Effect of incubation temperature on green sturgeon embryos, <Emphasis Type="Italic">Acipenser medirostris</Emphasis>

Regulation of river flow and the amount of winter rainfall are the major factors affecting the water temperature of the spawning grounds, for green sturgeon in the Klamath River. During the primary spawning period of green sturgeon, mid-April to June, the water temperature may vary from 8 to 21°C. To estimate the potential implications of this modified thermal regime, we examined the survival and development in three progeny groups of green sturgeon embryos from zygote to hatch, at constant incubation temperatures (11–26°C). Temperatures 23–26°C affected cleavage and gastrulation and all died before hatch. Temperatures 17.5–22°C were suboptimal as an increasing number of embryos developed abnormally and hatching success decreased at 20.5–22°C, although the tolerance to these temperatures varied between progenies. The lower temperature limit was not evident from this study, although hatching rate decreased at 11°C and hatched embryos were shorter, compared to 14°C. The mean total length of hatched embryos decreased with increasing temperature, although their wet and dry weight remained relatively constant. We concluded that temperatures 17–18°C may be the upper limit of the thermal optima for green sturgeon embryos, and that the river thermal regime during dry years may affect green sturgeon reproduction.     

Impact of photoperiod manipulation on day/night changes in melatonin, sex steroids and vitellogenin plasma levels and spawning rhythms in Senegal sole, Solea senegalensis

Photoperiod and temperature are known as the main synchronizers of seasonal reproduction in fish. This paper studied the role of photoperiod on the synchronization of F1 Senegal sole reproduction rhythms. Fish were maintained under constant short-photoperiod (9L:15D) from the winter solstice onwards (experimental group) or under naturally-changing photoperiod (control group), and water temperature naturally oscillated in both groups. Blood samples were collected during the reproduction season at pre-spawning (March), spawning (April) and post-spawning (May) to determine the endocrine status. Spawning events and egg quality parameters were also monitored. The results revealed a significant increase in nocturnal melatonin concentration from March to May in the control group, while in the experimental group such seasonal change did not occur. As to plasma levels of vitellogenin, testosterone, estradiol and 11keto-testosterone, differences between groups were found mostly in March, while in April and May levels were often similar. Spawning was observed in both groups, although the experimental group started slightly earlier and also finished earlier than the control group, perhaps as a result of the increase in sex steroids and VTG observed at pre-spawning. Briefly, reproduction rhythms persisted in the absence of the natural lengthening of photoperiod, although photoperiod manipulation altered the seasonal modulation of melatonin, increased sex steroids and vitellogenin at pre-spawning, and slightly advanced the timing of spawning.     

The annual reproductive cycle of the freshwater mussel Dreissena polymorpha Pallas in lakes

Summary The annual development of the gonads of Dreissena polymorpha was studied at three sampling sites in two lakes over 3 and 1 1/2 years, respectively. A resting stage occurred after the last spawning in summer/autumn. Oogenesis (accompanied by multiplying segmentation of the oogonia and early growth processes of its oocytes) restarted in specimens at least 1 year old at low temperatures (below 10° C) during winter and early spring. At one location (Fühlinger See) the onset of the spawning season was correlated with an increase of water temperatures above 12° C. At 2 m depth, two main spawning periods in May and August were normally recognized, the first at temperatures of 12–16° C, the second at 16–21° C. It was clearly demonstrated for the first time in Dreissena polymorpha that the oocytes became mature in successive cohorts within one gonad. A female mussel may spawn several times during the reproductive season. At 9 m depth, the onset of spawning also started at about 12° C; this occurred in late summer, with two spawning periods within 1 month at a temperature range of 12–16° C. At another location (Heider Bergsee) the size of the gonads and the oocytes was reduced during April of both years studied, when food supply was low simultaneously with rapidly rising water temperatures in this shallow lake. There was no spawning period during spring. The major spawning period was delayed until July (temperatures 19–22°C). This shows (1) the synchronizing influence of low winter temperatures on the annual reproductive cycle and (2) a temperature threshold of at least 12° C for the start of the spawning processes. The results are discussed with regard to the geographical limits of further spread of Dreissena polymorpha.     

Temperature selection and avoidance in the sand goby,Pomatoschistus minutus (Pallas), collected at different seasons

Synopsis The sand goby from the Oslofjord, Norway, is extremely eurythermal. In spring and autumn it avoids temperatures lower than about 4° C, in summer 6° C. Acclimation did not influence the lower avoidance temperature, but the critical thermal maximum, the upper avoidance temperature and the temperature where the whole fish darkened (the darkening temperature) varied with acclimation and season. The darkening temperature is suggested to be the upper temperature limit with the greatest ecological significance. The fish, collected at different seasons darkened at between 19.5 and 22° C. In the field the fish is not found at 20° C and higher.The preference temperature varied with season and with acclimation temperature, generally with low precision. In May, the preference temperature was 13.5° C, that is higher than the ambient temperature of 10° C. In summer, the temperature in sampling locality and preference temperature was the same, 17 and 16.5° C respectively. In October, temperature preference was 7.5° C as compared to 9° C in the field. The variation is explained as a behavioural thermoregulation to direct the fish towards optimal conditions at any time.The seasonal variation in preference temperature can not be ascribed only to seasonal variation in temperature, that is an acclimation phenomenon, but other factors are operative as well, factors which will modify the temperature tolerance in the fish.     

Seasonal variation in the temperature preference of Arctic charr (Salvelinus alpinus)

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Seasonal variation in thermal preference of Arctic charr from a North Norwegian population (70°N) was studied in an electronic shuttlebox, which allowed the fish to control the water temperature by moving between two chambers. The fish were acclimated to 12 °C and a natural photoperiod before measurements. Fish were tested in autumn (September–October), winter (January–February), spring (April–May) and summer (June–August).     

A preliminary report on the spawning behaviour and nature of sexual selection in the barbel, Barbus barbus (L.)

In the spring of 1974 the migration and spawning behaviour of barbel, Barbus barbus (L.) were observed. The migration and behaviour of males prior to the spawning attempts may be strategies designed to increase the quota of receptive females experienced by each male. Spawning attempts were divided into two categories: successful and failed. Successful attempts comprised six sequential sub-events: approach period, pre-spawning phase, spawning, post-spawning phase, dispersal period and inter-spawning period. The spawning and post-spawning phases did not occur in a failed attempt. The success or failure of attempts was dependent upon the number of males present. The advantage gained by females abandoning attempts when the male densities were high is discussed. In both the pre-spawning phase of failed attempts and the post-spawning phase of successful attempts, males attempted to drive away other male competitors by the use of male 'chase away' interactions.     

Acid phosphatase activity in pre- and post-spawning hake (Merluccius hubbsi)

1. The specific activity of muscle acid phosphatase (E.C. 3.1.3.1.) in pre- and post-spawning hake was investigated. 2. Specific activity values, 0.54 in pre-spawning hakes and 1.64 in post-spawning fish, have been obtained. 3. Using a histochemical test, acid phosphatase has been localized mainly in the connective tissue. The strongest reaction has been observed in post-spawning hake. 4. The increase of the lysosomal activity in the connective tissue may be related to the changes found in the muscle texture associated with spawning.     

Thermoregulatory activity in the Tecopa pupfish,Cyprindon nevadensis amargosae,an inhabitant of a thermal spring

Synopsis The final thermal preferendum of Tecopa pupfish Cyprinodon nevadensis amargosae collected from a thermal spring was determined in the laboratory in spatial and temporal thermal gradients. Temperatures chosen centred around 30°C — a value close to those reported for other warmwater species in the literature. Upper limits to final preferenda and thermal tolerance in all species of fish are proposed.     

Linked effects of dam-released floods and water temperature on spawning of the Clanwilliam yellowfish Barbus capensis

In South Africa, modified flow regimes designed to maintain ecosystem functioning at some pre-determined level are recommended for all rivers involved in major water-resource developments. One component of such flow regimes of special interest in the winter-rainfall region of the country is the small pulses of higher flow that occur in the dry season (November–April), here called freshes. Research was carried out in the Olifants River, in the winter-rainfall region of South Africa, on the link between freshes and spawning of an endemic, vulnerable cyprinid, the Clanwilliam yellowfish Barbus capensis. Experimental releases from Clanwilliam Dam on the Olifants River in a previous year showed that a greater than usual spawning success, assessed by larval recruitment levels, was correlated with hypolimnetic freshes released during the species' breeding season (October–January). In the study reported on here, a hypolimnetic fresh of the same size, duration and timing as those linked with successful spawning failed to induce spawning. Differences in the thermal regime of water releases appeared to be responsible. Two warm (19–21 °C), epilimnetic freshes of 15 hours duration were then released, and correlated with fish moving onto the spawn beds and exhibiting pre-spawning behaviour. However, the fish moved downstream away from the spawn beds when cold (16–18 °C) hypolimnetic baseflows were released for 15 hours between the two epilimnetic freshes and continually after the second one. The presence of free embryos and larval B. capensis indicated, from their developmental stages, that spawning had probably occurred before the experimental releases began, when warm (21–23 °C) epilimnetic water was spilling over the dam, and had halted once spillage stopped and hypolimnetic releases began. Indeed, the presence of dead and deformed young suggested that the cold water may have had a detrimental affect on those spawned during the earlier warmer spell. A summary table details the conditions, including the hydraulic characteristics of the spawn beds, believed to induce spawning and support early life stages of B. capensis. It is concluded that freshes released from Clanwilliam Dam at the appropriate time (October–January) should be able to increase spawning success of B. capensis, but only if the water temperature at the spawn site is at or above 19 °C and stable or rising. However, successful spawning will not necessarily lead to high recruitment if water temperatures are not then maintained at appropriate levels for some time for development of the embryos and larvae. This implies that additional epilimnetic releases will be required following critical trigger flows.     

Temporal variations in haematological and biochemical indices of the Caspian kutum, <Emphasis Type="Italic">Rutilus frisii kutum</Emphasis>

The pattern of haematology and blood biochemistry variations of healthy adult female kutum Rutilus frisii kutum (Cyprinidae) was investigated in the three reproductive states: maturing (autumn), pre-spawning (winter), and spawning (spring). Red blood cells, haemoglobin, and haematocrit were highest in autumn, whereas the highest values for white blood cells, mean corpuscular volume (MCV), and mean corpuscular haemoglobin (MCH) were observed in winter. With the exception of MCV and mean corpuscular haemoglobin concentration (MCHC), fish size had no effect on haematological and biochemical parameters. MCV was higher in larger fish, whereas the reverse trend was found for MCHC. Decreased levels of plasma glucose, cholesterol, and triglyceride in the pre-spawning period, when female ovaries were developing, may have been due to the combination of reproductive effects and food shortage in winter. Total protein levels were lower during the maturing period than during the pre-spawning period. The results of this study suggest that temporal variations in haematological and biochemical parameters of blood are significant and should be considered when these parameters are used to assess fish health status.     

Temperature preference in two populations of juvenile coho salmon,oncorhynchus kisutch

Synopsis Two groups of coho salmon,Oncorhynchus kisutch, were raised under identical regimes to test the hypothesis that the group from a stream with lower and less variable temperatures would have a lower and less variable preferred temperature than would the group from a stream with warmer and more variable temperatures. The preferred (modal) temperatures in an electronic shuttlebox of coho salmon young from a relatively cool, groundwater-fed stream were slightly lower and less variable than those of young from a warmer and more heterothermal stream (mean = 9.6° C, range: 6–16° C vs. mean = 11.6° C, range: 7–21° C). However, there was a great deal of variation within and among individual fish. While some genetic variation in thermal preference may exist, the species seems best characterized as tolerant of relatively large temperature fluctuations.     

Melatonin in the regulation of annual testicular events in carp Catla catla: evidence from the studies on the effects of exogenous melatonin, continuous light, and continuous darkness

The physiological significance of melatonin in the regulation of annual testicular events in a major carp Catla catla was evaluated through studies on the effects of graded dose (25, 50, or 100 µg/100 g body wt.) of melatonin exogenously administered for different durations (1, 15, or 30 days) and manipulation of the endogenous melatonin system by exposing the fish to constant darkness (DD) or constant light (LL) for 30 days. An identical experimental schedule was followed during the preparatory (February-March), pre-spawning (April-May), spawning (July-August), and post-spawning (September-October) phases of the annual cycle. Irrespective of the reproductive status of the carp, LL suppressed while DD increased the mid-day and mid-night values of melatonin compared to respective controls. Influences of exogenous melatonin varied in relation to the dose and duration of treatment and the reproductive status of the carp. However, testicular response to exogenous melatonin (at 100 µg, for 30 days) and DD in each reproductive phase was almost identical. Notably, precocious testicular maturation occurred in both DD and melatonin-injected fish during the preparatory phase and in LL carps during the pre-spawning phase. In contrast, testicular functions in both the melatonin-treated and DD fish were inhibited during the pre-spawning and spawning phases, while the testes did not respond to any treatment during the post-spawning phase. In conclusion, this study provided the first experimental evidence that melatonin plays a significant role in the regulation of annual testicular events in a sub-tropical surface-dwelling carp Catla catla, but the influence of this pineal hormone on the seasonal activity of testis varies in relation to the reproductive status of the concerned fish.     

Behavioral thermoregulation of largemouth bass,Micropterus salmoides,and bluegill,Lepomis macrochirus,in a nuclear reactor cooling reservoir

Synopsis Behavioral responses which allow largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus, to survive under unusually high temperature conditions were examined. Distribution of fish was ascertained by angling. Body temperatures of 4 fish were obtained using radio transmitters. Temperatures of other fish were measured after fish were captured by angling. Both species were restricted in range by lethal water temperatures and therefore inhabited a greater portion of a thermally altered reservoir in winter than in summer. Under unheated conditions (during reactor shutdown), bass occupied shallow areas with an abundance of submerged logs and stumps, a deep area with springs, and a cove where the effluent canal entered the reservoir. Commencement of reactor operation resulted in an increase in water temperature to more than 50°C in summer. Bass and bluegill retreated to three refuges and remained there until the reactor shut down and the reservoir cooled. In the refuges, bass experienced a wide variety of temperatures, but adults generally avoided temperatures above 31°C. Large adult bass (>40 cm) occupied particular positions in a refuge cove, medium size bass (15–40 cm) swam in the open water, and small bass (相似文献   

Use of a minifluviarium to study responses of young Sarotherodon niloticus (L) to hydrogen-ion concentrations and temperature

The reactions of O+ Sarotherodon niloticus (L) to varying pH and temperature were studied in the laboratory using a minifluviarium. S. niloticus was found to tolerate pH — values as low as 5.0 without any marked effect. At values between 3.0 and 5.0 the fish lost orientation and showed signs of hyperactivity. Below 3.0, they died shortly after removal from the test — yard.Thermal behavior was tested for values ranging between 30° and 43 °C. Young S. niloticus were observed to prefer temperatures between 30° and 36 °C and avoid higher temperatures. Temperatures above 41 °C were lethal. Larger fish (6.0 to 8.0 cm.) showed more tolerance to increasing temperatures, however, when pH was considered, there was no significant difference between the sizes studied (P > 0.05).     

Implications of early life stages in the natural history of the Gulf of Mexico sturgeon,Acipenser oxyrinchus de sotoi

Synopsis Gulf of Mexico sturgeon were collected during their natural spring spawning migrations from the Gulf of Mexico into the Suwannee River in Florida. Peak numbers were observed during March and April. During the summer periods the fish remained in the river over very localized bottom areas. In late fall, the fish migrated from the river into the Gulf of Mexico. Laboratory experiments revealed that maximum survival of eggs, embryos and larvae of Gulf of Mexico sturgeon occurred between 15 and 20° C. Although Gulf of Mexico sturgeon appear to have a high tolerance to warm water temperatures, their embryos and larvae exhibit high mortalities at temperatures of 25° C. Based on observations of Gulf of Mexico sturgeon migratory patterns and laboratory experiments we suggest that the timing and unusual migratory behavior of Gulf of Mexico sturgeon are associated with temporal water temperature changes in the river and the Gulf of Mexico. The requirements of a thermal refuge are discussed.     

Seasonal temperature patterns in an arctic and two subarctic Alaskan (USA) headwater streams

We investigated the thermal ecology of three Alaskan streams. Monument Creek (MC) and Little Poker Creek (LPC) are subarctic streams in interior Alaska; LPC is in a permafrost-dominated valley. Imnavait Creek (IC) is an arctic tundra beaded stream in the northern foothills of the Brooks Range. Water temperatures were recorded with automated dataloggers hourly (LPC) or bi-hourly (MC and IC). Records for MC extend through almost three entire years, while data from IC (three years) and LPC (one year) represent the majority of the ice-free season. We also collected winter water/ice temperatures from IC (1989–1990). Mean annual water temperatures were 1.1 °C (LPC), 2.3 °C (MC), and 2.9 °C (IC), while maxima were 5.8 °C (LPC), 13.0 °C (MC), and 21.4 °C (IC). Water temperature rose in the spring about twice as fast (both mean and maximum daily increase) in MC as in LPC, and again about twice as fast in IC as in MC. A similar pattern was observed during the autumnal decline in water temperature. Maximum daily amplitude followed a similar pattern, with MC (6.6 °C) intermediate between LPC (4.1°) and IC (11.6°). LPC accumulated approximately 400 degree-days above 0 °C, MC approximately 950 degree-days, and IC approximately 1000 degree-days. Although it is about 450 km north of the other streams, the tundra stream (IC) accumulated more degree-days, had higher maximum and mean temperatures, greater daily temperature amplitude, and steeper slopes of vernal temperature rise and autumnal temperature decline than the subarctic streams (LPC and MC). The absence of a canopy of riparian plants, channel morphology, and continuous sunlight during the arctic mid-summer accounted for these higher temperatures. Beaded tundra streams provide a highly seasonal (< 120 d ice-free) and spatially and temporally complex thermal environment.     

Comments on a study of the thermal behaviour of the American eel (Anguilla rostrata) and some statistical suggestions for temperature preference studies

Some suggestions are made concerning methods and statistical evaluation of results in temperature preference studies. The use of regression analysis is advocated rather than graphical methods for evaluating results from acute temperature preference studies and a method of assessing the final preferendum and its confidence interval is demonstrated. This method is applied to a previously published study of the acutely preferred temperature of the American eel (Barila & Stauffer, 1980). The final preferendum and its 95% confidence interval is shown to be 17.4° ± 2.0 °C. In direct contrast to conclusions there drawn, the preferred temperature is shown to depend on the acclimated temperature. Some critical comments are also made concerning other parts of the study.     

Effects of photoperiod and temperature on sexual recrudescence in the male weakfish,Cynoscion regalis

Synopsis Male weakfish,Cynoscion regalis, were collected in the south-west portion of Delaware Bay from April through August of 1992. Histological examination of testes collected from these specimens was used as a baseline for comparison with laboratory data. Weakfish testes were found to be of the unrestricted, continuous spermatogenic type and spermatogenesis was apparently prenuptial. The effects of photoperiod and temperature on gonadal maturation were studied in the laboratory using fish collected in June and July 1991. These fish were exposed to two months of simulated winter conditions prior to assignment to one of four experimental photoperiod/temperature regimes. The treatments included combinations of long day (LD,15 h light) or short day (SD, 9 h light) and high (HT, 20° C) or low (LT, 13° C) water temperatures. The four treatment groups were LD/HT, LD/LT, SD/HT, SD/LT. The LD/HT group was the only one to mature fully, expressing increased plasma androgen levels, increased gonadosomatic index (GSI) and advanced spermatogenesis, as well as hypertrophy of the sonic muscles, a seasonally expressed secondary sexual characteristic of male weakfish. High temperatures promoted the later stages of spermatogenesis, which were apparently inhibited by low temperatures. The presence of an endogenous annual cycle is suggested by the partial maturation of the testes and sonic muscles in all treatment groups, regardless of photoperiod/temperature regime.     

Environmental Determinants of Birth Seasonality in Night Monkeys (Aotus azarai) of the Argentinean Chaco

The night monkeys (Aotus azarai) of Formosa, Argentina provide an opportunity to investigate the influences of ambient temperature and photoperiod on reproduction in a highly seasonal environment: the Chaco. Between 1997 and 2000, we collected data to evaluate the relationship between rainfall, ambient temperature, photoperiod and food availability and the annual distribution of mating behavior and births in 15 groups of monkeys in the forests of the Eastern Argentinean Chaco. Our data show that the area is highly seasonal, characterized by significant fluctuations in rainfall, temperature, photoperiod and food availability. There are two rain peaks in April and November and a dry season lasting from June to August. Monthly mean temperatures were on average 11°C lower during winter months than they were during summer months. Temperatures <10°C and >33°C were also frequent through the year. Days are 3 h longer during the summer than during the winter months. Insect abundance and the percentage of tree species producing fruits, flowers or new leaves reached a low in the coldest winter months. Mating was infrequent, and we only observed it between May and September. Half the births (n = 13) occurred during a 2-week period in October. Infant survival during the first 6 mo of life was high (96%). Our findings suggest an environmental control of reproduction. Changes in photoperiod and temperature may promote reproductive activity in females that might conceive and begin pregnancy at a time void of high temperatures that could be metabolically challenging.     

Migration and spawning of female surubim (<Emphasis Type="Italic">Pseudoplatystoma corruscans</Emphasis>, Pimelodidae) in the São Francisco river,Brazil

Surubim, Pseudoplatystoma corruscans, is the most valuable commercial and recreational fish in the São Francisco River, but little is known about adult migration and spawning. Movements of 24 females (9.5–29.0 kg), which were radio-tagged just downstream of Três Marias Dam (TMD) at river kilometer 2,109 and at Pirapora Rapids (PR) 129 km downstream of TMD, suggest the following conceptual model of adult female migration and spawning. The tagged surubims used only 274 km of the main stem downstream of TMD and two tributaries, the Velhas and Abaeté rivers. Migration style was dualistic with non-migratory (resident) and migratory fish. Pre-spawning females swam at ground speeds of up to 31 km day^-1 in late September–December to pre-spawning staging sites located 0–11 km from the spawning ground. In the spawning season (November–March), pre-spawning females migrated back and forth from nearby pre-spawning staging sites to PR for short visits to spawn, mostly during floods. Multiple visits to the spawning site suggest surubim is a multiple spawner. Most post-spawning surubims left the spawning ground to forage elsewhere, but some stayed at the spawning site until the next spawning season. Post-spawning migrants swam up or downstream at ground speeds up to 29 km day^-1 during January–March. Construction of proposed dams in the main stem and tributaries downstream of TMD will greatly reduce surubim abundance by blocking migrations and changing the river into reservoirs that eliminate riverine spawning and non-spawning habitats, and possibly, cause extirpation of populations.