Atlantic cod larvae conserved 53% of yolk enthalpy (C) for growth (P), 42% was dissipated due to metabolism (R) while only 5% was lost via excretion (E).     

Oocyte development in the kuruma prawn Penaeus japonicus

Female kuruma prawns (Penaeus japonicus Bate) with undeveloped, early developing, developing, nearly ripe and ripe ovaries, were collected from Ise Bay, Japan, in 1984. Oocyte development of the kuruma prawn was classified into ten stages according to morphological characters, namely: (1) synapsis stage, (2) chromatin nucleolus stage, (3) early perinucleolus stage, (4) late perinucleolus stage, (5) oil globule Stage I, (6) oil globule Stage II, (7) yolkless stage, (8) yolk granule stage, (9) prematuration stage, and (10) maturation stage. The synapsis stage is a multiplication stage. The chromatin nucleolus stage, early and late perinucleolus stages are previtellogenesis and primary growth stages. Oil globule Stage I is an initial stage of primary vitellogenesis and secondary growth. Follicle cells on the oil globule Stage I oocytes expand rapidly and reach maximum size during oogenesis. Yolk granule stage oocytes are in the initial stages of secondary vitellogenesis. Strongly acidophilic yolk granules accumulate within basophilic vesicles of the cytoplasm. The yolk granules are first concentrated in the inner part of the cytoplasm, then gradually spread to the periphery. Cortical crypts, which are separated from the oocyte cytoplasm by the cytoplasmic membrane, are situated outside of oocyte cytoplasm. Germinal vesicle breakdown (GVBD) is initiated in the late phase of prematuration and continues until the late phase of maturation immediately prior to spawning. At the beginning of the maturation stage, the oocytes are ovulated, after which the nuclei further shrink and migrate out-wards. After ovulation, meiotic division of the ovarian oocyte progressed up to the metaphase of primary maturation division. Finally, the meiotic metaphase is visible just beneath the cytoplasmic membrane in the mature oocyte. Though ovulation is synchronous within the same ovary, GVBD is not completely synchronous. Ovulated mature oocytes have many club-shaped cortical crypts in the peripheral part of the cytoplasm and contain extensive accumulations of yolk granules dispersed throughout the cytoplasm. The apical end of the club-shaped cortical crypts and cytoplasmic membrane are coated by the vitellin envelope in the mature oocyte.     

Route of egg yolk protein uptake in the oocytes of kuruma prawn,Penaeus japonicus

The route of egg yolk protein uptake into the oocytes of kuruma prawn, Penaeus japonicus, was studied using immunohistochemical and electron microscopical methods. Although a significant immunofluorescence with anti-vitellin-immunoglobulin was observed in the enlarged follicle cells surrounding oil globule stage oocytes of the early vitellogenic ovary, no fluorescence was detected in shrunken follicle cells surrounding oocytes in the yolk granule stage. Electron microscopically, yolk granule stage oocytes have an irregular surface with numerous well-developed microvilli. In contrast, the surface of follicle cells is relatively smooth. The irregular surface of yolk granule stage oocytes was covered with a layer of electron dense material. Similar dense material was found in the spaces between the neighboring follicle cells on the yolk granule stage oocytes. The outer surface of the follicle cells on yolk granule stage oocytes was covered by dense materials which were similar to those found on the irregular surface of oocytes. Micropinocytotic vesicles containing dense material were found in the ooplasm near the irregular surface with numerous well-developed microvilli. Dense material was concentrated in the peripheral part of the small forming yolk bodies of yolk granule stage oocytes. This suggests that the electron dense material, probably egg yolk protein, transferred to the surface of yolk granule stage oocytes from the spaces between the neighboring follicle cells may be incorporated into the ooplasm by pinocytosis through the microvilli and subsequently aggregate to form yolk bodies.     

Utilization of yolk reserves during post-embryonic development in three teleostean species: the sea bream Sparus aurata,the sea bass Dicentrarchus labrax,and the pike-perch Stizostedion lucioperca

A comparative study of the use of yolk reserves during post-embryonic development was performed on three teleostean fishes of aquacultural interest: the sea bream Sparus aurata, the sea bass Dicentrarchus labrax, and the pike-perch Stizostedion lucioperca. The first part of the work was devoted to the structural development of the periblast, the vitellus and the oil globule during the endotrophic and endo-exotrophic phases of larval life. Observations using transmission electron microscopy revealed a perivitelline circulation system closely related to the liver, and suggested an important function of the periblast in the utilization of reserves. In the second part of the study, cytochemical reactions revealed the way in which the reserves are resorbed. Glycogen contained in the periblast at hatching was utilized during the endotrophic period. The successive appearance of lipoprotein particles in the periblast endoplasmic reticulum, Golgi apparatus, and perivetelline circulation zone is consistent with the mobilization of yolk and oil globule components. Comparison of fed and fasting individuals revealed that fasting tended to slow down rather than increase the utilization of reserves.     

Female reproductive biology and oocyte development of the red frog crab,Ranina ranina,off Hachijojima,Izu Islands,Japan

Speciments of the red frog crab, Ranina ranina, examined in this study were collected off Hachijojima, Japan from 1987–1988 and 1990–1991. Ovigerous females occurred from May to September, and their carapace length ranged from 61.8 to 102.1 mm. Minimum size at the maturity was estimated to be 50 to 60 mm carapace length. The lobule-type ovary had a longitudinal ovarian cavity at the center. Germinal zones were located along the sides of the cavity. Oogenesis was divided into five main and ten detailed stages: proliferation (oogonium); previtellogenesis (bouquet, early chromatin nucleolus, late chromatin nucleolus); primary vitellogenesis (oil globule and yolk granule); secondary vitellogenesis (primary yolk platelet, secondary yolk platelet and prematuration); and maturation (maturation) stages. Vitellogenesis started at the oil globule stage when weakly positive periodic acid-Schiff granules appear in the cytoplasm. Based on the gonadosomatic index and histological changes in ovary, the reproductive cycle was divided into five stages: multiplication, from December to January; developing, from February to March; ripe in April and early May; spawning, from late May to August; and recovery, from August to November. Each crab spawned more than once during the spawning season.     

Lipids and fatty acids of the benthic marine harpacticoid copepod<Emphasis Type="Italic"> Heteropsyllus nunni</Emphasis> Coull during diapause: a contrast to pelagic copepods

Many free-living copepods produce and store lipids prior to entering diapause (long-term dormancy). Heteropsyllus nunni Coull is the only marine harpacticoid copepod known to undergo any form of diapause. This study presents the first information on the types of lipids and fatty acids produced for long-term diapause in this benthic species. Sexually immature adults of H. nunni undergo diapause within a pliable self-made cyst. Prior to entering diapause (which lasts 3–4 months), they produce and store large amounts of orange lipid. The lipids apparently are utilized during diapause. Although some residual lipids remain, chiefly around the gonads, after the copepods emerge from their cysts, the lipid stores are visibly reduced. Typically, the copepods mate and produce eggs within 48 h after diapause is terminated. Light level and confocal laser scanning microscopy revealed that the lipid stores are distributed throughout the body in numerous oil droplets and not as a single oil sac, as seen in many marine calanoid copepods prior to overwintering (winter diapause). Transmission electron microscopy showed lipid spheres within the gut epithelium and large droplets of lipids stored extracellularly. Confocal laser scanning microscopy of copepods in pre-diapause, during diapause (encysted), post-diapause (recently excysted), and in reproductive condition, revealed that lipid stores are reduced following diapause, but are not totally absent. Analysis of lipid classes showed that H. nunni store predominantly wax esters/sterol esters (83% of total lipids) during diapause. The predominant lipid is most likely wax esters, as sterol esters typically are found only in small amounts in copepods. Fatty acid (FA) profiles of the copepods in diapause showed 16:0 to be most abundant followed by 16:1n-7 and 18:0; other FA occurred at concentrations <10% of total FA. Three polyunsaturated fatty acids (PUFA), 20:5n-3, 18:2n-6 and 20:4n-6, were found at concentrations <2% of total FA. These PUFA are "essential fatty acids" in H. nunni, obtained through dietary sources. The lipid classes and fatty acids present in H. nunni during diapause are compared to those of other copepods, some in a state of diapause and others not. It appears that lipid class and FA profiles are indicative of genetic makeup, type of diet or amount of food consumed prior to dormancy. Some classic paradigms of lipids and their association with copepod diapause are re-evaluated.Communicated by P.W. Sammarco, Chauvin     

Modulation of the free amino acid pool and protein content in populations of the brine shrimp Artemia spp.

 Free amino acid (FAA) and protein content were measured in various developmental stages of Artemia franciscana, from cysts to Instar III metanauplii. In addition, decapsulated cysts of 15 Artemia populations from different localities were compared with respect to their FAA and protein content. Furthermore, the content and composition of the FAA pool were modulated by hatching the cysts at various salinities, and by enriching the nauplii with algae or a lipid-enrichment emulsion. The FAA content increased threefold from cysts to nauplii, and Instar III metanauplii contained nearly 50% taurine of total FAA. Cysts of A. franciscana were found to contain one-third the amount of FAA compared to the other Artemia species investigated. The content and pool composition of FAA was successfully modulated in 11 of 13 populations, where by the content of FAA was significantly increased when hatched at high salinity. Finally, enrichment elevated the content of FAA and changed the pool composition, thereby showing a dietary effect. Algal enrichment also increased the protein content. Received: 27 September 1999 / Accepted: 17 July 2000     

Physiological energetics of developing embryos and yolk-sac larvae of Atlantic cod (Gadus morhua). I. Respiration and nitrogen metabolism

This paper provides the basis for a general model of catabolic metabolism for developing embryos and yolk-sac larvae of Atlantic cod (Gadus morhua L.). Yolk-dependent routine rates of oxygen consumption, ammonia excretion, and accumulation of ammonium ions were related to quantitative changes in contents of glucose, glycogen, lactate, free amino acids, proteins and lipid classes (lipid classes published separately) in order to determine the rate and sequence of catabolic substrate oxidation that occurs with development at 6.0°C, 34.5 S. The stoichiometric relation of the oxygen consumption and total ammonia production to substrate utilisation indicated that during the first 2 to 3 d of development, glycogen was the sole substrate of oxidative metabolism. After formation of the syncytium, free amino acids (75%) together with polar lipids (13%, mainly phosphatidyl choline) and neutral lipids (9%, mainly triacylglycerol) comprised the metabolic fuels of embryonic development. Following hatch (Day 16 post fertilisation), the fuels were free amino acids (32%), polar lipids (20%, mainly phosphatidyl choline), neutral lipids (17%, mainly triacylglycerol) and proteins (31%). Thus, the catabolic metabolism of endogenously feeding Atlantic cod larvae was predominantly fuelled by amino acids (67%) and lipids (32%), while glycogen only accounted for 1% of the total enthalpy dissipated. It is proposed that the above sequence of catabolic substrate oxidation is also generally applicable to other cold-water fishes which spawn eggs that do not contain oil glubules.     

Changes in protein-bound and free amino acids in the muscle of the tiger prawn Penaeus esculentus during starvation

Using the starvation technique, changes in protein and free amino acids were examined in Penaeus esculentus Haswell collected from Moreton Bay, Australia, by trawling in 1985. Prawns of 17.7±0.26 g wet weight were held at 25°C until 2 d after moulting. Groups of seven or eight were then starved fro 5, 10, or 15 d, with appropriate control groups. At the end of each period, ecreted amino acids were collected for 24 h and whole-muscle amino acids and free amino acids (FAA) g^-1 in each prawn were analysed. Concentrations of whole-muscle amino acids showed only minor changes with starvation, but concentrations of many of the FAA changed significantly. Total FAA averaged 1 182±45 mol g^-1 dry weight. Individual FAA, in order of abundance, were glycine, arginine, proline, taurine, threonine, hydroxyproline, alanine, glutamic acid, valine, aspartic acid and lysine; the remaining FAA each contributed <0.2% of the total. Only taurine and alanine did not show significant changes with starvation. Concentrations of glycine, arginine, hydroxyproline, glutamic and aspartic acid increased, while those of proline, threonine, valine and lysine decreased with starvation, that of proline approaching zero after 15 d starvation. Excreted amino acid-nitrogen represented <2% of excreted ammonianitrogen ornithine being the most abundant (35%), followed by leucine (22%) and lysine (17%). The relative abundance of excreted amino acids did not correspond with those of the FAA. It is suggested that, as starvation progresses, the muscle protein is progressively hydrolysed, but with the remaining muscle maintaining its amino acid composition. The liberated amino acids enter the FAA pool and become available for energy production. Proline may have an important role as an energy source, but the ability to synthesise proline may be limited, and thus the artificial food of penaeid prawns may be improved by its addition.     

Yolk resorption,onset of feeding and survival potential of larvae of three tropical marine fish species reared in the hatchery

This paper provides basic early life-history information on milkfish (Chanos chanos), seabass (Lates calcarifer) and rabbitfish (Siganus guttatus) which may explain in part the observed differences in their survival performance in the hatchery. Egg size, larval size, amount of yolk and oil reserves and mouth size are all greater in milkfish than in seabass, and greater in the latter than in rabbitfish. During the first 24 h after hatching, rabbitfish larvae grow much faster than milkfish and seabass larvae at similar ambient temperatures (range 26°–30°C, mean about 28°C). The eyes become fully pigmented and the mouths open earlier in seabass and rabbitfish (32–36 h from hatching) than in milkfish (54 h). Seabass larvae learn to feed the earliest. Yolk is completely resorbed at 120 h from hatching in milkfish, and yolk plus oil at 120 h in seabass and 72 h in rabbitfish at 26° to 30°C. Milkfish and seabass larvae have more time than rabbitfish to initiate external feeding before the endogenous reserves are completely resorbed. Delayed feeding experiments showed that 50% of unfed milkfish larvae die at 78 h and all die at 150 h from hatching. Milkfish larvae fed within 54 to 78 h after hatching had improved survival times: 50% mortality occurred at 96 to 120 h, and 10 to 13% survived beyond 150 h. Unfed seabass larvae all died at 144 h, while 6 to 13% of those fed within 32 to 56 h after hatching survived beyond 144 h and well into the subsequent weeks. Unfed rabbitfish larvae all died at 88 h, while 7 to 12% of those fed within 32 to 56 h after hatching survived beyond 88 h. A delay in initial feeding of more than 24 h after eye pigmentation and opening of the mouth may be fatal for all three species.Contribution No. 167 from the SEAFDEC Aquaculture Department     

Respiration and nitrogen metabolism of Atlantic halibut eggs (Hippoglossus hippoglossus)

Naturally spawned and fertilized eggs of Atlantic halibut,Hippoglossus hippoglossus L., were analysed for protein, free amino acids (FAA), ammonium ions and energy content. The chemical composition was found to be size-dependent but varied little during egg development. Ammonium ions did, however, accumulate during the late embryonic stage, and the trend in FAA content was downward during the same period. Rates of O₂ uptake and NH₃ excretion followed exponential patterns. A total of 1µmol O₂ was consumed and 120 nmol NH₃ excreted between the time intervals of fertilization and 1 d post hatch. Derived O:N ratios indicated that the dominant portion of the energy metabolism was lipid- or carbohydrate-based during the mid-development period but switched to FAA as hatch was approached.Correspondence should be addressed to: Zoological Laboratory, University of Bergen, Allégt. 41, N-5007 Bergen, Norway     

Amino acid metabolism and protein turnover in larval turbot (Scophthalmus maximus) fed natural zooplankton or Artemia

The present paper studied the influence of different food regimes on the free amino acid (FAA) pool, the rate of protein turnover, the flux of amino acids, and their relation to growth of larval turbot (Scophthalmus maximus L.) from first feeding until metamorphosis. The amino acid profile of protein was stable during the larval period although some small, but significant, differences were found. Turbot larvae had proteins which were rich in leucine and aspartate, and poor in glutamate, suggesting a high leucine requirement. The profile of the FAA pool was highly variable and quite different from the amino acid profile in protein. The proportion of essential FAA decreased with development. High contents of free tyrosine and phenylalanine were found on Day 3, while free taurine was present at high levels throughout the experimental period. Larval growth rates were positively correlated with taurine levels, suggesting a dietary dependency for taurine and/or sulphur amino acids. Reduced growth rates in Artemia-fed larvae were associated with lower levels of free methionine, indicating that this diet is deficient in methionine for turbot larvae. Leucine might also be limiting turbot growth as the different diet organisms had lower levels of this amino acid in the free pool than was found in the larval protein. A previously presented model was used to describe the flux of amino acids in growing turbot larvae. The FAA pool was found to be small and variable. It was estimated that the daily dietary amino acid intake might be up to ten times the larval FAA pool. In addition, protein synthesis and protein degradation might daily remove and return, respectively, the equivalent of up to 20 and 10 times the size of the FAA pool. In an early phase (Day 11) high growth rates were associated with a relatively low protein turnover, while at a later stage (Day 17), a much higher turnover was observed. Received: 19 March 1997 / Accepted: 14 April 1997     

Biochemical composition of the deep-sea red crab Chaceon quinquedens (Geryonidae): organic reserves of developing embryos and adults

Deep-sea red crabs Chaceon quinquedens (Smith) were collected in traps at depths of 860 and 1043 m in the northern Gulf of Mexico. Ovigerous crabs were maintained in the laboratory and the developing embryos were sampled every 2 wk until hatching. Proximate analysis (lipid, protein, carbohydrate, and ash) of embryos was performed to determine patterns and rates of organic reserve utilization during embryogenesis. Midgut gland, gonads, and clutch (as appropriate) of adult crabs (males, non-ovigerous females and ovigerous females) were analyzed for the same components as the embryos. Red crab embryos exhibited different patterns of yolk deposition and subsequent depletion of yolk components during embryogenesis. There was a range of lipid to protein (L:P) ratios among the different clutches examined, indicating plasticity in the relative proportions of lipid and protein yolk. The energy used for embryogenesis was estimated by converting the amounts of lipid, protein and carbohydrate in the embryos to their caloric equivalents; final values, taken from 9 mo-old embryos whose siblings were hatching as zoeae, were subtracted from the initial values of sibling embryos sampled at the time of collection (2 to 3 mo old). The amount of energy consumed during embryogenesis in the laboratory was relatively constant (0.12 to 0.13 cal egg^-1). There was considerable variability among the concentrations of organic reserves in the midgut gland of adult crabs and in the ovaries of females. Variations in midgut gland L:P ratios and ovaries were related to the reproductive status of the females, but there were no trends related to depth of capture.