Fishes and salinities in the St Lucia estuarine system—a review

The recorded salinity ranges of freshwater, estuarine and marine fish species in Lake St Lucia, a Ramsar and World Heritage Site, are documented. The freshwater group is most diverse and abundant under oligohaline conditions, although the Mozambique tilapia (Oreochromis mossambicus) was common under all salinity regimes. Estuary resident species also favoured oligohaline conditions but, in contrast to the freshwater taxa, were well represented in salinities up to 40 ‰. The marine group was most diverse and abundant within the salinity range 10–40 ‰, but a large number of species could also be found in salinities up to 70 ‰. Very few fish species were able to tolerate salinities between 70 ‰ and 110 ‰, with only O. mossambicus surviving for extended periods in salinities above 110 ‰. All the aquatic macrophytes and most of the zoobenthos within the lake appear to die out within the salinity range of 50–60 ‰, thus creating additional stress to those fish present under such conditions. The food resources least affected by extreme hypersalinity are the microphytobenthos and detritus food chains, with detritivorous fishes being dominant when the lake is in this state. Mass mortalities of fishes in Lake St Lucia have been recorded under both low (<5 ‰) and high salinity (>70 ‰) conditions. The fish kills are often triggered by exceptionally low or high water temperatures which affect the osmoregulatory abilities of these species. Hypersaline conditions and fish mortalities under the most recent closed estuary mouth conditions (2002–2005) are reviewed. If the surface area of St Lucia (35,000 ha) is compared to the total surface area of all South African estuaries (approximately 70,000 ha), then the possibility exists that the loss of the Lake St Lucia nursery area for estuary-associated marine fish species over the past few years may cause significant short-term declines in the future abundance of these taxa on both a local and regional scale.     

Effects of temperature and salinity on embryonic development of turbot (Scophthalmus maximus L.) from the North Sea, and comparisons with Baltic populations

Optimum temperature and salinity conditions for viable hatch were studied for turbot (Scophthalmus maximus L.) from the North Sea. Temperatures ranging from 6 to 22°C and salinities from 5 to 35‰ were used. Optimum conditions were observed to be between 12 and 18°C at salinities between 20 and 35‰. This contrasted with corresponding data for turbot from the southern Baltic proper, according to which survival sharply decreased in temperatures below 14°C and was high in salinities of 10 to 15‰. Thus, it is concluded that Baltic and Atlantic turbot should be considered as different races.     

Elevated Na+/K+-ATPase responses and its potential role in triggering ion reabsorption in kidneys for homeostasis of marine euryhaline milkfish (Chanos chanos) when acclimated to hypotonic fresh water

The milkfish (Chanos chanos) is an economic species in Southeast Asia. In Taiwan, the milkfish are commercially cultured in environments of various salinities. Na⁺/K⁺-ATPase (NKA) is a key enzyme for fish iono- and osmoregulation. When compared with gills, NKA and its potential role were less examined by different approaches in the other osmoregulatory organs (e.g., kidney) of euryhaline teleosts. The objective of this study was to investigate the correlation between osmoregulatory plasticity and renal NKA in this euryhaline species. Muscle water contents (MWC), plasma, and urine osmolality, kidney histology, as well as distribution, expression (mRNA and protein), and specific activity of renal NKA were examined in juvenile milkfish acclimated to fresh water (FW), seawater (SW 35‰), and hypersaline water (HSW 60‰) for at least two weeks before experiments. MWC showed no significant difference among all groups. Plasma osmolality was maintained within the range of physiological homeostasis in milkfish acclimated to different salinities, while, urine osmolality of FW-acclimated fish was evidently lower than SW- and HSW-acclimated individuals. The renal tubules were identified by staining with periodic acid Schiff’s reagent and hematoxylin. Moreover, immunohistochemical staining showed that NKA was distributed in the epithelial cells of proximal tubules, distal tubules, and collecting tubules, but not in glomeruli, of milkfish exposed to different ambient salinities. The highest abundance of relative NKA α subunit mRNA was found in FW-acclimated milkfish rather than SW- and HSW-acclimated individuals. Furthermore, relative protein amounts of renal NKA α and β subunits as well as NKA-specific activity were also found to be higher in the FW group than SW and the HSW groups. This study integrated diverse levels (i.e., histological distribution, gene, protein, and specific activity) of renal NKA expression and illustrated the potential role of NKA in triggering ion reabsorption in kidneys of the marine euryhaline milkfish when acclimated to a hypotonic FW environment.     

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

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

The effect of salinity on respiratory metabolism,survival and moulting in the first zoea of Macrobrachium amazonicum (Heller) (Crustacea,Palaemonidae)

Survival, duration of intermoult cycle and respiratory metabolism were evaluated as a function of salinity (0–35‰; 25° C) in early zoeae of the cinnamon shrimp, Macrobrachium amazonicum. Zoeae are extremely resistant to salinity, mortality occurring only in fresh and sea-water after several days. Moulting occurs in all salinities, longer cycles being recorded in 0 and 35‰ S. The metabolism-salinity curve is broadly U-shaped between 0 and 28‰ S but declines sharply in sea-water. Such physiological responses characterise the early zoeae as strongly euryhaline and typically estuarine. Data are discussed in relation to the degree of adaptation of the organism to the freshwater biotope and the position of the species within the generic pattern of adaptive radiation.     

Aquatic invertebrates of Lake Gregory,northwestern Australia,in relation to salinity and ionic composition

Lake Gregory is a large semi-permanent lake system in arid north-western Australia. Its catchment extends into humid areas and as a result the lake has dried only twice in the last 25 years. Although the system is mostly fresh, parts of it become saline as they dry. We identified aquatic invertebrates and undertook chemical analysis of water samples from several sites at Lake Gregory in 1989, when the main water-body was saline, and in 1991 and 1993, after the system had flooded and was fresh. During the period 1989–1993, salinities varied from 0.1‰ to 82‰, and ionic composition ranged from strong sodium chloride dominance, in saline water and fresh water of the eastern part of the system, to bicarbonate dominance in fresh water of the western area. At least 174 invertebrate species were recorded, including two mollusc species that were never collected live. This species richness is much higher than that recorded from other Australian arid zone lakes, probably owing to long periods of inundation with fresh water. The fauna was dominated by insects (42 per cent of total species richness), crustaceans (27 per cent) and rotifers (22 per cent). Most species (160) were restricted to fresh water; only 12 species were found in saline water. Only one ostracod occurred in saline conditions, although ostracods are a dominant group in Australian saline lakes. Among species restricted to fresh water, the proportion of rotifer and protozoan fauna that occurred in bicarbonate-dominated water was greater than the proportion of insect, crustacean and hydracarine fauna that did so. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some Primary Features of Salt Tolerance in Senna (Cassia acutifolia)

Studies on the germination of Cassia acutifolia (senna) seedsindicated, that they were highly tolerant of salinities up to16.0 mmhos cm^–1, and 50 per cent reduction in germinationoccurred, at about 20.0 mmhos cm^.1. Air temperature had a significanteffect on senna germination at substrate salinities between10.0 and 25.0 mmhos cm^–1. Seedling growth was more sensitive to salinity and alkalinitythan the germination stage. Young plant survival and total podyield were significantly reduced in soil salinities higher than11.0 minhoa cm^–1, and this was more pronounced when plantswere irrigated at short intervals with saline waters. The sensitivityof senna to higher levels of salinities was correlated withthe higher rate of chloride accumulation in the tissue resultingin specific chloride injury. However, the possibility of sodiuminjury cannot be excluded.     

Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes

The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. δ¹³C and δ¹⁵N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the literature. δ¹³C of plants ranged from –8.59‰ to –33.74‰, of benthic invertebrates from –17.0‰ to –20.52‰, of planktonic invertebrates from –20.08‰ to –22.34‰ and of fishes from –16.27‰ to –19.59‰. δ¹⁵N was generally greater at higher trophic levels. δ¹⁵N of plants was 0.95–2.92‰, of benthic invertebrates 1.69–6.54‰, of planktonic invertebrates 3.51–6.82‰ and of fishes 4.63–9.77‰. ¹³C enrichment tended to be associated with benthic food chains and ¹³C depletion with planktonic chains. Stable-isotope data suggested more varied diets for many species than implied by gut-contents data. Omnivory and trophic plasticity were widespread, and many consumers fed lower down the food chain than previous studies had suggested. Both stable-isotope and gut-contents analysis resolved differences between fishes feeding on planktonic and benthic prey and indicated that the herbivorous fish Sarpa salpa fed on a diet substantially different from that of other fishes. Zooplankton were important in the diets of several consumers (both primary and secondary), as was plankton derived detritus. One species of fish previously identified as planktivorous was shown to feed largely on benthic organisms, whilst several species of benthic invertebrates may feed on plankton-derived detritus. Although herbivores seemed to obtain most of their C from macroalgae, δ¹⁵N data suggested that many of these animals supplemented their intake of N, although gut-contents analysis did not provide evidence for such uptake. The isotopic data have elucidated several features of the food web which we would not otherwise have detected. Received: 26 April 1999 / Accepted: 24 September 1999     

Protoplast Formation of the Coccolithophorid <Emphasis Type="Italic">Pleurochrysis haptonemofera</Emphasis> in Hypoosmotic K<Superscript>+</Superscript> Solution: Shedding of the Coccosphere and Regrowth of the Protoplast in Normal Medium

Both coccolith-bearing cells (C-cells) and naked cells (N-cells) of the coccolithophorid Pleurochrysis haptonemofera can grow in salinities of more than 7‰ (about 20% of a “normal” sea water salinity [35‰]), with the highest growth rates in salinities of more than 14‰. Microscopic observations of cells suspended in 100 mM NaCl (7‰) showed that, while N-cells were swelling uniformly all over the cell surface, C-cells were bulging the plasma membrane from the hole of the coccosphere at the apical (flagellar) pole of the cell. Effects of several cations and anions on the morphological change of C-cells under hypoosmotic pressure were investigated. When 100 mM K⁺ was used, protoplasts were released from the coccosphere completely in almost all the cells. This phenomenon was shown with K⁺ most effectively. The protoplasts could grow in the fresh medium and form the first coccolith within 9 h.     

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

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

Effects of salinity and cadmium interaction on reproduction and growth during three successive generations ofOphryotrocha labronica (polychaeta)

The long-term effects of different cadmium (0.2 and 0.4 ppm) and salinity levels (30, 25, and 20 ‰ S) on growth and egg-mass production ofOphryotrocha labronica (La Greca & Bacci) were investigated over three generations. Low salinity levels and the presence of cadmium resulted in reduced growth rates, prolonged times to reach sexual maturity, and reduced size at maturity. Three-way analysis of variance showed significant interaction effects of generation and cadmium for the different growth processes tested. Using response-surface methods, 0.2 ppm cadmium was shown to have a greater effect on growth rate at the third generation than the first and second generations at the three salinities tested. Increased effects were observed from first to second generation at 0.4 ppm cadmium and 30 and 25 ‰ S, whereas effects decreased from second to third generation. At 0.4 ppm cadmium and salinity of 20 ‰ the first generation was not able to produce viable larvae.     

Relationship Between Medium Salinity, Body Density, Buoyancy and Swimming in Artemia franciscana Larvae: Constraints on Water Column Use?

Body density measurements were carried out on larval Artemia franciscana that had been held for 24 h at either 33 or 100‰ after hatching. Body density was low (1.0308–1.0342 g ml⁻¹) by comparison with marine crustacean zooplankters or benthic freshwater crustaceans, and very stable, being only 0.3% higher in 100‰ than in 33‰. Vertical and horizontal swimming in 2nd instar larvae was studied at 8.5, 17, 34, 50, 100, 150 and 250‰ at 23 °C. At 8.5–50‰ downwards swimming was always significantly faster than upwards swimming, but in 100‰ downwards swimming was much slower than upwards swimming, indicating substantial positive buoyancy. At 150 and 250‰ downwards swimming was impossible. Horizontal swimming speed was unaffected by salinity over the range 8.5–100‰, but could not be studied at 150 and 250‰ as larvae could not leave the surface film. An asymptotic relationship between salinity and viscosity was found over the range 8.5–250‰. Calculations indicate a rise from 1.197 to 1.513 cp between 8.5 and 100‰, but this does not significantly impede horizontal locomotion. It appears that water column use by early stage Artemia larvae, that use a pair of 2nd antennae for rowing-type locomotion, is constrained by the increasing positive buoyancy associated with living at salinities above that corresponding to neutral buoyancy (approximately 48‰).     

Biological effects of salinity gradient reversals in a southeast African estuarine lake

St Lucia Lake on the north coast of Natal, South Africa, has an area of 325 km² and is the largest estuarine complex in Africa. It consists of a 20 km tidal channel, averagingca. 400 m in width, linking the sea with the non-tidal lake which is H-shaped with a maximum length ofca. 40 km and width ofca. 20 km. Except during flood periods the depth of the lake does not exceed 2 m. The salinity gradient depends on evaporation, the configuration of the mouth and on the input of fresh water from four rivers which discharge into the northern and western areas of the lake. If fresh water input is high, the lake and much of the channel may be fresh. An intermediate stage features a normal salinity gradient while a third stage shows a reversed salinity gradient with salinities in excess of 100‰ in the upper reaches of the system. Changing salinities have marked effects on the biota. Aquatic macrophytes show cycles of appearance and disappearance depending on salinity tolerance and the presence of dormant stages. The resident benthic faunal species go through cycles of range expansion and contraction depending on prevailing salinities and recolonisation by dispersal phases. To date salinities in the southern part of the lake have approached, but not exceeded, lethal levels and this has therefore acted as a reservoir area. Catchment degradation and water abstraction are anticipated to exacerbate future salinity extremes. This has resulted in concern for the long term viability of this Ramsar site which has major southern African populations of hippopotamus and crocodile, provides breeding sites for South African Red Data water bird species and plays an important nursery role for marine fish and penaeid prawns.     

Changes in trophic linkages to shortfin eels (<Emphasis Type="Italic">Anguilla australis</Emphasis>) since the collapse of submerged macrophytes in Lake Ellesmere,New Zealand

Lake Ellesmere (Te Waihora) is a nationally important coastal brackish lake in New Zealand, however degradation in water quality and loss of submerged macrophytes over past decades have raised concerns in regards to the declining status of the lake’s commercial and customary fisheries, predominantly targeted at shortfin eels (Anguilla australis). We investigated foodweb dynamics and trophic linkages to shortfin eels in Lake Ellesmere using a combination of abundance assessments, dietary studies, and stable isotope analyses. Data from our study are compared with historical data sets on benthic invertebrate community composition and shortfin eel diets to trace changes in the trophic linkages to top predators that have occurred since the late 1960s. Stable isotope analyses indicate that the foodweb is predominantly driven by epipelic and phytoplankton derived carbon sources, although it was difficult to discriminate between these two carbon pools because of wind-driven resuspension of lake sediments. Comparison of our survey results with historical data sets indicates a clear shift in benthic biota from being dominated by phytofaunal species such as Potamopyrgus antipodarum (comprising 90% of total invertebrate biomass) during the 1960s, to now being almost entirely comprised of subterranean species such as Chironomus zealandicus and oligochaetes (together comprising 82% of total invertebrate biomass). This shift in benthic communities has resulted in significant changes in the size-specific diet of juvenile shortfin eels (<400 mm) from those reported for Lake Ellesmere during the mid 1970s, with Chironomus larvae now comprising 65% of the diets of juvenile eels, whereas historically P. antipodarum was the dominant food item (>30% of total biomass). This shift towards foraging on smaller sediment-dwelling species could have implications for juvenile eel bioenergetics, and may help explain why juvenile shortfin growth rates have significantly decreased in past decades. Juvenile shortfins now appear to switch to foraging on preyfish (mainly common bullies, Gobiomorphus cotidianus) at a smaller size (≈400 mm) than historically recorded (>500 mm). Dietary and stable isotope signatures indicated that small shortfins (100–299 mm) have considerable overlap in trophic position (δ¹³C = −20.4‰, δ¹⁵N = 13.6‰) with common bullies (δ¹³C = −20.5‰, δ¹⁵N = 13.7‰), the dominant fish in Lake Ellesmere (92% of total abundance CPUE), potentially indicating that these two species may directly compete for food resources. These findings again highlighted the importance of C. zealandicus in sustaining the fish populations of the lake. Handling editor: S. Declerck     

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

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

The screening of mutants and construction of mutant library for <Emphasis Type="Italic">Oryza sativa</Emphasis> cv. Nipponbare via ethyl methane sulphonate inducing

Following the sequencing of rice genome, the functional analysis of unidentified genes is gaining wide importance. Mutant isolation is one of the effective ways to isolate and clone the target genes and analyze their functions. To find the various mutants in the same genetic background, seeds of Oryza sativa cv. Nipponbare were treated with ethyl methane sulphonate (EMS). A total of 1056 mutants were screened for five categories in M₂ generation with the seedling frequency of 26.29‰ at three-leaf stage, but only 264 mutants were verified in M₃ generation with a frequency of 6.57‰. Among the mutants verified in M₃ generation, the frequency of leaf mutation was the highest (2.22‰), followed by seedling height (1.74‰) and the abiotic stress tolerance mutant (1.47‰). Nineteen characteristic mutations, including a big group of abiotic stress tolerant mutants such as herbicide resistant, salt tolerant and drought tolerant were identified at this stage. By observation of rice growth characteristics at different developmental stages, another 220 mutants have been isolated and verified in the M₃ generation with the mutant frequency of 53.9‰ covering about 28 mutant traits. Among those identified, the highest frequencies were obtained for appearance of brown rice mutant with 18.37‰, followed by panicle mutant with 13.47‰, and grain mutants with 9.06‰. All the mutants screened above were suitable for gene function analysis and for utilization in agronomy.     

Long-term changes in ecosystem health of two Hudson Valley watersheds, New York, USA, 1936–2001

We examined long-term ecological change in two Hudson River tributaries, the Wappinger and Fishkill Creek watersheds in Dutchess County, New York State. Fish data spanning 65 years (1936, 1988, 1992, and 2001) and shorter term macroinvertebrate data (1988, 2001) were used to assess the influence of land use practices. Between 1988 and 2001, macroinvertebrate index Biotic Assessment Profile (BAP) improved by 113–165% in the Fishkill Creek watershed, and fish Index of Biotic Integrity (IBI) improved by 117–140%. Fish IBI and fish species richness were significantly different (p < 0.01) between the watersheds, with Wappinger Creek in better condition. Long-term fish IBI scores showed degradation in both watersheds since the 1930s. Changes in species composition suggest community homogenization on par with overall changes in the fish fauna of New York. Most notable were increases in tolerant species and declines in intolerant or moderately tolerant species. Whereas Fishkill Creek IBIs showed decline in 1988 relative to 1936, followed by improvement, Wappinger Creek declined monotonically in environmental quality. Development has intensified in both watersheds, but Fishkill Creek is improving while Wappinger Creek watershed is undergoing less mitigated degradation. We find that older, semi-quantitative data can be used to construct environmental quality indicators, and can be of great use for measuring long-term change.     

Response of plants to calcium concentration in flowing solution culture with chloride or sulphate as the counter-ion

Summary Solution calcium concentrations required for the growth of a range of plant species, including both monocotyledons and dicotyledons, were determined in two experiments in which plants were grown in flowing solution culture at constantly maintained calcium concentrations ranging from 0.5 to 3000 μM. Calcium chloride was used as the calcium source in the first experiment, calcium sulphate was used in the second. At calcium concentrations of 10 μM and below, all species developed calcium deficiency symptoms. The severity of the deficiency was more pronounced in the dicotyledons than in the monocotyledons. However, cassava was much more tolerant than all other dicotyledons and equally as tolerant as rice, the most tolerant monocotyledon. Solution calcium concentrations required for 90% of maximum yield were generally lower for monocotyledons (3 to 20 μM) than for dicotyledons (7 to 720μM) when calcium chloride was used as the calcium source. When calcium sulphate was used, 7 out of 11 species, including 3 monocotyledons, required external calcium concentrations of 1200 μM and above. The results are discussed in relation to effects of solution composition and the choice of counter-ions on plant response to calcium and other macronutrient cations. It is concluded that yield depressions due to toxicity of excesses of chloride, and possibly other counter-ions, can lead to serious underestimation of limiting external cation concentrations for plant growth.     

Saline acclimation of striped mojarra <Emphasis Type="Italic">Eugerres plumieri</Emphasis> (Cuvier 1830) and optimal dosage of carp pituitary extract (CPE) to induce spawning

The main objective of the current study was to determine an optimal dosage of commercial carp pituitary extract (CPE) of the conventional heteroplastic hypophysation technique to induce spawning in the wild caught striped mojarra broodstock Eugerres plumieri under laboratory conditions. We also describe trials testing saline acclimation regimes (changes from 10‰ to 30‰) prior to hormonal induction. For saline acclimation, three treatments were performed: first and second treatments began 1-day after conditioning of broodstock fish with a total duration of the saline changes lasting 1-day and 2-days, respectively. The third treatment began 30-days after conditioning with a 7-day saline regime. After reaching 30‰, all fish from the first and second treatments died after the fourth and ninth days, respectively; while the fishes in the third treatment survived more than two years. These fish remain on public exhibit in the “Mundo Marino” Aquarium, Santa Marta, Colombia. Four treatments of hormonal induction were tested on females using a total concentration of 5-mg of CPE per kg of body weight: first, second and third treatments were applied in two hormonal doses that corresponded to 10%–90%, 30%–70% and 40%–60%, respectively, with time intervals between doses of 14-h for the first and second treatment and of 12-h for the third treatment. The fourth treatment was applied in four hormonal doses that it corresponded to 20%–20%–30%–30% with 12-h time intervals between doses. Only the fishes of the fourth treatment resisted the induction, continued to live and reached spawning artificially. Water temperature remained at 28 ± 1°C and at 30‰ salinity during the study. The “dry” method of fertilization was used. The fertilized eggs were incubated at 30‰ and 35‰ salinities. These eggs reached the Morula early stage, but were later attacked by protozoan. These results suggest that fast changes of saline and limited hormonal dosages do not offer effective results in Eugerres plumieri. This work provided fundamental procedures for the culture and maintenance of live broodstock for striped mojarra in saltwater and/or coastal lagoon habitats and provides an effective and viable dosage of CPE for artificial spawning and commercial production in this species.     

Zoospore production and motility of mangrove thraustochytrids from Hong Kong under various salinities

We investigated the effects of salinity on the zoospore production of four mangrove thraustochytrid isolates, Schizochytrium sp. KF1, Aurantiochytrium mangrovei KF6, Thraustochytrium striatum KF9 and Ulkenia sp. KF13. The zoospore motilities, which were based on curvilinear velocity (VCL) and straight-line velocity (VSL), were monitored using the Computer-Assisted Sperm Motility Analysis (CASA) Software system. The zoospore production of four isolates was suppressed at salinity above 15‰. Schizochytrium sp. produced the greatest number of zoospores at 15‰, while Aurantiochytrium mangrovei and Ulkenia sp. produced abundant zoospores in diluted sea water ranging from 7.5 to 15‰. Thraustochytrium striatum performed relatively poorly under all salinities. Salinity and exposure time, as well as their interactions, had significant impacts on most zoospore velocity measurements. The optimal velocities of zoospore motility also varied among isolates. Zoospores of Schizochytrium sp. and A. mangrovei had similar responses to salinity, with the highest motility at 7.3‰, followed by a decrease in velocities with increasing salinity. In contrast, the zoospore of T. striatum had optimal motility at 12‰ and remained highly motile from 15 to 20‰. The velocities of zoospores of Ulkenia sp. were the lowest among the tested thraustochytrids and had optimal motility at 12‰. Zoospores of all the isolates remained active after 4 h of exposure to aqueous medium, but the optimal salinity for each mode of swimming changed. The ecological significance of these data are discussed.