The ability of Tilapia mossambica (Peters) to enter deep water

Juvenile Tilapia mossambica (Peters) are extremely tolerant of depth and can compensate to a depth increase of 0 to 33 m in a few minutes. As the fish grow they become less able to compensate to deep water. At a total length of 15–18.5 cm small adult male T. mossambica can compensate to 20 m whereas females can only compensate to 13 m. Large adults (20–25 cm) of both sexes compensated to 11.5 m (range 9.5–13 m). Adult fish require 4 to 7 days for maximum depth compensation at 22°C. Analysis of the oxygen content of the swimbladder indicated that this gas accounts for over half the gas in surface equilibrated fish. Oxygen secretion into the swimbladder appears to be the mechanism of equilibration at depth.     

The effect of temperature on the ability of Tilapia mossambica Peters to enter deep water

The ability of adult Tilapia mossambica Peters to enter deep water was determined at 15, 22 and 30°C. At 30°C adults compensate to about 20m depth but at 15°C to only 7 m. Compensation is more rapid at high than at low temperatures. T. mossambica haemoglobin has a marked Root effect which is the same at 22 and 30°C. The oxygen affinity of the haemoglobin is higher at 15°C than at 30°C. There was no measurable difference in the rate of passive oxygen diffusion across the swimbladder wall in the temperature range 15–30°C. It is concluded that the ability to enter deeper water at higher temperatures is related to decreased oxygen affinity of the haemoglobin and higher rates of oxygen secretion and blood circulation.     

Biochemical indicators of thermal stress in Tilapia aurea (Steindachner)

Tilapia aurea muscle and liver adenylate nucleotides, the adenylate energy charge (EC), plasma glucose, cortisol and chloride were monitored during acute and chronic temperature stress. Muscle EC is unaffected during acute cold water exposure but decreases significantly when tilapia are exposed to chronic, sublethal, low temperature stress. The decrease in EC is primarily the result of a decrease in ATP concentration. Plasma glucose and cortisol increase when tilapia are exposed to 11–12° C for 60 min, 11 days, and a 5-week period. Incomplete compensation is evident in 5-week acclimated fish since glucose and cortisol levels are intermediate between controls and acutely stressed fish. Acclimation to 35° C does not significantly affect plasma glucose and cortisol compared to controls (22° C). Plasma chloride is relatively unaffected by acute and chronic temperature stress. Liver adenylates are not significantly affected when tilapia are subjected to a sudden drop in water temperature (22° down to 11° C). EC is a useful indicator of chronic low temperature stress in T. aurea , while plasma glucose and cortisol are sensitive to both acute and chronic temperature stress.     

The effects of temperature and salinity on Tilapia rendalli Boulenger 1896

Temperature and salinity tolerances of Tilapia rendalli were determined experimentally. Results indicate that they are tolerant over a wide range of temperatures (11-37°C), but are incapable of surviving in salinities above 19 ‰ The maximum salinity tolerance is at temperatures between 20–28°C. The osmotic concentration of the blood rises from 255 mosmol/1 in freshwater to 340 mosmol/1 in a salinity of 19‰ T. rendalli is restricted to the warmer waters of the Zambezi river system in central Africa and southwards to the Pongolo river, as well as certain tropical and subtropical brackish water lagoons and lakes. Evidence from these experiments suggest that the distribution of T. rendalli isgoverned by both temperature and salinity.     

The effect of temperature on routine metabolism in Tilapia rendalli boulenger

Using a continuous flow respirometer it was shown that young Tilapia rendalli had three distinct phases of oxygen consumption over the temperature range of 17–40° C. In the first phase (17–28° C) the metabolic energy demand followed the normal logarithmic increase with increasing temperature. Between 28 and 37° C the increased oxygen uptake was suppressed and showed a relatively small increase with increasing temperature. This feature was believed to be a significant energy saving function important to the growth of these fish which feed in the warm eulitoral margins of lakes during the day. The final phase shows a return to the original logarithmic increase in oxygen consumption. These results were related to, and compared with, actual changes in biomass at various temperatures and the theoretical and actual biomass changes were found to compare favourably.     

The importance of habitat temperatures for growth in the tropical cichlid Tilapia rendalli Boulenger

Like many cichlids living in shallow tropical freshwater systems of Africa, Tilapia rendalli exhibit a marked daily movement into warm shallow water during the day and return to cooler, deeper water at night. Such movements have an important impact on the growth of juvenile fish. Growth is enhanced by this movement and is predicted to be optimal if the fish occupy water with a temperature of 30°C during the day but retire to nocturnal habitats with temperatures of 18°C. The reasons for this phenomenon are discussed using a bio-energetic model incorporating measurements of feeding intensity, metabolic energy demands and assimilation efficiencies at temperatures ranging from 18°C—3°C and the ecological implications discussed using examples from natural systems.     

The influence of exposure to low temperature on Tilapia mossambica Peters (Cichlidae).

In the cichlid teleost Tilapia mossambica secondary chill coma following exposure to 11° C in freshwater is associated with decreases in plasma osmolarity, sodium and chloride ion concentrations. Fish exposed in seawater diluted to give a NaCl concentration of 5%0 show no signs of coma nor are there decreases in osmolarity or sodium and chloride ion concentrations.
It is suggested that the restrictions of T. mossambica to estuaries at the southern end of its distribution in southern Africa relates to the maintenance of near normal sodium and chloride ion concentrations at low temperatures during winter.     

Effects of constant and fluctuating temperatures on life span of Aedes taeniorhynchus adults

Male and virgin female Aedes taeniorhynchus were maintained on a sugar solution at constant temperatures, at split-temperatures, and at alternating temperatures from immediately after emergence until death in order to study the effect of temperatures on their longevity. Life spans were found to be temperature dependent at constant temperatures of 22, 27, and 32°C, but they were divided into ‘ageing’ and ‘dying’ phases at split-temperatures. The rate of ageing, which was independent of temperatures, was the same in males whether they were transferred from low to high or high to low temperatures. The rate of ageing was the same in females transferred from 22°C or 27 to 32°C, but much longer than expected when transferred from 22 to 27°C. Also, the rate of ageing was the same for females transferred from 32°C to either 22 or 27°C and from 27 to 22°C. The rate of dying was essentially temperature dependent in both males and females with slight temperature compensation occurring in some cases. Life spans were the same in males when alternated between 22?27°C, 27?32°C, and 22?32°C. In females they were same at 27?32°C and 22?32°C, but were much longer than expected at 22?27°C. It is concluded that the threshold theory is confirmed when mosquitoes are maintained at split-temperatures and at alternating temperatures in their optimum range of temperatures.     

A comparison of the abilities of three sympatric species of Petrotilapia (Cichlidae,Lake Malawi) to penetrate deep water

Synopsis The ability of three sympatric species ofPetrotolapia, from Monkey Bay, Lake Malawi, to penetrate deep water was tested using pressure chambers. The three species were found to differ in terms of the maximum pressure (= depth) to which each was able to equilibrate. Mean maximum equilibration pressures were for the form designated MOL 39.0 m, for MBB 35.5 m and for the form MOC 30.4 m. The rate of compensation to pressure changes was slower in MBB (2.59 m day^–1) than in other two forms (MOL = 3.97 m day^–1, MOC = 3.98 day^–1). Natural depth distribution of all three forms, in particular MBB and MOC, is not determined by limits imposed by swin bladder physiology.     

Tissue depletion and energy utilisation during routine metabolism by sub-adult Tilapia rendalli boulenger

The amount of fat and protein used by young Tilapia rendalli during starvation can be quantitatively assessed and correlated to the condition of the fish. It was shown that fish in good condition used fat in preference to protein during catabolism, irrespective of the time period of starvation, but this rapidly reversed as condition declined and fish in medium and poor condition utilised more protein than fat to maintain routine metabolism. The amount of energy required during routine metabolism was not affected by the ratio of fat to protein used and a mean energy requirement for these fish (varying between 40 and 60 g in mass) was estimated as 45.03 J g-¹d^-1 at 23°C. This estimate of routine metabolic energy requirement can be equated to oxygen consumption using an oxy-energy coefficient of 13.68 J mg O₂^-1.     

Toxicity of crude extracellular products of Aeromonas hydrophila in tilapia, Tilapianilotica

Extracellular products (ECP) secreted from Aeromonas hydrophila with haemolytic andproteolytic activity were studied with respect to temperature and time of incubation as well as thelethal toxicity on tilapia, Tilapia nilotica . The highest production of the haemolysin productwas achieved when Aer. hydrophila was grown at 35°C for 30 h. Tilapia erythrocytewas found to be more susceptible than sheep erythrocyte for determining the haemolytic activity.The haemolytic activity against tilapia erythrocyte was completely inactivated after heating theECP at 60°C for 10 min or 55°C for 15 min. The proteolytic activity was maximized whenthe bacterium was grown at 30°C for 36 h. Complete inactivation of the protease enzyme wasperformed after heating the ECP at 80°C for 10 min or 70°C for 15 min. Aeromonashydrophila was found to produce haemolytic and proteolytic exotoxin lethal to tilapia (LD₅₀ 2·1 × 10⁴ cell/fish), as well as heat stable unknown virulent factors thatwere responsible for 20% mortality. The lethality of ECP was decreased by heating andcompletely inactivated by boiling at 100°C for 10 min.     

Life history of Amitus fuscipennis (Hym., Platygastridae) as parasitoid of the greenhouse whitefly Trialeurodes vaporariorum (Hom., Aleyrodidae) on tomato as function of temperature

Life history parameters of Amitus fuscipennis MacGown and Nebeker as parasitoid of Trialeurodes vaporariorum (Westwood) were determined at 15, 20, 25 and 30°C on tomato using three different methods. For each method, immature development, mortality, longevity, fecundity, oviposition frequency and post-oviposition period were determined and temperature-dependent relations were estimated. Oviposition frequency was also estimated as a function of parasitoid age. Immature development had a maximum of 61 days at 15°C that decreased to 22 days at 30°C. Mortality in the grey stage was less than 2% at temperatures lower than 30°C, where it was 60%. Longevity fluctuated between 3 and 18 days. Fecundity increased from 338 eggs/female at 15°C to a maximum of 430 eggs/female at 25°C and then decreased to 119 eggs/female at 30°C. Oviposition frequency varied between 3 and 46 eggs/female per day and had its maximum on the first day after emergence of the parasitoid. Net reproduction rate, generation time and intrinsic rate of increase were calculated. The intrinsic rate of increase increased from 0.090 at 15°C to a maximum of 0.233 at 25°C and then decreased to 0.159 at 30°C. The influence of the methods to determine the life history parameters on the results is discussed. The results are compared also with the life history of Encarsia formosa Gahan (Hym., Aphelinidae) a parasitoid of the same host. The advantages and disadvantages of the pro-ovigenic A. fuscipennis in comparison with the synovigenic E. formosa are discussed.     

Influence of temperature on life-table parameters of Stethorus gilvifrons (Mulsant) (Coleoptera: Coccinellidae) fed on Tetranychus urticae Koch

The influence of temperature on life-table parameters, fecundity and survivorship of the predatory ladybird, Stethorus gilvifrons , fed on Tetranychus urticae was determined at seven constant temperatures of 15°C, 20°C, 25°C, 28°C, 30°C, 35°C and 40°C. No development was observed at 40°C, thus being regarded as the threshold for the development of S. gilvifrons . The results indicate a significant decrease in male and female longevity with increasing temperature from 15°C to 35°C. The longest and shortest longevity were 18.40 and 12.75 days for males and 17.40 and 8.80 days for females, respectively. The intrinsic rate of natural increase ( r _m ) and the net reproductive rate ( R ₀) of S. gilvifrons linearly increased with increasing temperatures from 15°C to 35°C, while the mean generation time ( T ) and doubling time (DT) decreased linearly within this temperature range. The highest values of r _m (0.240 females/female/day) and R ₀ (59.27 females/female) and the lowest mean generation time (17.01 days) and DT (2.88 days) were recorded at 35°C. The maximum (185.50 eggs) and minimum (25.50 eggs) measurement of total fecundity was also recorded at 35°C and 15°C, respectively. The results indicate that temperature greatly affected fecundity, survivorship and life-table parameters of S. gilvifrons , and that 35°C is a suitable temperature for population growth of this predator.     

Effects of temperature on the growth and survival of the European eel, Anguilla anguilla L.

Experiments to determine the growth rate of eels ( Anguilla anguilla L.) at different temperatures are described and show the optimum temperature for growth to be 22–23° C. The ultimate upper lethal temperature was found to be 38° C and the critical thermal maximum varied from 33 to 39° C for fish acclimated at 14 to 29° C. An attempt was also made to determine lower lethal temperatures. Eels enter a state of torpor at temperatures varying from 3° C for fish acclimated at 29° C to less than 1° C for fish acclimated at 23° C or below. The results have been used to estimate the growth rates expected from eels cultured in power station cooling water using different types of temperature control.     

Behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir

This study investigated behavioural thermoregulation by subyearling fall (autumn) Chinook salmon Oncorhynchus tshawytscha in a reservoir on the Snake River, Washington, U.S.A. During the summer, temperatures in the reservoir varied from 23° C on the surface to 11° C at 14 m depth. Subyearlings implanted with temperature-sensing radio transmitters were released at the surface at temperatures >20° C during three blocks of time in summer 2004. Vertical profiles were taken to measure temperature and depth use as the fish moved downstream over an average of 5·6–7·2 h and 6·0–13·8 km. The majority of the subyearlings maintained average body temperatures that differed from average vertical profile temperatures during most of the time they were tracked. The mean proportion of the time subyearlings tracked within the 16–20° C temperature range was larger than the proportion of time this range was available, which confirmed temperature selection opposed to random use. The subyearlings selected a depth and temperature combination that allowed them to increase their exposure to temperatures of 16–20° C when temperatures <16 and >20° C were available at lower and higher positions in the water column. A portion of the subyearlings that selected a temperature c. 17·0° C during the day, moved into warmer water at night coincident with an increase in downstream movement rate. Though subyearlings used temperatures outside of the 16–20° C range part of the time, behavioural thermoregulation probably reduced the effects of intermittent exposure to suboptimal temperatures. By doing so, it might enhance growth opportunity and life-history diversity in the population of subyearlings studied.     

Enhanced thermotolerance by hydrostatic pressure in the deep-sea hyperthermophile Pyrococcus strain ES4

Abstract: The combined effect of hydrostatic pressure and heat shock on thermotolerance was examined in the deep-sea hyperthermophilic archaeon Pyrococcus strain ES4. Pressure equivalent to the depth of isolation (22 MPa) enhanced ES4's survival at super-optimal temperatures (101–108°C) relative to low pressure (3 MPa). Pressure also raised the temperature at which a putative heat-shock protein (98 kDa) accumulated. ES4 grown at 95°C and 3 MPa displayed immediate enhanced thermotolerance to 105°C after being shifted to 22 MPa. Cultures grown at 95°C and 22 MPa and then heat shocked at 105°C and 3 MPa retained enhanced thermotolerance after decompression. These results suggest that this deep-sea hyperthermophile has developed pressure-induced responses that include increased survival to hyperthermal conditions.     

尼罗罗非鱼染色体的C带、Ag带和减数分裂联会复合体的研究

以Sumner法和界面铺张——硝酸银技术,对尼罗罗非鱼(Tilapia nilotica)染色体C带、Ag染带及减数分裂前期精母细胞联会复合体(SC)进行了显微和亚显微结构观察。 尼罗罗非鱼的2n=44,核型可分为三个组:第一组为4对亚中着丝粒染色体;第二组为17对亚端着丝粒染色体;第三组为具1对端着丝粒的特大染色体。 结构异染色质主要分布于着丝粒附近,其中Nos.6、8、15亚中着丝粒染色体短臂全部深染。带有银染核仁组织者(Ag-NORs)染色体的数目为2—6条,NORs均位于6、8、15亚中着丝粒染色体短臂。 银染色可清楚地显示尼罗罗非鱼的联会复合体(SC)结构和减数分裂行为。SC组型与有丝分裂染色体的组型有较好的一致性。     

Thermal acclimation of photosynthesis in black spruce [Picea mariana (Mill.) B.S.P.

We investigated the thermal acclimation of photosynthesis and respiration in black spruce seedlings [ Picea mariana (Mill.) B.S.P.] grown at 22/14 °C [low temperature (LT)] or 30/22 °C [high temperature (HT)] day/night temperatures. Net CO₂ assimilation rates ( A _net) were greater in LT than in HT seedlings below 30 °C, but were greater in HT seedlings above 30 °C. Dark and day respiration rates were similar between treatments at the respective growth temperatures. When respiration was factored out of the photosynthesis response to temperature, the resulting gross CO₂ assimilation rates ( A _gross) was lower in HT than in LT seedlings below 30 °C, but was similar above 30 °C. The reduced A _gross of HT seedlings was associated with lower needle nitrogen content, lower ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) maximum carboxylation rates ( V _cmax) and lower maximum electron transport rates ( J _max). Growth treatment did not affect V _cmax :  J _max. Modelling of the CO₂ response of photosynthesis indicated that LT seedlings at 40 °C might have been limited by heat lability of Rubisco activase, but that in HT seedlings, Rubisco capacity was limiting. In sum, thermal acclimation of A _net was largely caused by reduced respiration and lower nitrogen investments in needles from HT seedlings. At 40 °C, photosynthesis in LT seedlings might be limited by Rubisco activase capacity, while in HT seedlings, acclimation removed this limitation.