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Notes: Biochemical changes which occur during post-vitellogenic meiotic maturation of oocytes were investigated by measuring the concentrations of various phosphorus-containing fractions of the ovaries and mature eggs of four marine species with pelagic eggs, plaice, Pleuronecles platessa, cod, Gadus morhua, haddock, Melanogrammus aeglefinus, and whiting, Merlangius merlangus, and three freshwater species with demersal eggs, rainbow trout, Salmo gairdneri, pike, Esox lucius, and powan, Coregonus lavarelus. In the former group, protein phosphate was deposited at normal vertebrate levels in the ovaries during vitellogenesis but was exhausted during maturation, its decrease correlating with the uptake of water which rendered the mature egg buoyant in sea water. In plaice, phospholipid phosphate declined slightly during maturation, while inorganic phosphate increased by an amount slightly less than that which disappeared from the protein fraction. No such changes occurred on maturation in these three fractions in the freshwater species, in which little or no water uptake occurred. In plaice, the approximately five-fold increase in the water content of the oocyte was accompanied by a corresponding five-fold increase in the amount of potassium, the major inorganic cation of the oocyte. These pelagic eggs appear to be unique among the eggs of vertebrates in their high water content (c. 92%) and in the fact that the protein phosphate is almost entirely utilized before fertilization, while, in those freshwater fishes and other oviparous vertebrates that have been examined, the egg is of much lower water content (50–70%) and most of the protein phosphate, like the other major yolk constituents, is used during embryonic growth. This utilization at such an early stage in the life cycle constitutes an extreme example of heterochrony.

Notes: The only carotenoid detected in newly fertilized eggs of wild Atlantic salmon, Salmo salar, from western Scotland was astaxanthin at a concentration [μg carotenoid g−1 wet wt of eggs, mean ±S.D. (number of parental females)] of 6.2±1.2(7) in 1982, 6.4±1.8(20) in 1983, and 7.6 ± 13(6) in 1984. In eggs of farmed Atlantic salmon the only carotenoid detected was canthaxanthin at concentrations which varied significantly between farms depending on the level of synthetic canthaxanthin in the broodstock diet. Thus on two farms using feed with 50 μgg−1, the levels were 11.8 ± 3.4(7) and 12.3 ± 2.9(6), while on two farms using 75μgg−1 the levels were 18.7 ± 5.0(9) and 21.2 ± 2.7(21). The levels in eggs of one-seawinter fish (grilse) did not differ from those of two-seawinter fish reared on the same farm and diet. During development from newly fertilized egg to fry at the end of yolk-sac absorption, the quantity of carotenoid present per individual decreased, presumably as a result of metabolism. Despite large differences in quantity present, the quantity so metabolized was fairly constant at 2–4 μg carotenoid g−1 original egg weight for eggs from two-seawinter farmed and wild salmon, except that in eggs from farmed grilse it was 7 μg g−1. In fry from wild eggs, 99.14% of the remaining carotenoid was present in the integument (skin and fins) as astaxanthin, astaxanthin monoester and astaxanthin diester. In fry from farmed salmon eggs, 47 ± 8% of the carotenoid present was found in the unused yolk oil droplets and in the liver, and 37 ± 6% was found in the integument as canthaxanthin and an unidentified metabolite of canthaxanthin. These findings explain visible colour differences between fry from wild parents and fry from canthaxanthin-fed farmed parents, particularly in the fins, liver and residual oil droplets. The canthaxanthin metabolite was also found, together with canthaxanthin, in the skin of farmed adults fed canthaxanthin. Preliminary tests showed it to be unchanged by saponification but reduced by sodium borohydride. For eggs from the three farms incubated under the same conditions in the same season, percentage mortality both to the eyed stage and between hatching and first feeding varied significantly between farms, but percentage mortality between the eyed stage and hatching did not do so. Results combined from two seasons for eggs from three farms and one wild source showed that egg mortality between fertilization and the eyed stage was not significantly different between wild and farmed salmon, but mortality between the eyed stage and hatching, and between hatching and first feeding, were both significantly higher in farmed salmon than in wild salmon. Such differences could not be explained simply by the large differences in egg carotenoid content, but were almost certainly due to factors such as broodstock nutrition, broodstock management, and stripping and fertilization procedures.

Notes: A method is described by which the adult females of marine and freshwater teleosts can be distinguished by a biochemical test performed on a blood sample. The test depends on the measurement in the blood plasma of alkali-labile protein-linked phosphorus, a specific measure of yolk protein (vitellogenin). In vitellogenic females, values of 20–100 μg protein phosphorus ml plasma−1 are usually found, while in males, non-vitellogenic females and immature fish of both sexes the value is 〈7.5 and usually 〈5 μg ml−1. At the appropriate season, most females can be positively identified. Good results can be obtained 2–3 months before spawning, and in some species for an undefined period after spawning. The advantages of this method over immunological techniques for the determination of vitellogenin, such as radioimmunoassay and immunoelectrophoresis, are the wide range of vertebrate species to which it can be applied, and its low cost. Its disadvantages are its lower sensitivity and the larger volume of plasma (0.5 ml) which must be used.

Notes: Abstract An earlier study showed large changes in ovarian phosphoprotein, a characteristic component of vertebrate yolk, during post-vitellogenic meiotic maturation (ripening) of ovaries of teleosts with pelagic eggs. Here, the study of four phosphorus-containing ovarian fractions is extended to other teleost families with pelagic eggs and to species with demersal eggs. Fishes were caught in the sea and lakes of western Scotland between 1982 and 1984. In the codGadus morhua, spratSprattus sprattus, dragonetCallionymus lyra, Norway poutTrisopterus esmarkii, saithePollachius virens, lingMolva molva and flounderPlatichthys flesus, all of which spawn pelagic eggs, the massive water influx during ripening which renders the eggs buoyant was accompanied by large changes in yolk phosphoprotein which were apparent as decrease or disappearance of protein phosphorus as conventionally determined. During ripening of the demersal eggs of the herringClupea harengus, both the water uptake and the decrease in protein phosphorus were less pronounced. In the three-spined sticklebackGasterosteus aculeatus, sea sticklebackSpinachia spinachia, sand gobyPomatoschistus minutus and perchPerca fluviatilis, little or no changes in water content or protein phosphorus both usually increased in species with pronounced water uptake and decreased in species with little or no water uptake. Lipid phosphorus showed little change in all species examined except herring, in which it increased. It is concluded that the characteristic changes in phosphoprotein and other phosphorus-containing fractions are most pronounced in species with pelagic eggs exhibiting massive water uptake on ripening, but are found to a lesser extent in species with demersal eggs in which considerable water uptake accompanies ripening.