盐度对凡纳滨对虾体组织蛋白质积累、氨基酸组成和转氨酶活性的影响

本文研究了低、中和高三个盐度水平(分别为3‰、17‰和32‰)对凡纳滨对虾(Litopenaeus vannamei)各组织蛋白质的积累、肌肉谷草转氨酶和谷丙转氨酶活力、肌肉总氨基酸和游离氨基酸组成和含量的影响。结果显示,经过50d不同盐度水平的试验,低盐度组对虾的肝胰腺和血淋巴中可溶性蛋白质含量显著高于中、高盐度组(p<0.05),而肌肉中可溶性蛋白质含量在各处理组间无显著性差异;低、高盐度均导致肌肉中谷丙转氨酶和谷草转氨酶活力升高,但是各处理间的差异不显著;低、高盐度组凡纳滨对虾肌肉总氨基酸和总必需氨基酸含量均显著高于中盐度组(p<0.05),中、低盐度处理组非必需氨基酸含量差异不显著,而低盐度组对虾肌肉中蛋氨酸、丝氨酸、半胱氨酸和脯氨酸含量均显著低于中盐度组(p<0.05),其中脯氨酸为常见的5种主要渗透调节氨基酸之一;低、高盐度组对虾肌肉总游离氨基酸含量显著高于中盐度组(p<0.05),而盐度对机体绝大部分肌肉游离氨基酸含量的影响不显著(p>0.05)。结果显示,当环境盐度偏离凡纳滨对虾最适生长盐度时,其可通过在肝胰腺和血淋巴蛋白质积累及提高自身转氨酶活力,来获得机体在渗透调节供能时所需的氨基酸,而这些氨基酸以脯氨酸为主。     

Effect of hyper or hypo-osmotic conditions on neutral amino acid uptake and oxidation in tissues of the crab Chasmagnathus granulata

We investigated the transport of ¹⁴C-methylaminoisobutyric acid (¹⁴C-MeAIB) and ¹⁴C-alanine oxidation in hepatopancreas and jaw muscle of Chasmagnathus granulata submitted to 24, 72, and 144 h of hypo- or hyperosmotic stress. While ¹⁴C-MeAIB uptake increased in jaw muscle and hepatopancreas from crabs submitted to hyperosmotic stress, it did not change in tissues from animals submitted to hypo-osmotic stress. Incubation of jaw muscle and hepatopancreas from control groups with 1 mM ouabain did not decrease ¹⁴C-MeAIB uptake. However, ouabain prevented ¹⁴C-MeAIB uptake in hepatopancreas at 24 h of hyperosmotic stress. In contrast, in jaw muscle from crabs submitted to the same conditions, ¹⁴C-MeAIB uptake was not prevented by ouabain in the incubation medium. Jaw muscle from the control group produced four times more ¹⁴CO₂ from ¹⁴C-alanine than the hepatopancreas. During hypo-osmotic stress, amino acid oxidation does not seem to be one of the pathways implicated in the decrease of the amino acid pools in hepatopancreas and jaw muscle. In contrast, during hyperosmotic stress the reduction in ¹⁴C-alanine oxidation appears to be one of the mechanisms involved in the increase of the amino acid pool in the hepatopancreas.     

Free amino acid pools as effectors of osmostic adjustment in different tissues of the freshwater shrimp macrobrachium olfersii (crustacea, decapoda) during long-term salinity acclimation

To examine osmotic regulation during long-term acclimation to a hyperosmotic medium, hemolymph osmolality, [Na⁺] and total protein, tissue hydration, and free amino acid (FAA) pools in abdominal muscle, gills, central nervous tissue and hemolymph were quantified in the diadromous freshwater (FW) shrimp, Macrobrachium olfersii, during direct exposure to 21‰S seawater over a 20-day period. Hemolymph osmolality and [Na⁺] reach stable maxima within 24 h while total protein is unchanged. Muscle and nerve tissues rapidly lose water while gills hydrate; all tissues attain maximum hydration (+5%) by 5 days, declining to FW values except for gills. Total FAA are highest in muscle, reach a maximum by 2 days (+64%), declining to FW values. Gill FAA increase by 110% after 24 h, diminishing to FW values. Nerve FAA increase 187% within 24 h, and remain elevated. Hemolymph FAA decrease (-75%) after 24 h, stabilizing well below the FW concentration. During acclimation, muscle glycine (+247%), gill taurine (+253%) and proline (+150%), and nerve proline (+426%), glycine (+415%) and alanine (+139%) increase, while hemolymph leucine (-70%) decreases. Total FAA pools contribute 10-20% to intracellular (22-70 mmol/kg) and 0.5-2.4% to hemolymph (3-7 mOsm/kg) osmolalities during direct acclimation from FW. These data emphasize the modest participation of FAA pools in intracellular osmotic regulation during physiological adaptation by M. olfersii to osmotic challenge, accentuating the role of anisosmotic extracellular regulation, suggesting that, during the invasion of freshwater by the Crustacea, dependence on intracellular adjustment employing FAA as osmotic effectors, has become progressively reduced.     

Effect of season and artificial diet on amino acids and nucleic acids in gonads of green sea urchin Strongylocentrotus droebachiensis

The content of total and free amino acids (FAA) in green sea urchin (Strongylocentrotus droebachiensis) gonads varied with the season and feeding on an artificial diet. Glycine was the dominant amino acid in each season contributing 12.9-16.6% to the total amino acid (TAA) content, peaking in the spring. In the FAA profile, glycine accounted for 30.3-61.4% in different seasons. A grain-based artificial diet had noticeable effects on the total and FAA compositions of S. droebachiensis. Although, glycine was the dominant amino acid in the TAA profile during early harvesting, tyrosine in gonads became more dominant on week 9 of feeding. Furthermore, glycine was the dominant amino acid in the FAA pool after feeding the artificial diet. The total FAA content in the gonads increased significantly (P<0.05) from 20.6 on week 0 to 180.6 mg/g dry mass tissue on week 3. There were no significant (P<0.05) changes between week 6 and week 9. Deoxyribonucleic acid (DNA) content exceeded that of ribonucleic acid (RNA) in each season, while in cultured urchins, RNA content exceeded that of DNA only on week 6. The RNA/DNA ratio was significantly increased in the summer, whereas this ratio was increased up to week 6 followed by a decrease on week 9 in cultured counterparts.     

Seasonal variability of free amino acids in two marine bivalves, Macoma balthica and Mytilus spp., in relation to environmental and physiological factors

The seasonal variability of the intracellular free amino acid (FAA) concentration was studied in 5 Macoma balthica populations and 7 Mytilus spp. populations along their European distribution. Because of the well known physiological role of FAA as organic osmolytes for salinity induced cell volume regulation in marine osmoconformers, FAA variations were compared in bivalve populations that were exposed to high vs. low intraannual salinity fluctuations. In general, seasonal FAA variations were more pronounced in M. balthica than in Mytilus spp. In both bivalve taxa from different locations in the Baltic Sea, highest FAA concentrations were found in autumn and winter and low FAA concentrations were measured in summer. Seasonal patterns were less pronounced in both taxa at locations with constant salinity conditions. In contrast to Baltic Sea populations, Atlantic and Mediterranean bivalves showed high FAA concentrations in summer and low values in winter, regardless of seasonal salinity fluctuations. Significant seasonal FAA variations at locations with constant salinity conditions showed that salinity appeared not to be the main factor in determining FAA concentrations. The seasonal patterns of the main FAA pool components, i.e. alanine, glycine and taurine, are discussed in the context of seasonal variations in environmental factors (salinity, temperature) and physiological state (glycogen content, reproductive stage).     

Influence of salinity on the lipid composition and the fatty-acid pattern of muscle and hepatopancreas of the Chinese crab Eriocheir sinensis.

The values of principal lipids and fatty acids from muscle and hepatopancreas of crab E. sinensis living in fresh water or in sea water are determined. Lipid content from these two tissues does not significantly change following a variation in the salinity of the external medium. Nevertheless a slight decrease in the triglyceride concentration (+/- 20%) of hepatopancreas and a very slight increase in the polyunsaturated fatty-acid amount of phospholipids isolated from muscle and hepatopancreas are noted when the crab is transferred from fresh water to sea water.     

Seasonal patterns of nucleic acid concentrations and amino acid profiles of Parapenaeus longirostris (Crustacea, Decapoda): relation to growth and nutritional condition

The present work describes the seasonal changes in nucleic acid concentrations and amino acid profiles in the muscle of juvenile Parapenaeus longirostris and their relation to growth and nutritional condition. RNA content varied significantly between seasons, being the highest values attained in spring and the lowest in winter (p < 0.05). Similar results were obtained with RNA:protein and RNA:DNA ratios. In respect to total amino acid content (TAA), a significant increase from winter to spring was observed (p < 0.05) and the major essential amino acids (EAA) were arginine, histidine and leucine. Within non-essential amino acids (NEAA) glutamic acid, aspartic acid, glycine and proline were dominant. From winter to spring, a significant variation in NEAA content occurred (26.8; p < 0.05), mainly due to the significant increase of glutamic acid (79.1) and serine (66.7) (p < 0.05). EAA content did not vary significantly between seasons (p > 0.05). In opposition, during this period a significant decrease in the free amino acid content (FAA) was observed (p < 0.05); a higher percentage of decrease was attained in free non-essential (FNEAA – 42.9) in comparison to free essential amino acids (FEAA – 40.2). The significant increase in RNA and TAA contents from winter to spring may be related with protein synthesis. On the other hand, the lowest values obtained in winter may be due to a reduction in feeding activity; in this period the muscle protein must be progressively hydrolysed, which is evident with the higher FAA content. The liberated amino acids enter FAA pool and become available for energy production. In conclusion, it was evident that the seasonal cycle in activities such as feeding and growth with nucleic acids and amino acid analyses was noticed.     

盐度对哈氏仿对虾肌肉一般营养成分和氨基酸组成及含量的影响

通过调查不同盐度(12～36)环境下养殖的哈氏仿对虾(Parapenaeopsis hardwickii)肌肉一般营养成分和氨基酸组成及含量,研究了盐度对该虾肌肉营养品质的影响。结果显示,肌肉的水分随环境盐度升高出现显著的直线下降,而粗蛋白含量随环境盐度升高而直线升高;各盐度组的粗脂肪含量虽然没有明显差异,但其含量随盐度升高有一定的线性下降趋势;36盐度组的粗灰分含量比12、16、20和28盐度组的明显高,32盐度组的灰分含量比20和24盐度组的也明显高;所检测的肌肉干样16种氨基酸中,只有3种氨基酸的含量随盐度升高而升高,而其他13种氨基酸的含量随盐度升高明显降低,其中有10种氨基酸的含量在盐度12～24条件下的比盐度28～36条件下的明显高,而这些氨基酸含量在盐度12～24之间没有明显差异。各盐度组间氨基酸总量和鲜味氨基酸含量均没有明显差异;必需氨基酸和半必需氨基酸含量在盐度12～24条件下的均比盐度28～36条件下的明显高,而在12～24盐度组之间以及28～36盐度组之间均没有明显差异。必需氨基酸/氨基酸总量的比值和必需氨基酸/非必需氨基酸比值随盐度升高均明显线性降低;盐度12～24组的必需氨基酸指数(66.13～67.42)高于盐度28～36组的(62.56～64.46)。综上所述,盐度12～24环境下养殖的哈氏仿对虾肌肉营养价值相对较高,表现为低盐趋向,考虑到肌肉的水分含量和生长性能,哈氏仿对虾在养殖期间选择16～24盐度范围比较合适,同时也说明哈氏仿对虾适合大多数沿海地区环境的盐度条件。     

Influence de la température sur quelques activités enzymatiques chez Palaemon serratus

Variation in Esterase 2 C activities, involving the hydrolysis of 2-carboxylic esters, α-glucosidase acetyl-glucosaminidase and alkaline and acid phosphotases, in the hepatopancreas and the abdominal muscle of Palaemon serratus was examined by polyacrylamide gradient gel electrophoresis. Soluble proteins were measured in the hepatopancreas and the abdominal muscle, and trypsin and chymotrypsin activities in the hepatopancreas. The activities and the isoenzymatic variations in shrimps acclimated at 5 different temperatures (between 14 and 30°) were compared and the molecular weight of each isozyme evaluated. It was found that: (a) the concentrations of soluble proteins decrease in the hepatopancreas between 18 and 30°, but remain unchanged in the abdominal muscle; (b) esterase and phosphatase activities increase with temperature but in a more or less random manner, according to the isozyme under consideration; (c) glycosidase activities increase with temperature; and (d) trypsin activity varies in an inverse relation to chymotrypsin activity.     

Changes in free amino acids in the hemolymph of giant freshwater prawn Macrobrachium rosenbergii exposed to varying salinities: relationship to osmoregulatory ability

Changes in free amino acids (FAA) in the hemolymph of the giant freshwater prawn, Macrobrachium rosenbergii, were examined in individuals exposed to varying salinities for up to 1 week. In freshwater and under conditions of low salinity, total FAA concentrations were maintained between approximately 0.85 and 1 mM and did not exhibit changes in response to salinity exposure. Under high salinities, total FAA concentrations increased dramatically, reaching up to 2.1 mM depending on treatment. Examination of individual amino acid concentrations revealed that these increases were based on specific changes in glycine, arginine, alanine, proline and lysine. Among these, alanine showed the greatest increases, resulting in levels six-fold higher under high salinity than in freshwater and under low salinity. The other amino acid species showed increases of 2.5-fold compared to original values. These five FAAs in freshwater and under low salinity together occupied approximately 45% of total FAA contents and under high salinity comprised more than 70% of total FAA contents. These results suggest that specific hemolymph FAAs are involved in mediating response to salinity exposure in freshwater prawns.     

Physiological roles of free D- and L-alanine in the crayfish Procambarus clarkii with special reference to osmotic and anoxic stress responses

Under hyper-salinity stress from freshwater to 17 and 25 ppt seawater, red swamp crayfish Procambarus clarkii largely accumulated D- and L-alanine together with glycine, L-glutamine, and L-proline in both muscle and hepatopancreas. The increases of D- and L-alanine in muscle were the highest in all amino acids and reached 6.8- and 5.4-fold, respectively, from freshwater to 25 ppt seawater. These results indicate that both D- and L-alanine are the most potent osmolytes for intracellular isosmotic regulation in crayfish as well as other crustaceans thus far examined. Under anoxia stress below 0.1 mg/l dissolved oxygen for 12 h and subsequent recovery in normoxia for 12 h in freshwater, 17 and 25 ppt seawater, muscle ATP decreased dramatically in all salinity levels and almost depleted in seawater. Along with the decrease of muscle glycogen level, the significant increase of L-lactate was found in muscle, hepatopancreas, and hemolymph for each salinity level, suggesting the transport of L-lactate from muscle into hepatopancreas via hemolymph. Under anoxia, D- and L-alanine also largely increased in both muscle and hepatopancreas for each salinity level. The increase was much higher in seawater than in freshwater. Thus, both D- and L-alanine are possible to be anaerobic end products during prolonged anaerobiosis of this species.     

Variation in the free amino acid content of ovary, hepatopancreas and hemolymph of Penaeus schmitti during ovarian maturation (Crustacea, Decapoda, Penaeidae)

Quantitative and qualitative variations of free-amino-acids contents (FAA) of ovaries, hepatopancreas and haemolymph have been studied in the course of ovarian maturation in Penaeus schmitti. In the ovary, FAA content, expressed as microM/g ovary fresh weight, decreases from 56.2 to 23.6 microM between gonadosomatic index (GSI) 0.8 and GSI 7.1. There is an increase of hepatopancreas FAA content of 33.4% till GSI 4. Haemolymph FAA content increases from 0.32 to 1.76 microM/ml, with maximal values of 3.74 microM/ml when GSI are between 3 and 4. FAA content of ovaries, expressed as microM/g of animal, is 3.2 fold higher at the end of maturation, with a main increase in the first stages of ovogenesis. Maturation process has a quantitative effect on all FAA, but, on a qualitative point of view, it concerns mainly lysine, arginine and glycine. The main variations of AA composition (expressed as percentage of total FAA) are observed in haemolymph.     

Effects of photoperiod on gluconeogenic activity and total lipid concentration in organs of crabs, Neohelice granulata, challenged by salinity changes

Abstract. This study assessed the effects of long (LD) or short (SD) days on the conversion of [¹⁴C]-glycerol to [¹⁴C]-glucose and total lipid concentration in organs of the crab Neohelice granulata challenged by a change in external salinity. In the 20‰-acclimated crabs, no difference was found in the concentration of total lipids in the muscle, hepatopancreas, gills, or hemolymph between crabs acclimated to SD or LD. In SD crabs, the total lipid levels in the anterior and posterior gills did not decrease during an osmotic challenge. Only in the posterior gills did the total lipid levels decrease during acclimation to the 34‰ medium in LD animals. The total lipid concentration in the hemolymph decreased after 1 d of osmotic stress in SD, and increased in the hepatopancreas. In LD crabs, the lipid contents decreased gradually in muscle, and in the hepatopancreas on day 3 after transfer to 34‰ medium. In 20‰-acclimated crabs, the gluconeogenesis activity in both sets of gills was higher in LD than in SD animals. The gluconeogenesis capacity decreased in both sets of gills on the first day of osmotic challenge in SD, and in the posterior gills on the third day in LD crabs. These results suggest that in organs of N. granulata , photoperiod affects the metabolic adjustments to an osmotic challenge.     

Energy metabolism in eggs and larvae of the Senegal sole

Oxygen consumption in Solea senegalensis increased during the egg stage reaching values close to 4 nmol O₂ ind⁻¹ at hatching. After hatching, larval oxygen consumption continued to increase, reaching a maximum rate of 9.97⁻¹±87 nmol O₂ ind⁻¹ h⁻¹ 2 days after the opening of the mouth. Body nitrogen content decreased mainly after exhaustion of yolk reserves. Carbon content decreased during the whole endogenous feeding phase, although it decreased twice as quickly after yolk-sac absorption. The free amino acid (FAA) depletion rate was higher during egg development and the yolk-sac period. Complete yolk absorption coincided with the consumption of the 90% of initial FAA content in the eggs and the remaining FAA were consumed at a lower rate. Based on stoichiometrical calculations, FAA appears to be the most important energy substrate during the egg stage (86%) in the Senegal sole. During the period from hatching to the mouth opening, contributions of FAA and lipids as metabolic fuels were similar (41 and 47%, respectively). The decrease in larval protein content during starvation indicates that amino acids from body protein are used as energy substrates under food deprivation.     

Ontogeny of intracellular isosmotic regulation in the european lobster Homarus gammarus (L.).

Intracellular free amino acids were measured in the abdominal muscle of the three larval instars, postlarvae, and juveniles of the lobster Homarus gammarus, acclimated to seawater (35 per thousand) and to a dilute medium (22 per thousand), to study intracellular isosmotic regulation throughout the development of this species. Transfer to low salinity was followed by a highly significant drop of free amino acids level in all developmental stages. The main regulated amino acids were glycine, proline, and alanine. The level of regulation of total free amino acids changed at metamorphosis: the decrease in total free amino acids at low salinity was 46% in the three larval instars, but it was only 29% in postlarvae and 20% in juveniles. These results suggest that free amino acids, mainly glycine, proline, and alanine, are involved in intracellular isosmotic regulation in the lobster, with different levels of involvement in pre- and postmetamorphic stages. The ontogenetic changes in intracellular isosmotic regulation are discussed in relation to the changes in extracellular regulation (osmoregulation) in the lobster.     

Physiological mechanisms of buoyancy in eggs from brackish water cod

Newly fertilized eggs of brackish water (Gotland, Baltic Sea) and marine (Lofoten, Norway) cod were investigated with regard to specific gravity, wet and dry weight, water content, chorion weight, and content of protein, free amino acids (FAA), and ions. The eggs had neutral buoyancies equivalent to a salinity of 14^.3% (range 11^.5–16^.2%) in brackish water, and 33^.0% (range 31^.8–34^.5%) in the marine environment. A buoyancy model was developed and showed that this difference was mainly caused by differences in egg water content which was 96.6 ± 0^.47% and 92.7 ± 0.45% in the brackish and marine eggs, respectively. The higher water content of the brackish eggs resulted from increased water uptake during final oocyte maturation due to higher intracellular contents of FAA, Cl ^– and NH₄⁺. SDS polyacrylamide gel electrophoresis of eggs and oocytes, and measurements of egg protein content suggested that the FAA pool of both egg types originated from hydrolysis of specific yolk proteins. The main contributor seemed to be a protein with a molecular weight of 100 kDa.     

Effect of sudden salinity change on Penaeus latisulcatus Kishinouye osmoregulation, ionoregulation and condition in inland saline water and potassium-fortified inland saline water

Two trials were conducted to determine the effect of sudden decrease in salinity of raw and potassium-fortified inland saline water on western king prawn Penaeus latisulcatus osmoregulation, ionoregulation and condition. Prawns were subjected to salinity decrease over 1 h from 32 to 25 ppt in the first trial and from 27 to 20 ppt in the second trial in three water types: inland saline water with potassium fortified to 100% and 80% of the marine water concentration (IS100, IS80), and raw inland saline water (ISW). In the first trial condition and ingestion rate were monitored over 19 days following salinity change. In the second trial condition, haemolymph osmo- and iono-regulation were recorded over 48 h following salinity change. In the first trial, 100% mortality was observed in ISW by day 13, with final survival 94% in IS80 and 100% in IS100. Tail muscle moisture content increased significantly (P < 0.05) over time in both trials and in all water types, suggesting loss of energy reserves. In the second trial, serum osmolality, sodium concentration and osmoregulatory capacity decreased following salinity change, stabilising by 24 h in IS100 and IS80 but continuing to decrease till 48 h in ISW, suggesting partial breakdown of osmoregulatory function in the potassium-deficient medium. Prawns were stronger regulators of divalent than monovalent cations. These trials demonstrate that potassium-deficient inland saline water requires fortification with potassium to allow prawn survival and efficient osmoregulation.     

Tissue amino acid pool changes during the perinatal period of the rat

Total free amino acid content in foetal liver, kidney, skin and striated muscle increases sharply during pregnancy. After delivery, there is no significant change in tissue total amino acid pools. The essential free amino acid pool in striated muscle decreases after delivery. This decrease suggests a relationship with the increased protein content in striated muscle.     

高盐胁迫对凡纳滨对虾消化及免疫相关酶活力的影响

为探讨高盐对凡纳滨对虾(Litopenaeus vannamei)消化及免疫相关酶活力的影响,实验设置了30、40、50、60共4个盐度梯度。对虾体长(7.84±0.68)cm,养殖密度333尾/m~3,每个梯度设3个平行,实验周期30d。取血淋巴、肌肉、肝胰腺等组织,检测其超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、碱性磷酸酶(AKP)和酸性磷酸酶(ACP)及蛋白酶、脂肪酶、淀粉酶活力。结果表明,盐度显著影响凡纳滨对虾肝胰脏中胃蛋白酶、脂肪酶、淀粉酶的活力(P0.05);随着盐度增加,消化相关酶活力均不断下降,处理间差异显著(P0.05);盐度对凡纳滨对虾不同组织的免疫指标产生影响,表现为随着盐度升高,血淋巴中,AKP活力逐渐升高,ACP、CAT和SOD活力均表现为先升高后降低;肌肉中,AKP、ACP和SOD活力呈现先升高后降低的变化趋势;肝胰脏中,AKP活力呈现先降低后升高再降低的变化趋势,ACP活力高盐处理间差异不显著(P0.05),CAT活力先降低后升高,SOD活力盐度40后逐渐降低。实验结果初步说明,高盐显著影响凡纳滨对虾的消化及免疫相关酶活力,且盐度对不同组织中免疫酶活力影响存在一定的组织特异性,50以上的高盐胁迫对对虾消化和免疫相关酶活力的影响尤为显著。     

Final oocyte maturation in vivo and in vitro in marine fishes with pelagic eggs; yolk protein hydrolysis and free amino acid content

The role of free amino acids (FAA) in oocyte hydration during final maturation has been studied in plaice Pleuronectes platessa and lemon sole Microstomus kitt by in vivo and in vitro measurements. In vitro final maturation was initiated by the administration of human chorionic gonadotropin on large vitellogenic oocytes. The eggs produced in vitro had the same fraction of their total amino acid pool present in the free form as the in vivo hydrated eggs, regardless of whether FAA had been present in the incubation medium or not. The FAA pool in the mature egg was increased 10–15 times that of the oocyte, and the two FAA pool profiles differed strongly. The FAA profiles of the egg groups (intra- as well as interspecific) were almost identical except that the taurine content was lower in eggs in vitro . A major protein band of about 100 kDa was present on SDS electrophoretic gels of oocytes but missing on gels of hydrated eggs. This protein, presumably a lipovitellin, is the most likely origin of the egg FAA pool. We suggest that marine fishes with pelagic eggs share a common mechanism for oocyte hydration whereby partial hydrolysis of specific yolk proteins to FAA creates a major part of the osmotic potential needed for the water influx.