The rotifer fauna of Lake Kud-Thing,a shallow lake in Nong Khai Province,northeast Thailand

The species composition of the rotifer fauna of Lake Kud-Thing, Nong Khai Province, northeast Thailand was investigated in a monthly sampling program from January to December 1998. A remarkably rich rotifer community consisting of 183 taxa was recorded, including 32 new records to the Thai fauna. The most diverse genera were Lecane (23.5%), followed by Trichocerca (16.9%) and Lepadella (11.5%). Lecane isanensis n. sp. is described and figured. Thirteen species (Aspelta circinator, Collotheca tenuilobata, Lecane nelsoni, Lepadella benjamini, Lepadella eurysterna, Sinantherina ariprepes, Testudinella cf. insinuata, Trichocerca abilioi, Trichocerca inermis, Trichocerca montana, Trichocerca orca, Trichocerca rosea and Trichocerca simonei) are new to the Oriental region. Notably, the record of Trichocerca orca is the first since its discovery in New Zealand in 1913. The rotifers can be classified into three groups based on duration of appearance; (1) common, perennial; (2) uncommon, perennial; and (3) uncommon, sporadic species. The high species richness of rotifers, particularly members of the genera Lecane and Trichocerca, but low diversity of Brachionus together suggest that the lake is probably not eutrophicated.     

Swimming speed and Reynolds numbers of eleven freshwater rotifer species

We obtained data on the swimming speed of 11 freshwater rotifer species. These data were analyzed in terms of Reynolds numbers given the fact that rotifers are in the evolutionary boundary between the use of cilia and swimming appendages. Swimming speed ranged from 0.174 to 0.542 mm ^–1. Philodina acuticornis odiosa was the fastest rotifer in terms of absolute speed. However, Gastropus hyptopus, the smallest of the rotifers analyzed, was the fastest (2.849) in terms of body-lengths s^–1. Reynolds numbers (Re) among the 11 species analyzed varied from 0.023 to 0.301. Lecane furcata had the smallest Re, while Epiphanes senta had the highest Re. The two bdelloid rotifers analyzed in this work swam five times faster than they crept. The importance of Reynolds numbers and drag coefficients are discussed in view of the present results and data found in the literature.     

Rotifers as indicators of lake types in Estonia

Data on the pelagic rotifer fauna in 10 Estonian lakes accumulated for 20 years, as well as published data are analysed. It is possible to distinguish three main indicator groups among rotifers: (1) for oligo- and mesotrophic lakes (Ploesoma hudsoni, Keratella serrulata, Synchaeta grandis, Asplanchna herricki, Ascomorpha ovalis, Gastropus stylifer, Conochilus hippocrepsis); (2) for meso-and eutrophic lakes (Trichocerca capucina, Filinia longiseta, F. limnetica, Keratella quadrata, K. cochlearis tecta, K.c. hispida, Polyarthra euryptera, Keratella hiemalis, Trichocerca porcellus, T. pusilla); (3) for eutrophic lakes (Brachionus spp., Anuraeopsis fissa, Pompholyx sulcata, P. complanata, Trichocerca cylindrica, Hexarthra mira).     

The phylogeny of rotifers: molecular,ultrastructural and behavioural data

This work discusses the nature and significance of molecular, ultrastructural, and behavioural characters that can be used in phylogenetic analyses of rotifers.Recent molecular research has demonstrated the presence of very small amounts of 4-hydroxyproline in rotifers, probably arising from acetyl-cholinesterase or glycoproteins. Thus, rotifers appear to be the first known Metazoa without collagen.Ultrastructural work also has made some interesting discoveries. (1) The myelinic cuticle of the integument and pharynx of gastrotrichs is present in the pharynx of at least two rotifers (Philodina and Brachionus) and some Annelida. (2) The intracytoplasmic lamina (IL) of the syncytial ingestive integument of Acanthocephala is similar to the IL of the syncytial stomach of Bdelloidea. (3) The fibrous terminal web of primitive epidermal ciliated cells may have evolved in the skeletal IL of the syncytial, aciliated integument of rotifers. (4) Using the ultrastructural features of the skeletal, IL of the integument, I derived two possible dendograms of rotifer evolution. (5) These models and other ultrastructural data predict that Bdelloidea should be separated from Monogononta, while Seison has several characters which suggest that it should be more closely aligned to the Monogononta than previously proposed.Molecular and ultrastructural data suggest that rotifers are primitive Metazoa, probably derived by neoteny from ancestral, ciliated larvae. Finally, I argue that information on sensory organs and the behaviour of rotifers may offer unique insights into the evolution of the phylum.     

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.     

Freshwater Copepods and Rotifers: Predators and their Prey

Three main groups of planktonic animals inhabit the limnetic zone of inland waters and compete for common food resources: rotifers, cladocerans and copepods. In addition to competition, their mutual relationships are strongly influenced by the variable, herbivorous and carnivorous feeding modes of the copepods. Most copepod species, at least in their later developmental stages, are efficient predators. They exhibit various hunting and feeding techniques, which enable them to prey on a wide range of planktonic animals from protozoans to small cladocerans. The rotifers are often the most preferred prey. The scope of this paper is limited to predation of freshwater copepods on rotifer prey. Both cyclopoid and calanoid copepods (genera Cyclops, Acanthocyclops, Mesocyclops, Diacyclops, Tropocyclops, Diaptomus, Eudiaptomus, Boeckella, Epischura and others) as predators and several rotifer species (genera Synchaeta, Polyarthra, Filinia, Conochilus, Conochiloides, Brachionus, Keratella, Asplanchna and others) as prey are reported in various studies on the feeding relationships in limnetic communities. Generally, soft-bodied species are more vulnerable to predation than species possessing spines or external structures or loricate species. However, not only morphological but also behavioural characteristics, e.g., movements and escape reactions, and temporal and spatial distribution of rotifer species are important in regulating the impact of copepod predation. The reported predation rates are high enough to produce top-down control and often achieve or even exceed the reproductive rates of the rotifer populations. These findings are discussed and related to the differences between the life history strategies of limnetic rotifer species, with their ability to quickly utilize seasonally changing food resources, and adjust to the more complicated life strategies of copepods.     

Neuromuscular organization of the freshwater colonial rotifer, Sinantherina socialis, and its implications for understanding the evolution of coloniality in Rotifera

Coloniality among rotifers is rare, and while the adaptive significance of the lifestyle has been explored previously, there are few details about how it may have influenced the morphology of colony members. In this study, we use confocal laser scanning microscopy combined with cyto- and immunohistochemistry to determine if the colonial rotifer, Sinantherina socialis, differs in neuromuscular organization relative to other colonial and solitary forms. Our observations indicate that the patterns of serotonergic neurons and somatic muscles in S. socialis are broadly similar to other rotifers. At the neuronal level, the distribution of serotonergic (5HT-IR) neurons in S. socialis is most similar to colony-forming species of Conochilus: (1) paired nerve cords extend the length of the body; (2) the cerebral ganglion innervates the corona with paired neurites that form a neuronal ring; and (3) a single pair of neurites innervates the ventral sensory antennae. Unique to S. socialis is the presence of two additional neuronal rings that supply the corona and may function to modulate ciliary beat. At the muscular level, S. socialis displays a typical pattern of somatic muscle organization similar to other rotifers, but diverges from the pattern in three significant ways: (1) somatic circular muscles form complete rings; (2) circular muscles are distinguishable based on their size and position in the body; and (3) transverse muscles are present within the corona and presumably function to modify its shape for feeding and defensive purposes. These differences in neuromuscular organization may be adaptations to the colonial and/or sessile lifestyle, both of which are characteristic of S. socialis.     

Ecotoxicological studies with the freshwater rotifer Brachionus calyciflorus

The use of the freshwater rotifer Brachionus calyciflorus as a test organism for ecotoxicological studies was examined. Changes in the feeding-, swimming behavior- and demographic characteristics of the rotifers exposed to increasing concentrations of copper (Cu) were studied and the relationships between the different test parameters and their ecological relevance evaluated.Relatively simple short-term bioassay methods were developed to measure the swimming activity (2 hours) and the filtration (5 hours) rate. Life-table experiments were performed to asses the long-term effects of Cu on the rotifers. Significant reductions in the filtration rate, the swimming activity and the demographic parameter r were observed at 20, 12 and 5 g 1^–1 of Cu, respectively. The implications and the possible ecotoxicological applications of the results are discussed.     

The skeletal muscles of rotifers and their innervation

The skeletal muscles of rotifers are monocellular or occasionally bicellular. They display great diversity of cytological features correlated to their functional differentiation. The cross-striated fibers of some retractors are fast contracting and relaxing, with A-band lengths of 0.7 µm to 1.6 µm, abundant sarcoplasmic reticulum and dyads. Other retractors and the circular muscles are tonic fibers (A band > 3 µm), stronger (large volume of myoplasm) or with greater endurance (superior volume of mitochondria/ myoplasm). All of these retractor muscles are coupled by gap junctions and are innervated at two symmetrical points; they constitute two motor units implicated in withdrawal behaviour.The muscles inserted on the ciliary roots of the cingulum control swimming. They are multi-innervated and each of them constitute one motor unit. They have characteristics of very fast fibers; the shortest A-band length is 0.5 µm in Asplanchna.All the skeletal muscles of bdelloids are smooth or obliquely striated as are some skeletal muscles of monogononts. These muscles are well suited for maximum shortening and are either phasic or tonic fibers.All rotifer skeletal muscles originate from ectoderm and contain thin and thick myofilaments whose diameters are identical to those of actin and myosin filaments in vertebrate fast muscles or in insect flight muscles. There are no paramyosinic features in the thick myofilaments. The insertion, innervation, coupling by gap junctions and other cytological differentiations of rotifer skeletal muscles are reviewed and their phylogeny discussed.     

SEM of internal structures of Brachionus plicatilis (Rotifera)

Examination by scanning electron microscopy of sectioned rotifers provides views on their internal structures which complement the results of other techniques. Thus, additional information has been obtained for example, on the digestive tract, on nerve connections and on the morphology of the mastax. Our observations confirm that nearly all organs are connected in some way to the integument, suggesting that integument structures may be responsible for the holding together of the whole rotifer body.     

Additions to the rotifer fauna of south-east Asia: new and rare species from north-east Thailand

Ninety-three freshwater habitats in the north-eastern part of Thailand were surveyed for rotifers during March–October 1993. Two hundred species were identified, 120 of which are new to Thailand. Brachionus africanuss Segers, B. lyratus Shephard and Trichocerca hollaerti De Smet are new to Asia. Brachionus niwati n.sp. is described and figured. Brachionus donneri Brehm, Keratella edmondsoni (Ahlstrom) and Lecane blachei Berzi, endemic to south and southeast Asia, were found also.Comments are presented on some insufficiently known taxa. Of special zoogeographic interest is the record of several species previously considered endemic to Australia. An attempt is made to characterise the Thai rotifer fauna in the light of recent developments in rotifer zoogeography.     

Differential use of food resources by the instars of Chaoborus punctipennis

SUMMARY. 1. Differential use of food resources by instars I-1V of Chaoborus punctipennis was examined in a mesotrophic New Hampshire lake during midsummer when all instars coexisted. Diet composition and prey preference were quantified first, at night when all instars were feeding at the same depth, and second, during the day when the early instars (I-II) and instar III were segregated by depth. Relative abundance, per cent biomass, and per cent frequency of occurrence of soft and hard-bodied rotifers, flagellated phytoplankton, protozoans, and crustaceans in C. punctipennis diets were quantified using crop content analyses. 2. All four instars ingested large, flagellated phytoplankton (mainly Dinobryon and Ceratium). This unexpected result suggests that the effects of phytoplankton on Chaoborus growth and survival should be investigated. All instars also consumed rotifers (mainly Kellicottia, Gastropus, Polyarthra), but only instars III and IV fed upon crustaceans (mainly Daphnia, Bosmina and Diaphanosoma). Small rotifers (Gastropus spp., Keratella cochlearis, Trichocerca similis) occurred more frequently and were more abundant in early instar diets than late instar (III and IV) diets, whereas large rotifers (Asplanchna priodonta and Keratella crassa) were eaten only by instars III and IV. Zooplankton with gelatinous sheaths (e.g. Ascomorpha, Collotheca and Holopedium) were rarely ingested. 3. Developmental increase in gape diameter of C. punctipennis seemed to be the major proximate mechanism causing dietary differences among instars. Body widths of hard-bodied prey in C. punctipennis crops were always less than gape diameter. The relationship between prey body width and Chaoborus gape diameter, coupled with knowledge of prey escape behaviour, should be useful for predicting the presence of hard-bodied prey taxa in diets of other Chaoborus species. 4. All four instars of C. punctipennis selected soft-bodied, or weakly loricate, rotifer prey over crustaceans and phytoplankton. Early instars preferred the small rotifer T. similis and the protozoan Difflugia sp. to other rotifers and phytoplankton when feeding in the epilimnion or thermocline during the day or night. Late instars positively selected the rotifer, Asplanchna. Prey value (prey weight ingested per unit handling     

Pelagic rotifers of Lake Glubokoe from 1897 to 1984

After alteration in the pattern of drainage of run-off from the surrounding swamps and changes in the colour and transparency of the Lake Glubokoe water, the previously epilimnial Trichocerca similis, Conochilus unicornis and Keratella cochlearis showed a shift of their maximum numbers to deeper layers. Pompholyx sp. and Trichocerca capucina, which are regarded as indicators of eutrophic waters, have disappeared from the pelagic zone of the lake and Conochilus hippocrepis, Synchaeta pectinata, Gastropus stylifer, Asplanchna herricki, Ascomorpha ecaudis, Ascomorpha saltans, Euchlanis dilatata and Trichocerca porcellus have made their appearance. Most of the new species are considered to be indicators of oligotrophic conditions. However the total density of pelagic rotifers remained at the same level. Apparently the establishment of the new species of rotifers was possible due to some ‘rarefaction’ of the epilimnion, the disappearance of predaceous Mesocyclops leuckarti and the invasion of the pelagic zone by Peridinium cinctum.     

The ultrastructure of the integument and proventriculus in the raptorial rotifer Cupelopagis vorax (Monogononta: Collothecaceae: Atrochidae)

Members of the sessile rotifer species Cupelopagis vorax are unusual ambush predators that live permanently attached to submerged freshwater plants. Previous light microscopical research has revealed several uncommon features in this species including a stellate‐patterned integument and an expansive foregut region called the proventriculus. In this study, we apply transmission electron microscopy to explore the ultrastructure of both the integument and foregut to determine how they differ from other rotifers. Our results reveal that the integument is covered by a thick glycocalyx and is patterned with tubercles that originate from the intracytoplasmic lamina (ICL) within the syncytial epidermis. The ICL forms an apical layer within the syncytium, is electron dense and mostly amorphous, and forms tubercles up to 2.3 μm; these tubercles probably account for the patterned appearance of the integument and are similar to what has been found in other gnesiotrochan rotifers. The basal cytoplasm is highly granular and contains two types of membrane‐bound vesicles: large ovoid vesicles (320–411 nm) with amorphous, opaque contents, and secretory bulbs (110–264 nm) with electron‐lucent cores and occasionally electron‐dense contents. Only the secretory bulbs were observed to form connections to the apical plasmalemma, and so are probably exocytotic. Internally, the proventriculus is a large distensible sack that connects the anterior pharyngeal tube to the posterior mastax. The proventricular epithelium is a thin syncytium mostly covered with a dense glycocalyx and a strong brush border of microvilli underlain by a thin terminal web. The cytoplasm contains few organelles and there is no evidence that it is either secretory or has features (e.g., ICL) that might aid in maceration. We hypothesize that the thick glycocalyx might serve a protective function against the movements of live prey and/or against enzymes released from the rotifer's gastric glands that become regurgitated during feeding.     

Comparative morphology of the somatic musculature in species of Hexarthra and Polyarthra (Rotifera, Monogononta): Its function in appendage movement and escape behavior

Species of Hexarthra and Polyarthra are freshwater rotifers with well-known escape behaviors that result from interactions with planktonic predators. Both rotifers bear a suite of mobile appendages that function in evasive maneuvers and saltatory jumps through the water column, but the anatomical and functional bases of these actions are poorly understood. Here, we use a combination of phalloidin staining, confocal laser scanning microscopy, and video analysis to describe the morphology of the somatic muscles that supply the mobile appendages in order to understand how they function in escape behavior. Results show that species of Hexarthra, which bear six radially distributed limbs, possess a highly complex trunk musculature that supplies the inside of each limb with its own abductor and adductor muscles, i.e., a direct muscle supply. The singular dorsal and ventral limbs each receive a pair of large abductor and adductor muscles (four muscles total per limb), while the paired dorsolateral and ventrolateral limbs each receives three muscles (two abductors, one adductor per limb). Contraction of the abductor muscles creates a power stroke in the form of an anterior sweep of the limbs, which leads to a three-dimensional tumbling of the rotifer through the water column. Alternatively, species of Polyarthra possess 12 blade-like appendages that are arranged into four equal bundles; each bundle receives an indirect muscle supply that attaches to the shoulder of the paddles. A single longitudinal paddle muscle supplies each dorsolateral bundle, while a pair of longitudinal paddle muscles supplies each ventrolateral bundle. Contraction of these muscles, whether singly or in concert, functions to abduct the paddles in a power stroke, leading to rotation of the body and movement of the rotifer. The recovery stroke is hypothesized to be a multi-step process that begins with reorientation of the appendages prior to adduction, followed by contraction of various muscles to antagonize the paddle muscles. In total, these observations reveal novel complexities in the rotifer muscular system that aids our understanding of the biophysics of predator avoidance in appendage-bearing rotifers.     

The ciliate epibiont Epistylis pygmaeum: selection for zooplankton hosts, reproduction and effect on two rotifers

1. A clonal culture of the peritrich Epistylis pygmaeum was used for all observations and experiments. Motile cells preferentially attached to the eggs of three species of Brachionus but also attached to the body of adult B. angularis. Zooids on the transitory egg substratum developed only short stalks, while those on the body often developed long stalks and branched colonies. Selection for the eggs positions the ciliate near the cloaca, and thus high concentrations of fine particulate material excreted by the host. Settlement on eggs occurred equally well in the light and dark, and on moving and stationary eggs. 2. Motile Epistylis cells attached to a wide variety of rotifer and crustacean zooplankton, but exhibited some pronounced selectivity. They readily settled on the eggs of other rotifers (Epiphanes, Polyarthra), on the carapace of several cladocerans (Ceriodaphnia, Daphnia, Diaphanosoma), and on the egg sacs of a copepod (Tropocyclops). They settled less readily on the bodies of the rotifers Asplanchna and Synchaeta, and rarely or never settled on the rotifer Keratella, the cladocerans Bosmina and Scapholeberis, and the body of the copepod. 3. Epistylis populations initiated with a single zooid on Brachionus increased exponentially and often contained several hundred attached zooids and motile cells after 3 days at 20 °C. Observations of a culture initiated from a single telotroch provided new information about peritrich life cycles: (1) motile cells reproduced themselves at a rapid rate (λ = 4.26 day^?1); (2) telotrochs produced or transformed into swimming zooids and vice versa. Functions of the two types of motile cells remain to be clarified. Telotrochs likely are specialised for finding and attaching to hosts. Swimming zooids can feed and reproduce, producing both their own cell type and telotrochs. Together, they should enhance dispersal and population growth, especially when hosts are rare. 4. Life‐table experiments with two species of Brachionus showed that colonisation by Epistylis had no effect on adult survival but significantly decreased fecundity, by 29% in both cases. Zooids attached to eggs could be a weight burden, increase drag, and possibly inhibit egg development. Those on the body of B. angularis also could interfere with coronal cilia, inhibiting feeding and further slowing locomotion. The ability of E. pygmaeum to select and then interfere with its hosts indicates that this epibiont has the potential to influence the species structure of zooplankton communities.     

水蕹菜浮床对草鱼主养池塘轮虫群落结构的影响

研究了水蕹菜浮床对草鱼主养池塘轮虫群落结构的影响,共检出轮虫38种,隶属于2纲14属,其中浮床池塘出现轮虫36种,而非浮床池塘28种。浮床池塘与非浮床池塘的优势种组成基本类似,萼花臂尾轮虫（Brachionus calyciflorus）、裂足臂尾轮虫（Brachionus diversicornis）、裂痕龟纹轮虫（Anuraeopsis fissa）、暗小异尾轮虫（Trichocerca pusilla）以及长肢多肢轮虫（Polyarthra dolichoptera）为共有优势种;浮床池塘与非浮床池塘的轮虫平均密度分别为1892和2255 ind./L,差异极显著（p0.01）;浮床池塘与非浮床池塘轮虫平均生物量分别为1.535和1.405 mg/L,差异不显著（p0.05）。结果表明,水蕹菜浮床显著促进了轮虫种类数增加,提高了轮虫多样性和均匀度,并在一定程度上减缓了轮虫小型化。       

Age-specific Chaoborus predation on rotifer prey

SUMMARY. 1. This is the first study to examine predator-prey interactions between Chaoborm instars and rotifer prey. The predatory behaviour of instars I–III of Chaoborus pimctipennis and the diet selectivity of instars I—IV feeding on rotifers were examined in the laboratory. Prey used in direct observations of predatory behaviour included a variety of rotifers (Symhacta pectlnata, S. ohUmga, Polyarthra remata, Asplanchna girodi, Keratella crassa, spined and unspined forms of Keratella cochlearis) and two crustaceans (Bosmitia longirostris, Mesocyclops edax nauplii. 2. In general, strike efficiencies (percentage of strikes resulting in inges- tion) increased in successive instars I—III. Early instar (I and II) strike efficiencies were low when compared with other invertebrate predators. For a given instar. mean prey handling times varied among prey species more than strike efficiencies. Mean handling times for small, soft-bodied rotifers were lowest and those for wide, hard-bodied prey were highest. 3. Instar I exhibited significantly greater selectivity for the small, soft- bodied S. obUmga than for the larger S. pectinata, hard-bodied K. crassa, and spined and unspined forms of K. cochlearis. Instars II—IV positively selected both the large and small Symhaeta species over all Keratella species. The relationship between Chaobortts selectivity and prey value (weight of prey per unit handling time) can be described by a power function. Ingestion rates of rotifers by older instars (III and IV) are among the highest reported for invertebrate predators. 4. Rotifer vulnerability to Chaoborus predation probably depended on rotifer cuticle texture, body width, and hydrodynamic disturbances. Spined rotifers were not necessarily protected from Chaoborus predation because Chaohorus can manipulate and swallow them. Giguere et al.'s 1982) encounter rate model must be modified to predict encounter rates of slow-moving rotifer prey with Chaohorus.     

Ultrastructure of the rotifer integument: peculiarities of Sinantherina socialis (Monogononta: Gnesiotrocha)

The rotifer integument is a well‐described syncytium that contains an apical intracytoplasmic lamina (ICL) that functions for both skeletal support and muscle insertion. To date, there is limited information on the structure of the integument in species of Gnesiotrocha, a diverse subclade of Monogononta that consists of solitary, colonial, sessile, and planktonic species. In this study, we examined the ultrastructure of the integument in the colonial rotifer Sinantherina socialis to determine how it corresponds to that of other monogononts. The integument of S. socialis was broadly similar to that of other rotifers, consisting of a thickened glycocalyx, multilaminate ICL, and syncytial epidermis. However, it was different in several regards. The ICL consisted of three distinct layers from apical to basal: layer 1 consisted of at least two electron‐dense laminae; layer 2 was a thickened matrix of amorphous, electron‐dense material or was fibrous; and layer 3 was an electron‐dense lamina of varying thickness that covered the underlying syncytium. Significantly, layers 1 and 2 formed a ridge‐and‐groove like system of finger‐like projections across the trunk surface that has not been observed in other rotifers. A voluminous syncytial cytoplasm (up to 3 μm thick) was present beneath the ICL and was mostly electron lucent and with few organelles. Bundles of potential microtubules were scattered throughout the syncytium. We hypothesize that the voluminous cytoplasm with microtubules serves as skeletal support for the rotifer's sessile lifestyle, while the external ridges may function as a texture‐based deterrent to predators, or serves to trap secretions from the species' defensive glands. Basally, the epidermis was highly folded and bordered by a thin basal lamina that separated the plasmalemma from the blastocoel. Membrane‐bound vesicles were present throughout the integument's cytoplasm and are hypothesized to function in the secretion of extracellular matrix and in the maintenance of the ICL.     

Culture of rotifers with reference to some physico-chemical properties of water in nursery pond

Rotifers were cultured with five different organic and inorganic fertilizers in nursery ponds. Of the fertilizers used, mustard oil cake gave significantly (p < 0.01) higher production of rotifers than that of mohua oil cake followed by cow-dung, wheat bran, mixture of NPK and control. The higher production of rotifers was directly related with the higher doses of fertilizers. Among the rotifer species identified, the abundance of Brachionus caudatus and B. forficula were significantly (p < 0.01) higher than others. Available N, available P, exchangeable K and exchangeable Ca and exchangeable Mg were generally higher in ponds where organic fertilizers were used. Proximate composition of rotifers varied depending on the kinds of fertilizers. The multiple correlations of physico-chemical properties were highly significant (p < 0.01) with the growth and production of B. caudatus (R = 0.995), B. forficula (R = 0.932), Trichocerca capucina (R = 0.917), B. patulus (R = 0.901) and B. angularis (R = 0.892) and simply significant (p < 0.05) in the case of Keratella tropica (R = 0.880), Hexarthra intermadia (R = 0.875), B. calyciflorus (R = 0.864) and Filinia spp. (R = 0.856) contributing 91.20%, 86.86%, 84.09%, 81.18%, 79.57%, 77.44%, 76.56%, 74.65% and 73.27% of total effect of water properties on the growth of these species, respectively. The residual effect of nine different physico-chemical properties of water on the production of rotifers was 78.92% which indicates that these properties of water had only 21.08% influence on the production of rotifers.