Salinity effects on arm regeneration in Luidia clathrata (Echinodermata: Asteroidea)

The effect of salinity (20, 25, and 30?psu) on regeneration of two arms of adult starfish Luidia clathrata (n?=?8 per salinity treatment group collected from Pensacola Bay, Florida, USA 30° 20′ N, 87° 13′ W) was examined in a laboratory experiment (November 2009 to March 2010) to test the hypothesis that L. clathrata is adapted to euryhaline conditions found in bays with regards to arm regeneration. Regenerating arm condition (lengths and weights) relative to treatment was 20-psu treatment?<?25-psu treatment?<?30-psu treatment, and non-regenerating arm condition was 20-psu treatment?<?25-psu treatment?=?30-psu treatment. Luidia clathrata is not adapted to lower salinity conditions found in bays with regard to arm regeneration, despite the common occurrence of the species in bays. Lower salinity in bays should reduce the ability of L. clathrata to recover from damage sustained during, or just prior to, low-salinity periods.     

The effects of environmental salinity on the growth and physiology of totoaba Totoaba macdonaldi and shortfin corvina Cynoscion parvipinnis

Totoaba Totoaba macdonaldi and shortfin corvina Cynoscion parvipinnis, were acclimated and reared together at salinities of 0, 2, 5, 10, 20 and 35 for 56 days. Initial overall mean ± s.d . body masses of 67·6 ± 7·1 g T. macdonaldi and 37·3 ± 3·1 g C. parvipinnis increased to final overall masses of 217·4 ± 30·3 and 96·5 ± 16·5 g, respectively, at the end of the study. Totoaba macdonaldi was not able to tolerate salinities of 0 and 2 and C. parvipinnis of 0. In contrast, both species had 100% survival at salinities ≥ 10. Somatic growth was highest not at natural seawater salinity of 35, but at 10. Plasma osmolality ranged from 172·5 to 417·0 mOsmol kg^?1 for T. macdonaldi and from 207·0 to 439·5 mOsmol kg^?1 for C. parvipinnis and varied in direct proportion to salinity. The estimated isosmotic salinities of T. macdonaldi and C. parvipinnis were 12·3 and 13·4, respectively. Cynoscion parvipinnis reared at two had significantly lower plasma lysozyme activity (95·0 Units ml^?1) than fish held at salinities from 5 to 35 (ranging from 215·0 to 355·0 Units ml^?1), but without clear trends over this range. Blood neutrophil oxidative radical production (NBT) (ranging from 3·9 to 6·7 mg ml^?1) had some significant differences among salinities, but these did not follow a clear pattern. For T. macdonaldi, neither lysozyme activity nor NBT was affected by salinity. Ash content of whole fishes varied directly and moisture content inversely, with salinity for both species.     

Chronic effect of nitrite on the rearing of the white shrimp Litopenaeus vannamei in two salinities

The aim of this study was to determine the effects of nitrite on the growth and survival of the white shrimp L. vannamei in two different salinities. Nitrite concentrations tested in salinity 8 g/L were 0 (control), 2.5, 5.0, 10.0, and 20.0 mg NO₂^?-N/L, and in salinity 24 g/L were 0 (control), 5.0, 10.0, 20.0, and 40.0 mg NO₂^?-N/L. For these experiments, 30 experimental units with 30?L of useful volume were stocked with 20 juvenile L. vannamei (8.0 ± 0.50 g), corresponding to a stocking density of 100 shrimp/m², and cultivated for an experimental period of 30 days. A significant difference was found between the control and treatment groups with respect to growth and survival. The 2.5 mg NO₂^?-N/L treatment showed the best performance indexes in salinity 8 g/L, while the best growth performance indexes were found in the control and 5.0 mg NO₂^?-N/L treatments in salinity 24 g/L. Total mortality was observed in the 10 and 20 mg NO₂^?-N/L treatment groups from salinity 8 g/L and in the 40 mg NO₂^?-N/L treatment group in salinity 24 g/L. This study determined that concentrations of nitrite of up to 2.5 and 10 mg/L are acceptable for the rearing of L. vannamei in salinities of 8 and 24 g/L, respectively.     

EXPERIMENTAL MESOCOSM STUDIES OF SALINITY EFFECTS ON THE BENTHIC ALGAL COMMUNITY OF A SALINE LAKE

As closed-basin systems, saline lakes are prone to fluctuate in level and salinity with climate change and hydrologic alterations. Loss of many Great Basin lakes has resulted from the diversion of tributary streams for agricultural or municipal uses. At Mono Lake, an alkaline salt lake in eastern California, salinities have risen from 50 to 100 g·L^?1 in just 50 years. Experimental mesocosms were established to simulate some of the potential ecological effects that could have accompanied this change. The influence of salinity on diatom diversity, taxonomic structure, and primary production was tested using mesocosms deployed at Mono Lake. Mesocosm tanks were 500 L in volume, 1 m square, and 0.5 m deep, with open tops covered by 1 mm mesh net. Five treatments (50, 75, 100, 125, and 150 g·L^?1) with four replicates per treatment were used over a 2-month period. The diatom-dominated benthic algae were reduced both in standing crop (from 6 to <0.1 g·m^?2) and diversity (from 30 to 12 taxa) with increased salinity, with most loss occurring in salinities ≥75 g·L^?1. Photosynthetic oxygen production also was significantly lower at salinities ≥75 g·L^?1. Diatom indicator taxa for these shifts included Denticula sp., Nitzschia frustulum, N. monoensis, N. communis, and Stephanodiscus oregonicus increasing in relative abundance in higher salinity treatments, accompanied by decreases in Achnanthes minutissima, Cymbella minuta, N. dissipata, and Rhoicosphenia abbreviata. Exhibiting dominance at moderate salinity levels (75 to 125 g·L^?1) were Nitzschia frustulum, N. communis, N. palea, and Navicula crucialis. These latter species may be limited by both physiological stress at high salinity and grazing and competition at low salinity. The filamentous chlorophyte, Ctenocladus circinnatus, and cyanobacteria (Oscillatoria spp.) occurred only in salinity treatments from 50 to 100 g·L^?1. Diversion of tributary stream flow and resulting salinity increases in this lake threaten sustained benthic primary production and algal species diversity relative to conditions prior to stream diversion. The 1994 decision of the California State Water Resources Control Board to return stream flows to Mono Lake will raise the lake level and reduce salinity to around 75 g·L^?1 and is expected to increase the diversity and productivity of the benthic algae of this ecosystem.     

The effects of different temperature and salinity levels on the acute toxicity of zinc in the Pink Shrimp (Farfantepenaeus paulensis)

The purpose of this study was to measure the acute toxicity of zinc (Zn) on Farfantepenaeus paulensis at different salinities and temperatures by monitoring oxygen consumption. This aspect of the effect of zinc has not been studied in this important commercial species before. First, we examined the acute toxicity of zinc in F. paulensis at 24, 48, 72, and 96?h medium lethal concentration (LC₅₀). One hundred and fifty shrimp were employed for the routine metabolism measurement utilizing sealed respirometers. Ten shrimp were subjected to oxygen consumption measurements in one of the four concentrations of zinc (control, 0.5, 1.0, 2.0, and 3.0 mg?L^?1) at three salinities (36, 20, and 5) and three temperatures (25°C, 20°C, and 15°C). Zinc was significantly more toxic at a salinity of 5 than at 20 or 36. The oxygen consumption was estimated through experiments performed on each of the 12 possible combinations of three temperatures (25°C, 20°C, and 15°C) and three salinities (36, 20, and 5). The shrimp showed a significant reduction in oxygen consumption at a salinity of 5. The results show that the oxygen consumption decreases with respect to the zinc concentration in all temperatures studied. At the highest zinc concentration employed (3.0?mg?L^?1), the salinity 5 and the temperature at 25°C, oxygen consumption decreases 60.92% in relation to the control. The results show that zinc is more toxic to F. paulensis at lower salinities. The significance of the findings for the biology of the species close to sources of zinc is discussed.     

Salinity tolerance of the copepod Apocyclops dengizicus (Lepeschkin, 1900), a key food chain organism in the Salton Sea,California

The copepod Apocyclops dengizicus is a key item in the food chain of the Salton Sea where the salinity is currently 45 g 1^–1. The salinity of the Salton Sea may reach 90 g 1 ^–1 within the next 20 years. This study examined the salinity tolerance of this copepod.Large copepodite and adult A. dengizicus were introduced into various salinities with and without acclimation. The 96 h LC₅₀ without acclimation was 101 g 1^–1. Mortality (at 96 h) without acclimation was low at salinities of 90 g 1 ^–1 or less.Copepod cultures were maintained, with successful reproduction of at least one new generation, at salinities of from 0.5 to 68 g 1 ^–1 for at least 120 days. Copepods maintained at higher salinities, up to 79 g 1 ^–1, remained alive up to 90 days, but a new generation was not produced. In laboratory studies of larval production and survivorship, few nauplii were released at salinities of 68 g 1 ^–1 or higher, and none survived to the copepodite stage.     

Photosynthetic and respiratory responses of Gracilaria parvispora from the southeastern Gulf of California

Photosynthetic and respiratory responses (P–E curves) of Gracilaria parvispora from the southeast Gulf of California were studied at four temperatures (20, 25, 30, 35 °C) and salinity (25, 30, 35, 40 psu) combinations. The alga showed acclimation in its photosynthetic and respiratory responses to tropical temperature as well as to oceanic salinity. A positive effect of temperature on photosynthetic rate (P _max) was observed for all salinities. Photosynthetic rates for treatments at 20 and 25 °C were lower (<9.2 mg O₂?g dry weight (dw)^?1?h^?1) than for treatments at 30 and 35 °C (>12 mg O₂ g dw^?1?h^?1). G. parvispora showed limited tolerance to low salinities (25 psu) and low temperatures (20 °C) and the interaction between temperature and salinity was significant (analysis of variance, P?<?0.05). Responses to salinity indicated adaptation to oceanic salinity. Photosynthetic responses were lower at 25 psu than at higher salinities. The lowest P _max values (6.2–8.2 mg O₂?g dw^?1?h^?1) were observed at the lowest salinity (25 psu) regardless of temperature. Compensation and saturation irradiances (26–170 and 57–149 μmol photons m^?2?s^?1, respectively) indicate adaptation to lower irradiances in shallow (1–2 m depth) habitats, where turbidity can be high, and the capacity of shade adaptation has been developed. Results suggest distribution of this species is mainly related to salinity or temperature. The potential mariculture efforts of G. parvispora would be limited by low temperatures in winter, and indicate that this species will probably not be able to spread further due to low temperatures (<15 °C) in the upper part of the Gulf of California.     

GROWTH OF THE FILAMENTOUS GREEN ALGA CTENOCLADUS CIRCINNATUS (CHAETOPHORALES,CHLOROPHYCEAE) IN RELATION TO ENVIRONMENTAL SALINITY1

Clones of the filamentous green alga Ctenocladus circinnatus Borzi were isolated from algae collected at Abert Lake (Oregon) and Mono Lake (California). Stock cultures were exposed to varied salinities of natural lake water to examine the effects on growth rate, cell form, chlorophyll a, and water content. Growth rates were reduced in both clones with increased salinity over the range 25–100 g·L^?1 and were almost completely inhibited at 150 g·L^?1. Chlorophyll a increased between salinities of 25 and 100 g·L^?1, reflecting slower growth, higher proportions of akinetes, and smaller cell sizes as salinity increased. Tissue water content remained essentially constant from 25 to 100 g·L^?1 salinity. Shorter cell dimensions with increased salinity suggest that a lower surface-to-volume ratio may reduce the potential for passive loss of cell water. Prior acclimation of stock cultures to elevated salinity provided no enhancement of growth response at any salinity. The results indicate that environmental salinity can limit the productivity and distribution of Ctenocladus in nature.     

Iodine contributes to osmotic acclimatisation in the kelp Laminaria digitata (Phaeophyceae)

Iodide (I^?) retained by the brown macroalga Laminaria digitata at millimolar levels, possesses antioxidant activities, but the wider physiological significance of its accumulation remains poorly understood. In its natural habitat in the lower intertidal, L. digitata experiences salinity changes and osmotic homeostasis is achieved by regulating the organic osmolyte mannitol. However, I^? may also holds an osmotic function. Here, impacts of hypo- and hypersaline conditions on I^? release from, and accumulation by, L. digitata were assessed. Additionally, mannitol accumulation was determined at high salinities, and physiological responses to externally elevated iodine concentrations and salinities were characterised by chl a fluorometry. Net I^? release rates increased with decreasing salinity. I^? was accumulated at normal (35 S _A) and high salinities (50 S _A); this coincided with enhanced rETR_max and q_P causing pronounced photoprotection capabilities via NPQ. At 50 S _A elevated tissue iodine levels impeded the well-established response of mannitol accumulation and prevented photoinhibition. Contrarily, low tissue iodine levels limited photoprotection capabilities and resulted in photoinhibition at 50 S _A, even though mannitol was accumulated. The results indicate a, so far, undescribed osmotic function of I^? in L. digitata and, thus, multifunctional principles of this halogen in kelps. The osmotic function of mannitol may have been substituted by that of I^? under hypersaline conditions, suggesting a complementary role of inorganic and organic solutes under salinity stress. This study also provides first evidence that iodine accumulation in L. digitata positively affects photo-physiology.     

Ecological strategies in the ancient asexual animal group Darwinulidae (Crustacea, Ostracoda)

• 1 We investigated the relationship between geographical distribution and ecological tolerance within the ancient asexual family Darwinulidae. Distribution maps were compiled based on data from the literature, the Non‐marine Ostracod Distribution in Europe database and personal collections. Ecological tolerance was assessed experimentally by exposing individual ostracods to a combination of eight different salinities (range from 0 to 30 g L^?1) and three different temperatures (10, 20 and 30 °C).
• 2 The type species of the family, Darwinula stevensoni, is ubiquitous and cosmopolitan; the two species Penthesilenula brasiliensis and Microdarwinula zimmeri also have an intercontinental distribution. Two other darwinulid species tested here (Vestalenula molopoensis and P. aotearoa) are known only from their type localities. The latter is also true for most extant darwinulids.
• 3 Darwinula stevensoni and P. brasiliensis had a broad salinity tolerance, tolerating distilled water and also salinity up to 25–30 g L^?1, whereas the maximum salinity tolerance of V. molopoensis was 12 g L^?1 and of P. aotearoa, 20 g L^?1.
• 4 The results indicate that both ecological specialists and generalists, as well as intermediate forms, exist in the Darwinulidae and that taxa with the broadest ecological tolerance also have the widest distribution.

     

Influence of salinity and cadmium on the survival and osmoregulation of Callianassa kraussi and Chiromantes eulimene (Crustacea: Decapoda)

This study investigated the influence of salinity and cadmium on the survival and osmoregulatory capability of two decapod crustaceans, Callianassa kraussi and Chiromantes eulimene. Callianassa kraussi was able to survive in salinities of 5–55 over 96 h, whilst C. eulimene survived in 0–55 over the same time period. The 96-hour cadmium LC₅₀ for both species decreased progressively at salinities above and below their respective isosmotic conditions, with the decrease being slightly more pronounced below compared to above isosmotic salinity. A hypo-iso-osmoregulatory strategy was followed by C. kraussi as it hyper-osmoregulated at salinities between 5 and 25 and osmoconformed at salinities greater than 25. Chiromantes eulimene followed a hyper-hypo-osmoregulatory strategy; it hyper-regulated in salinities from 0 up to isosmotic conditions at about 28 (c. 780 mOsm kg^?1), followed by hypo-regulation up to 55. The effect of cadmium exposure on the osmoregulatory capacity of C. kraussi was more pronounced at hyper-regulating salinities (5–25) whilst on C. eulimene the influence was more pronounced at salinities above the isosmotic point (28). The influence of salinity and cadmium on both survival and osmoregulation of the two crustaceans are discussed by outlining the chemical and physiological mechanisms involved.     

Ionregulation in juvenile swordspine snook (Centropomus ensiferus,Poey, 1860) in relation to environmental salinity

Ninety‐nine swordspine snook Centropomus ensiferus (9.80 ± 0.3 g, mean ± SE) were studied in order to evaluate the influence of salinity on physiological properties under rearing conditions. Growth performance, survival rates, and ion concentrations (Na⁺, K⁺, Cl^?) as well proximal composition were measured over 76 days. Fish were exposed to three experimental salinities (0, 10, 20 ‰ , three replicates per treatment) and maintained in plastic tanks with a recirculation system equipped with flow‐through aquaria pumps (533 L per tank). Fish were fed twice daily to apparent satiation; at the end of the experiment the weight of fish kept in 10 ‰ was higher than that of fish kept in 0 and 20 ‰ , however no significant differences (P > 0.05) were observed among the experimental salinities. Survival was significantly lower in 10 ‰ salinity than in fish kept in 20 and 0 ‰ salinities. No significant differences (P > 0.05) were found in the Condition factor (K), specific growth rate (SGR), or in plasma Na⁺, K⁺, or Cl^? concentrations among treatments. Salinities also did not affect body composition (P > 0.05), but were significantly lower (P < 0.05) than at the start of the experiment. However, towards the end of the experiment a large accumulation of visceral fat in fish farmed in the three salinities (VFI > 4%) was observed. Water quality was within the optimum range (T: 28.7 ± 0.1°C; O2: 5.6 ± 0.1 mg L^?1; ammonia: 0.2 mg L^?1) for the growth of swordspine snook. Data indicates that C. ensiferus is an ionoregulator fish and able to cultivate successfully in various osmotic conditions, and in turn, maintain high levels of survival in captivity.     

Changes in amino acid composition in the tissues of African catfish (Clarias gariepinus) as a consequence of dietary L-carnitine supplements

A study was undertaken to examine the effect of different amounts of dietary lysine (13 and 21 g kg^?1 diet), lipid (80 and 160 g kg^?1 diet) and L ‐carnitine (0.2 and 1.0 g kg^?1 diet) on growth performance, proximate composition and amino acid metabolism of the African catfish (Clarias gariepinus). Juvenile African catfish (23 ± 1.5 g/fish) were stocked into 70‐L aquaria (16 aquaria, 28 fish/aquarium) connected to a recirculation system during a maximum period of 74 days. All groups were fed at a level of 24 g kg^?0.8 day^?1 in an experiment run at pair feeding. Animals receiving 1.0 g carnitine accumulated up to six times more carnitine in their tissues than animals receiving 0.2 g (P < 0.05). Acyl‐carnitine and free L ‐carnitine levels increased in the whole body and in tissues. Dietary L ‐carnitine supplements increased protein‐to‐fat ratios in the body, but did not affect growth rate. Protein‐to‐fat ratios were only affected when the biosynthesis capacity of L ‐carnitine was restricted due to low lysine levels and when there was a shortage of dietary fat. When lysine was offered at 21 g kg^?1 feed, dietary L ‐carnitine supplements did not affect the amino acid concentrations of body tissues. Dietary L ‐carnitine supplements raised the concentration of glutamic acid > aspartic acid > glycine > alanine > arginine > serine > threonine in skeletal muscle tissue (P < 0.05). Total amino acid concentration in muscle and liver tissues (dry‐matter basis) increased from 506 to 564 and from 138 to 166 mg g^?1, respectively, when diets were offered with high L ‐carnitine, low lysine and low fat levels. These data suggest that dietary L ‐carnitine supplementation may increase fatty acid oxidation and possibly decrease amino acid combustion for energy.     

Effect of temperature and salinity on the energetics of juvenile gray snapper (Lutjanus griseus): implications for nursery habitat value

Gray snapper (Lutjanus griseus) encounter a wide range of temperatures and salinities in nearshore and estuarine juvenile habitats. The energetic response of juvenile gray snapper to temperature and salinity was measured in laboratory experiments to determine the influence of these physicochemical factors on the potential value of different juvenile nurseries. Maximum consumption and growth rates of juvenile (25-50 mm SL) gray snapper were determined in 12-day trials at 20 temperature/salinity combinations representing conditions in juvenile habitats. Ad libitum feeding level of individual fish was measured daily. Maximum weight specific feeding rate increased significantly with temperature and salinity; however, the effect of salinity was much less than that of temperature. Linear growth rate and specific growth rate both increased with temperature, and salinity did not have a significant effect on either. Gross growth efficiency (K₁, growth×consumption⁻¹*100) increased with temperature and was significantly lower at high salinities, indicating increased energetic costs. The higher K₁ at lower salinities has several implications for juvenile gray snapper in low salinity habitats: (1) they would need less food to achieve the same somatic growth as juveniles in high salinity habitats; (2) they would have higher growth at limited ration levels as compared to high salinity habitats; and (3) they would have less impact on prey populations than higher salinity habitats assuming similar gray snapper densities.     

PHOTOSYNTHESIS AND RESPIRATION OF THE CONCHOCELIS STAGE OF ALASKAN PORPHYRA (BANGIALES,RHODOPHYTA) SPECIES IN RESPONSE TO ENVIRONMENTAL VARIABLES1

Photosynthesis and respiration of three Alaskan Porphyra species, P. abbottiae V. Krishnam., P. pseudolinearis Ueda species complex (identified as P. “pseudolinearis” below), and P. torta V. Krishnam., were investigated under a range of environmental parameters. Photosynthesis versus irradiance (P–I) curves revealed that maximal photosynthesis (P_max), irradiance at maximal photosynthesis (I_max), and compensation irradiance (I_c) varied with salinity, temperature, and species. The P_max of Porphyra abbottiae conchocelis varied between 83 and 240 μmol O₂ · g dwt^?1 · h^?1 (where dwt indicates dry weight) at 30–140 μmol photons · m^?2 · s^?1 (I_max) depending on temperature. Higher irradiances resulted in photoinhibition. Maximal photosynthesis of the conchocelis of P. abbottiae occurred at 11°C, 60 μmol photons · m^?2·s^?1, and 30 psu (practical salinity units). The conchocelis of P. “pseudolinearis” and P. torta had similar P_max values but higher I_max values than those of P. abbottiae. The P_max of P. “pseudolinearis” conchocelis was 200–240 μmol O₂ · g dwt^?1 · h^?1 and for P. torta was 90–240 μmol O₂ · g dwt^?1 · h^?1. Maximal photosynthesis for P. “pseudolinearis” occurred at 7°C and 250 μmol photons · m^?2 · s^?1 at 30 psu, but P_max did not change much with temperature. Maximal photosynthesis for P. torta occurred at 15°C, 200 μmol photons · m^?2 · s^?1, and 30 psu. Photosynthesis rates for all species declined at salinities <25 or >35 psu. Estimated compensation irradiances (I_c) were relatively low (3–5 μmol · photons · m^?2 · s^?1) for intertidal macrophytes. Porphyra conchocelis had lower respiration rates at 7°C than at 11°C or 15°C. All three species exhibited minimal respiration rates at salinities between 25 and 35 psu.     

Growth and physiological parameters of whiting (Sillaginodes punctata) in relation to salinity

This study assessed the impact of salinity on whiting (Sillaginodes punctata) in an attempt to understand the mechanisms by which salinity could potentially influence habitat selection and growth of King George whiting in southern Australia. The experiment included whiting of two age classes, young of the year (YOY) and 2⁺ year, at three salinities (30, 40, 50 ppt). YOY whiting showed no significant difference in length or weight gain, specific growth rate, feed intake, food conversion ratio or condition factor when exposed to the three salinities for 72 day. Plasma osmolality of YOY whiting was not significantly different at any salinity, although it was significantly lower than that of 2⁺ year whiting. The 2⁺ year whiting showed significantly higher plasma osmolality than the YOY. Blood plasma potassium and chloride levels of 2⁺ year fish at 50 ppt were significantly higher than those at 30 ppt and 40 ppt. Blood sodium levels at 50 ppt were significantly higher than at 30 ppt but the sodium level at 40 ppt was not different from 30 ppt or 50 ppt. Haematocrit of 2⁺ whiting was significantly higher at 30 than at 50 ppt while haematocrit at 40 ppt was not different from 30 or 50 ppt. The 2⁺ year‐old whiting had a more pronounced increase in plasma osmolality and plasma ions at high salinities, indicating poorer osmoregulatory capacity in older fish. This study provides physiological evidence to partially explain habitat occupancy and growth in relation to salinity of different age groups of whiting in southern Australia.     

EFFECT OF SALINITY ON PSEUDO‐NITZSCHIA SPECIES (BACILLARIOPHYCEAE) GROWTH AND DISTRIBUTION1

Salinity varies widely in coastal areas that often have a high abundance of Pseudo‐nitzschia H. Peragallo. Pseudo‐nitzschia is abundant in Louisiana waters, and high cellular domoic acid has been observed in natural samples but no human illness has been reported. To assess the threat of amnesic shellfish poisoning (ASP), we examined the effect of salinity on Pseudo‐nitzschia occurrence in the field and growth in the laboratory with special emphasis on the salinity range where oysters are harvested (10–20 psu). In Louisiana coastal waters, Pseudo‐nitzschia spp. occurred over a salinity range of 1 to >35 psu, but they occurred more frequently at higher rather than lower salinities. Seven species were identified, including toxigenic species occurring at low salinities. In culture studies, seven clones of three species grew over a salinity range of 15 to 40 psu, some grew at salinities down to 6.25 psu, and most grew at salinities up to 45 psu. Tolerance of low salinities decreased from Pseudo‐nitzschia delicatissima (Cleve) Heiden to P. multiseries (Hasle) Hasle to P. pseudodelicatissima (Hasle) Hasle emend. Lundholm, Hasle et Moestrup. In conclusion, although Pseudo‐nitzschia was more prevalent in the field and grew better in the laboratory at higher salinities, it grew and has been observed at low salinities. Therefore, the probability of ASP from consumption of oysters harvested from the low salinity estuaries of the northern Gulf of Mexico is low but not zero; animal mortality events from toxin vectors other than oysters at higher salinity on the shelf are more likely.     

Diversity of juvenile fish assemblages in the pelagic waters of Lebanon (eastern Mediterranean)

Oxygen consumption rates of nauplii of the brine shrimp Artemia franciscana Kellogg 1906 were determined over a range of salinities from 10 to 110 ppm, in temperatures from 0 to 30°C, using a multi-factorial design. The oxygen micro-sensors employed have a fast response time and are capable of accurately measuring oxygen concentrations at temperatures well below 0°C. Oxygen uptake rate ranged from 0.03 to 0.66 μmol O₂ mg⁻¹ h⁻¹ and was sensitive to changes in both salinity and temperature. Temperature was the dominant factor affecting oxygen consumption rates, which showed a significant increase with increasing temperature. A slight decrease was measured in oxygen consumption with increasing salinity related to differential solubility of oxygen in waters of different salinities. Thermal sensitivity of oxygen consumption determined from calculations of Q ₁₀, indicated physiological adaptation of Artemia nauplii to the ranges of temperatures tested. Handling editor: A. van Kerchove     

Effect of feeding different protein to energy (P/E) ratios on the growth performance and body composition of Oreochromis niloticus fingerlings

This study evaluated the growth performance and body composition of Oreochromis niloticus fingerlings (average initial weight 16.53 ± 0.44 g) fed 9 experimental diets (A, B, C, D, E, F, G, H and I) containing three different levels of protein (26, 31 and 36 g 100 g^?1) at three different gross energy (GE) levels (16, 19 and 22 MJ kg^?1) for a period of 64 days. Significant differences were observed in the feed consumption, body weight gain, specific growth rate (SGR), condition factor (k), feed conversion ratio (FCR), protein efficiency ratio (PER), net protein retention (NPR) and apparent net energy retention (ANER) values of fish when the energy level of diet was increased at different protein levels. The maximum weight gain, SGR and k were observed on diet F containing 36% protein and an energy level of 19 MJ kg^?1 of dry feed with a protein to energy (P/E) ratio of 18.96 (g protein MJ^?1 GE). A further increase in the energy content of the diet (22 MJ kg^?1) at the same protein level (Diet I) did not produce any improvement in the growth performance. Lowering the energy level at the same protein level significantly affected the growth performance. Fish fed diet B containing 31% protein and a lower energy level of 16 MJ kg^?1 with the same P/E ratio of 18.61 as diet F showed significantly lower weight gain and growth performance than diet F. Diets E and H containing 31% crude protein at all three energy levels produced similar results as diet B. The poorest FCR was observed when the diet contained both lower levels of protein and energy. Fish fed diet G, containing 26% protein at high energy level (22 MJ kg^?1), showed the best PER and NPR values. The PER and NPR were the poorest on diet C containing 36% protein at low energy level (16 MJ kg^?1). The body moisture content at all protein levels decreased (P < 0.05) with the increasing level of dietary energy whereas the body fat content increased (P < 0.05). Similar trends were observed in the body ash and energy content. Increasing the dietary energy content at lower protein levels did not show any difference (P > 0.05) in body protein content. Our results indicated the optimum P/E ratio for O. niloticus as 18.96 g protein per mega joule of gross energy at 36% dietary protein level and a dietary gross energy value of 19 MJ kg^?1.     

Effect of inland water salinity on growth performance and nutritional physiology in growing milkfish, Chanos chanos (Forsskal): field and laboratory studies

To investigate the effect of inland groundwater salinity on growth performance, feed conversion efficiency, nutrient retention and intestinal enzyme activity in milkfish, two experiments were conducted. In the first experiment (Expt I), a 100‐day monoculture of Chanos chanos [mean body weight (BW): 2.2 g] at different salinities (0, 10, 15, 20 and 25‰) was carried out in ponds fertilized with cowdung (about 10 000 kg ha^?1 year^?1) and poultry droppings (about 3000 kg ha^?1 year^?1). The fish were fed a compounded supplementary diet (containing 40% protein) at 5% BW day^?1. Studies have revealed that growth increased with each increase in the salinity level; the highest values in weight gain and energy assimilated were observed in ponds maintained at 25‰ salinity [weight: 322.2 g and specific growth rate (SGR): 8.3]. Highest values of condition factor (0.7) and exponential value (n) of the length–weight relationship (LWR; n = 3.25) were also observed in ponds maintained at 25‰ salinity. Dissolved oxygen (DO), biological oxygen demand (BOD), pH and nutrient release remained at the optimal level during the culture period. High values of chlorophyll a, net primary productivity (NPP), phytoplankton and zooplankton population coincided with the highest values of alkalinity and turbidity in ponds maintained at 25‰ salinity. Multivariate analysis revealed a significant positive correlation of chlorides (r = 0.91), conductivity (r = 0.89) and hardness (r = 0.96) with fish growth. Productivity indicating parameters viz. NPP (r = 0.45), nitrate (r = 0.94) and o‐PO₄ (r = 0.52) also showed a significant positive correlation with fish weight gain. In the second experiment (Expt II), milkfish (mean BW: 3.7 g) fry were exposed to different levels of salinity (0.0, 10, 15, 20, 25 and 30‰), and maintained for 90 days in the laboratory. Significantly (P < 0.05) high growth (percentage increase in BW: 183.1 and SGR: 1.2), feed conversion efficiency (64.5%) and intestinal enzyme activity (protease 5.1, amylase 4.1 and cellulolytic 3.2) were observed in the group maintained at 25 ppt salinity in comparison with other groups similarly maintained at low or high salinity levels. Carcass composition, muscle and liver glycogen levels were also significantly (P < 0.05) affected by salinity changes. The significance of these findings is discussed in this paper.