Growth, oxygen consumption, and protein and RNA synthesis rates in the yolk sac larvae of the African catfish (Clarias gariepinus)

The effect of spatial position and age within an egg-clutch on embryonic development and key metabolic enzymes in two clownfish species, Amphiprion ocellaris and Amphiprion frenatus

Since the size of newly hatched larval fish is directly related to egg size, small differences in initial egg size can be critical to survival and further development of offspring. Underlying processes causing size variation in fish offspring are still not entirely understood. In this study we investigated whether the spatial position of an individual egg within a clutch affects size variation in two benthic spawning coral reef fishes, the clownfishes Amphiprion ocellaris and A. frenatus. To evaluate the effects of within-clutch position on embryonic development, egg growth metrics and protein content were analysed on day 2, 5 and 8 after deposition (adp). Additionally the activities of the key metabolic enzymes citrate synthase (CS) and lactate dehydrogenase (LDH) were investigated to evaluate the physiological status of the embryos. Central eggs of A. frenatus were significantly longer and heavier than peripheral eggs only on day 2 and 5 adp (2.07 mg, 2.59 mm vs. 1.84 mg, 2.49 mm). No significant differences were observed in A. ocellaris between eggs originating from a central or peripheral (5 mm from edge) position (1.33 mg, 2.26 mm vs. 1.15 mg, 2,18 mm). Diameter of the eyes did not differ between the two fish species nor between different positions, for any age group. The protein content of eggs (7.5% of wet weight) was independent of age, position and species. Enzymatic activity increased from 2 adp until peak activity was observed for both enzymes on day 8 adp, independent from position. The range of CS- and LDH-activity was 0.3–13.0 and 0.2–71.7 U g^-1 wet weight, respectively. Significant differences in enzymatic activity were observed between age groups in both species, which in connection with significantly larger eggs of A. frenatus at day 2 and 5 adp could hint at a better O₂ supply of central eggs. Potential implications for captive breeding are given.

Post-prandial changes in protein synthesis in red drum (Sciaenops ocellatus) larvae

Protein synthesis is one of the major energy-consuming processes in all living organisms. Post-prandial changes in protein synthesis have been studied in a range of animal taxa but have been little studied in fish larvae. Using the flooding-dose method, we measured post-prandial changes in whole-body rates of protein synthesis in regularly fed red drum Sciaenops ocellatus (Linnaeus) larvae for 24-28 h following their daily meal. Fractional rates of protein synthesis increased from a baseline (pre-feeding) rate of 16% day(-1) to a post-prandial peak of 48% day(-1) ca. 8 h after feeding before declining to 12% day(-1) after 24-28 h. The overall mean daily rate of protein synthesis was calculated as 27% day(-1). Although suggested as energetically impossible in larval poikilotherms, our results show that rates in excess of 30% day(-1) can be attained by larval fishes for a few hours but are not sustained. The average daily energetic cost of protein synthesis was estimated as 34% of daily total oxygen consumption, ranging from 19% immediately before feeding to 61% during the post-prandial peak in protein synthesis. This suggests that during the post-prandial peak, protein synthesis will require a large proportion of the hourly energy production, which, given the limited metabolic scope in fish larvae, may limit the energy that could otherwise be allocated to other energy-costly functions, such as foraging and escape responses.

The energetics of embryonic growth

Embryos typically operate under much tighter energy constraints than older animals. This has had a profound impact on how energy is stored, mobilized and partitioned. The result is sometimes quite different ways of doing things. Growth, in particular, is a much more important activity during development. Compared with adults, specific growth rates (g) are extremely high (≥150%day(-1) for some fish). Production efficiencies are also much higher, particularly for early stages where values of 80-90% are not uncommon. Higher production efficiencies are possible, in part, because of lower unit costs at high g. Unlike in adults, the unit cost of growth does not appear to be fixed during early life. Energy also tends to be partitioned in a different manner, with compensatory partitioning being much more important during early life. Other differences include much higher routine metabolic intensities, smaller aerobic scopes and approximately isometric scaling of routine metabolism. The implications for ontogenetic growth models are discussed.

Growth and protein metabolism in red drum (Sciaenops ocellatus) larvae exposed to environmental levels of atrazine and malathion

Contaminant exposure can affect development, growth, and behaviour of fish larvae, but its effect on rates of protein synthesis and protein degradation are not known. The aim of the present study was to examine the effects of a single pulsed dose aqueous exposure to environmentally realistic levels of two contaminants, atrazine (0, 40 and 80 microgl(-1)) and malathion (0, 1 and 10 microgl(-1)), on growth and protein synthesis in red drum (Sciaenops ocellatus) larvae. Growth was assessed in terms of increase in length, weight, and protein content over an 8-day period following exposure. Rates of protein synthesis were measured by the flooding dose technique 2, 4, and 8 days after initial exposure to each contaminant by bathing larvae in seawater containing L-[2,6-(3)H] phenylalanine. Exposure to atrazine had no effect on larval growth in length, but caused marginally significant declines in growth in weight (P=0.05) and protein content (P=0.06). However, protein synthesis rates were significantly higher for atrazine-exposed larvae on days 4 (P=0.04) and 8 (P=0.01), suggesting an increase in rates of protein degradation. On day 8, the efficiency with which synthesised proteins contributed to growth was significantly lower (P=0.04) in atrazine-exposed larvae. In contrast, malathion had no significant effects on growth in length or protein content, but there were significant decreases in growth in weight over 8 days. The only other significant effect of malathion was an increase in protein synthesis on day 2 for treated larvae relative to controls. Previous work [Alvarez, M.C., Fuiman, L.A., 2005. Environmental levels of atrazine and its degradation products impair survival skills and growth of red drum larvae. Aquat. Toxicol. 74, 229-241] reported hyperactivity and increased metabolic rate in larval red drum exposed to atrazine, indicating a clear energetic cost. Our results further emphasise the energetic cost of atrazine exposure through elevated rates of protein synthesis and degradation resulting in reduced protein retention efficiency and lower growth rates. Overall, we conclude that exposure to atrazine from surface water run-off can increase the energy requirements and the larval phase duration in red drum larvae, possibly resulting in reduced survival and recruitment in cohorts exposed to atrazine.

Cost of protein synthesis and energy allocation during development of antarctic sea urchin embryos and larvae

Cold environments represent a substantial volume of the biosphere. To study developmental physiology in subzero seawater temperatures typically found in the Southern Ocean, rates and costs of protein synthesis were measured in embryos and larvae of Sterechinus neumayeri, the Antarctic sea urchin. Our analysis of the "cost of living" in extreme cold for this species shows (1) that cost of protein synthesis is strikingly low during development, at 0.41 +/- 0.05 J (mg protein synthesized)(-1) (n = 16); (2) that synthesis cost is fixed and independent of synthesis rate; and (3) that a low synthesis cost permits high rates of protein turnover at -1 degrees C, at rates comparable to those of temperate species of sea urchin embryos developing at 15 degrees C. With a low synthesis cost, even at the highest synthesis rates measured (gastrulae), the proportion of total metabolism accounted for by protein synthesis in the Antarctic sea urchin was 54%-a value similar to that of temperate sea urchin embryos. In the Antarctic sea urchin, up to 87% of metabolic rate can be accounted for by the combined energy costs of protein synthesis and the sodium pump. We conclude that, in Antarctic sea urchin embryos, high rates of protein synthesis can be supported in extreme-cold environments while still maintaining low rates of respiration.