Water quality during egg incubation influences yolk-sac fry sodium kinetics in Atlantic salmon, Salmo salar L.: a possible mechanism of adaptation to acid waters

Atlantic salmon ( Salmo salar L.) fry hatched from eggs transferred from high-Na to low-Na water during the eyed stage of development had a significantly higher V_max and lower K_m (P <0.01) of the sodium uptake mechanism than fry hatched from eggs incubated entirely in low-Na or high-Na water.
Fry hatched from eggs transferred to acid, high aluminium water during the eyed stage of development had a similar V_max and K_m to fry hatched from eggs incubated entirely in high- or low-Na water. Eggs incubated continuously in acid, high aluminium (low-Na) water produced fry with significantly lower K_m and V_max values than fry hatched from eggs incubated continuously in low-Na water. Eggs and fry in acid, high aluminium water continually lost sodium and mortality was 100% at 5 5 M O degree-days (2–3 weeks after hatching).
The results are discussed with respect to the influence of perivitelline fluid ion activities in eggs in acid, high aluminium water on the kinetic characteristics of sodium uptake in yolk-sac fry. A possible mechanism for the long-term adaptation of teleosts in acidified natural waters is also proposed.     

Kinetic characteristics of the sodium uptake mechanism during the development of embryos and fry of Atlantic salmon, Salmo salar L., in an improved water quality

The kinetics of active sodium uptake in dechorionated embryos, yolk-sac fry and start-feed fry of Atlantic salmon were compared in two groups reared either in low conductivity, untreated, river water (conductivity ∼ 46 μS cm⁻¹, pH 5.75), or in 'improved' river water buffered with sea water (conductivity ∼2200 μS cm ¹, pH 6.56), the latter treatment often being used in commercial hatcheries to avoid problems associated with periodic acidification.
Maximal transport rate ( V _max) increased during development in both groups but was always significantly higher in embryos and fry maintained in untreated river water. Values for K _m were not seen to vary during development up to 12 weeks after hatching and were not significantly different between groups, or from values reported for adult Atlantic salmon in fresh water.
The results are discussed with respect to the influence of Na⁺ concentrations in the perivitelline fluid of developing eggs and in the external medium surrounding fry on V _max and K _m. The ability of fry reared entirely in buffered river water to maintain sodium balance following transfer to untreated river water is also considered.     

Intraspecific brood mixing and reduced polyandry in a maternal mouth-brooding cichlid

Microsatellite loci were used to evaluate the level of polyandryand intraspecific brood mixing in Protomelas c.f. spilopterus,a paedophagous, maternal mouth-brooding cichlid from Lake MakaiAfrica. We found that broods were fertilized by one to threemales, which was a reduced level of multiple paternity comparedto other mouth-brooding cichlids. Low density of breeding malesand the risk of intraspecific predation are likely explanationsfor reduced polyandry. Intraspecific brood-mixing was foundin four out of the six broods examined, with the proportionsof foreign fry ranging from 6% to 65%. The potential originsof brood mixing are discussed, although no firm conclusionscan be drawn given the limited behavioral observations for thisspecies.     

Dissolved oxygen concentration and emergence of sea trout fry from natural redds in tributaries of the River Rhine

A total of 4289 sea trout Salmo trutta alevins swam up from six of eleven covered redds. They emerged only from those redds where the mean dissolved oxygen level was >6·9 mg l⁻¹ and the Sorting coe.cient, an indicator of intragravel void space, was <5. These results are discussed in relation to field studies using artificially buried salmonid eggs but also in relation to the ongoing programme for the reintroduction of Atlantic salmon in tributaries of the River Rhine.     

Influence of egg vitamin A status and egg incubation temperature on subsequent development of the early vertebral column in Atlantic salmon fry

The effect of egg vitamin A (VA) status and egg incubation temperature on the development of spinal disorders was investigated in Atlantic salmon Salmo salar fry. Atlantic salmon eggs were sorted into two groups with high VA (3·3 ± 0·1 μg retinol g⁻¹ dry mass) and low VA (2·2 ± 0·3 μg retinol g⁻¹ dry mass) status before fertilization and incubated at high (14° C) or low (8° C) temperature from 133 day degrees until the onset of feeding. High egg incubation temperatures increased the concentration of retinol in the eggs: the high VA and high temperature group displayed a significantly higher retinol concentration than the high VA and low temperature group ( P  = 0·001). After hatching, all experimental groups increased their retinol concentration. The source of the increased retinol levels was probably retinal, although astaxanthin may also be a VA precursor after hatching. Atlantic salmon fry incubated at high temperatures had increased amounts of notochord tissue. When measuring morphogenic activity in the notochord using the expression of sonic hedgehog ( shh , mRNA), however, no significant difference was found between the experimental groups. No clear effect of VA status or incubation temperature could be found on the formation of the early vertebral column although Atlantic salmon fry incubated at low temperatures had less regular constrictions of the prospective vertebral column than fry incubated at high temperatures.     

Experiments to test if allopatric Salvelinus alpinus are suitable year-round hosts of Gyrodactylus salaris (Monogenea)

There has been an increased focus on Salvelinus alpinus as a potential long-term host to Gyrodactylus salaris and, here, both susceptibility to G. salaris and ability to sustain a parasite population seasonally, was tested using fry and parr of S. alpinus from the River Skibotnelva, northern Norway. Fry were highly susceptible. Gyrodactylus salaris survived on allopatric S. alpinus parr during the 5 month-long winter when water temperatures were c. 1° C. Salvelinus alpinus fry also maintained a pulse of G. salaris infection for over 155 days from early May until autumn. Gyrodactylus salaris are thus able to reproduce and survive on S. alpinus for long periods and at low water temperatures. In spring, newly hatched fry of S. alpinus may serve as an important host to maintain a G. salaris metapopulation within a river system. The results suggest that S. alpinus are adequate long-term hosts of G. salaris independent of the presence of the co-occurring highly susceptible S. salar .     

鳜鱼(Sinipera chuatsi)鱼苗肠道微生态调节的研究

对鳜鱼鱼苗肠道菌进行好氧菌和兼性厌氧菌的分析鉴定 ,发现鳜苗肠道中存在哈夫尼亚菌属和气单胞菌属 ,其中哈夫尼亚菌属量为 4 .8× 10 6cfu/ g ,气单胞菌属量为 2 .4 3× 10 5cfu/ g。哈夫尼亚菌属和气单胞菌属的拮抗实验表明哈夫尼亚菌对气单胞菌的生长有一定的抑制作用。分别用哈夫尼亚菌、气单胞菌作饵料添加剂 ,前者将鱼苗成活率由 18%提高至 33%～ 4 0 % ,后者将鱼苗成活率由 18%降至 2 %～ 4 %。     

Yield and cooking qualities of somaclonal variants of cv. Russet Burbank selected for resistance to common scab disease of potato

We previously obtained somaclonal variants of the important French fry processing cultivar Russet Burbank with significantly enhanced resistance to common scab disease. In this study we have shown the commercial merit of a proportion of these variants through comparison of relative yield and tuber quality with the parent cultivar Russet Burbank. Whilst we showed a weak negative correlation between tuber yield (as assessed by weight of tubers per plant) and relative disease resistance within selected variants, we identified several with equivalent yields to the parent cultivar. Furthermore, two disease-resistant variants (TC-RB8 and NZ-24B) consistently yielded more tuber mass than the parent. The majority of our Russet Burbank variants showed equivalent tuber quality characteristics (occurrence of defects, tuber specific gravity and dry matter content, and flesh colour) and cooking qualities (fry colour and presence of dark end defects) to the parent cultivar. Independent testing by a commercial French fry processor confirmed these quality characteristics. We present data demonstrating that highly common scab disease-resistant somaclonal variants of Russet Burbank have commercially acceptable tuber yield and quality characteristics, comparable to the industry standard and parent Russet Burbank cultivar. We also demonstrate the value of in vitro cell selection techniques for potato cultivar improvement.     

The effects of water temperature and ration size on growth and body composition of fry of common carp, Cyprinus carpio

Experiment was conducted with the aim of determining the effect of varying water temperature and ration size on growth and body composition of fry of the common carp, Cyprinus carpio. Common carp fry with an initial body weight (BW) of 0.86 g were fed a diet (34.9% protein, 18.3 KJ/g diet) at four ration sizes 4%, 5%, 6% and 7% of their body weight per day and reared at two water temperatures 28 and 32 °C for 60 days. Fry fed with 6% ration showed the highest mean final body weight at 28 °C. Final body weight was significantly (P<0.05) affected by ration and temperature. Cyprinus carpio fry raised at 28 °C had higher feed efficiency (FE) (44.36%) than the fry reared at 32 °C (40.98%) with 4% ration. Further, feed efficiency decreased with increase in ration levels in both temperatures. Protein efficiency ratio (PER) was higher (1.26) at 28 °C than at 32 °C (1.17). At 6% ration, common carp fry showed highest specific growth rate (SGR) (3.82%/day) at 28 °C as compared with at 32 °C (3.57%/day). A linear increase in protein and lipid contents was evident with increasing ration levels up to 6% body weight at both temperatures 28 and 32 °C. Second-order polynomial regression analysis of weight gain and SGR indicated the breakpoints at ration level 6.04% and 6.08% body weight per day at 28 and 32 °C. Hepatosomatic index (HSI) not affected by temperature and ration size while, viscerosomatic index (VSI) influenced (P<0.05) by ration size and temperature. Based on the above results, it may be concluded that 6% BW/day ration is optimal for growth of Cyprinus carpio fry at both the temperatures 28 and 32 °C.     

Brown trout Salmo trutta redd superimposition by spawning Lampetra species in a lowland stream

Reproductive interaction between sympatric lampreys and salmonids was studied. The superimposition of brown trout Salmo trutta redds by spring-spawning river lamprey Lampetra fluviatilis and brook lamprey Lampetra planeri was examined in a small lowland stream of western Lithuania. A high superimposition rate of S. trutta redds by both L. fluviatilis (up to 83%) and L. planeri (up to 48%) was found, when the spawning intensity of Lampetra spp. was high. The occurrence of this phenomenon is the result of the overlap in the spawning habitat preferences at the reach-scale and at the microhabitat scale for the three species. One of the main requirements for Lampetra spp. spawning site selection was the negative streambed slope, an essential trait of the pool-riffle transitional zone. The structure of the salmonid redd created a considerable negative microhabitat slope suitable for Lampetra spp. spawning, which put the redds under a higher susceptibility to be superimposed. The timing of Lampetra spp. spawning overlapped closely with the emergence of S. trutta fry, suggesting a probable ecological effect of superimposition on S. trutta in the pre-emergent and emerging stages.