Effect of prey stage on life-table attributes of a genetically manipulated strain ofMetaseiulus occidentalis (Acari: Phytoseiidae)

Metaseiulus occidentalis females from the carbaryl-organophosphate-sulfur resistant strain (COS) lived longer (25.3 days versus 19.7 days), had a higher total fecundity (43.8 eggs female^–1 versus 33.6 eggs female^–1) and a higher daily fecundity rate (2.4 eggs female^–1 day^–1 versus 2.0 eggs female^–1 day^–1), and exhibited a higher intrinsic rate of increase (0.243 individuals female^–1 day^–1 versus 0.182 individuals female^–1 day^–1) and shorter generation time (13.9 days versus 17.0 days), at 24–28°C, 47–56%rh under continuous fluorescent light, when reared on a diet of 0–48-h-old eggs rather than a diet of mixed actives ofTetranychus pacificus McGregor on bean leaf disks. The sexratio of the progeny was female-biased for both diets, 2.1 females to 1 male forM. occidentalis reared on eggs and 2.0:1 : forM. occidentalis reared on mixed actives, suggesting that diet influences sex-ratio in some unknown way.There was no significant difference in oviposition rates for repeatedly-mated and once-matedM. occidentalis females reared on a diet of younger (0–24-h old) eggs compared to a diet of older (72–96-h old) eggs ofT. pacificus.The COS strain ofM. occidentalis exhibited life-table parameters comparable to the other strains reported in the literature, suggesting that the reproductive attributes of this acarine predator were not reduced as a result of artificial laboratory selection. Diet, a biotic factor, produced substantial differences in life-table parameters, suggesting that this factor can influence conclusions regarding the potential efficacy of biological control agents.     

Summer egg production rates of paracalanid copepods in subtropical waters adjacent to Australia's North West Cape

The biological oceanography of waters adjacent to Australia's North West Cape (21° 49 S, 114° 14 E) was studied during the austral summers of 1997/98 and 1998/99. We measured egg production rate (EPR) by the small paracalanid copepods that dominated the calanoid community. Bottle incubation experiments were conducted at a shallow (20 m) station in the mouth of Exmouth Gulf, and at a shelf-break station (80 m). In 1997/98, we measured EPR by Paracalanus aculeatus, P. indicus, Acrocalanus gracilis and Bestiolina similis, but in 1998/99, we concentrated on P. indicus. Maximal observed EPRs by Paracalanus and Acrocalanus species were 30 eggs female^–1 d^–1, but B. similis attained only 17 eggs female^–1 d^–1. Sporadic measurements of EPR by P. aculeatus minor (maximum 4 eggs female^–1 d^–1) and Parvocalanus crassirostris ( 9 eggs female^–1 d^–1) were also made. However, maximal EPRs were seldom achieved and were often less than 10 eggs female^–1 d^–1. There was no difference between EPR of either P. indicus or B. similis in 1997/98 and 1998/99, despite differences in temperature. Trophic resources severely limit copepod egg production in this area. We suggest that variability and skewness of egg production data derived from individual incubations may be used to judge the degree of food limitation of the population and the variability in feeding success between individuals. The dominance of small copepods and the invariance in their EPR suggest that pulses in physical forcing and subsequent primary production will be severely damped by trophodynamic processes before reaching larval fish.     

Daily egg production rate of the planktonic calanoid copepod Acartia lilljeborgi Giesbrecht in the Cananéia Lagoon estuarine system,São Paulo,Brazil

Seasonal variation in daily egg production rate of the planktonic calanoid copepod Acartia lilljeborgi Giesbrecht in relation to temperature, salinity and chlorophyll a concentration was studied in the Cananéia Lagoon estuarine system, from March 1995 to January 1996. Recently captured A. lilljeborgi adult females were individually incubated in bottles filled with surface water screened through a 40-m mesh, containing a natural assemblage of phytoplankton in the laboratory, at temperatures corresponding to ambient. Daily egg production rate ranged from 13.8±3.5 to 66.8± 15.1 eggs female^–1 d^–1 (mean ± 95% CL). The mean and maximum rates of daily egg production increased with temperature from 19.5 to 25.2 °C but then decreased with further increase in temperature at 28.4 through 29.1 °C, attaining the highest rates at approximately annual mean ambient water temperature (ca. 24–25 °C). The egg production rates increased linearly with chlorophyll a <40 m fraction. Hatching success varied from 68.6 to 91.9%. Cannibalism varied from 1.4±0.7 to 7.1±3.3 nauplii female^–1 d^–1 (mean ± 95% CL). These results suggest that water temperature and phytoplankton concentration are important factors affecting the egg production rate of A. lilljeborgi in the Cananéia Lagoon estuarine.     

Winter distribution and overwintering strategies of the Antarctic copepod species Calanoides acutus,Rhincalanus gigas and Calanus propinquus (Crustacea,Calanoida) in the Weddell Sea

During the Winter Weddell Gyre Study in September–October 1989, the horizontal and vertical distribution, stage composition and feeding condition of the three antarctic copepod species Calanoides acutus, Rhincalanus gigas and Calanus propinquus were studied. The data indicate that C. acutus and R. gigas have the bases of their distributional ranges (sensu Makarov et al. 1982) in the Antarctic Circumpolar Current (ACC) and in the Warm Deep Water (WDW) entering the Weddell Gyre (WG). C. propinquus lived mainly in the cold WG south of the ACC. C. acutus overwintered mainly in the WG as stage IV copepodites (C). The species mainly inhabited the layers below the T_max stratum and down to 2000 m, but C V and females occurred slightly higher than C III and IV. Males prevailed over females and were confined to a rather narrow layer between 500 and 1000 m. Feeding experiments suggested all deep-living stages to be resting. However, if this species spawns in late autumn the younger C I–II can stay in the Winter Water (WW). R. gigas inhabited mainly the T_max stratum. In the eastern part of the WG, R. gigas breed in the WDW in autumn and hibernate as C I–III and C V–VI in the first and second winter, respectively. In the ACC zone, however, its life cycle is different and winter breeding of overwintered adults occurs. Most of the C. propinquus population overwintered in the WG as C III–V, inhabiting the WW. In the upper water layers in the interior of the WG, C III dominated with upto 18,000 individuals 1,000 m³. Shallow living C. propinquus were in the active, feeding state. Persistence of active feeding zooplankton populations in the WW of the WG can be an important factor influencing processes of phytoplankton development and the particle flux.     

Egg production rates of the neritic marine copepod Acartia tumida Willey in the Aleutian Archipelago

Acartia tumida, a neritic copepod of the northern North Pacific Ocean and Bering Sea, is an unusually large member of its genus, adult females measuring 2.0–2.4 mm in total length. In the summers of 1986 and 1987 we investigated egg production of A. tumida in nearshore habitats of several islands in the Aleutian Island chain. A. tumida was found within protected embayments, where it could reach adult densities as high as 1000m^–3. Highest egg production rates were measured at Amchitka Island (up to 86 eggs copepod^–1 d^–1 at 6°C), where the phytoplankton was dominated by chain-forming Thalassiosira spp. In situ egg production rates at Amchitka were more than twice as high as maximum rates measured with cultured T. weissflogii, a single cell diatom, or during blooms of chain-forming Chaetoceros spp. at Adak and Kiska Islands. Approximately 12–24 h was necessary for recent feeding to be reflected in egg production. At high food concentrations 75% of spawning occurred at night and in discrete clutches, a pattern not observed at a lower food concentration.     

Daily egg production ofTemora longicornis (Copepoda,Calanoida) during winter and early spring in the Marsdiep (Southern North Sea)

Mature females of the copepodTemora longicornis from the Marsdiep tidal inlet were incubated at ambient water temperature during the winter of 1989/1990 to estimate their egg production during 24 hours. Throughout winter this production remained at a level of 0 to 10 eggs per female. In March a steep rise to 60 to 80 eggs coincided with an equally steep rise in chlorophyll-a from 4 to 20 g.l^–1. Excess food given during incubation tended to increase the observed production rate only in October at relatively high temperature. Additive effects of rising food level and temperature on daily egg production were found in spring. In March and April 1988 and 1990 the observed maximum daily egg production per female increased from about 20 at 5°C and 5 g.l^–1 chlorophyll to 70 at almost 10°C and 20 g.l^–1. The egg production in winter gives a prebloom potential to maintain a stock of premature stages ready to utilize the algal spring bloom. Early spawning before April can also contribute to the development of the abundance peak of adults in May–June. Due to growth rates increasing with temperature in the months March and April, most of the adults at their peak density may have hatched from eggs before the period of maximum egg production rate at the end of April. The exceptionally high production rate observed at the end of March may be related to a developingPhaeocystis bloom.     

Population growth rate of the parasitic rotifer Proales gigantea,and susceptibility to parasitization in the snail Lymnaea acuminata at different stages of embryonic development

Developing eggs of the host snail Lymnaea acuminata were experimentally parasitized with the parasitic rotifer Proales gigantea to study the population growth rate of the parasite within the snail egg capsule and the susceptibility of the host eggs at different stages of embryonic development. The population growth rate of P. gigantea was 0.46 ± 0.07 individual^–1 day^–1 at the ambient temperature of 18–22 °C. Snail eggs were most susceptible to rotifer attack during the initial stages of development, becoming progressively more resistant after the hippo stage. Yet, regardless of the stage of development, the host embryo was doomed to die without hatching even if one individual rotifer gained entry inside the egg capsule. The presence of P. gigantea within the parasitized egg capsules or in the mucilage had no effect on the developmental rates and hatching success of non-parasitized eggs within the same egg mass.     

The zooplankton community in the vicinity of the ice edge,western Weddell Sea,March 1986

Summary The zooplankton community in the vicinity of the ice edge in the west central Weddell Sea was investigated in the late austral summer (March 1986). Sampling was done with two ships operating concurrently, one in the pack ice and the other in the adjcent open sea. Metazoan microzooplankton (<1 mm) was most abundant in the epipelagic zone. It consisted mostly of copepod nauplii and copepods of the genera Oithona, Oncaea, Ctenocalanus and Microcalanus. While species composition was similar in both areas, vertical patterns differed in that the microzooplankton had sparse populations in the upper 50 m under the ice. This may have been related to water temperature which in the upper 50 m under the ice was more than 1°C cooler than in the open sea. Zooplankton in the 1–20 mm size range was dominated by the calanoid copepods Metridia gerlachei, Calanus propinquus and Calanoides acutus which constituted half the biomass in the upper 1000 m. Their populations had highest densities in the upper 150 m, though much of the C. acutus population resided below 300 m. Metridia gerlachei and C. propinquus underwent diel vertical migrations in both areas whereas C. acutus did not migrate. Species diversity in the epipelagic zone was moderate and the fauna was characterized by species typical of the oceanic east wind drift. Diversity increased with depth and was due primarily to the appearance of circumpolar mesopelagic copepods in Weddell Warm Deep Water. Biomass of 1–20 mm zooplankton in the 0–1000 m zone was low (1.1–1.3 gDWm^-2) compared to other Southern Ocean areas investigated with comparable methods. It is suggested that this is related to Weddell circulation patterns and the resulting low annual primary production in the central Weddell Sea.     

Life cycle of Macrothrix flabelligera Smirnov, 1992 (Cladocera, Macrothricidae), recently reported in the Neotropical region

Information on the life cycle of individual species is vital to an understanding of their ecology, particularly their distribution. In this investigation, aspects of the Macrothrix flabelligera (Cladocera, Macrothricidae) life cycle were studied in laboratory cultures under controlled conditions. Neonates from parthenogenetic females previously acclimatized were isolated and grown at constant temperature, in a 12-h/12-h light/dark cycle. Organisms were fed with a suspension of Scenedesmus bijugus at a concentration of 10⁵ cells ml^–1. Daily measurements of body length and age were made, to obtain the growth rate, size and age of primipara. M. flabelligera had high fecundity rates, producing broods of 13.6 eggs female^–1. At 23.0°C, the duration of embryonic and post-embryonic development was 35.9 h and 4.9 days, respectively. The mean longevity was 12.7 days. A length–weight relationship was established and used to convert measured length into weight, in order to plot weight growth curves, as subsidiary information for future secondary production calculations.     

Demographic Characteristics of Female Mottled Sculpin, Cottus Bairdi, in the Coweeta Creek Drainage, North Carolina

We quantified: (1) growth rate, (2) length-mass relationships, (3) size- and age-specific fecundity, (4) egg size-frequencies, and (5) size- and age-specific egg diameter relationships for reproductively active female C. bairdi from one of the southern-most extant populations of this species (Coweeta Creek drainage, North Carolina). Gravid females were collected during February and March in 1993–1995, and 1998. Cottus bairdi reached an age of 7+ and 79mm standard length. The youngest and smallest gravid female collected was a 41mm 1+ individual. Mature 1+ females were not uncommon and we collected 21 during our study. All females older than age 2 were mature. Mean fecundity for C. bairdi at Coweeta was 71 eggs (range 9–166 eggs). We found significant positive relationships between fecundity and female length, weight and age. Female length and weight also significantly affected mean egg diameter, although the relationship was not linear. Neither female size or age significantly affected mean maximum egg diameters. Female C. bairdi from the Coweeta Creek drainage possess a unique suite of reproductive characteristics that may represent adaptations to the local selective regime or ecophenotypic variation.     

Limnological control of brine shrimp population dynamics and cyst production in the Great Salt Lake, Utah

In the Great Salt Lake of Utah, the brine shrimp Artemia franciscanaKellogg is an important food resource for birds and they produce dormant cysts that are harvested and used extensively in the aquaculture industry. We analyzed the limnological factors controlling Artemia growth and cyst production over 12 months in 1994 and 1995. Laboratory experiments showed that inter-brood intervals were highly dependent on temperature and slightly on food level. At optimal temperatures and nutritious food, juveniles reached reproductive size within 7 d in the laboratory. In winter when temperatures were less than 3 °C, Artemia were absent from the lake, phytoplankton abundance was high (13 Chl a g l^–1), and the dominant grazers were ciliated protozoans. In the spring, cysts hatched when phytoplankton was abundant (15–30 g Chl a l^–1), and the Artemia grew and produced large clutches of ovoviviparous eggs. Estimated naupliar production from these eggs was 80 l^–1 from April to May. Despite the high production of nauplii, Artemia densities declined to 8 l^–1by June and the growing shrimp population grazed down the phytoplankton resource to <1 g Chl a l^–1. With the depleted phytoplankton food resource during the summer, Artemia growth slowed, lipid indices decreased, clutch sizes declined, and females switched primarily to oviparous cyst production. During the summer, there was limited production of ovoviviparous eggs, and limited recruitment of juveniles, probably due to low food. Although oviparous reproduction began in June, more than 90% of the cysts were produced after July when female densities had declined to 1.5 l^–1, but nearly all of them were producing cysts. Estimated cyst production was 650000 m^–2, or 4.54 × 10⁶ kg dry weight for the entire lake. The reported commercial harvest took 21% of the 1994 cyst production. That harvest had little impact on the subsequent year's population, as Artemia densities were ultimately controlled by algal production in the lake.     

Susceptibility of the cattle tick Boophilus microplus (Acari: Ixodidae) to isolates of the fungus Beauveria bassiana

The susceptibility of the tick Boophilus microplus to Beauveria bassiana was evaluated by inoculating eggs, larvae and engorged females of the tick with five fungal isolates at concentrations of 10⁶, 10⁷ and 10⁸ conidia/ml. Tick eggs (0.25 g) were immersed in 1 ml of a suspension of the different conidial concentrations for 1 min. Similar exposure was performed by immersion of 2000 larvae and homogeneous groups of nine engorged females in 2 and 20 ml of conidial suspension, respectively. Treated eggs, larvae and adults were placed in an incubator at 27 ± 1 °C and relative humidity above 80% for evaluation of the fungal action. All fungal isolates applied at all conidial concentrations reduced the hatching rate of larvae from treated eggs by 1.36–65.58% and increased the mortality rate of inoculated larvae by 0.8–70.49%. In the bioassay with engorged females, oviposition period was reduced by 9.69–47.80%, egg mass weight by 4.71–53.87%, estimated reproduction by 8.3–60.62%, egg production index by 5.03–54.20%, percent larval hatching by 0.27–13.96%, and the mortality rate of treated females was increased by 96.60–100%. The reduction of the estimated reproduction obtained for the treated groups ranged from 8.37 to 64.52%. The sporulation of the pathogen on dead females ranged from 3.70 to 88.88% depending on the isolate and concentration used. Isolates AM 09, CB 7 and JAB 07 were the most effective and effectiveness increased with increasing concentrations of conidia in the suspensions.     

Exploring the foraging environment of a natural enemy of Callosobruchus maculatus: Spatial egg distribution in stored cowpea

Knowledge of the spatial distribution of stored product insects may reduce the dependency on chemicals for control of these insects. Biological control, for instance, could be improved based on such knowledge. In this paper we describe the three-dimensional spatial oviposition pattern of Callosobruchus maculatus in stored cowpea. Individual C. maculatus females oviposited in clusters of 70±15 (SD) eggs. These clusters were variable in shape. In any cluster 90 to 95% of the eggs fitted into a volume of 19.1±3.5 cm³. The egg density was highest (0.6 eggs bean^–1) at the center of a cluster and decreased towards the periphery. A statistically significant relationship existed between the number of eggs n in a cluster and the cluster volume, V(cm³): V=11.5+0.11n. We also investigated the spatial egg distribution of beetles which emerged from egg clusters such as those produced by individual females. Their oviposition was not confined to one specific area but was scattered throughout the bean mass. A point pattern analysis showed that the density of the `parent' cluster had no effect on the spatial egg pattern. These results give insight into the foraging environment which the egg parasitoid Uscana lariophaga, a promising candidate for biological control of C. maculatus, is facing. We argue that the probability p of encountering at least one other bean with eggs after a parasitization is a function of the number n of beans that are visited: p=1–0.42 (0.37)^(n–1).     

Copepod feeding behaviour and egg production during a dinoflagellate bloom in the North Sea

Feeding strategies of copepods were studied during a dinoflagellate-dominated bloom in the North Sea in August 2001. The aim of this study was to evaluate the importance of mesozooplankton grazing as a biological loss factor of harmful algal blooms under natural conditions. Therefore, ingestion, egestion and egg production experiments were performed with the most abundant copepod species Calanus helgolandicus, Temora longicornis and Acartia sp. feeding on the natural phytoplankton community. Dinophysis norvegica and Ceratium furca were the most abundant dinoflagellate species at the time of the experiments. Grazing experiments as well as examination of fecal pellet content revealed C. helgolandicus fed efficiently on D. norvegica. Ingestion rates up to 47 cells female⁻¹ h⁻¹ were measured and a large proportion of the C. helgolandicus fecal pellets contained intact D. norvegica cells. Dinophysis cells were rarely seen in fecal pellets produced by T. longicornis, and never observed in pellets produced by Acartia sp. The ingestion rate of C. furca, which was the dominating Ceratium species, mimicked that of D. norvegica. C. helgolandicus grazed significantly on C. furca (16 cells female⁻¹ h⁻¹), while the ingestion rate of T. longicornis was low and Acartia sp. was not able to graze on C. furca. Egg production experiments revealed that 92% of the C. helgolandicus females produced eggs. The specific egg production rate and the proportion of females producing eggs among T. longicornis were low. This field experiment clearly shows that some copepod species feed efficiently on D. norvegica and C. furca under natural conditions, which may affect the bloom development of these dinoflagellates.     

Transmission of injected DNA sequences to multiple eggs of Metaseiulus occidentalis and Amblyseius finlandicus (Acari: Phytoseiidae) following maternal microinjection

The persistence of DNA injected into two species of adult female phytoseiids and its transmission to serial eggs deposited by them was assessed by the polymerase chain reaction (PCR). The effect of DNA concentration on persistence and transmission was examined in Metaseiulus occidentalis. M. occidentalis females were microinjected with plasmid DNA at three different concentrations (250, 500, 750 ng L^–1) and allowed to deposit one to five eggs before the females and their last eggs were analyzed. Plasmid DNA was found in 82% of the females assayed and in 70% of all the eggs analyzed (including the fifth eggs produced after microinjection). Transmission of DNA to multiple eggs was also examined in Amblyseius finlandicus. Females of this species are less traumatized by microinjection allowing analysis of transmission over a more extended number of eggs. Females were microinjected and allowed to deposit eggs until their death. DNA from every fifth egg was analyzed by the PCR. PCR products were amplified from 51% of the eggs and from all egg classes except the 30th egg. The persistence and presence of plasmid DNA in both eggs and females suggests that (1) maternal microinjection is a more efficient method for DNA delivery than traditional egg microinjection, (2) it may be possible to isolate transformants from fewer maternally-microinjected females than originally expected, and (3) maternal microinjection could be useful as a DNA delivery system in other phytoseiids.     

In situ primary production in young Antarctic sea ice

An in situ incubation technique used successfully to measure the photosynthetic carbon assimilation of internal algal assemblages within thick multiyear Arctic ice was developed and improved to measure the photosynthetic carbon assimilation within young sea ice only 50 cm thick (Eastern Weddell Sea, Antarctica). The light transmission was improved by the construction of a cylindrical frame instead of using a transparent acrylic-glass barrel. The new device enabled some of the first precise measurements of in situ photosynthetic carbon assimilation in newly formed Antarctic sea ice, which is an important component in the sea ice ecosystem of the Antarctic Ocean. The rates of carbon assimilation of the interior algal assemblage (top to 5 cm from bottom) was 0.25 mg C m^–2 d^–1 whereas the bottom algal community (lowest 5 cm) attained only 0.02 mg C m^–2 d^–1. Chl a specific production rates (P^Chl) for bottom algae (0.020 – 0.056 g C g chl a ^–1 h^–1) revealed strong light limitation, whereas the interior algae (P^Chl = 0.7 – 1.2 g C g chl a ^–1 h^–1) were probably more limited by low temperatures (< –5 °C) and high brine salinities.     

Does the cost of incubation set limits to clutch size in common eiders Somateria mollissima?

We examined the effect of natural clutch size on the cost of incubation in a population of common eiders Somateria mollissima nesting in Tromsø, northern Norway. The body condition of females at day 5 in the incubation period was not related to clutch size (3–6 eggs), but females incubating large clutches lost more mass and had a lower body condition at day 20 in the incubation period than females incubating small clutches. Females incubating large clutches had a slightly shorter incubation period and a lower egg predation rate. The results do not support the hypothesis that the female's ability to produce eggs is the only ultimate control of clutch size in eider. Instead the results suggest that there may be an interaction between the allocation of body reserves to eggs and incubation, and that females producing large clutches allocate more of their body reserves to incubation than females producing small clutches, in order to shorten the incubation period and to minimise the risk of predation on eggs.     

Biology of Moina mongolica (Moinidae,Cladocera) and perspective as live food for marine fish larvae: review

Moina mongolica, 1.0-1.4 mm long and 0.8 mm wide, is an Old World euryhaline species. This paper reviewed the recent advances on its autecology, reproductive biology, feeding ecology and perspective as live food for marine fish larviculture. Salinity tolerance of this species ranges from 0.4–1.4 to 65.2–75.4. Within 2–50 salinity, Moina mongolica can complete its life cycle through parthenogenesis. The optimum temperature is between 25 °C and 28 °C, while it tolerates high temperature between 34.4 °C and 36.0 °C and lower temperature between 3.2 °C and 5.4 °C. The non-toxic level of unionised ammonia (24 h LC₅₀) for M. mongolica is <2.6 mg NH₃–N l^–1. Juvenile individuals filter 2.37 ml d^–1 and feed 9.45×10⁶ algal cells d^–1, while mature individuals filter 9.45 ml d^–1 and consume 4.94×10⁶ algal cells d^–1. At 28 °C, M. mongolica reaches sex maturity in 4 d and gives birth once a day afterward; females carry 7.3 eggs brood^–1 and spawn 2.8 times during their lifetime. A variety of food can be used for M. mongolica culture including unicellular algae, yeast and manure, but the best feeding regime is the combination of Nannochloropsis oculata and horse manure. Moina mongolica reproduces parthenogenetically during most lifetime, but resting eggs can be induced at temperature (16 °C) combined with food density at 2000–5000 N. oculata ml^–1. The tolerance to low dissolved oxygen (0.14–0.93 mg l^–1) and high ammonia makes it suitable for mass production. Biochemical analyses showed that the content of eicospantanoic acid (20:53) in M. mongolica accounts for 12.7% of total fatty acids, which is higher than other live food such as Artemia nauplii and rotifers. This cladoceran has the characteristics of wide salinity adaptation, rapid reproduction and ease of mass culture. The review highlights its potential as live food for marine fish larvae.     

Measurement of guard-cell respiration rates using Cartesian-diver technique

Dark respiration rates of guard-cell protoplasts of Commelina communis L. were measured over a temperature range (15–30° C) using a Cartesian-diver microrespirometry technique. Measurements were made using a few microliters of suspension medium containing between 400 and 3 700 protoplasts. Respiration rates were approximately linear for at least 1 h at all temperatures. Respiration rates increased rapidly between 20 and 25° C to relatively high levels (6.11·10^-6 mol O₂ h^-1 protoplast^-1=1259 mol O₂ mg^-1 chlorophyll h^-1=22.97 mol O₂ mg^-1 protein h^-1) with no further increases above this temperature. Respiration rates were much lower in protoplasts 15–16 h old than in freshly prepared ones indicating considerable deterioration of their viability over this time period.     

Use of swimming speed and egg ratio as predictors of the status of rotifer cultures in aquaculture

This study evaluated the use of egg ratio (eggs rotifer^–1) and swimming speed (mm min^–1) as prediction criteria for production and culture quality in mass cultures of the rotifer Brachionus plicatilis. Egg ratio was determined to be a suitable predictor of rotifer growth and production in the cultures. Low egg ratios (i.e., 0–0.17 eggs rotifer^–1) indicate reduced rotifer population over time (i.e., negative net population growth rates). However, at this time egg ratio dynamics are not suitably understood to predict in advance a sudden population collapse.Swimming speed of reproductive, egg-carrying females in the exponential growth phase was 40–45 mm min^–1. During exponential growth swimming speed was independent of the food used. Lower swimming speeds were obtained in late stationary phase (10–25 mm min^–1) when yeast was used as a food source. Both environmental factors (e.g., accumulating metabolites) and changes in nutritional state of the rotifers may have affected the swimming speed, but environmental factors appear to be the most important. We believe that swimming speed has the potential of becoming an accurate predictor of culture quality in mass cultures of rotifers.