Feeding response of the polychaete Sabellaria alveolata (Sabellariidae) to changes in seston concentration

Sabellaria alveolata is a tube-building gregarious polychaete that constructs large biogenic reefs. In macrotidal shellfish ecosystems, this species competes for food with cultivated suspension-feeders. The suspension-feeding activity and clearance rate of S. alveolata were investigated in response to changes in seston concentration. A flow-through system was designed to study 225 cm² reef blocks with more than 500 individuals. The experimental conditions were characterized by increasing concentrations of suspended particulate matter ranging from 6.5 to 153.8 mg L⁻¹, while the organic content of the diet (microalgae Skeletonema costatum) decreased inversely from 49 to 9%, to mimic the dilution of organic matter by inorganic particles, characteristic of tidal resuspension. We showed that the clearance rate exponentially decreased in relation to an increase in SPM concentration. Clearance rate was estimated at 5.3 10^− 3 L h^− 1 or 0.93 L h^− 1 g^− 1 (dry weight) for the lowest seston concentration (SPM = 6.5 mg L^− 1) and reached the asymptote at CR = 1.97 10^− 3 L h^− 1 or 0.35 L h^− 1 g^− 1 (dry weight) when SPM exceeded 45 mg L^− 1. Using picture analyses of polychaete movements, we showed that, paradoxically, an increase in SPM concentration did not adversely affect the feeding activity of S. alveolata since the number of filtering individuals remained stable from SPM = 6.5 to 55.5 mg L^− 1. These values were applied at the scale of the bay of Mont-Saint-Michel (France) to demonstrate that the filtration pressure of large populations of wild suspension-feeders should not be underestimated when the carrying capacity has to be assessed in the context of increasing bivalve cultures.     

Brooding in the Chilean Oyster Ostrea chilensis: Unexpected Complexity in the Movements of Brooded Offspring within the Mantle Cavity

Brooding in invertebrates serves to protect embryos from stressful external conditions by retaining progeny inside the female body, effectively reducing the risk of pelagic stages being exposed to predation or other environmental stressors, but with accompanying changes in pallial fluid characteristics, including reduced oxygen availability. Brooded embryos are usually immobile and often encapsulated, but in some Ostrea species the embryos move freely inside the female pallial cavity in close association with the mother’s gills for as long as eight weeks. We used endoscopic techniques to characterize the circulation pattern of embryos brooded by females of the oyster, Ostrea chilensis. Progeny at embryonic and veliger stages typically circulated in established patterns that included the use of dorsal and ventral food grooves (DFG, VFG) to move anteriorly on the gills. Both embryos and veligers accumulated around the mother’s palps, and remained there until an active maternal countercurrent moved them to the gill inhalant area. Both food grooves were able to move embryos, veligers, and food-particle aggregates anteriorly, but the DFG was more important in progeny transport; early embryos were moved more rapidly than veligers in the DFG. A microcirculation pattern of embryos was apparent when they were moved by gill lamellae: when they were close to the VFG, most embryos lost gill contact and ´´fell´´ down to the DFG. Those that actually reached the DFG moved anteriorly, but others came into contact with the base of the lamellae and again moved towards the VFG. The circulation pattern of the progeny appears well-suited for both cleaning them and directing them posteriorly to an area where there is more oxygen and food than in the palp region. This process for actively circulating progeny involves the feeding structures (gill and palps) and appears to be energetically costly for the female. It also interferes with feeding, which could explain the poor energy balance previously documented for brooding females of this species.     

Carbon isotope signatures reveal that diet is related to the relative sizes of the gills and palps in bivalves

In marine bivalves, the relative sizes of the gills and palps appear to be a useful functional trait that reflect feeding mode, i.e. suspension feeders have relatively larger gills than palps for pumping, whereas deposit feeders have relatively larger palps than gills for sorting. Also, within a species, the relative sizes of the gills and palps are related to changes in local food conditions. However, there is still no firm evidence showing that differences in the relative gill and palp sizes between species are related to diet selection. Based on the knowledge that carbon and nitrogen isotope signatures of an animals tissues reflect past diet, we compared the relative gill and palp sizes of bivalves from Roebuck Bay, northwestern Australia with their carbon and nitrogen isotope signatures. The carbon isotope signatures distinguished clear differences in diet between bivalves along a gradient from suspension to deposit feeding, and strikingly this pattern was closely followed by the relative sizes of the gills and palps of the bivalves. This study confirms that relative gill and palp sizes in bivalves are a functional trait that can be used to compare resource use between species. Furthermore, these data may suggest that morphospace occupation, as determined by relative gill and palp sizes of bivalves, could reflect a gradient of resource use between species.     

Impact of seston characteristics on qualitative particle selection sites and efficiencies in the pseudolamellibranch bivalve Crassostrea gigas

To date, knowledge of the qualitative particle selection sites and conditions in the widely-distributed bivalve Crassostrea gigas is incomplete, having focussed either on heterogeneous particles, or on particles intentionally too large to enter the gill principal filament tracts. We used endoscope-directed sampling and the intact diatom-empty, cleaned frustule approach to unambiguously establish qualitative selection sites and the influence of seston quality (varying proportions of intact diatoms and empty, cleaned frustules) and quantity (particle loads) on the degree of qualitative selection. Normally-feeding oysters were presented test mixtures of the naturally-occurring Actinoptychus senarius (small enough to enter the gill principal filaments), and the potential selection sites (gill: dorsal and ventral collecting tracts; labial palps: anteriorly-deposited pseudofaeces), were sampled for comparison with the proportions and concentrations of the ambient medium. Qualitative selection was demonstrated at both the gills and labial palps. Gill selection efficiency was shown to be directly proportional to seston quality and quantity, using a technique independant of pseudofeces mucus content. The oyster gill is thus able to increase ingested food quality when environmental food quality is low and / or when seston concentrations are high, which is typical of oyster habitats. Palp selection efficiency was directly proportional to seston quality, but at the highest concentration tested, no qualitative selection was observed on the labial palps, probably due to overload on these smaller organs. The partial functional redundancy of these key processing organs in heterorhabdic species such as oysters and scallops may enhance their success in high-turbidity habitats.     

Influence of diet on pre-ingestive particle processing in bivalves: II. Residence time in the pallial cavity and handling time on the labial palps

Previous studies have demonstrated that bivalve molluscs respond to changing food conditions through processes such as preferential selection and ingestion of particulate matter. Little is known, however, about the underlying mechanisms accountable for these responses. To further explain feeding processes at the level of the pallial organs, we determined pallial cavity residence times, or the amount of time it took particles to travel from the inhalant aperture to the stomach, in two species of bivalves, Crassostrea virginica and Mytilus edulis, under conditions of differing particle quality, particle concentration, and temperature. From these residence times, particle-handling times on the labial palps were determined. Diets of three different qualities were tested, including Rhodomonas lens cells, particles prepared from ground Spartina sp. detritus, and a 50/50 mixture of both. Bivalves were delivered one of the three diets along with 10-μm fluorescent polystyrene beads (tracer), removed from feeding chambers at intervals from 30 s up to 20 min, and placed in liquid nitrogen to halt particle transport. Digestive systems of bivalves were then dissected and examined for the presence of tracer beads. Particle-residence times in the pallial cavity and handling times on the labial palps of C. virginica were significantly affected by changes in diet type. Particle-handling times on the palps decreased with increasing diet quality and ranged from 2.2 min (100% R. lens) to 22.8 min (100% ground Spartina sp.), accounting for 88% and 99%, respectively, of the total time particles spent in the pallial cavity. In contrast, diet quality had little effect on particle-residence times in the pallial cavity of M. edulis. However, residence times were affected by temperature and diet concentration. Temperature significantly affected residence times at particle concentrations of both 20 and 100 particles μl⁻¹, whereas particle concentration affected residence times at 20 °C, but not at 5 °C. Particle-handling times on the labial palps ranged from less than 1 to 5.5 min, depending on temperature and concentration, accounting for 50% to 82%, respectively, of the total time particles spent in the pallial cavity. We suggest that (1) observed interspecific differences in particle handling on the labial palps may be due to differences in palp morphology and function, and (2) particle sorting and selection on the labial palps is a rate-limiting step of pre-ingestive feeding processes in by bivalves.     

The sorting of food particles by Abra sp. (bivalvia: tellinacea)

The selection of food particles by Abra tenuis (Montagu), A. alba (Wood) and A. nitida (Müller) has been investigated.Material for ingestion smaller than 30μm is not selected according to size by A. tenius. Particles smaller than 0.5 μm are retained by the palliai organs and ingested but only particles larger than 1 μm appear to be retained with an efficiency approaching 100 %. The mesh size of the gill filter is found to be ≈ 3.0 × 0.5 μm.A. tenuis does not appear able to discriminate between particles smaller than 20 μm by their food value; however, relatively large silica particles which are devoid of food are partially rejected by the labial palps in favour of particles of similar size but having a bacterial coating. To a lesser extent the physical nature of particles seems to influence their selection by A. tenuis; clean angular particles are rejected in favour of clean rounded ones.Small, light particles appear to be transported on the gills directly to the mouth without coming into contact with the palps. Larger, heavier particles tend to drop from the gill to be caught by the palps which extend posteriorly to cup the entire ventral margin of the inner demibranch when the animal is feeding.The material ingested by A. alba is significantly finer than that taken into the mantle cavity indicating that the pallial organs actively select food by size. Selection of material for ingestion by size in A. nitida appears to be optional since only some of the animals examined had stomach contents significantly finer than material from the mantle cavity.     

Filter feeding,deviations from bilateral symmetry,developmental noise,and heterochrony of hemichordate and cephalochordate gills

We measured gill slit fluctuating asymmetry (FA), a measure of developmental noise, in adults of three invertebrate deuterostomes with different feeding modes: the cephalochordate Branchiostoma floridae (an obligate filter feeder), the enteropneusts Protoglossus graveolens (a facultative filter feeder/deposit feeder) and Saccoglossus bromophenolosus (a deposit feeder). FA was substantially and significantly low in B. floridae and P. graveolens and high in S. bromophenolosus. Our results suggest that the gills of species that have experienced a relaxation of the filter feeding trait exhibit elevated FA. We found that the timing of development of the secondary collagenous gill bars, compared to the primary gill bars, was highly variable in P. graveolens but not the other two species, demonstrating an independence of gill FA from gill bar heterochrony. We also discovered the occasional ectopic expression of a second set of paired gills posterior to the first set of gills in the enteropneusts and that these were more common in S. bromophenolosus. Moreover, our finding that gill slits in enteropneusts exhibit bilateral symmetry suggests that the left‐sidedness of larval cephalochordate gills, and the directional asymmetry of Cambrian stylophoran echinoderm fossil gills, evolved independently from a bilaterally symmetrical ancestor.     

Does skimming flow reduce population growth in horse mussels?

Skimming flow was induced in a field flow-through flume with model and live horse mussels as roughness elements. A growth experiment was conducted in the flume with locally available seawater and natural seston. Horse mussel population growth was compared in turbulent isolated element (control) and skimming flow (treatment) and with regulated natural seston levels, indicated by C = bulk flow seston concentration, C¹ = seston concentration in the benthic boundary layer, near the inhalant, which just meets the maintenance ration of the mussel population. We were able to control the bulk seston within the range: 1.2 to 5 times of C¹ during the growth experiment. No significant difference between control and skimming flow treatments was found in: tissue growth, RNA-DNA ratios, or condition factor. Extrapolating from the experimental results we predict that under minimum growth enhancing seston concentrations at a high horse mussel density (71 m²), skimming flow does not reduce population growth.     

Survival,osmoregulation and ammonia-N excretion of blue swimmer crab, Portunus pelagicus, juveniles exposed to different ammonia-N and salinity combinations

Ammonia-N toxicity to early Portunus pelagicus juveniles at different salinities was investigated along with changes to haemolymph osmolality, Na⁺, K⁺, Ca²⁺ and ammonia-N levels, ammonia-N excretion and gill Na⁺/K⁺-ATPase activity. Experimental crabs were acclimated to salinities 15, 30 and 45‰ for one week and 25 replicate crabs were subsequently exposed to 0, 20, 40, 60, 80, 100 and 120 mg L^− 1 ammonia-N for 96-h, respectively. High ammonia-N concentrations were used to determine LC₅₀ values while physiological measurements were conducted at lower concentrations. When crabs were exposed to ammonia-N, anterior gill Na⁺/K⁺-ATPase activity significantly increased (p < 0.05) at all salinities, while this only occurred on the posterior gills at 30‰. For crabs exposed to 20 and 40 mg L^− 1 ammonia-N, both posterior gill Na⁺/K⁺-ATPase activity and ammonia-N excretion were significantly higher at 15‰ than those at 45‰. Despite this trend, the 96-h LC₅₀ value at 15‰ (43.4 mg L^− 1) was significantly lower (p < 0.05) than at both 30‰ and 45‰ (65.8 and 75.2 mg L^− 1, respectively). This may be due to significantly higher (p < 0.05) haemolymph ammonia-N levels of crabs at low salinities and may similarly explain the general ammonia-N toxicity pattern to other crustacean species.     

Functional anatomy of the respiratory system of Branchipolynoe species (Polychaeta, Polynoidae), commensal with Bathymodiolus species (Bivalvia, Mytilidae) from deep-sea hydrothermal vents

 The gills of three species of Branchipolynoe have been studied in order to better understand the morphological and anatomical adaptations of their respiratory system. These Polynoidae live commensally inside the pallial cavity of different species of Bathymodiolus (Mytilidae), found clustered near deep-sea hydrothermal vents and cold seeps, and which harbor chemolithoautotrophic bacteria in their gills. As the mussels exploit hydrothermal fluid, the pallial cavity is perfused with a sulfide-rich hydrothermal water. The gills of Branchipolynoe species are well-developed branched outgrows of the body wall, located on the parapodia, and filled with coelomic fluid. They do not contain blood vessels. Living animals are red, due to the presence of extracellular hemoglobins in the coelom. The gill epidermis is made of supporting cells and a few ciliated cells arranged in longitudinal rows along the branches. Myoepithelial and ciliated cells line the interior of the coelomic cavity which contains the respiratory pigments. Coelomic fluid circulation inside the gills and body cavity is probably facilitated by both the cilia and myoepithelial contractions. The cuticle, the epidermis, and the coelomic epithelium are completely devoid of bacteria. The gill surface areas per unit body weight and the minimum diffusion distances, between external milieu and coelomic hemoglobins, have been calculated and compared with data already obtained on vascular gills of littoral or hydrothermal species of Polychaeta. In Branchipolynoe species, the respiratory surface area is very large, similar to that of a free-living hydrothermal species Alvinella pompejana, and the minimum diffusion distance is short, similar to that of the littoral species Arenicola marina. Although the organization of these coelomic gills in Branchipolynoe species is totally different from that of usual vascular gills, their characteristics represent a unique and effective respiratory system in Polynoidae which has adapted to the hypoxic and sulfide-rich micro-habitat which probably holds in the mantle cavity of vent mussels. In the gill epidermis, numerous secondary and large compound lysosomes are present which might be involved in sulfide detoxification. Accepted: 5 August 1998     

Effects of seston variability on the clearance rate and absorption efficiency of the mussels Aulacomya maoriana, Mytilus galloprovincialis and Perna canaliculus from New Zealand

The clearance rates (CR in l g⁻¹ h⁻¹) and net absorption efficiencies (AE) of three co-occurring mytilid species were estimated to determine the effects of variation in ambient seston quantity (total particulate matter, TPM, mg l⁻¹) and quality (particulate organic matter, POM, mg l⁻¹; percent organic matter, PCOM=POM/TPM) on these physiological functions. CR_S estimates were significantly different among the species (Mytilus galloprovincialis>Perna canaliculus=Aulacomya maoriana), but were not correlated with differences in species-dependent mean body size (P. canaliculus>M. galloprovincialis>A. maoriana). AE estimates were independent of mean body weight, and did not differ among the species. For all three species, CR responded in a simple linear manner to seston organic content, either in terms of POM (for A. maoriana and M. galloprovincialis), or PCOM (for P. canaliculus). The AE response, although also of a simple linear type, was species-dependent and involved interactions of two or three seston components: TPM, POM and PCOM for A. maoriana; POM and PCOM for M. galloprovincialis; and TPM and PCOM for P. canaliculus. For all three species, seston variation explained 15-20% of the variation in CR and 52-59% of the variation in AE. Comparisons among the species indicated that two very different responses to variation in seston quantity and quality exist. First, significant differences in CR result from species-dependent differences in the magnitude of the response to seston variation. Second, species-dependent responses to variation in seston variation resulted in the similarity of the AE responses. Thus, the three species appear to have evolved different strategies for dealing with seston variation, but with the end result that their AE responses do not differ. Finally, no evidence was found of a negative association between CR and AE for any of the three species, suggesting that under the seston conditions experienced in this work, these species do not have the physiological compensatory capacity to reduce CR in order to increase AE. The importance of a comparative (i.e., multi-species) approach utilising ambient seston is emphasised by the findings of this research if we are to understand better the feeding and digestive physiologies of suspension-feeding organisms such as mussels.     

Nutritional value of the cryptophyte Rhodomonas lens for Artemia sp.

Juvenile or adult Artemia sp. are often used as live prey for the rearing of early life stages of some crustacean, fish and cephalopod species. The improvements of both Artemia growth and its biochemical composition are key issues for the suitable use of Artemia biomass in these rearing processes. In this study we evaluated the growth and survival rates of Artemia fed with the cryptophyte Rhodomonas lens in comparison with different microalgal species commonly used in aquaculture: the prasinophyte Tetraselmis suecica, the prymnesiophyte Isochrysis galbana Parke, and the eustigmatophyte Nannochloropsis gaditana. Microalgae were cultured semi-continuously in nutrient saturated conditions and with a daily renewal rate of 30% of the volume of cultures, to obtain biomass of controlled and optimized composition. Considerable differences in Artemia growth were observed, as well as in the survival rate. At day 8 of rearing, Artemia fed R. lens had the highest length (4.9 ±0.6 mm, P < 0.001), followed by individuals fed T. suecica (4.2 ± 0.7 mm), I. galbana (3.6 ± 0.7 mm) and finally those fed N. gaditana (1.5 ± 0.2 mm). The survival rate of Artemia fed N. gaditana (18 ± 3%) was much lower (P < 0.001) than values found for the remaining groups (69 to 88%). The growth rate of Artemia obtained with R. lens was in general much higher than with other microalgal diets previously reported in the literature. The higher protein content of R. lens could explain the higher growth obtained with this species, but differences of Artemia growth with the different diets could not be explained solely on the basis of the gross composition of microalgae. Factors such as cell size and digestibility all seem to contribute to the results observed. Another trial was carried out to investigate differences in Artemia growth and on its biochemical composition when fed the best two diets: R. lens or T. suecica. The fatty acid (FA) and total amino acid (AA) composition of both microalgal species and the composition of Artemia were assessed as well. As found in the first experiment individuals fed R. lens (group ARHO) grew faster than those fed T. suecica (group ATET), attaining 3.6 ± 0.3 mm and 3.2 ± 0.4 mm (P < 0.001), respectively, after 5 days of rearing. The much higher AA content obtained in R. lens may be on the basis of the higher growth obtained with this species. Protein and carbohydrate levels in Artemia juveniles were very similar in both groups (64-68% of dry weight, and 8-10%, respectively). Lipid was slightly lower in ARHO (12%) than in ATET (15%, P < 0.01). Regarding the FA composition, juveniles from group ARHO contained higher levels of eicosapentaenoic acid (EPA, 6.2%) than juveniles from ATET (4.1%, P < 0.01), whereas docosahexaenoic acid (DHA) was only found in juveniles from ARHO (1.1%). Taking into account that the daily productivity of R. lens culture was higher than, or at least equal, the remaining microalgal species this cryptophyte is confirmed as an excellent diet to optimize the growth of Artemia, as well as to improve its biochemical composition.     

Effect of deltamethrin on the gills of Aphanius dispar: a microscopic study

Aphanius dispar, a freshwater fish (mean total length ± sd, 3.42 ± 0.33 cm) was exposed to different concentrations of deltamethrin (2.25, 2.50 and 3.00 μg L⁻¹), an insecticide used to control Dubas bug, Ommatissus lybicus in Oman. The histopathological changes in the structure of the gills in fish exposed to deltamethrin was studied using light, transmission and scanning electron microscopy. In light microscopy, the fish exposed to 2.25 μg L⁻¹ deltamethrin, showed hypertrophy and hyperplasia of chloride cells, while in 2.50 μg L⁻¹, additional changes like vacuolization, lifting of the lamellar epithelium and fusion of secondary lamellae were observed. The most severe alteration including vacuolization, desquamation of cells and dilation of intercellular space was recorded at 3.00 μg L⁻¹. Transmission and scanning electron microscopy, supports the findings of light microscopy and further document the ultrastructural damage caused, especially in exposure to 2.50 and 3.00 μg L⁻¹. Al l changes observed are described in detail. The deltamethrin exposure concentration of 2.25 μg L⁻¹ seems to be a threshold above which any small increase in concentration results in severe damage. All present results have been compared with those of previous studies on gill damage caused by various chemical substances. The impacts of the damage on the functioning of gills as a respiratory organ are discussed.     

Stable isotope fractionation in the digestive gland, muscle and gills tissues of the marine mussel Mytilus galloprovincialis

Mytilus galloprovincialis is a common species in the Mediterranean. It is a sedentary filter-feeding organism that assimilates carbon and nitrogen isotopic ratios in tissues from its food sources. The δ¹³C and δ¹⁵N values have been used to demonstrate differences in isotopic composition between digestive gland, muscle and gills of this mussel. For δ¹³C, mean values were - 21.99 ± 0.50‰, - 19.70 ± 0.44‰, and - 19.96 ± 0.44‰, respectively; and for δ¹⁵N, they were 5.16 ± 0.90‰, 7.67 ± 0.79‰ and 7.77 ± 0.85‰, respectively. The fractionation or enrichment factor for ¹³C values between digestive gland and muscle, between digestive gland and gills, and between muscle and gills were - 2.29 ± 0.16‰, - 2.04 ± 0.14‰ and 0.27 ± 0.07‰, respectively, within the expected range of ¹³C fractionation at filter feeders reported elsewhere. In contrast, low fractionation values were found for ¹⁵N with - 2.45 ± 0.24‰, - 2.51 ± 0.16‰ and - 0.11 ± 0.16‰, between digestive gland and muscle, between digestive gland and gills, and between muscle and gills, respectively. Through isotopic fractionation of M. galloprovincialis, the depleted values were found in the digestive gland, followed by gills and then by muscle tissue. Statistical analysis (PERMANOVA) was performed to check for significant differences in δ¹³C and δ¹⁵N isotopic signatures between tissues and localities. The current study demonstrates significant differences in the δ¹³C and δ¹⁵N isotopic composition between digestive gland, muscle and gills tissues in M. galloprovincialis living in the oligotrophic environment of the Balearic Islands.     

3D models of lamprey corticoid receptor complexed with 11-deoxycortisol and deoxycorticosterone

The serum of Atlantic sea lamprey, a basal vertebrate, contains two corticosteroids, 11-deoxycortisol and deoxycorticosterone. Only 11-deoxycortisol has high affinity [K_d ∼ 3 nM] for the corticoid receptor [CR] in lamprey gill cytosol. To investigate the binding of 11-deoxycortisol to the CR, we constructed 3D models of lamprey CR complexed with 11-deoxycortisol and deoxycorticosterone. These 3D models reveal that Leu-220 and Met-299 in lamprey CR have contacts with the 17α-hydroxyl on 11-deoxycortisol. Lamprey CR is the ancestor of the mineralocorticoid receptor [MR] and glucocorticoid receptor [GR]. Unlike human MR and human GR, the 3D model of lamprey CR finds a van der Waals contact between Cys-227 in helix 3 and Met-264 in helix 5. Mutant human MR and GR containing a van der Waals contact between helix 3 and helix 5 display enhanced responses to progesterone and glucocorticoids, respectively. We propose that this interaction was present in the CR and lost during the evolution of the MR and GR, leading to changes in their response to progesterone and corticosteroids, respectively.     

Tissue damage and leukocytic infiltration following attachment of the mite Unionicola intermedia to the gills of the bivalve mollusc Anodonta anatina

Unionicola intermedia lives as a parasite in the gill region of Anodonta anatina. It attaches to the gills of its host by means of the pedipalps which cause displacement, rupture, and erosion of the gill epithelium. The pedipalps are sunk deeply into the underlying connective tissue of the gills and produce a leukocytic infiltration into the damaged area and a consequent edema of the gill filaments.     

Cloning and localization of MCdef, a defensin from Manila clams (Ruditapes philippinarum)

A defensin-like peptide was previously detected in hemocytes of Manila clams (Ruditapes philippinarum). In the current study, we cloned and characterized this defensin, designated MCdef. Cloning produced a full-length gene sequence of 201 bp predicted to encode a 66-amino-acid precursor protein maturing to a 44-amino-acid residue. Amino acid sequence analysis showed that MCdef is similar to defensins from marine mollusks and ticks. Phylogenetic analysis suggested that MCdef is closely related to defensins from Mytilus galloprovincialis (Mediterranean mussel) and Crassostrea gigas (Pacific cupped oyster). The three-dimensional structure of MCdef was modeled using the solution structure of C. gigas defensin as a template. With the exception of three variable loop areas, the modeled structure of MCdef was identical to that of C. gigas defensin. MCdef antiserum was raised against a synthetic MCdef peptide and verified by Western blotting using recombinant MCdef. RT-PCR analysis demonstrated high levels of MCdef mRNA in hemocytes and adductor, foot, gill, mantle, palp, and siphon tissues of Vibrio tapetis-infected Manila clams, whereas in V. tapetis-uninfected Manila clams, the level of MCdef mRNA was low in adductor, palp, and siphon tissues and even lower in the other tested tissues. Immunohistochemical analysis revealed high MCdef expression was detected in the gill, the mantle, and the digestive tubules of the diverticulum of V. tapetis-infected Manila clams. Minimum inhibitory concentration (MIC) of the purified rMCdef was determined. MCdef showed highest activity against Streptococcus iniae and Staphylococcus aureus.     

Effect of water temperature,salinity, and their interaction on growth,plasma osmolality,and gill Na,K-ATPase activity in juvenile GIFT tilapia Oreochromis niloticus (L.)

We used a central composite rotatable experimental design and response surface methodology to evaluate the effects of temperature (18–37 °C), salinity (0–20‰), and their interaction on specific growth rate (SGR), feed efficiency (FE), plasma osmolality, and gill Na⁺, K⁺-ATPase activity in GIFT tilapia juveniles. The linear and quadratic effects of temperature and salinity on SGR, plasma osmolality, and gill Na⁺, K⁺-ATPase activity were statistically significant (P<0.05). The interactive effects of temperature and salinity on plasma osmolality were significant (P<0.05). In contrast, the interaction term was not significant for SGR, FE, and gill Na⁺, K⁺-ATPase activity ⁽P>0.05). The regression equations for SGR, FE, plasma osmolality, and gill Na⁺, K⁺-ATPase activity against the two factors of interest had coefficients of determination of 0.944, 0.984, 0.966, and 0.960, respectively (P<0.01). The optimal temperature/salinity combination was 28.9 °C/7.8‰ at which SGR (2.26% d¹) and FE (0.82) were highest. These values correspond to the optimal temperature/salinity combination (29.1 °C/7.5‰) and the lowest plasma osmolality (348.38 mOsmol kg⁻¹) and gill Na⁺, K⁺-ATPase activity (1.31 µmol Pi. h⁻¹ g⁻¹ protein), and resulted in an energy-saving effect on osmoregulation, which promoted growth.     

Morphological observations on the gills of dendrobranchiate shrimps

Gill morphology, traditionally, has played an important role in attempts to reconstruct the phylogenetic history of the Crustacea Decapoda. We examined the gills of dendrobranchiate shrimps (Crustacea, Decapoda, Dendrobranchiata) to test the assumption that all members of the clade have gills that are “dendrobranchiate” (highly branching) in form, from whence the taxon name Dendrobranchiata comes. Currently, the Dendrobranchiata consists of two superfamilies and seven families. Specimens from two genera in each of the known families were examined using light and scanning electron microscopy. Members of the family Luciferidae, all of which lack gills as adults, were not examined. Only one genus was examined for the Penaeidae (because they have been the subject of numerous previous studies) and Sicyoniidae (a monogeneric family). All gills examined have secondary branches that are further subdivided, conforming to existing and rather broad definitions of dendrobranchiate gills. Families with “typical” dendrobranchiate gills, which consist of curved secondary branches that in turn bear branched (dendritic) tubular tertiary elements on their distal surfaces, include the Penaeidae, Aristeidae, and Solenoceridae. In other families, secondary and tertiary gill elements are sometimes quite flattened, and the tertiary elements are not dendritic, giving the gill a distinctly non-dendrobranchiate appearance. Flattened biserial secondary branches and their flattened tertiary elements are particularly obvious in gills of the monogeneric family Sicyoniidae (Sicyonia). Within the family Sergestidae, gills of the genus Sergestes are unusual in having secondary branches that arise from the main gill axis in an alternating pattern; these gills also have distinctly oval tertiary elements that are not further subdivided and are directed basally rather than distally. Another sergestid genus, Petalidium, displays gills that differ from those of Sergestes; in Petalidium the secondary branches also come off the main gill axis in an alternating pattern, but these branches are more widely spaced and have relatively larger and broader tertiary elements when compared with gills of Sergestes. The family Benthesicyemidae also contains species with different gill types; Gennadas is shown to have flattened, plate-like tertiary elements, whereas Benthesicyemus has more typical dendrobranchiate gills. The significance of this variation in gill morphology within families and within the Dendrobranchiata as a whole is unclear at this point; rearrangements of the currently accepted phylogeny and resulting classification based solely on gill morphology are not recommended at this time.