Salinity Tolerance Tests Research Articles

Evaluation of Salt Tolerant Garlic Cultivars Based on Physiological and Yield Responses

An aggravated salt concentration in soil restricts to intensify the crop productivity. In a salinity tolerance test, five Allium sativum cultivars viz. BARI Rashun-1, BARI Rashun-2, BARI Rashun-3, BARI Rashun-4 and Local (Natore local) were comapared subjecting four level of salt stress viz. 0, 4, 8 and 12 dS m-1. Total dry matter (TDM) (g) plant-1, bulb yield and yield supporting traits of all cultivars were depressed with successively induced salt. But, TDM productions, yield and yield supporting traits were less degraded in BARI Rashun-4 and BARI Rashun-3 at 12 dSm-1 salinity and had a stronger ability to continue constant osmotic potential maintaining the uttermost K+/Na+ ratio. The variety BARI Rashun-4 showed higher activity of antioxidant enzyme and less cell membrane damage at 12 dSm-1 salt level. BARI Rashun-3 and BARI Rashun-4 were considered as a relatively saline tolerant due to higher antioxidant enzyme synthesis, ion homeostasis and less degradation of yield. SAARC J. Agric., 19(2): 181-193 (2021)

Salinity tolerance of larvae Aedes aegypti inland and coastal habitats in Pasangkayu, West Sulawesi, Indonesia

Abstract. Ratnasari A, Jabal AR, Syahribulan, Idris I, Rahma N, Rustam SNRN, Karmila M, Hasan H, Wahid I. 2021. Salinity tolerance of larvae Aedes aegypti inland and coastal habitats in Pasangkayu, West Sulawesi, Indonesia. Biodiversitas 22: 1203-1210. Aedes aegypti L. is the primary arboviral vector generally found in freshwater, but it is also observed in brackish water. The study analyzes habitat characteristics, larvae adaptation, and oviposition preference in salinity levels over the coastal and inland ecosystem in Pasangkayu District of West Sulawesi. The larvae were reared until adults and have larval of first progeny were examined the salinity tolerance in five salinity levels. Ovitrap-based experiments were carried out in the laboratory using adult Ae. aegypti colonies from inland and coastal areas. Eggs on filter paper (ovitrap) were identified and counted. Data were analyzed using LC50 (larvae with salinity tolerance) and Pearson correlation (correlation between the larvae phase two ecosystem factors). Total larvae observed in coastal areas and inland are 1437 and 1288, respectively. The salinity tolerance test showed that Instar IV is highly adapted to the saline environment. The larvae from the coastal (inland) area can tolerate salinity up to 13 (10) ppt. Mosquitoes can lay many eggs in 3 ppt salinity: 27.1% and 20.8% for coastal and inland colonies, respectively. Pearson correlation analysis showed a significant correlation between the larval instar stage of Ae. aegypti from coastal and inland ecosystems with the ability to survive at the salinity level (p < 0.01). This study is expected to be a source of information on the adaptation of Ae. aegypti mosquito to salinity in coastal and inland ecosystems. The findings can be considered in vector control efforts on brackish water habitats.

Screening of Salinity Tolerance and Genome-Wide Association Study in 249 Peanut Accessions (Arachis hypogaea L.)

Salinity stress is one of the important abiotic stresses in crops. In this study, ten different concentrations of NaCl solutions were tested to determine the optimal level of NaCl concentration for salinity tolerance test at the germination stage in peanut, and 0.6% NaC1 was suitable for the test. A total of 249 peanut accessions were tested with 0.6% NaC1 and radical root lengths of the accessions were measured. The results showed that there were significant genetic variations on the tolerance to salinity stress among the tested accessions. Through a Genome-Wide Association Study (GWAS) using the Axiom_Arachis array with 58K SNPs, three putative SNPs with significant relation to radicle root length were identified on chromosomes Aradu.A03, Araip.B01, and Araip.B05.

Biological and Ethological Response of Black Sea Golden Grey Mullet (Chelon auratus Risso, 1810) Fries to Different Salinities and Temperatures

The aim of this paper was to investigate the biological and ethological response of golden grey mullet Chelon auratus (Risso, 1810) fries collected from Romanian Black Sea shallow waters to different salinities and temperatures, in order to document the optimal conditions for controlled rearing. The species’ potential for aquaculture is enhanced by its eurihalyne and eurithermal adaptability, allowing it to grow in a variety of ecosystems, including the Romanian Black Sea area, with its highly variable salinity and temperature specificities. Three experimental set-ups were designed: a salinity tolerance test, with 5 salinity regimes (0.3‰, 5‰, 10‰, 15‰ and 20‰), a temperature tolerance experiment, involving both temperature decrease (down to 8°C) and increase (up to 34°C), and an extreme salinity test, reaching a maximum value of 95‰. The aggregated results obtained from the three experiments indicated that golden grey mullet fries can indeed tolerate a wide range of temperatures (8°C - 36°C) and salinities (5‰-70‰), with the optimal range between 10‰ and 30‰ salinity, at temperatures of 10°C - 25°C. The practical purpose of this investigation was supporting the diversification of local mariculture species, as mullets can be excellent candidates for the enhancement of aquaculture in the area.

Taxonomic and functional profiling of nitrifying biofilms in freshwater, brackish and marine RAS biofilters

In recirculating aquaculture systems (RAS), the crucial step of eliminating toxic N compounds like ammonia and nitrite is mediated via nitrifying microorganisms and takes place in biofilters. In this study, analyses of microorganisms colonizing biocarriers of nine moving-bed biofilters of three different RAS operated with freshwater, brackish or marine process water uncovered site specific communities. Illumina-based amplicon sequencing of the V4-region of the 16S rRNA gene revealed a high microbial diversity with 1000–2500 species-level operational taxonomic units (OTUs) in all biofilters with the highest diversity in the brackish RAS. Proteobacteria, Bacteriodetes, Plantomycetes, Chloroflexi and Nitrospirae represented the most abundant phyla. 76 out of 674 known genera occurred in all nine biofilters and were defined as core-taxa, including nitrifying bacteria (Nitrosomonas and Nitrospira) as well as members of the (heterotrophic) genera Planctomyces, Blastopirellula, Nannocystis and Lewinella. Nitrifying communities composed of different, closely related and so far uncultured members of Nitrosomonas and Nitrospira were identified, strongly indicating that several potentially novel ammonia and nitrite oxidizing species are present in RAS biofilters. Relatives of known comammox Nitrospira were detected in the brackish biofilters, revealing 94–99 % identity of the 16S rRNA gene sequence to Ns. inopinata. Salinity tolerance tests with biocarriers derived from biofilters of the three distinct RAS showed an unexpected broad physiological flexibility with regard to salinity. Nitrification performance of freshwater nitrifiers was drastically reduced with increasing salinity and nearly completely inhibited at 15 PSU, while the brackish and marine nitrifiers showed a high resistance and maintained nitrification activity in a broad range of salt concentrations. This data can help to improve the nitrification process in RAS with changing salinity of the process water.

MORPHOPHYSIOLOGY OF RHIZOBIA ISOLATED FROM NATIVE FORAGE OF FABACEAE OF THE CAATINGA

ABSTRACT The rhizobia found in Fabaceae plants of the Caatinga may have potential as fodder in the semiarid region, thus increasing the availability of feed for animal production in this region. This study aimed to characterize the morphophysiology of rhizobia strains of the forage species Mimosa tenuiflora (Jurema preta), Macroptilium atropurpureum (Siratro), and Desmanthus pernambucanus (Jureminha). The soil used as the substrate was collected at specific locations in the municipalities of Sertânia, Arcoverde, and São Bento do Una, state of Pernambuco. The characterization of rhizobial colonies included growth period, diameter, elevation, transparency, exopolysaccharides production, and color. In addition, salinity, temperature, and pH tolerance tests of the native rhizobia were conducted. Evaluation of cultures showed that the isolates formed colonies with flat elevation, moderate production of exopolysaccharides, coloration varying from cream to white, and a smooth surface. Physiological tests of abiotic stress resistance showed that the native species isolated from M. tenuiflora were more resistant when grown in soils from the municipality of Sertânia and isolates from M. atropurpureum and D. pernambucanus had high resistance to high temperatures, regardless of place of farming. It can be concluded that native rhizobia from the Semiarid region of Pernambuco show resistance to stress caused by high temperatures, salinity variation, and pH. These characteristics are influenced by soil and the botanical species in symbiosis with the rhizobia.

PHYSIOLOGICAL CHARACTERIZATION OF DIAZOTROPHIC BACTERIA ISOLATED FROM Brachiaria brizantha RHIZOSPHERE

ABSTRACT The objective of this study was to evaluate the ability of diazotrophic bacteria isolated from Brachiaria brizantha rhizosphere to grow at different pH values and salt concentrations, to produce indoleacetic acid (IAA), and to solubilize phosphate. Both acidity and salinity tolerance tests were performed on modified solid FAM medium. Acidity resistance tests were performed at pH values of 4.0, 5.0, 6.0, and 7.0, while, salt resistance was evaluated at concentrations of 0.01, 5.02, 9.99, 14.96, 19.98, 24.95, 29.98, 34.94, 39.97, 44.94, and 49.96 gL-1 NaCl. For the IAA production assay, bacterial strains were cultivated in liquid DYGS medium both in the absence and presence of tryptophan (Trp). In addition, phosphorus solubilization assay was performed in GL liquid medium. All strains grew at every pH value tested, and a high diversity was observed after salt resistance, IAA production, and phosphate solubilization testing. Strains UNIFENAS 100-51, UNIFENAS 100-52, UNIFENAS 100-60, UNIFENAS 100-63, and UNIFENAS 100-65 were those with the best growth at the highest salt concentrations. Furthermore, in the presence of Trp, strains UNIFENAS 100-63 and UNIFENAS 100-69 were the ones with the highest IAA production. Strain UNIFENAS 100-52 showed the best response to the in vitro phosphate solubilization assay. Based on these results, it can be seen that studies related to the physiological and metabolic characteristics of diazotrophic bacterial strains are important to ensure greater success in the field.

Effects of Salinity on Survival and Growth of Gurami Sago (Osphronemus goramy, Lacepède, 1801) Juveniles.

Gurami Sago Osphronemus goramy (O. goramy) are an herbivorous freshwater finfish species native in Indonesia. This species has not yet been cultured commercially in brackish water. A 60-days study was conducted to evaluate the effects of salinity on survival and growth of O. goramy. Two independent experiments were performed to determine the effects of salinity on survival and growth of juvenile O. goramy, first one was to determine the median lethal salinity (MLS-5096 h) and second one was to assess the survival and growth at different sub-lethal salinities. In MLS-5096 h study 0.0, 4.0, 8.0, 12.0 and 16.0 ppt salinities were used to initially find out the salinity tolerance range. Accordingly, a definitive salinity tolerance test was done in next phase to find out exact median lethal salinity by directly transferring the test species to 13.0, 14.0, 15.0 and 16.0 ppt salinity for 96 h. The median lethal salinity of O. goramy was estimated at 14.0 ppt. In the second experiment, survival and growth of the O. goramy were recorded at salinities 4.0, 8.0 and 12.0 ppt along with 0.0 ppt as control during 60 days. Osigni goramy exhibited lowest final average weight at 12.0 ppt salinity and significantly highest at 4.0 ppt salinity. Highest SGR and weight gain were obtained at 4.0 ppt followed by 0 ppt, 8 ppt and 12 ppt salinity. All treatments were significantly (p<0.05). Survival rate of O. goramy varied between 76.45% (at 0.0 ppt) and 66.66% (at 12.0 ppt). The O. goramy grew and survived satisfactorily at 0.0 to12.0 ppt salinities, implying that the species can be cultured commercially in brackish water, in view of in Indonesia, there are many abandoned shrimp ponds.

Phenotypic and molecular assessment of chickpea rhizobia from different chickpea cultivars of India.

In the present study, heterogeneity in natural chickpea rhizobia populations associated with 18 different chickpea (Cicer arientinum) cultivars of India was investigated. Physiological diversity of 20 chickpea rhizobia was characterized based on phenotypic parameters such as Bromothymol blue (BTB) test, pH, temperature and salinity tolerance. Based on response to BTB test and pH tolerance, all chickpea rhizobia were further divided into slow growers/alkali producers (14 isolates) and fast growers/acid producers (6 isolates). The temperature (upto 40°C) and salinity (NaCl) tolerance (upto 6%) tests provided a wide description of physiological diversity among the rhizobial isolates. The intrinsic antibiotic resistance of each isolate against 14 different antibiotics distinguished all chickpea rhizobia into five clades at the level of 80% similarity coefficient. Further, based on UPGMA phylogeny of carbon utilization profile, all isolates were dispersed into six clusters at the level of 85% similarity coefficient, which indicated a remarkable variability among the rhizobia. The evaluation of nodule-forming efficiency of all isolates revealed that the isolate ACR15 was more competent for nodule formation than all other isolates. The representative strain from each carbon metabolic cluster was further subjected for molecular identification through 16S rRNA gene characterization. Neighbour-joining method-based phylogeny of 16S rRNA gene sequence revealed a high degree of species diversity among the isolates. Further, the prominent nodule-forming isolate such as ACR15 was identified as Mesorhizobium ciceri, while other isolates showed similarity with other species of Mesorhizobium genus. The present study contributed to the knowledge that besides M. ciceri and M. mediterraneum, chickpea can also be nodulated by many other native chickpea rhizobia which indicates the impact of exploration of promising native populations. These findings may support the further investigation of symbiotic as well as stress responsive genes of chickpea rhizobia leading to develop more effective inoculant strains for wide agricultural applications.

The effect of salinity on survival and growth of the freshwater stenohaline fish spotted snakeheadChanna punctata(Bloch, 1793)

AbstractTwo independent experiments were performed to determine effects of salinity on survival and growth of adult Channa punctata. The purpose of the first one was to determine the median lethal salinity (MLS-5096h) and that of the second one was to assess survival and growth of the fish at different sub-lethal salinities under field conditions. 5, 10, 15, 18 and 20 g l−1 salinities were used initially to determine the range of salinity tolerance. After 100% mortality had been obtained at 20 g l−1 in the first phase, a definitive salinity tolerance test was carried out in the next phase to find out the median lethal salinity by direct exposure of the test species to 10–18 g l−1 salinity for 96 h. The estimated MLS-5096h for C. punctata (11.50 cm length; 12.05 g weight) was 13 g l−1. In the second experiment, survival and growth performances of the fish were recorded at two sub-lethal salinities viz., 5 and 10 g l−1, along with those in fresh water as a control. Salinities up to and including 10 g l−1 di...

Halophilic and thermotolerant Gymnoascus species from several special environments, China

This study introduces three new Gymnoascus species (Gymnoascaceae, Onygenales), G. halophilus, G. stercorarius and G. thermotolerans, isolated from sediments in Chaka Salt Lake, compost and cornfield soil, respectively, in China, based on a polyphasic characterization including morphology, physiology and molecular phylogeny. Phylogenetic relationships were assessed based on the nuclear internal transcribed spacer (ITS = ITS1 + 5.8S + ITS2) region and a combined multilocus alignment of the ITS, 18S subunit rRNA gene and 28S subunit rRNA genes. Our study identified phylogenetic and phenotypic characters that differentiated the three new species from known species in the genus. Salinity and temperature tolerance tests revealed that G. halophilus was an obligate halophile while G. stercorarius and G. thermotolerans were halotolerant and thermotolerant. A key to accepted species of Gymnoascus is provided.

Effect of salinity on survival and growth of giant freshwater prawn Macrobrachium rosenbergii (de Man)

Two independent experiments were performed to determine the effects of salinity on survival and growth of juvenile Macrobrachium rosenbergii, first one was to determine the median lethal salinity (MLS-5096h) and second one was to assess the survival and growth at different sub-lethal salinities under field condition. In MLS-5096h study 0, 5, 10, 15, 20, 25 and 30ppt salinities were used to initially find out the salinity tolerance range. Accordingly, a definitive salinity tolerance test was done in next phase to find out exact median lethal salinity by directly transferring the test species to 21, 22, 23, 24, 25, 26 and 27ppt salinity for 96h. The median lethal salinity of M. rosenbergii was estimated at 24.6ppt. In the second experiment, survival and growth performances of the prawn were recorded at different sub-lethal salinities viz., 5, 10, 15 and 20ppt along with 0ppt as control during 60 days culture period. The prawn exhibited lowest final average weight at 20ppt salinity and significantly highest at 10ppt salinity. Highest SGR and weight gain were obtained at 10 ppt followed by 5ppt, 15ppt and 0ppt salinity but differences among treatment were not significant (P>0.05). Survival rate of prawn varied between 91% (at 0ppt) and 78% (at 20ppt). The prawn grew and survived satisfactorily at 0–15ppt salinities, implying that the species can be cultured commercially at wide salinity range. M. rosenbergii can be considered as an ideal species to promote, in view of current and future climate variables as more and more coastal areas of India are going to be vulnerable to saline water inundation.

The diatom Thalassiosira faurii (Gasse) Hasle in the Ziway–Shala lakes (Ethiopia) and implications for paleoclimatic reconstructions: Case study of the Glacial–Holocene transition in East Africa

The species Thalassiosira faurii (Gasse) Hasle was found dominating the planktonic diatom community during summer 2012 in Lake Langano which is part of the Ziway–Shala alkaline lake system in Ethiopia. In a previous study, the species had been recorded in high abundance in 13.5–12calka old sediments from the neighbor Lake Abiyata. Using a transfer function for conductivity, peaks in abundance had been interpreted as dry spells at the Pleistocene–Holocene transition since the species was considered strictly halophilous.In this study, a strain of Thalassiosira faurii was isolated from Lake Langano and grown in the laboratory. The observation of its morphology and reproduction, and comparison between modern and fossil populations helped to improve the taxonomic definition of the species. The autecology of the species was also investigated through a salinity tolerance test. The results revealed that the species was much more sensitive to salinity than previously believed. A new conductivity optimum was derived from the experiment and incorporated into the transfer function. The reassessment of lake conductivity variations along the core of Lake Abiyata showed that the intensity of the dry periods preceding the onset of the Holocene had been probably over-estimated.The reconsideration of the species relationship to conductivity may have important consequences for paleoclimatic reconstructions in tropical Africa where Thalassiosira faurii has been reported in abundance. The use of experimentation on local diatom strains allows paleoecologists to solve the problems of low representation of some species in modern dataset and of regional autecological variability within morphotypes.

Isolation, bioprospecting and diversity of salt-tolerant bacteria associated with sugarcane in soils of Pernambuco, Brazil

ABSTRACT The selection of salinity tolerant bacteria may provide greater promotion of plant growth in soils with salt stress. This study aimed to isolate and select bacterial isolates of sugarcane, tolerant to salinity and plant growth promoters, and assess genetic diversity. To do so, endophytic root and rhizosphere of sugarcane, were isolated in culture medium with and without NaCl. The bacterial population density, the potential for biological nitrogen fixation (BNF), production of indole acetic acid (IAA), inorganic phosphate solubilization and quorum sensing molecule production were evaluated. Furthermore, the genetic diversity was assessed by Denaturing Gradient Gel Electrophoresis (DGGE) of nifH. Salinity tolerance tests were also conducted. There was no statistical difference in population density. As for the potential for BNF, IAA production, phosphate solubilization and quorum sensing molecule production, there was a high percentage of positive isolates. In the technique of DGGE nifH, the dendrogram showed high genetic variability. So there was the selection of bacteria that can contribute to the better development of sugarcane in saline soils.

Salinity and temperature requirements for larviculture of the Monkey River prawn Macrobrachium lar (Fabricius, 1798) (Decapoda: Caridea: Palaemonidae)

The present study investigated the effects of salinity and temperature on the survival and development of larvae of the Monkey River prawn Macrobrachium lar. Larvae of specific morphological development stages (zoeae I, III, V and VII) were exposed to various salinities ranging from 0 to 30±0.5‰ during salinity tolerance tests; while zoea I larvae were reared at temperatures of 26±0.5°C, 28±0.5°C, and 30±0.5°C during temperature tolerance tests.The results of the salinity tolerance tests demonstrated that newly-emerged larvae of Macrobrachium lar are able to tolerate fresh or brackish-water of approximately 10‰, but require gradually increasing salinities post-hatch reaching 30–35‰; which probably needs to be maintained until metamorphosis into post-larvae (PL). Larval stages I–II required a range of 10–15‰, III–IV required 15–25‰ and V–VI required 25–30‰. Stages VII to XIII required 30–35‰, following which salinity may be reduced after PL1. Larval survival and growth were found to be significantly reduced when maintained outside these salinities. Larvae kept in freshwater (0‰) die within 4days unless transferred to brackish-water.Results of the temperature tolerance investigations revealed that a temperature range of 30±0.5°C produced optimal survival and growth. As a result of the current investigation, baseline data on the salinity and temperature requirements of M. lar larvae have been collected and will be useful in further larviculture research work with this species. A salinity acclimation protocol has also been developed that will be useful in developing a mass culture technique for hatchery production of PL.

Transgenic tomato cv. Pusa Uphar expressing a bacterial mannitol-1-phosphate dehydrogenase gene confers abiotic stress tolerance

A bacterial mannitol-1-phosphate dehydrogenase (mtlD) gene driven by the constitutive cauliflower mosaic virus (CaMV) 35S promoter was transferred into tomato plants using an Agrobacterium tumefaciens-mediated transformation protocol in an attempt to improve abiotic stress tolerance in the transformed plants. Transgene integration was confirmed by PCR analysis and Southern blot analysis, and transgene expression was confirmed by reverse transcription (RT)-PCR and direct mtlD (EC 1.1.1.17) activity. Upon exposure to low temperature stress (4°C) in a cold chamber, transgenic plants survived up to 48 h, while non-transformed plants were unable to survive and gradually died. Transgenic plants subjected to the chilling stress showed a significant decrease in electrolyte leakage and increased lipid peroxidation, as assessed by measuring malondialdehyde (MDA) content. Under the cold condition, transgenic plants also showed a significant increase in the activities of antioxidant enzymes (superoxide dismutase and catalase) and in relative water content (RWC) in comparison to non-transformed plants. Drought (polyethylene glycol in medium) and salinity (sodium chloride in medium) tolerance tests revealed that transgenic lines exhibited a higher tolerance for abiotic stresses than non-transformed plants. These findings indicate that the introduction of a bacterial mtlD gene into tomato conferred tolerance to abiotic stresses to the transformed tomato plants.

Distribution pattern of zooplankton in the han river estuary with respect to tidal cycle

The monthly distribution of zooplankton communities in Han River estuary was investigated at two stations from July 1998 to June 1999. Monthly mean abundance of total zooplankton varied remarkably, with the range from 20 indiv.·m-3 to 19,600 indiv.·m-3. During the study period, dominant species of zooplankton community were dinoflagellateNoctiluca scintillans, copepodsParacalanus indicus, Paracaanus crassirostris, Acartia hongi, Acartia ohtsukai, and meroplanton cirriped larvae. According to tidal states, relative high abundance occurred at high tide without regard to season. The temporal distribution of abundance implied that the reduced salinity probably limited the zooplankton populations and the fluctuations of salinity were an important factor in the variation of abundance. However, the results of salinity tolerance test shows that the variations in salinity do not directly influence the decrease of abundance. This study shows that the relatively high abundance of zooplankton near high tide seems to be related with the expansion of abundant zooplankton inhabiting Incheon coastal waters through tidal currents.

Responses of cobia Rachycentron canadum larvae to abrupt or gradual changes in salinity

Cobia Rachycentron canadum has recently been recognized as a potential candidate for aquaculture because this species exhibits high growth rates during the larval and juvenile stages. A series of salinity tolerance tests were performed on larval cobia in order to identify the salinity requirements of this species during culture. The effect of spawning salinity on larval tolerance is also discussed. The 18-h survival of cobia larvae 3, 5, 7 and 9 days post-hatch (dph) following abrupt transfer to salinities ranging from 4 to 48 ppt was evaluated using logistic regression. The salinity range within which 90% of the larvae would be expected to survive appeared to be age-dependent and was narrowest at 3 dph (20.1–35.6 ppt) and wider at 7 and 9 dph (7.5–32.8 ppt). The 18-h tolerance of larvae to abrupt changes in salinity was unaltered by spawning salinities of 28.0 and 36.5 ppt. In the second part of the study, rearing salinities were dropped by 5 ppt day − 1 from 32–34 ppt (control) to 5, 10, 15 and/or 20 ppt beginning on 1, 4, 7, 10 or 13 dph. Larval survival from hatching through 10 days following the initial drop in salinity was significantly ( P < 0.05) lower (< 2%) in the low salinity treatments than the control (12–15%) when the salinity drop was initiated 1 and 4 dph. No significant differences in larval survival were detected between the control (12.5%) and 20 ppt treatment (8.9%) when the salinity drop began on 7 dph but survival in the 10 ppt treatment (3.2%) was significantly lower than the control. When the salinity drop was initiated on 10 dph, no significant differences in survival (10.7–14.7%) were detected among treatments. Finally, no significant differences in survival (9.6–15.4%) were found when the salinity drop was initiated 13 dph and terminated 22 dph. However, when a similar study was extended to 28 dph survival from 13 to 28 dph was significantly lower in the 5 (49.4%) and 10 (72.5%) ppt treatments than the control (96.5%) due to disease. No significant differences in standard length were observed for larvae within each experiment irrespective of rearing salinity. The results of this study indicate that rearing cobia larvae in salinities as low as 15 ppt may be possible beginning 13 dph.

Arachidonic acid requirements in larval summer flounder, Paralichthys dentatus.

The arachidonic acid (20:4n-6,AA) requirements of larval summer flounder weredetermined for the rotifer- and Artemia-feeding stages. Experimental emulsionscontained adequate n-3 highly unsaturated fattyacid (HUFA) ratios and emulsion levels of AAwere set at 0, 3, 6, 9, and 12% (AA0, AA3,AA6, AA9, and AA12). Examination of fatty acidlevels in live feeds and larval tissuesconfirmed the physiological incorporation offatty acids relative to dietary levels. In thefirst experiment, survival, growth, andsalinity tolerance (2-h in 70‰) were measuredat 18 days after hatch (dah) after feeding thelarvae the various levels of AA. Larvae fedAA6-enriched rotifers were better able tosurvive the salinity tolerance test. AAenrichment up to 12% had no effect on growthand survival. In the second experiment, larvaewere fed AA0- or AA6-enriched rotifers until 23dah, followed by unenriched 24- and 48-h Artemia nauplii until 32 dah. These larvaethen were subdivided and fed AA-enriched Artemia from 33-45 dah. At the end of thisexperiment, larvae fed AA6-enriched rotifershad higher survival, increased growth, andsurvived better in the salinity tolerance test(2-h in 80‰). The enrichment of Artemiadid not have any effect on these variables.Thus, the provision of AA6-enriched rotifers(10 mg AA g−1 DW) early in larvaldevelopment may serve to enhance larval stresstolerance at the rotifer stage while alsoincreasing larval survival, growth, and stresstolerance later in the Artemia stage.

汽水棲巻貝ワカウラツボ（腹足綱：ワカウラツボ科）の分布に関係する要因

Factors affecting the spatial distribution of the brackish water snail Iravadia (Fairbankia) sakaguchii were investigated in the field in the Waka River Estuary (34°10'N, 135°10'E) of central Japan and in the laboratory. The snails occurred under stones partially buried on intertidal muddy flats. A tracking survey of marked snails released beneath stones revealed that many of the snails moved among the stones. Observations in tide-simulating tanks indicated that most of the snails came out from beneath the stones and were active during both daytime and nighttime submergence. Salinity tolerance tests in the laboratory showed that the snails died within 6 days at 0 psu, 7 days at 5 psu, and 12 days at 10 psu, whereas no snails died during 13 days of exposure to higher salinity conditions (20-35 psu). Neither immigration nor retention rates of snails differed significantly between partially buried stones and non-buried stones artificially placed in the field. This indicates that the extent of burial of the stones is not critical for habitat selection by the snails. Preference tests conducted in the laboratory and in the field revealed that the snails prefer mud to sand under the stones. Retention and survival rates were lower for snails released with stones in the lower intertidal zone than for those released with stones in the middle intertidal zone, and this suggests the importance of tidal exposure in habitat selection of I. (F) sakaguchii.