The effect of spawning salinity on eggs of spotted seatrout (Cynoscion nebulosus, Cuvier) from two bays with historically different salinity regimes

Spotted seatrout are capable of spawning in a wide range of salinities. Along the Texas Gulf Coast, bay salinities increase from an average of 14 ppt in Galveston Bay to an average of 40 ppt in Lower Laguna Madre due to the negative gradient of freshwater inflow from north to south. Tagging studies have shown that the majority of spotted seatrout do not migrate between adjacent bay systems. Spawning salinity has been shown to affect many properties of eggs including the diameter and salinity of neutral buoyancy. Spotted seatrout from two historically different salinity regimes (Matagorda Bay (MB) and Upper Laguna Madre (ULM)) were kept in the laboratory and induced to spawn in three salinities: 20, 30, and 40 ppt. The purpose of this study was to evaluate eggs at each of the three salinities and between the two bay systems. Two-way ANOVA showed a significant effect on the egg diameter of bay and spawning salinity, and a significant interaction between bays and spawning salinity. No significant difference in size at hatch was found between spawning salinities or between bays. Hatch rates in spawning salinity were >90% in all cases. Regression of wet weight on spawning salinity was highly significant for both bays. Eggs spawned in 20 ppt have the largest wet weight and eggs spawned in 40 ppt have the smallest wet weight, irrespective of parental bay origin. Percentage of water varied between 92% for 20 ppt spawned eggs and 86% in 40 ppt spawned eggs. Neutral Buoyancy Salinity (NBS) of eggs increased with increasing spawning salinity. Eggs spawned by the Upper Laguna Madre fish held at 20 ppt were not positively buoyant at 20 ppt. The results of this study suggest that spotted seatrout are locally adapted to the prevailing salinity regime within an estuary.     

Salinity tolerance of laboratory-reared larvae of the California killifish, Fundulus parvipinnis Girard

Newly hatched larvae of the California killifish ( Fundulus parvipinnis ) reared in the laboratory, were tolerant of salinities from fresh water to 70‰. Their salinity tolerance was influenced by incubation salinity; larvae hatched in lower incubation salinities exhibited greater freshwater tolerance than those hatched in higher salinities. In gradual acclimation tests, the upper median lethal salinity for the larvae was 130‰. Freshwater tolerance of the larvae decreased with age; yolk sac larvae were completely tolerant of fresh water while larvae more than 15 days old were least resistant.     

Reproductive cycle in female Waigieu seaperch (Psammoperca waigiensis) reared under different salinity levels and the effects of dopamine antagonist on steroid hormone levels

Waigieu seaperch (Psammoperca waigiensis) is a tropical marine finfish species, which may inhabit wide range of salinity during the entire life cycle. Regardless of the wide salinity tolerance, little is known about how salinity may influence the reproductive endocrinology of this important tropical species. In the present study, we investigated the seasonal variations in steroid hormone levels, oocyte maturation (OM) and ovulation in fish reared under different salinity levels. In addition, we investigated the effects a dopamine antagonist (domperidone: DOM) during the peak spawning period. Mature brood fish at 3 years old were cultured in four different salinities of 5, 10, 20 and 30‰ (part per thousand, ppt) from March to December 2007. Blood samples were collected monthly and key steroid hormones (testosterone (T), 11-ketotestosterone (11-KT), 17β-estradiol (E2) and progesterone (P)) levels in female fish plasma were analyzed using enzyme immunoassay method. OM, ovulation and several reproductive performance indexes were evaluated twice per month during the breeding season. Plasma hormone analysis showed significant differences in fish groups cultured in different salinities during the seasonal cycle. The gonadosomatic index (GSI) gradually increased from March, peaking in July at 10 and 30‰, and then decreased thereafter until December. Plasma steroid levels (E2, T, 11-KT and P) were observed in variable concentrations during the spawning period and showed monthly fluctuations that were apparently salinity dependent during on and off-seasons. Interestingly, 11-KT levels were found in small amounts in female fish and peaked in September at salinities of 10 and 20‰. DOM exposure produced significant differences in steroid hormone levels that were apparently dependent on dose, exposure time and the individual hormone. The present study indicated that holding Waigieu seaperch brood fish in different salinities during the breeding season produced significant effects on gonadal development and spawning incidences. The first spawning was observed on 8th of April for all groups after 100% water exchange at night. No significant differences of absolute and relative fecundity were observed between groups. Fish held at 10 ppt salinity during the breeding season spawned naturally, but maturity and spawning rates were reduced and no hatching was observed at the same salinity. Fish holding at 5‰ resulted to 100% mortality in brood fish. This indicated that salinity limits for oocyte maturation or ovulation and subsequent reduction in spawning, but embryonic development requires a higher salinity. The effect of salinity on embryo development and hatching rate suggests that in breeding season the brood fish spawned in areas where the salinity and other parameters are favorable.     

Survival and development of horseshoe crab (Limulus polyphemus) embryos and larvae in hypersaline conditions

The horseshoe crab Limulus polyphemus spawns in the mid- to upper intertidal zone where females deposit eggs in nests below the sediment surface. Although adult crabs generally inhabit subtidal regions of estuaries with salinities from 5 to 34 ppt, developing embryos and larvae within nests are often exposed to more extreme conditions of salinity and temperature during summer spawning periods. To test whether these conditions have a negative impact on early development and survival, we determined development time, survival, and molt cycle duration for L. polyphemus embryos and larvae raised at 20 combinations of salinity (range: 30-60 ppt) and temperature (range: 25-40 degrees C). Additionally, the effect of hyperosmotic and hypoosmotic shock on the osmolarity of the perivitelline fluid of embryos was determined at salinities between 5 and 90 ppt. The embryos completed their development and molted at salinities below 60 ppt, yet failed to develop at temperatures of 35 degrees C or higher. Larval survival was high at salinities of 10-70 ppt but declined significantly at more extreme salinities (i.e., 5, 80, and 90 ppt). Perivitelline fluid remained nearly isoosmotic over the range of salinities tested. Results indicate that temperature and salinity influence the rate of crab development, but only the extremes of these conditions have an effect on survival.     

The effect of parental acclimation to spawning salinity on the survival of larval Cynoscion nebulosus

The yolk and oil depletion of eggs and larvae of spotted seatrout Cynoscion nebulosus , produced by fish collected from two bays with historically different salinity regimes (Matagorda Bay (MB; 18-24%) and Upper Laguna Madre (ULM; 40–50%), Texas, U.S.A. and spawned in salinities of 20, 30 and 40%, differed in their response to both salinity and history. Time to 90% yolk depletion was significantly longer for low salinity bay fish (MB) kept at 20%, but not for high salinity bay fish (ULM) at 20%. The neutral buoyancy salinity of 1 and 2 day old MB 20% larvae was significantly lower than that of MB larvae spawned in 30 or 40%. Overall, eggs and larvae spawned by MB fish were able to hatch out and survive to 3 days post-hatch in lower salinities than those from ULM. Furthermore, the tolerance of eggs and larvae to very low salinities increased with decreasing spawning salinity. The ability of 1–9 day old ULM, but not MB, larvae to survive 18 h exposure to salinities above or below that of spawning exhibited an age-dependent pattern with day 3 being the most sensitive. This study shows that the response of spotted seatrout eggs and larvae to changes in salinity is dependent upon the spawning salinity of the adults and the prevailing salinity regime within the bay.     

Tissue Distribution, Effects of Salinity Acclimation, and Ontogeny of Aquaporin 3 in the Marine Teleost, Silver Sea Bream (Sparus sarba)

The purpose of the present study was to ascertain the tissue-specific expression of the water channel protein, aquaporin 3 (AQP3), during salinity acclimation and larval development of silver sea bream (Sparus sarba). A cDNA fragment encoding aquaporin 3 (aqp3) from silver sea bream gill was cloned and from the deduced amino acid sequence a polyclonal antibody was prepared. AQP3 was found to be present in gill, kidney, liver, brain, heart, and spleen but not in whole blood. The abundance of AQP3 was significantly highest in gills of hypoosmotic (6 ppt) and isoosmotic (12 ppt) acclimated sea bream when compared to seawater (33 ppt) and hypersaline (50 ppt)- acclimated sea bream. Spleen tissue also displayed significantly high levels of AQP3 protein in hypoosmotic and isoosmotic salinities whereas the AQP3 abundance in brain, liver, heart, and kidney remained unchanged across the range of salinities tested. The ontogenetic profile of AQP3 was also investigated from developing sea bream larvae and AQP3 was first detected at 14 days posthatch (dph) and increased steadily up to 28–46 dph. In conclusion, this study has demonstrated that AQP3 expression is modulated in gill and spleen tissue of salinity acclimated sea bream and that it can be detected relatively early during larval development.     

Evidence of concurrent local adaptation and high phenotypic plasticity in a polar microeukaryote

Here we investigated whether there is evidence of local adaptation in strains of an ancestrally marine dinoflagellate to the lacustrine environment they now inhabit (optimal genotypes) and/or if they have evolved phenotypic plasticity (a range of phenotypes). Eleven strains of Polarella glacialis were isolated and cultured from three different environments: the polar seas, a hyposaline and a hypersaline Antarctic lake. Local adaptation was tested by comparing growth rates of lacustrine and marine strains at their own and reciprocal site conditions. To determine phenotypic plasticity, we measured the reaction norm for salinity. We found evidence of both, limited local adaptation and higher phenotypic plasticity in lacustrine strains when compared with marine ancestors. At extreme high salinities, local lake strains outperformed other strains, and at extreme low salinities, strains from the hyposaline lake outperformed all other strains. The data suggest that lake populations may have evolved higher phenotypic plasticity in the lake habitats compared with the sea, presumably due to the high temporal variability in salinity in the lacustrine systems. Moreover, the interval of salinity tolerance differed between strains from the hyposaline and hypersaline lakes, indicating local adaptation promoted by different salinity.     

Reduced salinities compromise the thermal tolerance of hypersaline specialist diving beetles

Inland saline waters are globally threatened habitats that harbour unique assemblages of specialist invertebrates. In many Mediterranean regions, irrigation associated with intensive agriculture is lowering the salinity of these habitats, resulting in the loss of their specialist biota, although the mechanisms by which reductions in salinity lead to species loss are poorly understood. In the present study, the effects of reduced salinity on the temperature tolerance and thermal acclimatory abilities of two related species of hypersaline water beetles, Nebrioporus baeticus (Schaum) and Nebrioporus ceresyi (Aubé), are explored. Both upper (UTL) and lower thermal limits (LTL) are assessed, and both salinity and temperature are found to influence the thermal biology of Nebrioporus. Mean UTLs are greater in individuals of both species acclimated at high salinities, with salinity appearing to be more important than acclimation temperature in determining UTL. In both taxa, the lowest mean LTLs are recorded in individuals acclimated at the highest salinities and lowest temperatures; temperature‐dependent acclimation is only reported after exposure to relatively high salinities. The data show that salinity influences the thermal tolerance and acclimatory ability of these hypersaline beetles, and that lowered salinity compromises the ability of adult Nebrioporus to cope with both heat and cold. Such an effect may partly explain why specialist species are lost from hypersaline habitats subject to salinity reductions, and suggests that ongoing reduction in salinity may compromise the ability of such specialist taxa to cope with rapid climate change.     

Determining the optimum temperature and salinity for larval culture,and describing a culture protocol for the conservation aquaculture for European smelt Osmerus eperlanus (L.)

Populations of anadromous European smelt Osmerus eperlanus (L.) are declining across its geographical range in northern Europe, but no practical culture techniques exist to develop stock enhancement programmes for this species. In this study, a culture protocol is described to rear fish from fertilised eggs to mature adults in 2 years involving the use of ‘green water’, live feed and artificial diets. The sequence of embryonic development for eggs incubated at 10°C/0 ppt was described and photographed. To determine the optimum conditions for larval culture, fertilised eggs were reared at a range of salinities (0–20 ppt) and temperatures (5–18°C) until first feeding. Best hatching success (ca. 97%), size at hatch (ca. 0.8 mm) and survival to first feeding (ca. 96%) of larvae were achieved under combined conditions of low salinity (0–0 ppt) and temperature (5–10°C). No larvae survived a salinity of 20 ppt. The time taken from fertilisation to hatch (FtH) and hatching duration (HD) were temperature-dependent ranging from 42 days FtH and 10 days HD at 5ºC, to 10 days FtH and 2 days HD at 18°C irrespective of salinity. The results indicate that conservation programmes could utilise existing salmonid hatchery facilities (i.e. freshwater, ≤10°C water temperature) for stock enhancement. Since on-growing of smelt involves the logistical and technical problems of live feed production, it is recommended that smelt enhancement programme utilise freshwater hatchery facilities to rear fish until hatching, and then stock out onto known spawning grounds in rivers allowing hatched larvae to drift into estuaries to complete the larval and juvenile phases. This approach would minimise the time spent in the hatchery post-hatching, eliminate the need for live food production, prevent the development of predator-naïve fish, and hence would mimic the natural life cycle of the species as closely as possible.     

Effects of temperature, salinity, and air exposure on development of the estuarine pulmonate gastropod Amphibola crenata

The primitive pulmonate snail Amphibola crenata embeds embryos within a smooth mud collar on exposed estuarine mudflats in New Zealand. Development through hatching of free-swimming veliger larvae was monitored at 15 salinity and temperature combinations covering the range of 2-30 ppt salinity and 15-25 °C. The effect of exposure to air on developmental rate was also assessed. There were approximately 18,000 embryos in each egg collar. The total number of veligers released from standard-sized egg collar fragments varied with both temperature and salinity: embryonic survival was generally higher at 15 and 20 °C than at 25 °C; moreover, survival was generally highest at intermediate salinities, and greatly reduced at 2 ppt salinity regardless of temperature. Even at 2 ppt salinity, however, about one-third of embryos were able to develop successfully to hatching. Embryonic tolerance to low salinity was apparently a property of the embryos themselves, or of the surrounding egg capsules; there was no indication that the egg collars protected embryos from exposure to environmental stress. Mean hatching times ranged between 7 and 22 days, with reduced developmental rates both at lower temperature and lower salinity. At each salinity tested, developmental rate to hatching was similar at 20 and 25 °C. At 15 °C, time to hatching was approximately double that recorded at the two higher exposure temperatures. Exposing the egg collars to air for 6-9 h each day at 20 °C (20 ppt salinity) accelerated hatching by about 24 h, suggesting that developmental rate in this species is limited by the rates at which oxygen or wastes can diffuse into and from intact collars, respectively. Similarly, veligers from egg capsules that were artificially separated from egg collars at 20 °C developed faster than those within intact egg collars. The remarkable ability of embryos of A. crenata to hatch over such a wide range of temperatures and salinities, and to tolerate a considerable degree of exposure to air, explains the successful colonization of this species far up into New Zealand estuaries.     

GROWTH AND ORGANIC OSMOLYTES OF GEOGRAPHICALLY DIFFERENT ISOLATES OF MICROCOLEUS CHTHONOPLASTES (CYANOBACTERIA) FROM BENTHIC MICROBIAL MATS:RESPONSE TO SALINITY CHANGE1

The comparative growth and osmotic acclimation often culture strains of the marine benthic cyanobacterium Microcoleus chthonoplastes Thuret isolated from microbial mats in Germany, Spain, Egypt, the United States, Mexico, Chile, and Australia were investigated in salinities ranging from freshwater to twice seawater. All isolates showed a broad growth versus salinity response consistent with the dominance of this species in intertidal and hypersaline microbial communities. Growth optima, salinity preferences, and maximum growth rates differed for each isolate and could be related to the habitat from which they were isolated. This is most obvious when comparing strains from brackish habitats with those from a hypersaline lake. While the former isolates exhibited sharply pronounced growth optima under hyposaline conditions, cultures from the hypersaline environment grew best in salinity more than double seawater. The major low-molecular weight organic compounds present in all M. chthonoplastes strains were the carbohydrates glycosylglycerol and trehalose. This was proven by using ¹³C-nuclear magnetic resonance spectroscopy. Glycosylglycerol was synthesized and accumulated with increasing salinities, indicating its role as an osmolyte. In contrast, trehalose was present in relatively high concentrations under hyposaline conditions only. Differences in the patterns of growth versus salinity, as well as in those of osmotic acclimation among the M. chthonoplastes isolates, point to the development of different physiological ecotypes within the species.     

Some aspects of osmotic and ionic regulation in Adriatic sturgeon Acipenser naccarii. I: Ontogenesis of salinity tolerance

The salinity tolerance of various early life stages (prelarvae, larvae and fry) of the Adriatic sturgeon ( Acipenser naccarii ) was investigated using acute exposures in a 96h-LC₅₀ test. The results were compared with a series of parallel observations on the morphological development of the osmoregulatory organs. The highest salinities tolerated by prelarave and larvae were approximately iso-osmotic with sturgeon plasma. Once, however, the organs involved in homeostatic osmoregulatory mechanisms in the adult had developed (renal-branchial-gut system), the sturgeon was able to switch from hyper-osmoregulation to hypo-osmoregulation. Nevertheless, at the most advanced age tested (150 days old), water at a salinity of approximately 20% appeared to be the upper threshold for tolerance of acute exposure by this species.     

Effect of salinity on osmoregulatory patch epithelia in gills of the blue crab Callinectes sapidus

In euryhaline crabs, ion-transporting cells are clustered into osmoregulatory patches on the lamellae of the posterior gills. To examine changes in the branchial osmoregulatory patch in the blue crab Callinectes sapidus in response to change in salinity and to correlate these changes with other osmoregulatory responses, crabs were acclimated to a range of salinities between 10 and 35 ppt. When crabs that had been acclimated to 35 ppt were subsequently transferred to 10 ppt, both the size of the osmoregulatory patch on individual gill lamellae and the specific activity of Na+, K+-ATPase in whole-gill homogenates increased only after the first 24 h of exposure to dilute seawater. Enzyme activity and size of patch area increased gradually and reached their maxima (increasing by 200% and 60%, respectively) 6 days following transfer to 10 ppt seawater and then remained at these levels. Patch size at acclimation varied inversely with the salinity for seawater dilutions below 26 ppt (the isosmotic point of the crab), although it did not vary in salinities at or above 26 ppt. Thus, the size of the patch clearly is modulated with acclimation salinity, but it increases only in those salinities in which the crab hyperosmoregulates. An increase in the total RNA/DNA ratio in gill homogenates, the lack of mitotic figures in the lamellae, and the lack of incorporation of bromodeoxyuridine into nuclei of lamellar epithelial cells during acclimation to dilute seawater were interpreted as evidence that no cell proliferation had occurred and that increases in the size of the osmoregulatory patch occurred through differentiation of existing gas exchange cells or of undifferentiated epithelial cells into ion-transporting cells.     

Variable salinity tolerance in ascidian larvae is primarily a plastic response to the parental environment

Both phenotypic plasticity and local genetic adaptation may contribute to a species’ ability to inhabit different environmental conditions. While phenotypic plasticity is usually considered costly, local adaptation takes generations to respond to environmental change and may be constrained by strong gene flow. The majority of marine species have complex life-cycles with pelagic stages that might be expected to promote gene flow and plastic responses, and yet several notable examples of local adaptation have been found in species with broadcast larvae. In the ascidian, Ciona intestinalis (Linnaeus, 1767),—a common marine species with broadcast spawning and a short larval stage—previous studies have found marked differences in salinity tolerance of early life-history stages among populations from different salinity regimes. We used common-garden experiments to test whether observed differences in salinity tolerance could be explained by phenotypic plasticity. Adult ascidians from two low salinity populations [2–5 m depth, ~25 practical salinity units (PSU)], and two full salinity populations (25–27 m depth, ~31 PSU) were acclimated for 2–4 weeks at both 25 and 31 PSU. Gametes were fertilized at the acclimation salinities, and the newly formed embryos were transferred to 10 different salinities (21–39 PSU) and cultured to metamorphosis. Adult acclimation salinity had an overriding and significant effect on larval metamorphic success: tolerance norms for larvae almost fully matched the acclimation salinity of the parents, independent of parental origin (deep or shallow). However we also detected minor population differences that could be attributed to either local adaptation or persistent environmental effects. We conclude that differences in salinity tolerance of C. intestinalis larvae from different populations are driven primarily by transgenerational phenotypic plasticity, a strategy that seems particularly favourable for an organism living in coastal waters where salinity is less readily predicted than in the open oceans.     

Tolerance of seahorse Hippocampus kuda (Bleeker) juveniles to various salinities

In line with current conservation efforts, some success in the captive breeding of the seahorse Hippocampus kuda (Teleostei: Syngnathidae) has been achieved. To evaluate the salinity tolerance of these hatchery‐bred juveniles, 9‐week‐old H. kuda were transferred without prior acclimatization from ambient full strength seawater (32–33 ppt) to salinities ranging from freshwater to 85 ppt. Survival, growth, and total body water content were determined after 4 and 18 days of exposure. Juvenile H. kuda are able to survive in dilute seawater (15 ppt) for at least 18 days without any compromise in growth (both wet and dry body weight), survival, and total body water. Fish abruptly transferred to freshwater succumbed within 4–24 h, while survival of 5 ppt‐reared fish decreased to ca. 65% in 18 days. Although 10 ppt‐reared seahorses had growth and survival comparable with the control (30 ppt seawater), total body water was significantly elevated indicating reduced adaptability. The upper limit of H. kuda salinity tolerance was 50 ppt. Fish reared at salinities ≥55 ppt succumbed within 24 h. Like several other marine teleosts, growth and survival of juvenile H. kuda tended to peak in diluted seawater salinities of 15 and 20 ppt. These results indicate the possibility of growing hatchery‐bred H. kuda in brackishwater environments.     

Salinity Tolerance in Some Selected Aquatic Oligochaetes

Salt tolerance of the freshwater tubificid Limnodrilus hoffmeisteri varied from an LD 50 of 10 ppt to 10.5 ppt for mature and immature worms without sediment, 9.4 to 10.5 in sand, and 14.3 for immatures acclimated to 5 ppt. Ilyodrilus templetoni was similarly intolerant to higher salinities. The estuarine Tubificoides gabriellae tolerated salt water, but was susceptible to freshwater, with LD 50's of 2 and 3.5 when acclimated to 5 and 10 ppt sea water. It survived immersion in freshwater for 3 hours. The estuarine naidids Paranais litoralis and frici experienced mortalities at both high and low salinities but showed a wide tolerance range. The coastal tubificid Monopylephorus irroratus showed almost complete tolerance to the salinity range employed. The findings reflected field distributions especially when interstitial salinities were measured, but worms did not occupy the full range of habitats possible in terms of salinity alone.     

Salinity tolerance and osmotic regulation in the diamond killifish,Adinia xenica

Synopsis Salinity tolerances and plasma osmotic regulatory capacity were determined in individuals of Adinia xenica following laboratory acclimations. Survival of individuals was better than 90% of those entered into the acclimation sequence from an initial acclimation salinity of 17.0 ppt down to fresh-water, and up to 95.0 ppt. Survival of individuals transferred from 95.0 to 105.0 ppt was low. Adinia showed most consistent plasma osmotic regulation in the range of ambient salinities from 17.0 to 60.0 ppt, but responded well over the ambient salinity range from 0.5 ppt to 85.0 ppt. Plasma osmotic concentrations were higher at common ambient salinities, but in a generally similar overall pattern of response, compared with such euryhaline cyprinodontids as Cyprinodon variegatus and Fundulus kansae.     

Salinity tolerance of larval Rapana venosa: implications for dispersal and establishment of an invading predatory gastropod on the North American Atlantic coast

The lack of quantitative data on the environmental tolerances of the early life-history stages of invading species hinders estimation of their dispersal rates and establishment ranges in receptor environments. We present data on salinity tolerance for all stages of the ontogenetic larval development of the invading predatory gastropod Rapana venosa, and we propose that salinity tolerance is the dominant response controlling the potential dispersal (=invasion) range of the species into the estuaries of the Atlantic coast of the United States from the current invading epicenter in the southern Chesapeake Bay. All larval stages exhibit 48-h tolerance to salinities as low as 15 ppt with minimal mortality. Below this salinity, survival grades to lower values. Percentage survival of R. venosa veligers was significantly less at 7 ppt than at any other salinity. There were no differences in percentage survival at salinities greater than 16 ppt. We predict that the counterclockwise, gyre-like circulation within the Chesapeake Bay will initially distribute larvae northward along the western side of the DelMarVa peninsula, and eventually to the lower sections of all major subestuaries of the western shore of the Bay. Given the observed salinity tolerances and the potential for dispersal of planktonic larvae by coastal currents, establishment of this animal over a period of decades from Cape Cod to Cape Hatteras is a high probability.     

A study on early tolerance of Mactra chinensis philippi to salinity

In order to evaluate the early tolerance of Mactra chinensis to salinity, the treatments of salinity gradients and salinity gradual changes were set in this study, and the post growth and development of juveniles were analyzed in recovery experiment, respectively. The result showed that the optimum hatching of zygotes was found at a salinity from 24 to 32, which is narrower than that of larvae (20–32); a slight of low salinity (16–32) will benefit the early growth and development of M. chinensis; at planktonic and creeping stages, low salinity stress (20) was conducive to promoting the growth of juvenile M. chinensis philippi; 4, 48 was the ultimate salinity of M. chinensis; The range of early tolerance of larvae M. chinensis philippi to salinity can be widened through a short period of salinity acclimation.     

Behavioral aspects of cold tolerance in blackchin tilapia,Sarotherodon melanotheron,at different salinities

Synopsis Cold tolerance and behavioral responses of blackchin tilapia, Sarotherodon melanotheron, to rapidly decreasing temperatures were investigated at salinities of 5, 15, and 35 parts per thousand (ppt). Cold tolerance did not significantly differ with salinity or social rank. Mean temperatures were 10.7° C for beginning loss of equilibrium, 9.6° C for complete loss of equilibrium, and 6.9° C for death at all salinities. Behavioral activity declined with decreasing temperature and ceased between 10–12° C. Certain behavioral actions were significantly more frequent at 15 or 35 ppt salinity than at 5 ppt. The northward range expansion by introduced populations of the blackchin tilapia in the United States probably will be limited by its lower lethal temperature limits, but may also be affected by temperatures at which social behavior becomes disrupted.