Larvae In Seawater Research Articles

Rapid detection of salmon louse larvae in seawater based on machine learning

The proliferation of salmon lice is one of the most challenging problems in salmon farming, seriously affecting the welfare of both farmed and wild salmonids. The detection of salmon lice in seawater, especially in the (pre-) infectious stage, supports the accurate management of salmon lice proliferation. Methods for detecting salmon lice in seawater to date involve traditional light and fluorescence microscopy and Polymerase Chain Reaction (PCR) methods. However, these methods require sample pre-processing and are laborious and time-consuming, rendering them difficult to apply for the task of continuous, rapid salmon lice detection in large water volumes. This study aims to develop a rapid and easy-to-use method for the detection of salmon lice in seawater. A novel approach was introduced for the detection of salmon lice at different larval stages in seawater by leveraging machine learning. A setup for the rapid acquisition of images of salmon lice in seawater was developed, and a dataset comprising 8316 images encompassing salmon lice “Nauplius Live,” “Nauplius Shell” and “Copepodite” was created. Then 16 object detection models including one- and two-stage Convolutional Neural Network (CNN-) based models and Transformer-based models were trained, tested, and compared on this comprehensive dataset. RT-DETR showed the best performance among all models tested with a precision of 0.972 and a recall of 0.978. The YOLO series models, except for YOLOv3, showcased remarkable inference speeds (ranging from 152 to 416 frames per second) while maintaining high precision (ranging from 0.968 to 0.977) and recall (ranging from 0.964 to 0.970). To our knowledge, this is the first time machine learning has been applied to the task of rapidly detecting salmon louse larvae at different stages in seawater samples. The results demonstrate that the machine learning approaches can achieve rapid easy-to-use and cost-effective detection of salmon lice in seawater. In the future, this study has the potential for application in measuring salmon louse larvae numbers in aquatic environments, supporting the enhancement of the welfare of both farmed and wild salmon.

A cold bath for a formalin-free laboratory: alternative fixative methods in early developmental stages of the sea urchin Paracentrotus lividus (Lamarck, 1816)

Fixatives are widespread in biological and medical research because they allow preserving specimens for a long time. Historically, formaldehyde has been the most used fixative so far, but new solutions are needed because of its carcinogenicity. In this study, we tested alternative fixative methods to find a harmless, economic, and simple-to-use methodology to fix samples for larval morphological analysis in Paracentrotus lividus. In two separate experiments, P. lividus embryos were fixed after 48 h post-fertilization by adding Formalin Free Tissue AccustainTM, NaOH-buffered Formalin Free Tissue AccustainTM, glacial ethanol and denatured ethanol at different concentrations (from 10 % to 70 %) and by submerging the vials containing the larvae in seawater at 0 °C and maintained at 4 °C for 144 h. Our results suggested that all the alternative fixatives tested do not guarantee a good quality of larvae for morphological purposes, while larvae that faced the thermal shock and were kept at 4 °C did not show any evidence of damage throughout time. The results of this study candidate this method as a good and safe substitute of formalin in studies that require morphological and taxonomic recognition and shed light on its use in other kinds of studies as well.

The abundance and larval performance of Aedes phoeniciae in supralittoral rock-pools

The mosquito Aedes phoeniciae is a potential disease vector that inhabits the coastal rock-pools of the Southeastern Mediterranean Sea. Our year-long study examined the abundance and distribution of Ae. phoeniciae in 49 rock-pools along HaBonim Beach Nature Reserve (Israeli coast) on a monthly basis (September 2016 to August 2017). Additionally, the physical, chemical, and biological characteristics of the rock-pools were measured. Our results showed a correlation between the abundance of Ae. phoeniciae and abiotic (salinity, pool volume, and pH) and biotic (bacterial, micro-phytoplankton, and chironomid abundance) characteristics. A complementary experiment was conducted to examine the role of bacteria and phytoplankton on Ae. phoeniciae larval performance by rearing larvae in seawater (SW) or seawater without microbes (FSW, 0.2-µm). Ae. phoeniciae grown in SW exhibited a high survivorship rate (~ 77%), while lower survivorship rate was measured in the FSW treatments (~ 45%). Furthermore, a higher number of adult females were found in the SW compared to FSW treatments (35 and 11, respectively), while the number of male adults remained similar. Our results suggest that Ae. phoeniciae larvae rely on the water characteristics and especially on the microbial communities that habitat the rock-pools. These results may enable improved mosquito control of Ae. phoeniciae along the Southeastern Mediterranean Sea.

The anti-biofouling behavior of high voltage pulse electric field (HPEF) mediated by carbon fiber composite coating in seawater

One of the most important research areas in the marine industry is to investigate new and effective anti-biofouling technologies. In this study, high voltage pulse electric field (HPEF) mediated by carbon fiber (CF) composite coating was utilized to prevent the fouling of bacteria, microalgae and barnacle larvae in seawater. The plate count, 2, 3, 5-triphenyl-tetrazolium chloride (TTC) reduction assay and neutral red (NR) staining and larval motility detection showed that the inactivation rates were at the highest levels, which reached 99.1%, 99.9%, 99.7%, 98.7% and 85% respectively for Pseudomonas sp., Vibrio sp., iron bacteria, Navicula sp. and the second stage nauplii of Balanus reticulatus, under the HPEF with 19 kV pulse amplitude, 23.15 kHz frequency and 0.5 duty cycle. The field-emission scanning electron microscopy (FE-SEM) of Navicula sp. revealed that the HPEF brought about the cell lysis and the cell organic matter release on the coating, which could be the mechanism of the inactivation by the HPEF. Additionally, the FE-SEM and Raman spectroscopy indicated that the HPEF hardly damaged the coating.

Rafting on floating fruit is effective for oceanic dispersal of flightless weevils.

Terrestrial species, especially non-vagile ones (those unable to fly or swim), cannot cross oceans without exploiting other animals or floating objects. However, the colonisation history of flightless Pachyrhynchus weevils, inferred from genetic data, reveals their ability to travel long distances to colonise remote islands. Here, we used captive-bred Pachyrhynchus jitanasaius to analyse (i) the physiological tolerance of weevils (egg, larva and adult stages) to different levels of salinity; (ii) the survival rate of larvae in a simulated ocean environment in the laboratory; and (iii) the survival rate of larvae in a field experiment in the ocean using fruit of the fish poison tree floating on the Kuroshio current in the Pacific Ocean. We found that the survival rate of larvae in seawater was lower than in fresh water, although if the larvae survived 7 days of immersion in seawater, some emerged as adults in the subsequent rearing process. No adults survived for more than 2 days, regardless of salinity level. After floating separately for 6 days in salt water in the laboratory and in the Kuroshio current, two of 18 larvae survived in the fruit. This study provides the first empirical evidence that P. jitanasaius larvae can survive 'rafting' on ocean currents and that the eggs and larvae of these weevils have the highest probability of crossing the oceanic barrier. This ability may facilitate over-the-sea dispersal of these flightless insects and further shape their distribution and speciation pattern in the Western Pacific islands.

Extralimital Senegalese species during Marine Isotope Stages 5.5 and 11 in the Canary Islands (29° N): Sea surface temperature estimates

The presence of Harpa doris Röding, 1798 in marine deposits of the last interglacial period, ~130–120ka (marine isotope stage or MIS 5.5) in the Canary Islands (Gran Canaria, Lanzarote and Fuerteventura) enabled us to compare this occurrence with its present habitat in the Gulf of Guinea and the Cape Verde Islands, well to the south. This comparison leads to the conclusion that sea surface temperatures (SSTs) in the waters around the Canary Islands during the last interglacial period were at least 3.3°C higher than today. H. doris is found in association with the large gastropod Persististrombus latus (Gmelin, 1791) as well as the coral Siderastrea radians (Pallas, 1766). The presence of these extralimital southern, warm-water species in the Canary Islands during the last interglacial period also implies a northward expansion of plankton-feeding larvae in seawater with a high chlorophyll-a content. Such conditions would require a shortening of the southern arm of the cool Canary Current that dominates the waters around the Canary Islands at present.Marine deposits dating to ~400ka (MIS 11) are also found on the Canary Islands. In these deposits, the presence of Saccostrea cucullata (Born, 1778) allows a comparison with its present habitat in the Gulf of Guinea. In this analysis, we conclude that SSTs in waters around the Canary Islands during this major interglacial period were at least 4.2°C higher than today. Middle Pleistocene fossils of S. cucullata have also been found in the western Mediterranean Sea and Morocco, as well as the Cape Verde Islands. If these deposits also date to MIS 11, SST warming could have been a regional phenomenon, including much of the eastern Atlantic Ocean and Mediterranean Sea.

Acidic Seawater can Promote Larval Metamorphosis in the Marine Mud Snail, Nassarius obsoletus

Abstract Elevated levels of atmospheric CO2 have had the unintended effect of acidifying the world's oceans by at least 0.1 pH unit since the beginning of the industrial revolution. Current models of the effects of continued CO2 release anticipate a further increase in ocean acidity by 0.14 to 0.4 pH units by the end of this century. Numerous marine organisms with calcareous shells or exoskeletons are expected to undergo deleterious effects, including shell or exoskeletal dissolution or calcification with increased metabolic costs. While many studies have documented potential effects of ocean acidity on adult calcareous organisms, less work has focused on embryonic or developmental changes. Alterations in ocean biochemistry can affect metabolic processes beyond calcification, and our investigations into the development of the local intertidal mudsnail, Nassarius obsoletus, led us to hypothesize that rising ocean acidity would increase incidents of larval shell decalcification, decrease larval growth rates, and induce precocious metamorphosis. As an initial study of potential effects of future acidic conditions on larval N. obsoletus, we raised larvae in seawater adjusted to lower than normal pH levels with hydrochloric acid (HCl), measured larval growth every 5 days in 15 randomly selected individuals from each culture, and conducted experiments on larval metamorphosis in physiologically competent larvae. We found no major trend in growth patterns of larvae from pH 8.2 to 7.7. However, results from a number of pharmacological experiments demonstrated that larvae grown in acidic conditions metamorphose more readily than controls. Our investigations are far from a definitive exploration of the effects of oceanic acidity on the development of this marine mollusc, but our data suggest that key developmental processes in marine invertebrates may be influenced in unexpected ways by continued climatic changes.

염분농도에 따른 해양미세조류(Nannochloropsis oculata)의 지질 및 지방산의 변화

The quality and quantity of food organisms in fish seed production are important. The marine microalgae Nannochloropsis oculata are used as initial food organisms in the field. We investigated the effects of salinity (0, 10, 20, 30, 40 and 50 psu) on the lipid and fatty acid composition of N. oculata. Cultivation of N. oculata at varying salinities showed the highest growth rate at 20 psu. Total lipid content ranged from 17.26 to 18.63% at salinities from 0 to 50 psu). The nonpolar lipid content increased markedly at 30 psu and was highest at 15.55%. The polar lipid content was lowest at 30 psu, by 84.45%. It was also found that the omega-3 and EPA contents were inversely proportional to salt concentration. For the polar and nonpolar lipid compositions, there was no significant effect of salinity. Omega-3 polyunsaturated fatty acid content especially the content of EPA in the seawater larvae is the essential fatty acid in this food organism. It is thus advantageous to culture N. oculata at 20 psu.

Effects of elevated pCO2 on the early development of the commercially important gastropod, Ezo abalone Haliotis discus hannai

We used an up-to-date, a high accuracy CO2 manipulation system to investigate the sensitivity of organisms to CO2 acidification, rearing marine calcifiers under elevated CO2 in running water. We evaluated the effects of elevated partial pressures of carbon dioxide (pCO2) in seawater on larvae of the commercially important marine gastropod Ezo abalone Haliotis discus hannai. In larval Ezo abalone, no effect of exposure to <1100 μatm pCO2 seawater was observed in fertilization, malformation, or mortality rates until 15 h after fertilization. However, compared to control larvae in seawater (450 or 500 μatm pCO2), the fertilization rate and the hatching rate (15 h after fertilization) decreased with increased pCO2 exposure (1650 and 2150 μatm pCO2) and the malformation rate increased significantly, with the larval shell length being smaller 75 h after hatching. These results suggest that ocean acidification will potentially impact the marine population of Ezo abalone as a human food source in the future.

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

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

EVALUATION OF THREE METHODS FOR TRANSPORTING LARVAE OF THE RED ABALONE HALIOTIS RUFESCENS SWAINSON FOR USE IN REMOTE SETTLEMENT

Three closed systems were evaluated for the transport of abalone larvae for use in remote settlement associated with mass culture activities. The first of these systems maintained the larvae in seawater, the second in seawater with oxygen added, and the third in wet condition without seawater but with oxygen added. Survival of the larvae was determined within each system over periods of 10, 16, and 36 h. In a separate experiment, larval settlement in aquaria was determined after holding the larvae in the three different transport systems for 10 h. The results showed the best survival was obtained for the larvae in water alone, with survival rates ranging from 97% at 10 h to 63% at 36 h. In the system without water these rates were 88–50% respectively. The use of oxygen in the transport systems only produced a positive effect at 36 h. Larval settlement after 10 h showed no significant differences in relation to transport system, from 60% settlement of larvae transported in water to 54% settlement of larvae in the wet condition, not suspended water.

Application of real-time PCR for simultaneous identification and quantification of larval abalone

A paucity of direct studies of marine invertebrate larval dispersal motivated the development of a high-throughput method for identification and quantification of pinto abalone ( Haliotis kamtschatkana) larvae in seawater. DNA extracted from sample retentate provided template to screen for species-specific cytochrome oxidase I (COI) mitochondrial DNA sequence via quantitative PCR (QPCR) technology. Primers and a dual-labeled probe were designed and used to identify and quantify DNA from the target species in blind tests of unknown samples alongside a standard template quantity series. Quantity estimates derived from QPCR standard curves were verified via direct enumeration of larvae using light microscopy. Multiplex reactions containing an internal positive control minimized underestimation of quantity and false negatives via partial or full PCR inhibition, respectively. Planned controlled field release and collection experiments to examine larval dispersion patterns via sampling over short and long postrelease times anticipate similar QPCR assays for other marine invertebrate species to aid investigations of larval dispersal in the marine environment.

Effect of humic acids on speciation and toxicity of copper to Paracentrotuslividus larvae in seawater

The effects of humic acid (HA) on the toxicity of copper to sea urchin Paracentrotus lividus larvae were studied in chemically defined seawater. Square Wave Anodic Stripping Voltammetry (SWASV) was employed to study the complexation of copper in seawater medium. A simple complexation model assuming one ligand type and a 1:1 reaction stoichiometry successfully explained the inverse titration experiments. A conditional stability constant of 6.53±0.05 and a complexating capacity of 230±7 μmol Cu/g HA were obtained. Sea urchin bioassay tests with two endpoints, embryogenesis success and larval growth were carried out in order to study the toxicity of dissolved copper in both the presence and absence of HA. The toxicity data obtained fitted well into a logistic model, and the high sensitivity of both endpoints (EC 50 were 41.1 μg Cu/l and 32.9 μg Cu/l, respectively) encourages their use for biomonitoring. The HA had a clearly protective effect, reducing the toxicity of Cu to the sea urchin larvae. The labile copper, rather than the total copper concentrations, explained the toxicity of the Cu–HA solutions, and the Cu–HA complexes appeared as non-toxic forms. These results are in agreement with the Free Ion Activity Model, because the labile Cu concentrations in this buffered and chemically defined medium covary with the free ion activity of the Cu, validating the model to naturally occurring HA in the marine environment.

Immunolocalization of Vacuolar-Type H+-ATPase in the Yolk-Sac Membrane of Tilapia (Oreochromis mossambicus) Larvae

To investigate the involvement of the yolk-sac membrane in ion absorption, developmental changes in whole-body cation contents, cellular localization of vacuolar-type H(+)-ATPase (V-ATPase), and size and density of pavement and chloride cells in the yolk-sac membrane were examined in tilapia (Oreochromis mossambicus) larvae in fresh water (FW) and those transferred to seawater (SW) at 2 days before hatching (day-2). The whole-body content of Na(+) in embryos and larvae adapted to both FW and SW increased constantly from day-2 to day 10, although they were not fed through the experiment. The yolk-sac membrane of FW larvae at days 0 and 2 showed V-ATPase immunoreactivity in pavement cells, but not in chloride cells. No positive immunoreactivity was detected in SW larvae. Whole-mount immunocytochemistry showed that some pavement cells were intensively immunoreactive, whereas others were less or not immunoreactive. Electron-microscopic immunocytochemistry revealed that V-ATPase immunoreactivity was present in the apical regions of pavement cells in FW larvae, especially in their ridges. The pavement cells in FW larvae were significantly smaller in size but higher in density than those in SW. These results suggest that pavement cells are the site of active Na(+) uptake in exchange for H(+) secretion through V-ATPase in FW-adapted tilapia during early life stages.

Effect of an organophosphorus insecticide, fenitrothion, on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg−1, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC50s ranged from 32.9 μg l−1 (Zoeae 2) to 10.7 μg l−1 (Mysis 3), and from 3.9 μg l−1 (Zoeae 3) to 2.0 μg l−1 (Mysis 3), respectively; 48 and 96 h LC50s in postlarvae (PL) at the same salinity ranged from 1.8 μg l−1 (PL1) to 0.6 μg l−1 (PL5), and from 0.3 μg l−1 (PL7) to 0.4 μg l−1 (PL15). In juveniles, 96 h LC50s were 0.8 μg l−1 in seawater and 1.5 μg l−1 in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC50. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal and sublethal concentrations of fenitrothion.

Development of multicellular complexes of chloride cells in the yolk-sac membrane of tilapia (Oreochromis mossambicus) embryos and larvae in seawater.

Morphological changes in the chloride cells (CCs) in the yolk-sac membrane of euryhaline tilapia (Oreochromis mossambicus) embryos and larvae were examined in relation to environmental salinity. Half of a brood of embryos spawned in fresh water (FW) were transferred directly to seawater (SW) 1 day before hatching; the other half was maintained in FW. The embryos and larvae in both FW and SW contained a rich population of CCs in the yolk-sac membrane; the CCs were visualized by whole-mount immunocytochemistry with an antiserum specific for Na+,K+-ATPase. The sectional areas of CCs increased markedly following SW transfer, whereas they remained small in the embryos and larvae maintained in FW. Scanning electron microscopy showed that the apical opening of CCs was enlarged in the fish transferred to SW. Transmission electron microscopy revealed enhanced cellular activity in SW, as evidenced by well-developed mitochondria and tubular systems. The CCs in SW frequently formed a multicellular complex, consisting of a main CC and one or two accessory cells. Accessory cells interdigitated with the main cells and extended their cytoplasmic processes to the apex of the main cell. The three-dimensional arrangement of the cells participating in the complex was identified by confocal laser scanning microscopy. Such complexes were rarely observed in FW fish. The activated CCs in the yolk-sac membrane in the SW fish probably function as ion-extruding sites during embryonic and larval stages until gill CCs become functional.

Morphological and Physiological Responses of Echinoderm Larvae to Nutritive Signals

SYNOPSIS. Echinoid larvae have been found previously to develop shorter arms as phytoplankton concentrations increase. In the present study, the skeletal dimensions of larvae of the sea urchins Lytechinus pictus and Strongylocentrotus purpuratus were measured after exposure to dissolved organic compounds in seawater. The presence of glucose or individual amino acids (at 1 or 2 μM), a mixture of 16 different amino acids (100 nM each), or algal exudate resulted in larvae with shorter arms (by 12 to 88%), relative to larvae in seawater with no additions. Larvae exposed to mixtures of amino acids also had changes in the constituents of their internal free amino acid pools (as determined by HPLC). For another echinoid, Dendraster excentricus, amino acid transport (T, from 500 nM) by individual larvae (n = 47) scaled to arm length (L) as follows: T = 2.06L0.81 (0.81 ± 0.26,95% confidence intervals). Mass (M) and metabolic rate (MR) did not scale in the same manner (as transport) to arm length for larvae of the echinoid Centrostephanus coronatus (MR = 148L1.51; M = 1.7L2.01). These characteristics may scale to arm length independently from transport rate under certain conditions. Larvae of echinoderms respond morphologically to “signals” in their environment that may indicate the availability of dissolved and paniculate nutrients. This in turn will have consequences for their ability to take up and metabolize these nutrients. The response may be mediated by surface receptors for dissolved organic compounds, or by changes in the sizes of intracellular substrate pools.

Electron-microscopic studies of iodine-binding and peroxidase activity in the endostyle of the larval amphioxus (Branchiostoma lanceolatum)

The asymmetric endostyle in the larval amphioxus (Branchiostoma lanceolatum) was examined by light-and electron-microscopic cytochemistry (peroxidase; incubation in diaminobenzidine) and autoradiography (incubation in 125I-). Compared to the adult the same cellular zones were also found in the larval endostyle, with the exception of zone 1, which was absent. The corresponding adult and larval zones had a similar morphology. All cells in zones 5a, 5b, and 6 were reactive for peroxidase. A reaction product was also present in the lateral 2 to 3 cell rows of zone 3. The dense reaction product was located on the inner surface of membranes of the rough endoplasmatic reticulum, Golgi apparatus and vesicles, and multivesicular bodies as well as on the outer surface of the luminal plasma membrane. An incomplete row of granule-containing, peroxidase-negative cells was located between zones 5b and 6. After incubation of larvae in sea water containing 125I-, autoradiographic grains were selectively concentrated over the lumen at the apical surface of all peroxidase-positive zones. The highest grain density occurred in relation to zone 5a, which in the adult has been recognized as the iodination center. Few grains were located over the cytoplasm. Methimazole, an inhibitor of peroxidase, abolished the cytochemical reaction and the appearance of autoradiographic grains. The observations indicate that iodination in the larval endostyle takes place extracellularly and is catalyzed by peroxidase bound in the plasma membrane.

Osmoregulation and respiration in a marine chironomid larva, Paraclunio alaskensis Coquillett (Diptera, Chironomidae)

The hemolymph of larvae acclimated in freshwater (19 mosmol/L) and seawater (897 mosmol/L) was analyzed and levels of Na+ (191 mM, 247 mM), Mg2+ (8 mM, 14 mM), Cl− (60 mequiv./L, 126 mequiv./L), and osmolarity (417 mosmol/L, 530 mosmol/L) were determined. Paraclunio alaskensis larvae were shown to be both euryhaline and hyperosmotic and hyposmotic regulators. The isotonic point of the hemolymph was 475 mosmol. Whole larvae contained 72% water and actively regulated water content (signified by changes in weight) over a wide range of external media. The basal respiration rate of larvae in seawater (0.032 μg O2∙mg dry weight−1∙h−1) indicated active cuticular respiration. The significance of these findings in relation to the intertidal habitat is discussed.

Larval Anisakis simplex (Rudolphi, 1809, det. Krabbe, 1878) and larval Hysterothylacium sp. (Nematoda: Ascaridoidea) in euphausiids (Crustacea: Malacostraca) in the North-East Atlantic and northern North Sea

ABSTRACTOver 26000 specimens representing five euphausiid species collected, mostly in 1969, in the North-East Atlantic and northern North Sea were examined for parasites. Hysterothylacium sp. larvae were rare, occurring in only two euphausiid samples from inshore localities; the 9 larvae found (3.8 to 12.3 mm long) are described and illustrated. Infection with larval Anisakis simplex was virtually restricted to Thysanoessa spp. and appeared to be discontinuous. Infection was absent to the west of Scotland, and rare to the north of Scotland and at the Faroes. Larval A. simplex was not uncommon in offshore regions of the northern North Sea at depths between 100 and 200 m; the prevalence rate there for individual euphausiid species in individual samples was mostly 0 to 40% but an exceptionally high rate of 78.0% was recorded. Larvae in euphausiids do not become encapsulated but appear to remain active. Experimental observations on the sedimentation rate of A. simplex eggs and hatched larvae in sea water at 10°C are discussed in relation to embryonation and hatching at different temperatures, and depth of the sea. New host records are claimed for larval A. simplex in Nyctiplutnes couchii, and for larval Hysterothylacium sp. in Thysanoessa inermis. No individual euphausiid harboured more than one parasite, either larval nematode or ellobiopsid (see also SMITH, 1981). Morphological and morphometric observations on larval A. simplex from euphausiids are reported elsewhere (SMITH, 1983).