Drinking rate, uptake of bacteria and microalgae in turbot larvae

The drinking rate of turbot larvae increased from 14 to 120 nl larva^-1 h^-1 from day 2 to 11 after hatching, which gave a slightly increased specific drinking rate (calculated per biomass) from day 2 to 7 (0·8–1·9 nl μg carbon^-1 h^-1. The clearance rate of both algae and bacteria was 10–100 times higher than the drinking rate, which indicated that the larvae had an active uptake of both algae and bacteria. On day 2 and 4 after hatching highest clearance rate was observed for Tetraselmis sp. On day 6 about the same clearance rate was observed for bacteria, Isochrysis galbana and Tetraselmis sp. Until day 4 the turbot larvae had a higher ingestion rate of Tetraselmis sp. than of I. galbana , whereas on day 6 the rates were similar (28–41 ng carbon larvae^-1 h^-1). The assimilation efficiency was somewhat higher for I. galbana than for Tetraselmis sp., and on day 6 the assimilated algae constituted 1·5 and 0·9% of the larval biomass for I. galbana and Tetraselmis sp., respectively.     

Oxygen consumption in Oreochromis niloticus (L.) in relation to development, salinity, temperature and time of day

Oxygen consumption of Oreochromis niloticus at different stages of development was studied in relation to salinity, temperature and time of day, using a Warburg apparatus. The oxygen consumption of newly hatched (0–14 h) larvae was 3.40 μl O₂ larva⁻¹ h⁻¹, of older yolk sac larvae 10.09 μl O₂ larva⁻¹ h⁻¹, and of one-month-old fry 32.99 μl O₂ larva⁻¹ h⁻¹. The QO₂ values showed a decrease with development and growth, ranging from 21.2–26.0 μl O₂ mg⁻¹ h⁻¹ in newly hatched larvae to 2.97 μl mg⁻¹ h⁻¹ in one-month-old fry. Changes in oxygen consumption occurred with salinity, the highest being at 17%o. Active larvae (12-24 mm T.L.) showed a doubling of consumption with a 10° C rise in temperature, and their Q₁₀ factor increased from 2.25 to 3.43 with increasing size. Day-old yolk-sac larvae, late yolk-sac larvae (5 days old) and fry of 12 14 mm length all showed a depression in oxygen consumption at midnight followed by a dawn rise.     

Effects of development, temperature and salinity on metabolism in eggs and yolk-sac larvae of milkfish, Chanos chanos (Forsskål)

Oxygen uptake rates and yolk-inclusive dry weiGhts were measured during the egg and yolk-sac larval stages of milkfish, Chanos chanos (Forsskal). Oxygen uptake by eggs and yolk-sac larvae was measured to assess the effects of four salinities (20,25,30,35 ppt) at 28°C. The effects of three temperatures (23,28,33°C) on oxygen uptake by yolk-sac larvae were determined at a salinity of 35 ppt. Dry weights were measured throughout embryonic development at 28°C and the yolk-sac stage at 23.28 and 33°C.
Oxygen uptake rates of eggs increased more than fivefold during embryogenesis (0.07±0.03 to 0.40 ± 03 μl O₂ egg ⁻¹ h ⁻¹;blastula to prehatch stage). Larval oxygen uptake did not change with age but was affected by rearing temperature (0.33 ± 0.08, 0.44 ± 0.07 and 0.63 ± 0.13 μl O₂ larva ⁻¹ h⁻¹ at 23, 28 and 33°C, respectively; Q₁₀= 1.93). Acute temperature changes from 28 to 33°C caused significant increases in oxygen uptake by embryos (Q ₁₀= 1.69–3.58) and yolk-sac larvae (Q ₁₀=2.55). Salinity did not affect metabolic rates.
Dry weight of eggs incubated at 28°C decreased 13% from fertilization to hatching. Incubation temperatures from 23–33°C did not affect dry weights at hatching. Rearing temperatures significantly affected the rate of larval yolk absorption (Q ₁₀= 2.25).     

The ontogeny of drinking in the rainbow trout, Oncorhynchus mykiss (Walbaum)

Drinking was measured by the rate of uptake of tritiated dextran in fresh water by the alevins and fry of rainbow trout at various stages of development during a 40-day post-hatch period. Drinking increased almost S-fold during the initial 16 day yolk-sac stage. Drinking rate increased most between 16 and 23 days, the transitional period between yolk-sac absorption and first feeding. The maximum weight-specific drinkingrateof 3.24μlg⁻¹ h⁻¹ recorded for 40-day-old fry was higher than previously recorded for adults. Abrupt transfer from an adaptation temperature of 10 to 19° C increased drinking significantly (Q₁₀= 1.2), but sudden transfer to 1 1‰ salinity sea water caused a substantial fall in drinking rate in 23-day fry. A 24-h period of adaptation to 1 1‰ and 15‰ salinity restored drinking to a rate similar to that in fresh water. The water drunk by 31-day fry fed to satiation was initially higher than by unfed fry, but drinking rates subsequently fell below the control level. The results are discussed in terms of osmoregulation and the uptake of dissolved or suspended substances by the intestinal tract for the purpose of immunization.     

Energy partitioning in the Antarctic collembolan Cryptopygus antarcticus

Abstract. 1. Consumption, production and assimilation rates were determined for two age groups of Crypropygus antarcticus to give an estimate of energy utilization, and to investigate low temperature adaptation in its energy partitioning.
2. Feeding selectivity shown in laboratory preference tests was supported by gut analysis of field animals from contrasting sites. Although moulting rate was not significantly affected by food type, rates of growth were slowest and mortality highest when fed on a non-preferred substrate.
3. Both a radio labelling and a more direct method for measuring dry weight consumed gave similar results for Cvpropygus feeding on algae. The consuniption rate for animals when feeding on algae was lower than that on moss peat. The assimilation efficiency for immature animals feeding on algae was 46% and for mature animals was 19%; the values when feeding on moss peat were 7% and lo%, respectively, The net production efficiency ranged from 35%(inimatures) to 13% (matures) and was similar on both substrates.
4. Food consumption exceeded assimilation over the range 2.5–10°C, but the two converged from 2.5 to 0°C. Immature Cryptopygus maintained a net positive energy balance over 0–10°C, whilst below 1S°C respiration exceeded assimilation for mature individuals.
5. An estimate of the annual dry matter consumption (7 g m^-1 y^-1) by Ctypropygus in a moss turf at Signy Island agrees with one based on respiration data alone (Davis, 1981). The consumption at an alga-dominated site was c . 26 g m^-2 y^-l, and Crypropygus may have a locally limiting effect on net priniary production at such sites.     

Estimates of larval survival of cod by releases of genetically marked yolk-sac larvae

In the spring of 1995, 18 million genetically marked yolk-sac cod larvae Gadus morhua were released into a 2.9-km², nearly land-locked fjord in western Norway. Four quantitative surveys were conducted, 11, 33, and 63 days, and 1 year after the first release. Almost 100% of the collected cod larvae were successfully identified to GPI-1 * genotype. The marked cod larvae constituted 18% of all sampled cod larvae in the first survey and 9% in the two next. The average rate of mortality was estimated to be 23% day ⁻¹ for the first 10 days after release and 12% day ⁻¹ during the next month after release. After 1 year (April 1996), the number genetically marked I-group cod in the fjord was estimated to be <120. The effect of the historical programme of large-scale releases of yolk-sac larvae on recruitment were evaluated and found to be small.     

Oxygen consumption by eggs and larvae of striped mullet, Mugil cephalus, in relation to development, salinity and temperature

Oxygen consumption rates during embryonic and the first 38 days of larval development of the striped mullet were measured at 24° C by differential respirometry. Measurements were obtained at the blastula, gastrula and four embryonic stages, and at the yolk-sac, preflexion, flexion and post-flexion larval stages.
Oxygen uptake rates of eggs increased linearly from 0.024 μl O₂ per egg h^-1 (0·323 μl O₂ mg^-1 dry wt h^-1) by blastulae to 0·177 μlO₂ per egg h^-1 (2·516 μlO₂mg ¹dry wth^-1) by embryos prior to hatching. Respiration rates did not vary significantly among four salinities (20,25, 30, 35%₀).
Larval oxygen consumption increased in a curvilinear manner from 0·243 μl O₂ per larva h^-1 shortly after hatching to 18·880 μl O₂ per larva h^-1 on day 38. Oxygen consumption varied in direct proportion to dry weight. Mass-specific oxygen consumption rates of preflexion, flexion, and postflexion larvae did not change with age (10·838 μl O₂ mg ¹dry wt h^-1).
Larval oxygen consumption rates did not vary significantly among salinities 10–35%. Acute temperature increases elicited significant increases in oxygen consumption, these being relatively greater in yolk-sac larvae ( Q₁₀ = 2·75) than in postflexion larvae ( Q₁₀ = 1·40).     

Oxygen requirements of embryos and larvae of the largemouth bass, Micropterus salmoides (Lacépède)

Starting with the second day after fertilization, largemouth bass embryos and larvae became increasingly sensitive to oxygen deficiency until the sixth day of life. On this day few survived exposure to 1 mg O₂/l for 3 h at 20°C; many were damaged at 2 mg/1, but not at 2.5. Death was by asphyxiation or by starvation resulting from an apparent inability to close the lower jaw. On the seventh day the larvae became more resistant again, possibly because opercular movement began on that day. At 25°C the effects of reduced oxygen concentration were intensified, and even a concentration of 2.5 mg/1 became lethal in 3 h. At 3 mg O₂/l and 20° the normally quiescent yolk-sac larvae became very active and swam vertically to at least 5 or 6 cm above the substrate; 4 and 5 mg/1 had this effect at 23–24°. This behaviour could result in losses by predation and displacement from the nest.     

Radioactive strontium (85Sr) in marking whitefish [Coregonus lavaretus (L.)] larvae and the dispersal of larvae from river to sea

Anadromous whitefish [ Coregonus lavaretus (L.)] yolk-sac larvae were marked with a radioactive strontium isotope, ⁸⁵Sr. Before marking the method was tested in accumulation-elimination tests using various strontium concentrations. The first-phase effective half-life of ⁸⁵Sr in yolk-sac larvae was 4 days. The mean ⁸⁵Sr radioactivity was 81 Bq per larva at the day of release and the half-life of the slow component was 51 days, so the strontium label was easily detected up to 60 days after marking. The larvae were released into the River Simojoki about 12 km upstream from the river mouth and recaptured from early May to the end of July. Marked larvae were found at the river mouth 12–13 days after release, while the last marked fish in the river were found at 16 days. It is likely that all leave the river within 2 to 3 weeks post-hatching. Two months after marking some larvae had attained a distance of 10 km from the river mouth.     

Diel abundance, migration and feeding of fish larvae (Eleotridae) in a floodplain billabong

Eleotrid larvae (2.1–16 mm) were collected from surface waters of a billabong in south-eastern Australia. Estimates of larval density in plankton net samples at night averaged 148.3 larvae per m³ and 16.6 larvae per m³ during the day. In contrast, pump samples provided density estimates of 8.3 larvae per m³ at night and 0.9 larvae per m³ during the day. Larval densities did not differ between open water, snag (fallen tree) and Typha habitats, but Typha habitats yielded larger larvae than other habitats. 32.9% of larvae in pump samples were damaged and unmeasurable, creating a bias favouring larger larvae. The modal length of larvae in net samples at night was 5–6 mm, compared with 3–4 mm during the day, reflecting both greater net avoidance by larger larvae during the daytime and dispersal of smaller larvae from the surface at night. Dispersion patterns of larvae suggest that classes of larvae smaller than, and larger than 5.0 mm exhibit reciprocal diel vertical migration behaviour linked to ontogenetic changes in diet. Larvae less than 5 mm fed only during the day and preyed exclusively on rotifers, whereas larger larvae continued to feed at night and consumed mostly planktonic crustaceans.     

Early development of milkfish: effects of salinity on embryonic and larval metabolism, yolk absorption and growth

During embryogenesis of Chanos chanos , more than half of the yolk was consumed and the majority of it was converted into larval tissue. Salinity affected both yolk absorption and embryonic and larval growth. Larvae hatched in 20% had larger yolk reserves but were smaller and grew more slowly than larvae in 35 and 50%. Larvae hatched in 35 and 50% had equal amounts of yolk but those from 35% were larger. Oxygen consumption rates increased during development (from 0.06 ± 0.01 μl O₂ egg^–1 h^–1 by blastulae to 0.37 ± 0-01 μl O₂ egg^–1 h^–1 by prehatch embryos and 0–43 ± 0–03 μl O₂ larva ^–1 h ^–1 by newly-hatched larvae) and were significantly affected by salinity. Eggs and yolk-sac larvae incubated in 35% consumed more oxygen than those in the low and high salinities. Salinity affected both the rate and pattern of yolk utilization but salinity-related differences in metabolism, yolk absorption, and growth were not related directly to the osmotic gradient. Low salinity retarded yolk absorption while high salinity reduced yolk utilization efficiencies. Differences in oxygen consumption rates were probably related to variations in the relative amounts of metabolically active embryonic and larval tissue and/or higher activity levels rather than differential osmoregulatory costs. 35% is probably the most suitable salinity for incubation and larval rearing of milkfish.     

The energy balance of the Australian brine shrimp, Parartemia zietziana (Crustacea : Anostraca)

SUMMARY. Assimilation budgets (i.e. assimilation = respiration + excretion + production) are presented for cohorts of P. zietziana in two salt lakes. Shrimps in Pink Lake had an assimilation rate of 1631.6 kJ m⁻² year ⁻¹, those in Lake Cundare 212.1 kJ m⁻² year⁻¹. In both lakes, respiration accounted for 60–80% of assimilation. Assimilation rates for individuals (derived as assimilation = ingestion minus faecal output) are also given and compared with respiratory rates of individuals. The comparisons indicated that energy was often consumed at a higher rate by respiration than it could be supplied by assimilation. Starvation due to a low assimilation efficiency was suggested as a cause of the consistent mortality, variable growth rate of individuals and unpredictable recruitment which were characteristic of the cohorts of P. zietziana in both lakes. An analysis of mortality showed that the young had the poorest survival, as predicted by a theoretical model of a starving zooplankter and a comparison of the increase with weight of ingestion and respiration. Gross growth efficiency (production: assimilation) was 15–30%, about the same as published data on Anostracans. Net growth efficiency (production : consumption) was 5–12% and generally lower than published values reflecting the difficulty P. zietziana has in balancing its budget.     

Larval competition for food between wild and hatchery-reared ayu, Plecoglossm altivelis Temminck et Schlegel, in culture ponds

To examine the larval competition between wild and hatchery ayu in the culture ponds, mixed rearing of 580 000 wild and 520 000 hatchery larvae was carried out in two 25-m³ ponds for 3 months, in contrast to the control in which 860 000 wild larvae were reared in another pond.
The number of wild larvae in the mixed-rearing treatments decreased rapidly 20 days after the start of mixed rearing, in contrast to hatchery larvae. Mortality of wild larvae was almost 100% at the end of the experiment (3 months), while the hatchery larvae showed the usual survival rate of 15–16%. In the control pond, however, 16% of the wild larvae survived. The wild larvae grew much slower (0.10mmday ^-1) than the hatchery larvae (0·26 mm day ^-1) in the mixed-rearing ponds, whereas the wild larvae in the control pond showed almost the same growth rate (0·24 mm day ^-1) as hatchery larvae. On day 6 the gut fullness of wild larvae was only 30% of that of the hatchery larvae in the mixed-rearing experiments. On day 46 the wild larvae occurred deeper in the mixed-rearing ponds than the hatchery larvae. This depth difference in vertical distribution appeared to cause a disadvantage for the wild larvae in the competition with hatchery larvae, since the food was supplied at the surface. Thus, the wild larvae starved and died.     

Population dynamics and feeding of mayfly larvae in some acid and alkaline New Zealand streams

SUMMARY. 1. Population dynamics (density, biomass, annual production), gut contents and feeding rates of mayflies ( Deleatidium spp.; Leptophlebiidae) were compared in two naturally acid (mean pH≃4.8). brownwater streams and two alkaline (mean pH 7.5), clearwater streams in South Westland, New Zealand.
2. Mean densities of larvae (range 234–2318 m⁻²) were higher in alkaline streams on most of the six bimonthly sampling dates. Mean biomass (range 0.020–0.376 g larval dry weight (LDW) m⁻²) was always highest at the stable, spring-fed, alkaline site and was lower at the acid sites and another alkaline site where the population was always dominated by small larvae.
3. Annual production was high at the more stable, alkaline site (10.35 gLDW m⁻²) but much lower at the other sites (2.49–3.77 g m⁻²).
4. Gut contents of larvae were dominated by fine (45–75 μm widest diameter) paniculate matter (69–99%), diatoms (up to 21%) and. at one site, filamentous algae (8–13%).
5. Grazing rates of mayflies on epilithon were significantly higher on stones taken from acid than alkaline streams and material grazed from the former contained a higher proportion of inorganic material (87–93% and 61–83% inorganics, respectively).
6. Higher grazing rates may reflect lower quality of epilithic food in acid, brownwater streams, a factor that could contribute to the lower productivity of Deleatidium populations at these sites.     

Population growth rates of two closely related rotifer species: effects of food quantity, particle size, and nutritional quality

SUMMARY. 1. The relationship between population growth rates and the concentrations of several algal species was determined in laboratory experiments with the rotifers Brachionus rubens and B. calyciflorus .
2. The effects of food quantity were well described by a modified Monod model with a threshold for zero population growth. The model parameters depended on particle size and nutritional quality of the food algae. Differences between the rotifer species were significant and reflected their varying food-size preferences.
3. For each rotifer species, thresholds were lowest for algae in the most readily ingested size range. The lowest thresholds were 0.07–0.09 mgC 1⁻¹ with algae of about 5 μm equivalent spherical diameter (ESD) for B. rubens , and 0.19 mgC 1⁻¹ with algae of about 10 μm ESD for B. calyciflorus .
4. Maximal growth rates ( r _max) were slightly below 0.8 day⁻¹ for both rotifers with most algal species. The highest r _max values for both rotifers were observed when Cyclotella meneghiniana was provided as food. With this alga, B. calyciflorus had a significantly higher r_max (1.02 day⁻¹) than B. rubens (0.838 day⁻¹).
5. From a comparison of the relationship between growth rates and ingestion rates, Chlamydomonas reinhardii appeared to be of low nutritional quality for B. rubens .
6. Egg ratios were related to growth rate and were not influenced by the algal food used. Egg development times and average mortality rates were estimated from the relationship between egg ratio and growth rate. B. calyciflorus appeared to have a high average mortality rate (0.383 day⁻¹) compared to B. rubens (0.083 day⁻¹).     

Episodic exposure to acid and aluminium in soft water: survival and recovery of brown trout,Salmo trutta L.

Yolk-sac fry, swim-up fry and 1–2 yr juveniles of brown trout, Sulmo trutta L., were exposed to episodes of aluminium and low pH, maximum aluminium concentration 12 μmol l⁻¹ (323 μg l⁻¹), minimum pH 4.5, total duration up to 54 h (yolk-sac fry) or up to 78 h (swim-up fry and juveniles), in an artificial soft water medium, [Ca] 20 μmol l⁻¹ (0–8 mg l⁻¹) (nominal baseline: pH 5.6, zero aluminium concentration). Yolk-sac fry mortality was nil or very low. A marked increase in susceptibility, with high mortalities, occurred when the yolk was fully absorbed. Mortality of juveniles exposed to two successive episodes was lower than would have been expected on the basis of comparisons with mortalities in single episodes, and mortality declined as the interval between the two episodes was increased. Disturbance of sodium, potassium or calcium balance or gill damage in surviving yolk-sac fry or juveniles was still evident 5 to 6 days after the end of a single episode.     

Influence of dissolved humic materials on carbon assimilation and alkaline phosphatase activity in natural algal-bacterial assemblages

SUMMARY. Mixed natural assemblages of algae and bacteria exhibited lower rates of ¹⁴C assimilation and high rates of dissimilation of recent photosynthate when amended with low concentrations (7.2 mg 1^-1) of unfractioned dissolved humic materials (DHM). The extent of the inhibition or stimulation was greatest in the smaller (1–5 μm) assemblage particles. In different algal-bacterial assemblages, additions of DHM markedly enhanced community alkaline phosphatase activity (APA), particularly under low light regimes, DHM of low apparent molecular weight was much more stimulatory to both ¹⁴C assimilation and APA than DHM of high apparent molecular weight, supporting the belief that DHM molecular weight is an important determinant of DHM interactive capacity. Higher concentrations of D HM (either unfractionated, or molecular weight fractionated) produced greater APA responses. Addition of phosphate enhanced the disparity in rates of ¹⁴C assimilation of samples incubated under low and high light regimes, increased the rates of ¹⁴C assimilation, and depressed APA. There were indications of interactions between DHM and phosphorus in several experiments. Two hypotheses were invoked to explain increases in APA in response to DHM: (1) increased competition between algae and bacteria for phosphate following bacterial release from substrate limitation, or (2) DHM may have acted as a sequestering agent for organophosphorus compounds, and in so doing, gradually depleted available phosphate. In either case, it is clear that DHM alters phosphorus cycling. This DHM characteristic may be ecologically as important as its ability to complex trace metals.     

Growth response of pikeperch larvae in relation to body size and zooplankton abundance

The most critical period at onset of feeding in pikeperch Stizostedion lucioperca is short (<5 days at 20° C). The larvae are sensitive to prey density during the first week of exogenous feeding. First-feeding larvae of 6.5 mm total length ( L_T ) needed prey densities of >585 prey l⁻¹ to maintain mass (C_maint), whereas 5 days older larvae of 7 mm L _T C_maint= 55 prey l⁻¹ and for 11 mm L _T larvae C_maint<10 prey 1⁻¹. Changes in specific growth rates for larvae of 7 and 11 mm were similar to a type-II functional response curve reaching a specific growth rate of 26 and 30% day⁻¹, respectively, at 1000 prey l⁻¹, whereas the 6·5 mm larvae showed a linear growth response reaching a specific growth rate of only 9% day ⁻¹ at 1000 prey l⁻¹. The results suggest that prey density is a limiting factor, which might contribute to the high variation between year-class Strengths.     

A limnological investigation of the tarn Syslaktjønn, W Norway

An investigation covering hydrography, chemistry, vascular and cryptogamic plants, nitrogen fixation, phytoplankton biomass and production, and zooplankton was carried out from April to November 1976 in tarn in W Norway, The volume of the tarn was 18000 m³ and the turnover time about 30 d. Temperature ranged between 3.6 and 23.4°C and pH between 4.8 and 5.5. Nuphar luteum and Carex rostrata were the two dominating vasculars-with biomasses of 117 and 97 g m⁻², respectively The biomass of the bryophytes ( Sphagnum spp.) was about 510 g m⁻² and the production of the order 0.2–2.1 μg (mg d.w.)⁻¹h⁻¹. Nitrogen fixation in association with Sphagnum spp. was estimated at 25 g yr⁻¹ for the whole tarn. Phytoplankton was dominated by diatoms, green algae and chrysophyceans. The chlorophyll a content ranged from 2 to 20 mg m⁻³ and the carbon assimilation rates from 0.03 to 20 mg C m⁻³h⁻¹ at 0–4 m depths. Production in the period was of the magnitude 22 g C m⁻². The copepod Eudiaptomus gracilis was the most common netzooplankter. Large numbers of rotationrians were found during summer.