Food intake,growth, food conversion,and body composition of catfish exposed to different salinities

The effects of different salinities (0, 2, 4, 6 and 10‰) on food intake, growth, food conversion, and body composition of the freshwater catfish Mystus vittatus (Bloch) were studied. Under a restricted feeding schedule daily intake of food was found to be salinity dependent. Fish reared in 10‰ consumed more Tubifex tubifex, converted less efficiently and displayed poor growth as compared to individuals reared in fresh water. Fish flesh production decreased from 483 g (fresh water) to 177 g (10‰ salinity) as the salinity was increased. Water content of the fish was found to decrease with increase in salinity, while maximum ash (25.56%) and fat (42.25%) were exhibited by fish reared in 10‰ salinity.     

A Preliminary Study on the Effects of Salinity on Growth and Survival of Mulloway Argyrosomus japonicus Larvae and Juveniles

Abstract.— Tko experiments were conducted to determine the effects of salinity on growth and survival of mulloway Argyrosomus japonicus larvae and juveniles. First, 6-d-old larvae were stocked into different salinities (5, 12.5, 20, 27.5 and 35 ppt) for 14 d. Larvae grew at all salinities, but based on results for growth and survival, the optimum range of salinity for 6-d-old to 20-d-old larvae is 5–12.5 ppt. During this experiment larvae held in all experimental salinities were infested by a dinoflagellate ectoparasite, Amyloodinium sp. Degree of infestation was affected by salinity. There were very low infestation rates at 5 ppt (0.2 parasites/larva). Infestation increased with salinity to 20 ppt (33.1 parasites/larva), then declined with salinity to 35 ppt (1.5 parasites/larva). For the second experiment, juveniles (6.1 ± 0.1 g/fish) were stocked into different salinities (0.6, 5, 10, 20 and 35 ppt) for 28 d. Juveniles were removed from freshwater 3 d after transfer as they did not feed, several fish died and many fish had lost equilibrium. However, when transferred directly to 5 ppt. these stressed fish recovered and behaved normally. Trends in final mean weight and food conversion ratio of juvenile mulloway suggest that fish performed best at 5 ppt. Although salinity (5 to 35 ppt) had no significant ( P > 0.05) effect on growth, survival, or food conversion ratio of juveniles, statistical power of the experiment was low (0.22). Based on these results we recommend that mulloway larvae older than 6 d be cultured at 5 to 12.5 ppt. Optimum growth of juveniles may also be achieved at low salinities.     

Salinity effects on osmoregulation and gill morphology in juvenile Persian sturgeon (<Emphasis Type="Italic">Acipenser persicus</Emphasis>)

The effect of abrupt and 5-day gradual salinity transfers from freshwater (FW) to 11 ‰ Caspian Sea brackish water (BW) was investigated in juvenile Persian sturgeon Acipenser persicus with three different weight groups: 1–2 g (1.62 ± 0.27 g), 2–3 g (2.55 ± 0.41 g) and 3–5 g (4.28 ± 0.76 g). Mortality rates, blood osmotic pressure, gill morphology and branchial Na⁺, K⁺-ATPase (NKA) activity were measured 4 and 10 days after abrupt transfer and 9 and 15 days after the initial gradual transfer (i.e. 4 and 10 days after reaching Caspian Sea salinity). Fish under 3 g could not survive increased salinity, and the blood osmotic pressure of the remaining surviving fish increased and remained elevated. However, heavier fish were able to survive and successfully acclimate, even to rapid salinity change with osmotic pressure reduced to Caspian Sea osmolality levels. At the gill level, the developmental increase in chloride cell volume and a higher NKA content most probably allow juveniles weighing more than 2 g to sharply increase NKA activity if the fish are transferred to BW. The rapid chloride cell proliferation occurring with increased salinity should strengthen this acclimation response. Therefore, a drastic physiological change occurs when fish weigh more than 2 g that allows migration to higher salinities. The triggering signal on chloride cells must be further investigated in order to optimize this functional step.     

Osmoregulation,growth and moulting cycles of the giant freshwater prawn (Macrobrachium rosenbergii) at different salinities

The giant freshwater prawn, Macrobrachium rosenbergii, is a species with a high commercial value in aquaculture. Two experiments were performed to determine the effects of salinities on the osmoregulation, growth and molting cycles of M. rosenbergii during growout. The first experiment was designed to determine whether these animals are capable of adapting to the changes in salinity seen in salinity intrusions in tropical deltas, with an incremental increase in salinity of 3‰ per day from 0‰ to 30‰ Haemolymph osmolality was rapidly regulated up to salinities of 15‰ , whereas animals conformed at higher salinities. The second experiment determined the growth, moulting cycle, osmolality, muscle water content and mortality during a 4‐month experiment at 0‰, 15‰ or 25‰ salinity. The weight gains in 0‰ and 15‰ were not significantly different and were comparable to the growth rates achieved in production farms with body mass increases of 2.6 and 2.3‐fold their initial body mass, respectively, after 4 months. The 25‰ group suffered from low growth, high mortality and a significantly lower moulting frequency. These data show that this species can be reared in brackish water up to 15‰, allowing for farming in the large areas impacted by salt water intrusions in tropical deltas.     

Effects of different salinity and temperatures on the growth,survival, haematocrit and blood biochemistry of Goldfish (Carassius auratus)

The aim of the present study was to investigate the effects of different salinities (0‰, 6‰ and 12‰) and temperatures (23, 27 and 31 °C) on the food consumption, growth, blood biochemistry and haematocrit of Goldfish. After 45 days of exposure to different salinities and temperatures, Goldfish showed a good adaptation to these salinities and temperatures in terms of blood biochemistry (glucose and triglyceride) and haematocrit. Salinities (0‰ and 6‰) and temperatures (23 and 27 °C) did not affect the weight gain, specific growth rate, final biomass and feed conversion rates, but these parameters were significant (P<0.05) at 12‰ salinity and 31 °C temperature. Plasma total protein levels decreased with the increase in salinity (P<0.05), while they were independent of temperature. In conclusion, Carassius auratus, a freshwater stenohaline fish, showed good growth in saline waters with maximum 12‰ salinity and 31 °C temperature.     

Effect of Salinity on Growth,Feed Utilization,and Survival of Tilapia rendalli Under Laboratory Conditions

ABSTRACT

Juvenile T. rendalli were evaluated for 10 weeks to determine the effect of salinity on growth, feed utilization, and survival in tanks. Fish weighing 3.94 ± 0.44 g were stocked into twelve 50-L rectangular tanks at 15 fish /tank. The fish were raised in three salinity levels (5, 10, 15‰, and freshwater as a control). There were three replicate tanks per treatment. After the feeding experiment, a digestibility trial was conducted for two weeks. After 70 days, fish in the 10‰ treatment grew significantly larger (P < 0.05) than those in 5‰, 15‰, and freshwater. T. rendalli cultured in 10‰ had significantly lower feed conversion ratios and higher feed conversion efficiency and protein efficiency ratios. Survival of the fish was significantly (P < 0.05) different and depended on salinity level. The apparent digestibilities of crude protein, fat, ash, and gross energy were significantly higher (P < 0.05) in T. rendalli cultured in the 10‰ salinity treatment. However, apparent digestibility of dry matter did not differ significantly (P < 0.05) between 10‰ and 5‰. The results obtained indicate that 10‰ is optimal for T. rendalli in tank culture.     

Experimental assessment of the effects of sublethal salinities on growth performance and stress in cultured tra catfish (Pangasianodon hypophthalmus)

The effects of a range of different sublethal salinities were assessed on physiological processes and growth performance in the freshwater ‘tra’ catfish (Pangasianodon hypophthalmus) juveniles over an 8-week experiment. Fish were distributed randomly among 6 salinity treatments [2, 6, 10, 14 and 18 g/L of salinity and a control (0 g/L)] with a subsequent 13-day period of acclimation. Low salinity conditions from 2 to 10 g/L provided optimal conditions with high survival and good growth performance, while 0 g/L and salinities >14 g/L gave poorer survival rates (p < 0.05). Salinity levels from freshwater to 10 g/L did not have any negative effects on fish weight gain, daily weight gain, or specific growth rate. Food conversion ratio, however, was lowest in the control treatment (p < 0.05) and highest at the maximum salinities tested (18 g/L treatment). Cortisol levels were elevated in the 14 and 18 g/L treatments after 6 h and reached a peak after 24-h exposure, and this also led to increases in plasma glucose concentration. After 14 days, surviving fish in all treatments appeared to have acclimated to their respective conditions with cortisol levels remaining under 5 ng/mL with glucose concentrations stable. Tra catfish do not appear to be efficient osmoregulators when salinity levels exceed 10 g/L, and at raised salinity levels, growth performance is compromised. In general, results of this study confirm that providing culture environments in the Mekong River Basin do not exceed 10 g/L salinity and that cultured tra catfish can continue to perform well.     

Salinity and temperature tolerance of brown-marbled grouper Epinephelus fuscoguttatus

Grouper have to face varied environmental stressors as a result of drastic changes to water conditions during the storm season. We aimed to test the response of brown-marbled grouper to drastic and gradual changes in temperature and salinity to understand the grouper’s basic stress response. The results can improve the culture of grouper. Brown-marbled grouper, Epinephelus fuscoguttatus (6.2 ± 0.8 g) were examined for temperature and salinity tolerances at nine different environmental regimes (10, 20, and 33 ‰ combined with 20, 26 and 32 °C), in which the fish were subjected to both gradual and sudden changes in temperature and salinity. The critical thermal maximum (50 % CT_MAX) and the upper incipient lethal temperature (UILT) were in the ranges of 35.9–38.3 and 32.7–36.5 °C, respectively. The critical thermal minimum (50 % CT_MIN) and the lower incipient lethal temperature (LILT) were in the ranges of 9.8–12.2 and 14.9–22.3 °C, respectively. The critical salinity maximum (50 % CS_MAX) and the upper incipient lethal salinity (UILS) were in the ranges of 67.0–75.5 and 54.2–64.8 ‰, respectively. Fish at temperature of 20 °C and a salinity of 33 ‰ tolerated temperatures as low as 10 °C when the temperature was gradually decreased. Fish acclimated at salinities of 10–33 ‰ and a temperature of 32 °C tolerated salinities of as high as 75–79 ‰. All fish survived from accumulating salinity after acute transfer to 20, 10, 5, and 3 ‰. But all fish died while transferred to 0 ‰. Relationships among the UILT, LILT, 50 % CT_MAX, 50 % CT_MIN, UILS, 50 % CS_MAX, salinity, and temperature were examined. The grouper’s temperature and salinity tolerance elevated by increasing acclimation temperature and salinity. On the contrary, the grouper’s temperature and salinity tolerance degraded by decreasing acclimation temperature and salinity. The tolerance of temperature and salinity on grouper in gradual changes were higher than in drastic changes.     

Effect of salinity at constant 10 °C on grow-out of anadromous Arctic charr from Labrador

The goal is to determine the requirements allowing cultured Salvelinus alpinus to thrive in seawater, as they do in the wild. In late-June, eight families of individually identified 1+ year-old charr (mean wt: 427 g) of a domesticated strain derived from the Fraser River population were directly transferred from freshwater (9 °C) to salinities of either 0, 10, 20 and 30 ppt at 10 °C, then on-grown in tanks until December. Cumulative mortality was 16% in 30 ppt salinity, and < 4% in the lower salinities. Repeated measures analysis revealed somatic growth was inhibited by both elevated salinity and sexual maturation. Among immature fish, final mean weight and condition factor in 30 ppt salinity was 490 g and 1.2, compared to nearly 1 kg and > 1.7 in 0 and 10 ppt. In 20 ppt salinity, growth was initially similar to that in ≤ 10 ppt salinity but deteriorated from September onwards. Sexually maturing fish in ≤ 10 ppt salinity attained a final mean weight about 35% less than immatures. Plasma osmolality was only slightly elevated in the 30 ppt salinity, remaining < 340 mOsm kg^− 1. Food intake and conversion were affected by the interaction between salinity and time, being optimum in 0 and 10 ppt treatments. Family effects on final body size were large, but the effect of salinity on growth was independent of family. In conclusion, despite their large body size, direct transfer of this strain from freshwater to seawater does not appear viable for commercial aquaculture.     

Effects of Temperature and Salinity on Weight Gain, Oxygen Consumption Rate, and Growth Efficiency in Juvenile Red-Claw Crayfish Cherax quadricarinatus

Abstract.— Weight gain and metabolic rates, as determined by oxygen consumption rates, were examined in juvenile Australian red-claw crayfish Cherax quadricarinatus exposed to different temperatures (16–32 C in 2 C increments) or salinities (0–30 ppt in 5 ppt increments). Mean weight gain, molting frequency, and survival (%) were dependent on temperature and salinity. In freshwater (0 ppt), maximal weight gain and molting frequency were observed at 28 C with maximal survival observed over the temperature range of 24–30 C. Metabolic rates in freshwater were temperature dependent (mean Q₁₀= 2.44). Maximal weight gain and molting frequency were observed at salinities of 0 and 5 ppt (28 C); however, survival was reduced at salinities ≥ 5 ppt. Metabolic rates were not salinity dependent and did not differ significantly over the salinity range from 0–20 ppt. Growth efficiencies, calculated by dividing weight gain by total metabolic energy expenditure (i.e., weight gain + metabolic rate), were highest at a temperature of 20 C (0 ppt) and at salinities of 0 and 5 ppt (28 C). These data suggest that, at higher culture temperatures, maximal weight gain of red-claw juveniles may be reduced when food resources are limited. Maximal weight gain, at optimal temperatures (28 C) with unlimited food supply, does not appear to be effected by low salinity conditions. Because of the potential commercial value of red-claw, culturists, should be aware of the relationship between environmental condition and metabolic energy requirements to ensure maximal weight gain and survival of juveniles.     

Response of a freshwater air-breathing fish, Clarias batrachus to salinity stress: an experimental case for their farming in brackishwater areas in Andaman, India

The study was conducted to assess the effects of salinity on growth and biochemical composition of freshwater catfish, Clarias batrachus. A static nonrenewable acute toxicity bioassay test was conducted and LC₅₀ of salinity for 96-h exposure to the fingerling (14.5 cm) was 12.52 ‰. Based on these results, two sublethal salinity levels, viz. 4 and 8 ‰ were selected to study the long-term effects of salinity on C. batrachus for a period of 90 days. From the study, it was found that growth and survival rate were less in saline water (4 and 8 ‰). Maximum growth and survival were recorded in freshwater (0 ‰ salinity) and subsequently at 4 and 8 ‰. To assess the biochemical alteration, few important biomarkers were estimated. At the end of 90 days rearing period, glucose level in the brain and blood of C. batrachus was found to decrease with salinity. The level of liver and muscle glycogen in the fish reared at 4 ‰ was lower than that of control. Ascorbic acid in all organs under study was found to decrease with increasing salinity, which was attributed to stress mitigation effect of vitamin C. Acetylcholine esterase (AchE) activity recorded a gradual decrease with increasing salinity. Metabolic enzymes, alkaline phosphatase (ALP) activity and adenosine triphosphosphtase (ATPase) activity also reduced both in liver and muscle tissues with increasing salinity. From the present investigation, it can be concluded that exposure to higher salinity significantly (P < 0.01) affects the growth and physiological response of Clarias batrachus.     

Osmoregulation in populations of an endangered hardyhead (Atherinidae: Craterocephalus fluviatilis McCulloch, 1912) from different salinity regimes

Abstract – Fragmented populations of freshwater fish may develop genotypic and phenotypic differences as adaptations to local habitat conditions. These differences contribute significantly to biological diversity and may lead to speciation. In the Murray–Darling Basin, Australia, the Murray hardyhead Craterocephalus fluviatilis, listed as ‘endangered’ by the World Conservation Union, has a wide but fragmented distribution that is apparently related to salinity. To determine whether this pattern has a physiological basis, we compared osmoregulation in fish from two isolated populations in different salinity regimes (Wyndgate: 0.4–1.5‰; Disher Creek: c. 1.0–45‰). In laboratory trials, fish from both populations remained healthy at high salinities (5–65‰). The Disher Creek population maintained a significantly lower blood osmotic concentration than the Wyndgate population at salinities ≤1‰, suggesting that there is a physiological difference between them. The findings have implications for the conservation of C. fluviatilis and other fish populations whose distributions are fragmented by salinity.     

长江口中华鲟幼鱼血液水分、渗透压及离子浓度的变化规律

为了研究长江口中华鲟幼鱼盐度适应过程及其调节规律,将7月龄幼鱼直接转入0(淡水对照),5,10,15等4个盐度组中养殖32天,分别在0.5,1,2,4,8,16,和32 d 检测幼鱼血液水分、血清渗透压和血清Na 、Cl-、K 的浓度,结果显示：试验过程中,淡水和盐度5组中华鲟幼鱼血液各项指标始终保持一致,未呈现显著性差异。盐度10和15组,中华鲟幼鱼血液水分含量呈先下降后上升趋势,下降程度与盐度呈正相关,16 d时各组幼鱼血液水分无显著性差异。中华鲟幼鱼转入盐度10和15条件下,其血清渗透压与Na 和Cl-浓度的变化趋势一致,表现为先上升后下降,最后达到新的平衡;12 h是其上升和下降的拐点。而血清K 浓度的变化趋势与血清渗透压和Na 、Cl-离子不同,呈现先下降后趋于平稳的趋势。从结果可以看出,中华鲟幼鱼与其他广盐性鱼类一样,其盐度适应过程可分为2个阶段,即临界期和调整期。     

Effects of Salinity on Growth, Survival, and Selected Hematological Parameters of Juvenile Cobia Rachycentron canadum

Cobia Rachycentron canadum juveniles (119.7 mm TL, weight 8.5 g) were reared for 10 wk at three salinity levels: 5 ppt, 15 ppt. and 30 ppt. Growth and survival were determined through biweekly sampling. Blood samples obtained at termination of the study were analyzed to determine hematocrit, blood osmolality, and total protein. Results indicated that the overall growth of fish was significantly affected by salinity. Mean (± SE) total length (TL) and weight of fish reared at a salinity of 30 ppt were 201.7 ± 2.6 mm and 47.6 ± 1.9 g, respectively, followed by fish reared at 15 ppt (182.2 ± 1.7 mm, 34.1 ± 1.6 g). and 5 ppt (168.3 ± 5.8 mm TL, 28.3 ± 2.3 g). Differences in specific growth rates among treatments for the 10-wk period were also significant. No differences were detected in mean survival among fish reared at salinities of 5, 15, and 30 ppt (84, 94, and 94%, respectively). However, fish reared at salinity 5 ppt appeared to be in poor health as skin lesions, fin erosion, and discoloration were evident. Analysis of blood revealed that, while no differences existed among treatments with respect to plasma total protein, fish reared at a salinity of 5 ppt exhibited significantly reduced hematocrit (25% vs. > 30%) and plasma osmolality values (318 vs. > 353 mmolkg) relative to fish reared at higher salinities. Cobia can tolerate exposure to low salinity environments for short periods of time without mortality; however, moderate to high salinities are required for sustained growth and health of this species.     

Performance of <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis> postlarvae reared in indoor nursery tanks under biofloc conditions at different salinities and zero-water exchange

Shrimp farming at low salinity is a trend that will continue to grow globally. Performance of Litopenaeus vannamei postlarvae in the nursery at different salinities with a biofloc technology (BFT) system needs to be explored further, as the nursery is currently used as a transitional stage between the hatchery and grow-out ponds. Hence, this study evaluated the effect of seven salinity levels (2, 4, 8, 12, 16, 25, and 35 ‰) on the performance of L. vannamei postlarvae reared with a BFT system and zero-water exchange at 2000 org/m³. Additionally, this study evaluated the water quality of all salinity treatments. After 28 days of culture, the findings showed that, under biofloc conditions, salinity affected the performance of some variables of water quality in some cases, but only the combination of a high nitrite-N concentration (>4 mg/l) and low salinity (2 and 4 ‰) caused up to 100 % shrimp mortality in the first 2 weeks. In the rest of the treatments (8, 12, 16, 25, and 35  ‰), shrimp survival was >72 %. Shrimp mortality was affected by salinity, especially when it decreased from 35–25–16 to 12 and 8 ‰. The organisms reared at low salinities presented lower final weights and specific growth rate than those reared at higher salinities. An inverse relationship was shown between the ion concentration and the final weight of shrimp.     

The effects of a sudden salinity change on cortisol, glucose, lactate, and osmolality levels in grouper Epinephelus malabaricus

Grouper Epinephelus malabaricus (weighing 46.37?±?5.10?g) previously maintained in 24‰ seawater were transferred to 14, 19, 24 (control), 29, and 34‰ seawater. Serum cortisol, glucose, lactate, and osmolality levels were measured at 7 time points during 240?min. Serum cortisol and glucose levels of fish transferred to 29 and 34‰ seawater significantly increased to the highest after 10 and 20?min, respectively. No significant differences in serum cortisol and glucose levels were observed for the fish after 30?min among all treatments. Serum lactate level of fish transferred to 14, 19, 29, and 34‰ seawater was significantly lower than that of the control fish after 10-30?min. However, no significant differences in serum lactate were observed 60?min among five treatments. The serum osmolality of the fish following 240-min transfer increased directly with salinity, whereas the osmoregulatory capacity value (medium osmolality-plasma osmolality) of the fish following 240-min transfer was inversely related to salinity. It is concluded that grouper showed strong osmoregulation in 14-34‰ seawater. Serum cortisol and glucose levels of fish transferred to 29 and 34‰ seawater increased rapidly in 10-30?min, indicating an early stress response.     

Physiological effects of salinity on Delta Smelt, <Emphasis Type="Italic">Hypomesus transpacificus</Emphasis>

Abiotic factors like salinity are relevant to survival of pelagic fishes of the San Francisco Bay Estuary. We tested the effects of 4 parts per thousand (ppt) salinity increases on Delta Smelt (DS) in a laboratory experiment simulating salinity increases that might occur around the low-salinity zone (LSZ) (<6 ppt). Adult DS, fed 2 % body mass per day, starting at 0.5 ppt [freshwater (FW)], were exposed to weekly step-increases of 4 ppt to a maximum of 10 ppt saltwater (SW) over 19 days, and compared to FW controls. DS (n = 12/treatment per sampling) were sampled at 24, 72, and 96 h (1, 3, and 4 days) post-salinity increase for analyses of hematocrit, plasma osmolality, muscle water content, gill chloride cell (CC) Na⁺/K⁺-ATPase (NKA) and apoptosis after being weighed and measured (n = 3 tanks per treatment). No apparent increase in length or weight occurred nor did a difference in survival. Following step-increases in SW, hematocrit increased over time. Other fish responses generally showed a pattern; specifically plasma osmolality became elevated at 1 day and diminished over 4 days in SW. Percent muscle water content (%) did not show significant changes. CCs showed increased NKA, cell size and apoptosis over time in SW, indicating that CCs turnover in DS. The cell renewal process takes days, at least over 19 days. In summary, DS are affected by salinities of the LSZ and ≤10 ppt, though they employ physiological strategies to acclimate.     

盐度对杂交东方鲀存活和摄食的影响

采用盐度骤变和渐变的方法,研究了盐度0、5‰、10‰、15‰、20‰、25‰、30‰、35‰、40‰、45‰、50‰、55‰、60‰共13个梯度对菊黄东方鲀(♀)×红鳍东方鲀(♂)杂交F1代存活和摄食的影响。研究表明,盐度从30‰骤变到15‰～50‰时,杂交F1存活率最高,显著高于盐度0、5‰、10‰、55‰和60‰梯度的存活率(P<0.05),其中盐度10‰的梯度中杂交F1代存活率约为33.3%,而盐度0、5‰、55‰和60‰梯度的存活率均低于1%;盐度5‰～50‰为杂交F1可摄食盐度,其中20‰～35‰是最佳摄食盐度。盐度渐变时,盐度5‰～50‰梯度中杂交F1代存活率最高,显著高于盐度0、55‰和60‰梯度的存活率(P<0.05),其中盐度0的梯度中杂交F1代存活率最低,约为12%;盐度0～60‰为杂交F1可摄食盐度,其中盐度20‰、25‰、30‰、35‰和40‰时,杂交F1摄食率无显著差异,在盐度30‰时摄食量和摄食率均达到最大。表明,菊黄东方鲀(♀)×红鳍东方鲀(♂)杂交F1代是广盐性鱼类,对盐度适应能力较强,而且适应盐度渐变的能力强于盐度骤变。     

The effect of reduced salinity on growth,food conversion and protein efficiency ratio in juvenile spotted grunter, Pomadasys commersonnii (Lacépède) (Teleostei: Haemulidae)

Salinity has been proven to have a significant effect on the growth and survival of anadromous fish species; however, there is a paucity of information regarding its effect on euryhaline marine species. Experiments were conducted to examine the effect of hyposalinity on the osmoregulation and growth of juvenile spotted grunter, Pomadasys commersonnii (Lacépède). Although the spotted grunter is considered to be a strong osmoregulator, growth performance and survival was compromised below isosmotic concentrations. The growth rate, condition and food conversion of fish in low salinity (5‰) were lower than in either isosmotic (12‰) or hyperosmotic (25‰ and 35‰) conditions. Mortality was also significantly higher at 5‰. From these results, it is concluded that P. commersonnii can be successfully cultured in salinities ranging from 12‰ to full-strength sea water (35‰).     

Observations on salinity tolerance and osmoregulation in laboratory-reared Macrobrachium rosenbergii post-larvae (Crustacea: Caridea)

The tolerance of postlarval Macrobrachium rosenbergii to gradual and rapid increases in salinity was determined. Mortalities occurred at salinities around 25‰ and increased rapidly at levels ≥30‰ in both cases. However, acclimation substantially increased survival time at 35‰.Freezing point depressions of blood were measured from laboratory-reared M. rosenbergii postlarvae and juveniles exposed to various salinities from fresh water to approximately 35‰. The blood concentration was hyperosmotic to the medium at salinities from fresh water to about 17–18‰ and hypoosmotic at higher salinities. Postlarvae maintained a nearly constant blood concentration (freezing point depression = ?0.89 ± 0.13°C) over a wide range of external salinities (fresh water to about 27–30‰). The animals' osmoregulatory mechanisms failed at salinities ≥30‰, and thereafter the blood concentration paralleled that of the medium. The blood concentrations of juvenile shrimp grown for 5 months at salinities from fresh water to about 15‰ (freezing point depression = ?0.88 ± 0.07°C) closely resembled those of postlarvae.The osmoregulatory performance of young M. rosenbergii is generally similar to that of other brackishwater animals, but in their ability to hyperosmoregulate effectively in fresh water they more closely resemble fresh water species. It is suggested that M. rosenbergii may be able to conserve salt in dilute media by producing blood-hypoosmotic urine.An interesting stress symptom often preceded death of postlarvae in high salinities. The animals changed gradually from nearly transparent to opaque white and then died, usually within a day or so.