Zoospore chemotaxis of mangrove thraustochytrids from Hong Kong

Zoospores of mangrove isolates of Schizochytrium mangrovei KF6, KF7, KF12 (three strains), Thraustochytrium striatum KF9 and Ulkenia sp. KF13 were examined for their chemotactic responses to amino acids, carbohydrates, ethanol, and leaf extracts using a capillary root model. Most leaf extracts of mangrove plants and a marsh grass tested were shown to induce moderate chemotactic responses in zoospores of both S. mangrovei KF6 and Ulkenia sp. KF13. Of the remaining amino acids and carbohydrates evaluated, glutamic acid and pectin induced strong attraction in zoospores of S. mangrovei KF6 and Ulkenia sp. KF13, suggesting these are the major components in leaves which may be responsible for the chemotactic response of thraustochytrid zoospores in nature. Zoospores of T. striatum KF9, in general, showed a weak chemotactic response to all the tested compounds and extracts except cellulose, which elicited a moderate response. The ecological significance of the data presented is discussed.     

Zoospore Production Biology of Pythiaceous Plant Pathogens

Zoospores are major dispersal and infective propagules of pythiaceous species. Built upon a recently developed ‘wet‐plate’ method, the objectives of this study were to develop a better understanding about zoospore production biology. Four broth media and five incubation temperatures were evaluated with 12 isolates of Phytophthora nicotianae and 17 other pythiaceous species in this study. The ‘wet‐plate’ method worked the best for heterothallic species, especially those isolates that do not produce chlamydospores. These species included Phytophthora citrophthora, P. nicotianae, Phytophthora palmivora and Phytophthora tropicalis. They readily produced 10⁵–10⁶ zoospores/ml. Overall, most species and isolates produced more zoospores with 20% clarified V8 broth than the other three media: rye, lima bean and carrot. The optimal temperature for nutrient‐deprived culture without free‐flowing water to produce sporangia typically is 5°C cooler than that for vegetative growth. Fresh and revived cultures are more prolific than those that had been subcultured multiple times. These findings will assist oomycete researchers, adding quality, productivity and efficiency to their future zoospore‐based studies.     

Isolation and characterization of polyunsaturated fatty acid producing Thraustochytrium species: screening of strains and optimization of omega-3 production

An isolation program targeting Thraustochytrids (marine fungoid protists) from 19 different Atlantic Canadian locations was performed. Sixty-eight isolates were screened for biomass, total fatty acid (TFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) content. Analysis of fatty acid methyl ester results discerned four distinctive clusters based on fatty acid profiles, with biomass ranging from 0.1 to 2.3 g L⁻¹, and lipid, EPA, and DHA contents ranging from 27.1 to 321.14, 2.97 to 21.25, and 5.18 to 83.63 mg g⁻¹ biomass, respectively. ONC-T18, was subsequently chosen for further manipulations. Identified using 18S rRNA gene sequencing techniques as a Thraustochytrium sp., most closely related to Thraustochytrium striatum T91-6, ONC-T18 produced up to 28.0 g L⁻¹ biomass, 81.7% TFA, 31.4% (w/w biomass) DHA, and 4.6 g L⁻¹ DHA under optimal fermentation conditions. Furthermore, this strain was found to produce the carotenoids and xanthophylls astaxanthin, zeaxanthin, canthaxanthin, echinenone, and β-carotene. Given this strain’s impressive productivity when compared to commercial strains, such as Schizochytrium sp. SR21 (which has only 50% TFA), coupled with its ability to grow at economical nitrogen and very low salt concentrations (2 g L⁻¹), ONC-T18 is seen as an ideal candidate for both scale-up and commercialization.     

Eicosapentaenoic and docosahexaenoic acids production by and okara-utilizing potential of thraustochytrids

Nine thraustochytrid strains isolated from subtropical mangroves were screened for their eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) production potential in a glucose yeast extract medium. Their ability to utilize okara (soymilk residue) for growth and EPA and DHA production was also evaluated. EPA yield was low in most strains, while DHA level was high on glucose yeast extract medium, producing 28.1–41.1% of total fatty acids, for all strains, with the exception of Ulkenia sp. KF13. The DHA yield of Schizochytrium mangrovei strains ranged from 747.7 to 2778.9 mg/l after 52 h of fermentation at 25°C. All strains utilized okara as a substrate for growth, but DHA yield was lower when compared with fermentation in a glucose yeast extract medium. Journal of Industrial Microbiology & Biotechnology (2001) 27, 199–202. Received 11 December 2000/ Accepted in revised form 29 June 2001     

Motility and Chemotaxis in Zoospores of Phytophthora palmivora (Butl.) Butl.

Zoospores of Phytophthora palmivora were motile for 84 h indistilled water at the optimum temperature, 17 °C. Motilitytime was markedly reduced by high zoospore density, by CaCl₂,MgSO₄.7H₂O, glutamine, glucose, by buffer solutions and by frequentcontact of zoospores with solid surfaces. The zoospores encystedinstantly and disintegrated at pH 2.2–5.0 and in 1.0 mMCuSO₄ and FeCl₂ and 1.0 per cent (w/v) peptone solutions. Velocityof movement increased as the temperature rose from 8 to 33 °C. The zoospores responded chemotactically to an extract of cocoapod but not to the exudate. Amino acids of the extract as wellas other amino acids and sugars individually attracted the zoospores.Attracted zoospores quickly encysted and germinated; the germtubes were uniformly directed towards source of stimulus.     

The effect of the weight of the seedling-derived tuber on subsequent clonal generations in a potato breeding programme

Cultures of Polymyxa graminis were maintained in roots of barley plants grown in sand at different temperatures using Wisconsin soil temperature tanks. At 17 – 20°C, the minimum time from inoculation with cystosori to the production of zoospores from the inoculated roots was 2 – 3 wk. At 11 – 20°C many zoospores were produced but the incubation period was longer at the lower temperatures. Above 20°C little fungal development occurred. The duration of motility of zoospores ranged from c. 1 h to > 24 h. Bovine serum albumen (BSA) prolonged motility but glycine and glucose had no effect or, at higher concentrations, were toxic. Zoospores were rapidly immobilised by zinc ions in solution at or above 10μg/ml. In some experiments BSA added to the zoospore suspension greatly increased transmission of barley yellow mosaic virus (BaYMV) while glucose, glycine and ovalbumen decreased it. When seedlings were incubated with zoospore suspensions for 24 h at different temperatures, BaYMV transmission was high (> 60%) at 10, 15 and 20°C but there was little at 5 or 25°C. In experiments to determine the time taken for zoospore penetration, seedlings were incubated in suspension for different periods of time and then rinsed in zinc sulphate solution to kill free zoospores. Between 3 and 3·5 h was needed for zoospores to establish infection. Transmission occurred equally to plants of various ages between 3 days and 7·5 wk.     

Halocafeteria seosinensis gen. et sp. nov. (Bicosoecida), a halophilic bacterivorous nanoflagellate isolated from a solar saltern

Recently, heterotrophic nanoflagellates (HNF) have been reported to actively ingest prokaryotes in high salinity waters. We report the isolation and culture of an HNF from a Korean saltern pond of 300‰ salinity. The organism is biflagellated with an acronematic anterior flagellum and never glides on surfaces. The mitochondria have tubular cristae. Neither transitional helix nor spiral fiber were observed in the transition zones of the flagella. The cell has a cytostome supported by an arc of eight microtubules, suggesting that our isolate is a bicosoecid. Our isolate had neither mastigonemes, lorica, body scales, nor cytopharynx and thus could not be placed in any of the presently described bicosoecid genera. Phylogenetic analysis of 18S rRNA gene sequences from stramenopiles confirmed the bicosoecid affinities of our isolate, but did not place it within any established genus or family. Its closest relatives include Caecitellus and Cafeteria. The optimal range of growth temperature was 30–35°C. The isolated HNF grew optimally at 150‰ salinity and tolerated up to 363‰ salinity, but it failed to grow below 75‰ salinity, indicating that it could be a borderline extreme halophile. On the basis of its morphological features and position in 18S rRNA trees we propose a novel genus for our isolate; Halocafeteria, n. gen. The species name Halocafeteria seosinensis sp. nov. is proposed.     

Influence of changes in sea water salinity on the growth,photosynthetic pigment content,and cell size of the benthic alga <Emphasis Type="Italic">Attheya ussurensis</Emphasis> Stonik,Orlova et Crawford, 2006 (Bacillariophyta)

The study deals with the effect of changes in salinity from 32 to 4‰ (at an interval of 4‰) on the growth, chlorophyll a and carotenoid contents, and cell size of the benthic alga Attheya ussurensis (Bacillariophyta). A. ussurensis showed high tolerance to reduced salinity and ability to adapt to salinity changes from 16 to 12‰. In this salinity range, the cells restored their shapes, sizes, and physiological functions. The number of cells and photosynthetic pigment content were highest at a salinity reduction to 24‰. At 8‰, algal cells remained alive, but the process of cell division was inhibited; as a result, the number of cells was significantly lower than in the control, the cells did not restore their sizes and shapes and remained deformed until the end of the experiment. A drop in salinity to 4‰ caused a complete loss of cell viability of A. ussurensis within a day of exposure to this factor.     

Salinity and the distribution of Cladocera in Warri River,Nigeria

Hydrobiological investigations of the water quality and plankton of Warri River started in 1981, shortly before the commissioning of the Delta Steel Plant on the banks of the river at Aladja. The 150 km of river gradates from pure freshwater through brackish to marine and so provides a suitable habitat for a study of the limits of migration of any group of zooplankton. The Cladocera of Warri River consists of two bosminids, thirteen chydorids, three daphniids, three macrothricids, one moinid, and two sidids. All except the sididPenilia sp. are well known freshwater forms, which are limited in longitudinal distribution to areas with salinity below 2.5‰. Penilia sp. found in Warri River were restricted to the truely brackish-water areas with salinity values of 7‰ −8‰. In this respect they represent the first reported brackish water Cladocera in Africa. They also differ fromPenilia avirostris Dana found in marine habitats in certain morphological details, and so the Warri RiverPenilia may be a new taxon.     

Temporal changes in zooplankton composition in a hypersaline,Antarctic lake subject to periodic seawater incursions

Colonisation of Lake Fletcher, a hypersaline, meromictic lake in the Vestfold Hills, Antarctica, by the calanoid copepod Drepanopus bispinosus, the cyclopoid copepod Oncea curvata and an undescribed cydippid ctenophore is discussed. In 1978, salinity directly under the ice was 66‰ and repeated net hauls found no zooplankton. In 1983, adults of D. bispinosus were found, and in 1984, a reproductively active population of this species. Surface water salinity in 1984 was 56‰. During winter 1986, surface salinity was 54‰ and three zooplankton species (D. bispinosus, O. curvata and an undescribed cydippid ctenophore) had established populations in the lake. In 1986/87, high tides caused nearby Taynaya Bay to flood into the lake, and three further species (the calanoid, Paralabidocera antarctica, and two harpacticoids, Harpacticus furcatus and Idomene sp.) were found in the lake. It appears that periodic flooding after 1978 caused a salinity decrease in the lake from 66 to 54‰, and this enabled some invertebrate species to maintain year-round populations, whereas others require marine incursions to re-establish summer only populations.     

Regulation of attachment, germination, and appressorium formation by zoospores ofLagenidium giganteum and related oomycetes by chitin, chitosan, and catecholamines

Summary Lagenidium giganteum (Oomycetes: Lagenidiales), a facultative parasite of mosquito larvae, infects the larval stage of most species of mosquitoes and a very limited number of alternate hosts. Host infection by this and other members of Oomycetes is initiated by motile, laterally biflagellate zoospores. Chemical bases for the various degrees of host specificity exhibited by these parasites is not known, but presumably involves receptors on the zoospore surface recognizing compounds either secreted by or on the surface of their hosts. Surface topography had no detectable effect onL. giganteum encystment or appressorium formation. Scanning electron microscopy documented the detachment of flagella during zoospore encystment. Bulbous knobs at the basal end of the detached flagellum were interpreted as encysting zoospores dropping the axoneme and/or the basal body and associated structures to which flagella are attached. Multiple signals appear to be involved in the initial steps ofL. giganteum host invasion. Zoospores of this parasite did not encyst on powdered preparations of chitin or chitosan (deacetylated chitin). Upon dissolution of chitosan in dilute acid followed by drying these solutions to form thin, transparent films, zoospores readily encysted. The degree of reacetylation of these films and the spacing of acetylated and deacetylated residues had no significant effect on zoospore encystment. Zoospores of a strain ofLagenidium myophilum isolated from marine shrimp, that also infects mosquito larvae, encysted on chitosan films. No encystment of spores of the plant parasitePhytophthora capsici was observed on chitin or chitosan films. Simulation of cuticle sclerotization by incubating chitosan films with different catecholamines and tyrosinase significantly reduced zoospore encystment. Zoospores that encysted on chitosan films did not germinate in distilled water. Germination could be induced by adding microgram quantities of bovine serum albumin or proteins secreted by motile zoospores into the water, and to a lesser degree by some amino acids, but not by various cations. Zoospores encysted and germinated on the pupal stage of some mosquito species. Appressoria were occasionally formed, but most subsequently sent out another mycelial branch, apparently without attempting to pierce the pupal cuticle. Methylation of pupal exuviae with ethereal diazomethane or methanol/HCl significantly increased zoospore encystment. Modification of chitin by catecholamines, lipids and protein on the epicuticular larval surface all affected host invasion.Abbreviations BSA bovine serum albumin - CID collision-induced dissociation - DOPA 3,4-dihydroxyphenylalanine - ESI-MS electrospray mass spectrometry - ESI-MS/MS tandem electrospray mass spectrometry - SDS-PAGE sodium dodecyl sulphate polyacrylamide gel electrophoresis - WGA wheat germ agglutinin - ZAP zoospore aggregation pheromone     

Forecasting infections of the red rot disease on Porphyra yezoensis Ueda (Rhodophyta) cultivation farms

Pythium porphyrae is a fungal pathogen responsible for red rot disease of the seaweed Porphyra (Rhodophyta). Infection forecasts of Porphyra by P. porphyrae were estimated from the epidemiological observations of Porphyra thalli and numbers of zoospore of P. porphyrae in laboratory and cultivation areas. Four features of forecasting infections were determined by relating zoospore concentrations to the incidence of thallus infection; infection (in more than 1000 zoospores L⁻¹), microscopic infection [less than 2 mm in diameter of lesion (in from 2000 to 3000 zoospores L⁻¹)], macroscopic infection [more than 2 mm in diameter of lesion (in from 3000 to 4000 zoospores L⁻¹), and thallus disintegration (in more than 4000 zoospores L⁻¹). High zoospore concentrations led to more infection. The tendency that zoospore concentration of P. porphyrae increased with the rate of infection of Porphyra thalli was generally observed in forecasting infections in both the laboratory and in cultivation areas. Based on the Porphyra cultivation areas, the accuracy and consistency of forecasting infections suggest that this method could be employed to manage and control red rot disease.     

Influence of salinity on Na+ and K+ accumulation, and gas exchange in Avicennia germinans

We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψ_w) and leaf osmotic potential (Ψ_s) decreased. Leaf Ψ_w was at least −0.32 MPa lower than the Ψ_w of solution. Na⁺ and K⁺ ions explained about 78 % of decrease in Ψ_s. K⁺ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely, Na⁺ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate (P _N) and stomatal conductance (g _s) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO₂ concentration (C _i) followed the same trend. The P _N as a function of C _i showed that both the initial linear slope and upper plateau of the P _N vs. C _i curve were markedly affected by high salinity (40 and 55 ‰).     

Effects of extreme changes of sea water temperature and salinity on the development of the sand dollar <Emphasis Type="Italic">Scaphechinus mirabilis</Emphasis>

The combined effects of temperatures of 14, 17, 20, 22, and 25°C and salinities of 36–12‰ on embryos and larvae of the sand dollar Scaphechinus mirabilis was studied. Embryonic development is the most sensitive stage in the early ontogenesis of S. mirabilis. It is completed at a temperature of 14–20°C in a salinity range of 36–24‰ and at temperature of 22°C to 26‰. The fertilization proceeds in wider ranges of temperature and salinity. Among the swimming larvae, blastulae showed the greatest resistance to variations of these environmental factors. All the larvae survived at a temperature of 14–22°C and a salinity of 36–20‰, and more than 70% of them at 18‰. The pluteus I is the most vulnerable stage; probably this is related to the formation of the larval skeleton and transition to phytoplankton feeding. The survival of larvae at the age of 20 days was 100% at 14–22° C and a salinity of 36–24‰, most of them survived at 14–20°C and a salinity 18‰. The temperature 25 ° C is the most damaging for early development of S. mirabilis. The duration of development of that species lasts 28.5–29 days at 20°C and a salinity of 32.2–32.6‰. At 20 and 22°C, the larvae settled and completed metamorphosis more quickly if sand from the parental habitat was present. The larvae did not settle during the experiment (14 days) at 14 ° C and in the absence of sand.     

Cross-linking bridges associated with the microbody-lipid globule complex inChytriomyces aureus andChytriomyces hyalinus

Summary Determining how the orientation and association among organelles are maintained within zoospores of theChytridiales is important to understanding the control of zoospore motility. Zoospores of the aquatic fungi,Chytriomyces aureus andC. hyalinus, contain microbody-lipid globule complexes with an elongate microbody adjacent to the portion of a lipid globule facing the cell's interior and a fenestrated cisterna (the rumposome) opposed to the surface of the lipid globule toward the plasma membrane. Mitochondria are intimately associated with the microbody. Electron microscopy of the microbody-lipid globule complex fixed in glutaraldehyde and osmium tetroxide, with or without tannic acid, reveals cross-linking bridges connecting the rumposome to the plasma membrane, to the microbody, and to microtubules of the rootlet extending from the kinetosome. It is concluded that these bridges are responsible, at least in part, for the consistent location of the microbody-lipid globule complex in the zoospore body. The possible role of the rumposome as a receptor organelle is discussed.     

Studies on Antagonistic Effects of Trichoderma Isolates Against Phytophthora cactorum

Bioassays were used to demonstrate the antibiotic effect of Trichoderma isolates on P. cactorum. When both fungi were grown on benomyl-containing PDA medium, the mycelial growth of Trichoderma was suppressed. However, the production of antibiotics by this fungus remained active, leading to inhibition of the mycelial growth of P. cactorum. The antibiotic effect of Trichoderma on zoospores and cysts was tested on a PDA substrate precultured with Trichoderma on cellophane sheets. On the substrate of some Trichoderma isolates, lysis of zoospores, formation of extracellular vesicles, and hypertrophy of the water expulsion vesicle did occur, both resulting in the death of the zoospores. Conidial suspensions of Trichoderma isolates also induced zoospore lysis. It is presumed that membrane-active peptide antibiotics (peptaibols) are involved in zoospore lysis. The peptaibol paracelsin caused lysins of zoospores at a concentration of 2.5 × 10^?4 M. The effect on cysts depended on the Trichoderma isolate tested and the age of Trichoderma preculture. Old cultures (after beginning of sporulation) affected cysts more severely than young cultures (before sporulation) which usually were not lethal to the cysts but induced preferably microsporangium formation, inhibition of cyst germination, and retardation of germ tube growth.     

Survival, osmoregulation and oxygen consumption of YOY coastal largemouth bass,Micropterus salmoides (Lacepede) exposed to saline media

The effect of salinity on survival, osmoregulation and oxygen consumption was determined on coastal young-of-the-year (YOY) largemouth bassMicropterus salmoides by exposing them to saline media of 0, 4, 8, 12, and 16‰. The data indicated a decrease in survival with longer exposure time and increased salinity. There were no significant differences in plasma osmolality with increased salinity from 0 to 8‰ but osmolality was significantly greater at 12‰ than 0‰ and osmolality from 16‰ was greater than all other salinity treatments. No significant differences in hematocrits were detected between 0 and 12‰, but hematocrits in the 16‰ treatment were significantly reduced compared to all other treatments. YOYM. salmoides are good osmoregulators up to 8‰ but increased salinity caused measurable osmoregulatory dysfunction. Oxygen consumption rate increased significantly as salinity increased, suggesting that adaptation of this species to hypersaline media is in part accompanied by increased energy expenditure.     

Ökologische Untersuchungen an einem marinen Pilz aus der Umgebung von Helgoland

Zusammenfassung 1. Der aus dem Gezeitenstrom zwischen Insel und Düne Helgoland erstmalig isolierte PilzThraustochytrium kinnei n. sp. zeichnet sich durch besonderen Habitus und Entwicklungsgang von den bisher beschriebenen Arten des gleichen Formenkreises ab.2. Hierdurch bot er sich als leicht zu identifizierendes Objekt für die mitgeteilten Untersuchungen zur Ökologie mariner Niederer Pilze an.3. Wir verfolgen die Vorkommen Niederer Pilze der GattungenThraustochytrium, Schizochytrium und Dermocystidium an fünf Dauerstationen in der Wesermündung und der Deutschen Bucht. Hier zeigte sich, daßT. kinnei nur bei Helgoland in den Monaten Juli bis Dezember mit einiger Sicherheit aufzufinden war, während er im April bis Juni 1965 fehlte.4. Aus dem Verhalten vonT. kinnei und dem Fehlen einer typischen Gradation müssen wir schließen, daß es sich hierbei um einen Uferbewohner handelt, der in Zoosporenform im Gezeitenstrom mitgeführt wird.5. Weitere Untersuchungen zur Physiologie des Pilzes sind im Gange und sollen Aufschluß über seine spezifischen Ansprüche geben.

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Ecological investigations on a marine fungus from the area near Helgoland

A new fungusThraustochytrium kinnei n. sp. was isolated for the first time from tidal currents between the island Helgoland and its nearby dune. It is characterized by a habitus and life cycle different from those of related species previously described. These differences allow for an easy identification and thus make the new species a suitable object for ecological studies on lower marine fungi. The presence of lower fungi from the generaThraustochytrium, Schizochytrium andDermocystidum was recorded at 5 permanent stations in the Weser estuary and the German Bight.T. kinnei was found during the period from July to December and only near Helgoland. Its restricted distribution seems to indicate that the new species is a littoral form which is transported in the form of zoospores in the tidal currents. Further investigations on the physiology ofT. kinnei are presently being carried out.

     

Larval salinity tolerance of the South American salt-marsh crab, Neohelice (Chasmagnathus) granulata: physiological constraints to estuarine retention, export and reimmigration

The semiterrestrial crab Neohelice (=Chasmagnathus) granulata (Dana 1851) is a predominant species in brackish salt marshes, mangroves and estuaries. Its larvae are exported towards coastal marine waters. In order to estimate the limits of salinity tolerance constraining larval retention in estuarine habitats, we exposed in laboratory experiments freshly hatched zoeae to six different salinities (5–32‰). At 5‰, the larvae survived for a maximum of 2 weeks, reaching only exceptionally the second zoeal stage, while 38% survived to the megalopa stage at 10‰. Shortest development and negligible mortality occurred at all higher salt concentrations. These observations show that the larvae of N. granulata can tolerate a retention in the mesohaline reaches of estuaries, with a lower limit of ca. 10–15‰. Maximum survival at 25‰ suggests that polyhaline conditions rather than an export to oceanic waters are optimal for successful larval development of this species. In another experiment, we tested the capability of the last zoeal stage (IV) for reimmigration from coastal marine into brackish waters. Stepwise reductions of salinity during this stage allowed for moulting to the megalopa at 4–10‰. Although survival was at these conditions reduced and development delayed, these results suggest that already the zoea-IV stage is able to initiate the reimmigration into estuaries. After further salinity reduction, megalopae survived in this experiment for up to >3 weeks in freshwater, without moulting to juvenile crabs. In a similar experiment starting from the megalopa stage, successful metamorphosis occurred at 4–10‰, and juvenile growth continued in freshwater. Although these juvenile crabs showed significantly enhanced mortality and smaller carapace width compared to a seawater control, our results show that the late larval and early juvenile stages of N. granulata are well adapted for successful recruitment in brackish and even limnetic habitats.     

Laboratory spawning cues in Menidia beryllina,and M. peninsulae (Pisces,Atherinidae) with notes on survival and growth of larvae at different salinities

Synopsis Spawning patterns of inland silversides, Menidia beryllina, and tidewater silversides, Menidia peninsulae, were examined in the laboratory under several combinations of ‘tidal’ and diel light cycle cues. M. beryllina showed a high frequency of spawning throughout the day when held under constant conditions (24L: OD, current velocity 8 cm sec⁻¹) and when ‘tidal’ and diel light cycles were presented singly or in combination. In contrast, M. peninsulae demonstrated a high frequency of spawning only when presented a combination of ‘tidal’ and diel light cycle cues and spawned predominantly at night. Menidia beryllina embryos were euryhaline. Hatching ranged from 73 to 78% at salinities of 5,15 and 30‰ M. peninsulae embryos showed an inverse relationship between the percentage hatch and the incubation salinity, 90% at 5‰ and only 65% at 30‰ Survival and growth of larval M. beryllina from the day of hatching through 16 days old was optimal at 15‰ Although survival of M. peninsulae larvae was optimal at 30%, no trend was apparent in growth of larvae held for 16 days at 5, 15 or 30‰ salinity. Contribution No. 508 from the Gulf Breeze Environmental Research Laboratory