Murray D. Wiegand

Composition, accumulation and utilization of yolk lipids in teleost fish

Lipid reserves in teleost eggs are stored in lipoprotein yolk and, in some species, a discrete oil globule. Lipoprotein yolk lipids are primarily polar lipids, especially phosphatidylcholine and phosphatidylethanolamine (PE), and are rich in (n−3) polyunsaturated fatty acids, especially 22:6(n−3) (docosahexaenoic acid, DHA). Oil consists of neutral lipids and is rich in monounsaturated fatty acids (MUFA). Egg lipids are derived from dietary fatty acid, fatty acid mobilized from reserves and possibly fatty acid synthesized de novo. There is selective incorporation of essential fatty acids, particularly DHA, into yolk lipids and discrimination against incorporation of 22:1(n−11). Lipid is delivered to the oocyte by vitellogenin, which is rich in polar lipids, and likely also by other lipoproteins, especially very low density lipoprotein, which is rich in triacylglycerol (TAG). All classes of lipid may be used as fuel during embryonic and larval development and MUFA are preferred fatty acids for catabolism by embryos. Catabolism of oil globules is frequently delayed until latter stages of development. In some species, DHA derived from hydrolysis of phospholipid may be conserved by transfer to the neutral lipid. Recent work has expanded knowledge of the role of DHA in membrane structure, especially in neural tissue, and molecular species analysis has indicated that PE containing sn-1 oleic acid is a prime contributor to membrane fluidity. The results of this type of study provide an explanation for the selection pressures that influence yolk lipid composition. Future work ought to expand knowledge of specific roles of individual fatty acids in embryos along with knowledge of the ecological physiology of ovarian recrudescence, environmental influences on vitellogenin and yolk lipid composition, and the control of yolk lipid accumulation and utilization.

Maternal influences on population dynamics: evidence from an exploited freshwater fish

We used a field experiment, population modeling, and an analysis of 30 years of data from walleye (Sander vitreus; a freshwater fish) in Lake Erie to show that maternal influences on offspring survival can affect population dynamics. We first demonstrate experimentally that the survival of juvenile walleye increases with egg size (and, to a lesser degree, female energy reserves). Because egg size in this species tends to increase with maternal age, we then model these maternal influences on offspring survival as a function of maternal age to show that adult age structure can affect the maximum rate at which a population can produce new adults. Consistent with this hypothesis, we present empirical evidence that the maximum reproductive rate of an exploited population of walleye was approximately twice as high when older females were abundant as compared to when they were relatively scarce. Taken together, these results indicate that age- or size-based maternal influences on offspring survival can be an important mechanism driving population dynamics and that exploited populations could benefit from management strategies that protect, rather than target, reproductively valuable individuals.

Utilization of yolk fatty acids by goldfish embryos and larvae.

In each of two separate experiments, eggs from a single female goldfish were fertilized, incubated at 22°C and sampled regularly up to day 6 when the larvae could be expected to commence feeding. Hatching normally occurred on Day 4. Lipids were extracted from the eggs and larvae and the neutral lipid and neutral phospholipids were isolated on aminopropyl columns. Fatty acid analysis of the eggs revealed the typical situation in fish where the phospholipids were rich in polyunsaturated fatty acids (PUFA) and the neutral lipids were rich in monounsaturated fatty acids (MUFA). Assay of lipid masses revealed that little depletion of lipid occurred until after hatch and that the neutral phospholipids were the principal fraction consumed. Although the neutral lipid mass did not change substantially during development, its fatty acid profile did. The proportions of several PUFA in the neutral lipids, especially 22∶6(n−3), 20∶5(n−3) and 20∶4(n−6), increased substantially during development while proportions of MUFA and 18∶2(n−6) declined. This appears to be a mechanism by which the larva can retain essential fatty acid released on hydrolysis of phospholipid while deriving the benefits of catabolism of phospholipid as fuel, namely the provision of phosphate and choline for intermediary metabolism and for the synthesis of macromolecules and neurotransmitter.

Incorporation of yolk fatty acids into body lipids of goldfish (Carassius auratus L.) larvae raised at two different temperatures

In five separate experiments, eggs from a single female goldfish were fertilized at 20°C. They were incubated at 22°C for 6 hours, after which some of the eggs were transferred to 13°C. When a defined post-hatch developmental stage was reached, lipid extracts were prepared from larvae, both with yolk sacs intact and after removal of the yolk sac by dissection. Other larvae were sampled at yolk exhaustion. Gas chromatographic analysis of fatty acid profiles revealed that larvae incorporated 16:0, 18:0, 20:4 (n−6) and 22:6 (n−3) into their tissues in proportions higher than those present in the eggs from which they were derived. At 22°C, these trends were particularly apparent at yolk exhaustion. At 13°C, proportions of polyunsaturated fatty acids in the bodies of newly hatched larvae were higher than those in the 22°C larval bodies. Monounsaturated fatty acids were preferentially depleted during development, especially in larvae from high quality eggs. No dependence of egg quality, as assessed by larval viability at 22°C, on total egg lipid mass or fatty acid composition was found. Larvae from the lowest quality eggs showed a reduced preference for incorporation of (n−3) polyunsaturated fatty acids into their tissues.

Effects of maternally transferred organochlorine contaminants on early life survival in a freshwater fish

Laboratory research has shown that female fish can pass toxic organochlorines (OCs) from their bodies to their eggs, killing their offspring if sufficient quantities are transferred. We conducted a controlled incubation study using gametes from a wild, OC-contaminated walleye (Sander vitreus) population (Bay of Quinte, Lake Ontario, Canada) in order to assess among-female variation in offspring early life survival in relation to ova concentrations of planar OCs (polychlorinated dibenzo-p-dioxins and furans and planar polychlorinated biphenyls) and a suite of other maternal and ova characteristics. Equal volumes of ova from each female were fertilized, pooled, and incubated together as an experimental cohort. Relative survival of each females offspring was estimated as the proportion of surviving larvae (at approximately 5 d posthatch) that she contributed to the cohort as determined by microsatellite DNA parentage assignment. Total planar OC concentration (expressed as toxic equivalency of 2,3,7,8-tetrachlorodibenzo-p-dioxin) of ova was positively related to maternal age and size and to ova lipid content. However, early life survival did not decline with increasing ova planar OC concentrations. Similarly, we observed no significant relationships between early life survival and ova thiamine content, ova fatty acid composition, or maternal age or size. Early life survival was more strongly correlated with date of spawn collection, thyroid hormone status of the ova, and ovum size. Maternally transferred planar OCs do not appear to negatively influence female reproductive success in this walleye population.

Age-Dependent Survival, Reproduction and Photorepair Activity in Daphnia magna (Straus, 1820) After Exposure to Artificial Ultraviolet Radiation

Abstract We examined age-related vulnerability of Daphnia magna to UV-B (ultraviolet-B radiation, 280–320 nm), the age-related relationships between UV-B dosage and reproduction, and the effects of duration of PRR (photorecovery radiation) on survival and fecundity. Animals were exposed to 0, 6, 9 or 12 h UV-B (peak emission 312 nm) at 1, 2, 3 or 4 days of age and followed to 12 days. Survival decreased with increasing exposure to UV-B, but increased with age at exposure. Duration of UV-B, but not age at exposure, decreased offspring production. Survival increased with an increase in duration of PRR for animals of all ages; however, the effect was not age related. Three-day-old animals were exposed to 6 h of UV-B followed by 0–600 min of PRR. Survival was greatest in controls, lowest in the group that received no PRR and similar for all other groups. Most mortality occurred within the first 72 h postirradiation. Offspring production was highest in light controls, lowest in the UV-B–exposed group that received no PRR and not significantly different among other groups. This study demonstrates the need to consider age when examining the effects of UV-B on zooplankton and the need to monitor responses over a sufficient length of time.

Effects of rearing temperature on development and survival of embryonic and larval goldfish

Abstract The effects of rearing temperature on a number of survival and development parameters were examined in goldfish. Females were induced to ovulate between 4 and 33 days after warming from 12°C to 20°C. Eggs were fertilized in a Tris-saline medium and incubated in moist air until eyeing at which time they were immersed in water. The optimum temperature for rearing eggs and larvae was 22°C. At 27°C and 17°C, there was a higher incidence of abnormal larvae at hatching and reduced larval viability compared to 22°C in some, but not all, experiments. Eggs incubated at 12°C produced inviable larvae. High proportions of 12°C larvae were abnormal at hatching and fish raised at 12°C failed to feed.

The effect of chronic exposure to artificial UVB radiation on the survival and reproduction of Daphnia magna across two generations.

We examined the effects of daily (chronic) exposure to artificial UVB radiation on the survival and reproduction of Daphnia magna over two generations. Control and experimental animals in each generation (parental and F1) were exposed to 16 h of UVA radiation and photosynthetically active radiation daily. In addition, experimental animals were exposed to 6 h of UVB during the middle of the light period. Survival and reproduction were followed for 12 days for each individual. Survival and production of F1 were significantly lower in the UVB exposed parental generation Daphnia than in controls. F1 exposure to UVB significantly decreased F1 survival and reproduction. Reproduction was lowest in UVB exposed F1 animals whose parents were also exposed to UVB. Adverse effects of UVB on offspring production may be magnified in successive generations suggesting that short‐term experiments could underestimate the impact of increased UVB exposure on populations.

UVB radiation affects growth, reproduction and tissue structure of Daphnia magna across several temperatures.

We examined the effects of daily exposure to UVB on growth, reproduction and histological characteristics of Daphnia magna over two generations at 20, 22, 25 and 30°C. Animals were exposed to 16 h of UVA and photosynthetically active radiation daily. Treated animals received 6 h of UVB during the light phase. Parental (P) generation growth and reproduction was impaired by exposure to UVB at all temperatures, with the poorest production at 30°C. First brood size decreased with UVB exposure; it was lowest at 30°C. Although F1 length at birth increased with P generation age, F1 produced by UVB‐exposed mothers were smaller at all temperatures. The F1 generation was followed at 20 and 25°C; at both temperatures UVB exposure reduced F1 growth and reproduction. F1 growth and F2 production were lowest when both P and F1 generations were exposed to UVB. UVB exposure damaged ovarian and gut tissue at both 25 and 30°C; the consequences of this exposure were more severe at 30°C. The observed tissue damage may relate directly to the UVB‐induced impairment of growth and reproduction. This study provides new insights into the effects of UVB on an important component of the pelagic zooplankton.

Maternal influences on thiamine status of walleye Sander vitreus ova

Concentrations of the various forms of thiamine (vitamin B(1) ) were determined in walleye Sander vitreus ova from three central North American lakes. Total thiamine concentrations in ova from Lake Winnipeg S. vitreus were approximately three times greater (mean 12 nmol g(-1) ) than in those from Lakes Erie or Ontario. The percentage of thiamine in the active form (thiamine pyrophosphate, TPP) was highest in Lake Ontario ova (mean 88%) and lowest in those from Lake Winnipeg (mean 70%). Neither ova total thiamine concentration nor per cent ova thiamine as TPP showed any consistent relationships with maternal age, size, morphometric condition, somatic lipid concentrations or liver lipid concentrations. Ova total thiamine concentration, however, was negatively related to ovum size in some populations, as well as among populations, and was positively related to liver total thiamine concentration. Maternal transfer of thiamine to ova appears to be independent of female ontogenetic or conditional state in S. vitreus.