Comparison of growth, diet and food consumption of sea-run and lake-dwelling Arctic charr

Sea-run post-smolt Arctic charr Salvelinus alpinus , (15–26 cm) from Storvatn, northern Norway (70°39'48"N) had significantly higher average specific growth rates in two years (1·64 and 1·66) than the corresponding lake-dwelling charr (0·53 and 1·20). The post-smolts displayed fast compensatory growth in the first 2–3 weeks of their sea residency, but then almost stopped growing prior to their return to fresh water. Lake-dwelling charr grew more evenly during the same time period. Thus, the anadromous charr may return to the lake after only 5–6 weeks in the sea, because the potential to maintain a high growth rate in the sea is reduced. The marine diet consisted mainly of the two crustacean plankton species Calanus finmarchicus , and Thysanoëssa , sp. (88%), and less of fish (6%), insects (4%) and benthos (2%). The diet of lake-dwelling charr consisted mainly of insects (58%, mostly chironomid pupae) and zoobenthos (29%), and less of zooplankton (13%) during the same time period. Although post-smolts had the highest growth rates, they had significantly lower food consumption rates and higher frequencies of empty stomachs than the corresponding lake-dwelling fish. Possible explanations for this paradox are discussed in relation to stomach evacuation rates, water temperature, feeding behaviour and the energy content of the food in the two environments.     

Salinity tolerance of freshwater acclimated, small-sized Arctic charr, Salvelinus alpinus from northern Labrador

Arctic charr, Salvelinus alpinus , less than 150 mm in size were frequently captured at sea in northern Labrador in areas where salinities of 30‰ or higher had been recorded. These captures were inconsistent with many earlier reports for other areas that indicated Arctic charr less than 150 mm in size were not found at sea. A series of salinity challenge tests was carried out in the field, using wild Ikarut River charr, and in the laboratory, using cultured Fraser River charr, to understand more about the potential fate of these small fish. The results of challenge tests with small Arctic charr (< 120 mm) indicated that at intermediate salinities (10–20‰), these fish can readily survive. In laboratory tests with salinities at 30‰, survival was size dependent and would suggest that in natural situations, small charr would require periodic access to fresh or brackish water to stay alive. The influence of water temperature on salinity tolerance may be important when fish are exposed to temperatures that are below 0° C.     

Migration, growth and survival of wild and hatchery-reared anadromous Arctic charr (Salvelinus alpinus) in Finnmark, Northern Norway

Two groups of anadromous Arctic charr ( Salvelinus alpinus ) (size 200–350 mm) reared in heated water (6–12° C) under simulated natural photoperiod were individually tagged and released in spring 1988. The fish were released at two sites, in the estuary of the River Halselva and in the fjord, 2 km from the river mouth. Growth, timing of migration and survival of these hatchery-reared fish was compared to that of wild anadromous charr of the same size over a 4-year period. The hatchery-reared charr had poorer growth than the wild fish during their first year in sea water. They also resided longer in the sea and had a slightly lower survival than wild fish. During the second year, hatchery-reared charr displayed good growth, and after the third sea-season the fish were ready for slaughter at a size of approximately 800g. The results suggest that the successful development of Arctic charr ranching will be dependent upon production and release strategies that lead to improved migratory and feeding behaviour of the fish during their first season at sea.     

武湖日本沼虾繁殖生物学研究

武湖日本沼虾产卵场位于全湖沿岸带．越冬虾主要繁殖期为春夏季(4月中旬～7月中旬,水温20．5～31℃)。当年虾繁殖期为秋季(7月中旬～9月中旬,水温31～23℃),7月中下旬为新老世代交替期．非繁殖季节雄虾多于雌虾,繁殖季节雌虾多于雄虾．越冬虾绝对繁殖力明显大于当年虾．绝对繁殖力与体长呈幂函数关系,与体重呈直线相关．相对繁殖力RW为常数,其95％置信区间为1067．76±16．94eggs·g^-1。     

Adult feeding time, lipid accumulation, and overwintering in Aglais urticae and Inachis io (Lepidoptera: Nymphalidae)

The influence of restricted feeding time on the subsequent survival of adult Aglais urticae and Inachis io during diapause was tested in the laboratory. Abdominal lipid weight increased in the first 7 days of feeding by A. urticae and up to day 15 in I. io. Lipid as a proportion of dry weight also increased during this time. Individuals of both species feeding for 0–3 days began overwintering at significantly lower weights, and percentage weight loss during overwintering was more rapid than for those feeding for longer periods. Differences in fresh weights at the beginning of the overwintering period are reflected by differences in overwintering survival. In A. urticae , all 0–3 day feeders died in less than 150 days, in contrast, over 75% of 7–30 day feeders survived this period. In I. io , all 0–1 day feeders died within 160 days, less than 50% of 3 day feeders survived, whilst over 90% of7–15 day feeders were alive after this time. In I. io individuals feeding for one day, fresh weight is correlated with survival time suggesting that a larger body size may enhance survival time if feeding time is restricted.     

In vivo and in vitro effects of oestradiol-17β on lipid metabolism in Notemigonus crysoleucas

The effects of oestradiol-17β on the gonosornatic index, liver size, hepatic and body lipid levels in the cyprinid teleost, Notemigonus crysoleucas , were investigated. Administration of oestradiol to female TV. crysoleucas during the gonadal preparatory and prespawning seasons stimulates increases in ovarian size. During the early spawning season oestradiol therapy results in a reduction of ovarian gonosomatic index. Oestrogen treatment of males causes a suppression of testicular growth. In female fish exposed to long (15-5L/8-5D) or intermediate (12L/12D) photoperiods oestradiol increases body fat reserves. At short photoperiods (9L/15D) oestrogen treatment of females results in body fat store depletion Low doses deplete and high doses of oestradiol increase body lipid reserves in male fish. The hepatosomic index increases in both male and female fish following oestrogen treatment. Oestradiol therapy during the gonadal preparatory season, but not during the prespawning season, increases total liver lipids. The in vitro effects of oestradiol on liver lipid and carbohydrate metabolism were also examined. Under the conditions used in these experiments, lipid depletion was observed in liver slices incubated with or without oestradiol. Pretreatment of fish with oestradiol before liver tissue was removed drastically reduced in vitro lipid depletion. Oestradiol retards the gluconeogenesis and glycogenesis seen in liver slices incubated in a hormone-free medium.     

The combined effects of ambient temperature and enforced sustained swimming activity on body temperatures of arctic charr (Salvelinus alpinus L.)

1. 1.|The difference between tissue temperatures and ambient water temperatures (ΔT) of the ectothermic Arctic charr (Salvelinus alpinus L.) ranged between 0.2 and 0.6°C.

2. 2.|For fish held at 5.7°C there were no significant differences in ΔT of exercising fish and those of controls.

3. 3.|By contrast, for fish held at 1.7°C sustained exercise led to a significant increase in ΔT of all body compartments compared with fish held in standing water (controls).

4. 4.|It is suggested that Arctic charr are capable of a limited control of metabolic heat exchange between body compartments and surrounding water when subjected to sustained exercise and ambient temperatures <2°C.

Influence of maturity status on the annual cycles of feeding and growth in Arctic charr reared at constant temperature

Temporal changes in feeding and growth of immature (1 +), maturing male (1 +), and mature male and female (3+) Arctic charr were studied by monitoring feed intake and growth of individually-marked fish for over 1 year. The fish were held at a constant temperature (4°C) under conditions of liberal feed supply. Feed intake and growth remained low in the period December-April, with only 20–60% of the fish having fed on each occasion that feed intake was monitored. Feed intake and growth increased markedly during the late spring and summer, but the increases were delayed by approximately 1–2 months in the immature fish compared with their maturing counterparts. Maturing fish decreased feeding during the late summer and by September there had been an almost complete cessation of feeding. This was reflected in changes in fish body weight and condition, both of which declined from August-September onwards. By contrast, the immature fish peaked in weight and condition in September, and weight loss during the autumn tended to be less rapid than observed for the maturing fish. The fish appeared to reduce feeding once a'threshold condition' of 1–4—1–5 had been attained. It is suggested that the fish may become anorexic once there has been replenishment of the energy reserves required for overwintering and, in the case of maturing individuals, for the completion of gonadal growth and Spawning.     

PCB impairs smoltification and seawater performance in anadromous Arctic charr (Salvelinus alpinus)

The impacts of polychlorinated biphenyl (PCB) exposure on smoltification and subsequent seawater performance were investigated in hatchery-reared, anadromous Arctic charr (Salvelinus alpinus). The fish were subjected to a 2-month summer seawater residence, after which they were orally dosed with 0 (Control, C), 1 (Low Dose, LD) or 100 mg Aroclor 1254 kg(-1) body mass (High Dose, HD) in November. They were then held in fresh water, without being fed (to mimic their natural overwintering in freshwater), until they had smolted in June the next year. The smolts were then transferred to seawater and fed to mimic their summer feeding residence in seawater, followed by a period without food in freshwater from August until maturation in October. Compared with C and LD charr, the HD charr had either a transient or a permanent reduction in plasma growth hormone, insulin-like growth factor-1, and thyroxin and triiodothyronine titers during the period of smoltification. These hormonal alterations in the HD charr corresponded with impaired hyposmoregulatory ability in May and June, as well as reduced growth rate and survival after transference to seawater. Consequently, fewer fish in the HD group matured in October compared to the other two treatments. The HD fish had a liver PCB concentration ranging between 14 and 42 mg kg(-1) wet mass, whereas there were similar, and very low, liver PCB concentrations in LD and C fish throughout the smolting period. Our findings suggest that PCB might compromise mechanisms important for fitness in a fish species living in an extreme environment.     

Seasonal cycles in total chemical composition of two Lake Baikal benthic-pelagic sculpins (Cottocomephorus, Cottoidei)

Annual cycles in chemical composition of the body, liver, gonads, red and white muscles were determined for two medium fat sculpins, Cottocomephorus grewingki and C. inermis , endemic to Lake Baikal. Their total lipid content ranged from 3 to 9% during the year. The content of defatted dry substance was 14–17%, similar to the protein content of the other Baikalian cottoid fishes. The prespawning period was characterized by a positive lipid and protein balance in both species. In C. grewingki the liver performed largely a metabolic function, whereas in C. inermis it served also as a storage site for lipid reserves. During spawning, total body lipids of females of both species showed a two- to threefold decrease. Males of C. grewingki guarding nests deplete greatly their total body lipids, which decrease seven- to ninefold by the time of larval hatching in comparison with the prespawning period, and constitute 1–2%. After spawning, lipid reserves of C. grewingki were quickly restored to the initial level (from about 3 to 9%) and maintained during the long sexual maturation period. In C. inermis total body lipids increased only twofold in comparison to those observed during the spawning period.     

The effect of salty diets and gradual transfer to sea water on osmotic adaptation, gill Na+, K+-ATPase activation, and survival of brook charr, Salvelinus fontinalis, Mitchill

The intensity and duration of the period of osmotic disturbance during introduction of brook charr into sea water were decreased by introducing the fish according to a gradient of salinity over a period of 6 days. Survival in summer increased from 25 to 90% with the use of a salinity gradient. However, kinetics and levels of activation of the gill Na⁺, K⁺-ATPase were not affected by the mode used for introducing brook charr into sea water. Neither was its level of activity modified by the use of a salted diet when the fish were in fresh water. The addition of 8 and 12% of salt to the diet prevented the plasma electrolyte surge of concentrations during the first days in sea water. In very cold water, survival rate was also drastically improved by giving an 8% salted diet during the 6 weeks preceding the introduction into sea water. These results show that both salty diets and exposure to brackish water during 6 days help brook charr face osmotic stress and improve their survival rate when introduced into full-strength sea water. The combined use of these preconditioning strategies might facilitate rearing this species in sea cages or silos.     

Marine feeding of anadromous Salmo trutta during winter

Juvenile and adult anadromous trout Salmo trutta utilize the sea for feeding during the winter in the Skagerrak. This finding conflicts with the traditional view that anadromous trout overwinter in fresh water. Adults, just prior to spawning, were captured at sea in October to December, and spent fish were caught at sea from October to April, showing that the fish may leave the stream and move to sea just after spawning and spend the winter there. During mid‐winter (January to February), the feeding probability (chance of finding a fish with food in its stomach) increased markedly with increasing body length, with no similar effect during early and late winter (October to December and March to April). Among individuals with food in their stomach (72·5%), there was no evidence for variation in feeding intensity [stomach fullness = (mass of stomach content)(fish body mass)⁻¹] among early, mid‐, and late winter.     

Time of start of spawning in Atlantic cod (Gadus morhua) females in relation to vitellogenic oocyte diameter, temperature, fish length and condition

Spawning time of female Atlantic cod ( Gadus morhua L.) can be predicted to within 3 days using vitellogenic oocyte diameters measured over the last month before spawning. Simulations show that a l°C drop in temperature during vitellogenesis delays spawning by about 8–10 days. Similar results were obtained with fish on low ration for 4–8 months before spawning. Moderately fed females held over two to four consecutive spawning seasons demonstrated a significant delay (⋍3–40 days) in the date of first spawning as the fish grew older and more fecund. Forecasting studies on spawning migrating Arcto-Norwegian cod gave no evidence of a significant effect of fish length on the time of spawning. Warmer water temperature during vitellogenesis for the larger fish appears to compensate for the negative effect of fecundity On spawning time.     

Reproductive biology of the endangered Oxleyan pygmy perch Nannoperca oxleyana Whitley

The reproductive biology of the Oxleyan pygmy perch Nannoperca oxleyana is described from simultaneous studies of wild populations in north-eastern New South Wales and mature fish held in aquaria. In the wild, 50% of males and females matured at total lengths of 24·0–25·9 and 28·0–29·9 mm, respectively. The species displays sexual dichromatism during the spawning season, with males developing more intense red and brown fin and body colouration, and black pelvic fins. Captive male broodfish displayed territoriality during the breeding season, closely guarding sites within artificial, plant-like substrata in which pairs of fish spawned adhesive eggs. Protracted serial spawning of wild and captive fish occurred from September to April and May at mean water temperatures ≥16·6° C and day length ≥10·7 h. Captive broodfish spawned on an average of 57% of days during the 256 day spawning period. Gonado-somatic indices averaged 0·7% for all ripe males and 4·1–4·2% for all ripe females collected. Mean total and batch fecundities of captive females were 1323 eggs per fish and 7·8 eggs per fish per day, respectively, and relative fecundity was 587 eggs g⁻¹ of body mass. Batch fecundity of wild females was estimated at 7·8 eggs per fish. The adaptive significance of this reproductive strategy in a harsh, variable environment is discussed.     

Observations on interbreeding between dwarf and normal arctic charr,Salvelinus alpinus,from Stora Rösjön,central Sweden

Synopsis The spawning behaviour of dwarf and normal arctic charr, Salvelinus alpinus, was studied through trough observations in October 1988. The experimental fish consisted of reared, three-summer old progeny of artificially bred dwarf and normal charr from an isolated body of water in central Sweden. The spawning behaviour of three normal female charrs was studied and video-recorded. The study showed that the arctic charr is potentially polyandric both within and between forms. The normal female was courted and mated both by normal and dwarf males. It was also noted that antagonistic behaviour on behalf of the female was much more common towards dwarf males than normal males. Guarding tactics were only observed in normal males, whereas sneaking tactics were employed both by dwarf and normal males. The dwarf as well as normal males mated the female charr either by courting the female or by joining the spawning fish at oviposition. Only dwarf males were observed resting silently on the bottom close to the redd.     

The post‐spawning movements of migratory brown trout Salmo trutta L.

The post spawning behaviour of sea trout Salmo trutta was studied over a 2 year period in the river and estuary of the River Fowey, south‐west England. Forty‐five sea trout kelts were trapped immediately after spawning in December and intraperitoneally tagged with miniature acoustic transmitters. The subsequent emigration into coastal waters was monitored using acoustic receivers deployed throughout the river catchment. The levels of gill Na⁺K⁺ATPase activity in sea trout kelts sampled at the same time as the tagged fish were within the range of 2·5 to 4·5 μmol Pi per mg protein per h indicating that the post‐spawning fish were not physiologically adapted to salt water. The tagged kelts were resident in fresh water between 4 and 70 days before entering the estuary. Sixty two per cent of the tagged kelts subsequently migrated successfully into coastal waters, with a higher success rate for male fish (75%) than females (58%). There was a significant size related difference in the run‐timing of the kelts with the larger fish moving more quickly into coastal waters after spawning than smaller fish. Seaward migration within fresh water was predominantly nocturnal and generally occurred in conjunction with increasing river discharge and rising water temperature. Migration through the estuary continued to be predominantly nocturnal and occurred during an ebbing tide. Residency within the estuary varied amongst individuals although it was invariably short, with most fish moving out into coastal waters within one to two tidal cycles. Five tagged kelts returned from the coastal zone and re‐entered fresh water during April and June. Marine residence time varied between 89 and 145 days (mean 118 days) and the minimum estimated marine survival was c. 18%. One of these sea trout was subsequently recaptured after successfully spawning in the vicinity where it had been previously tagged demonstrating a degree of spawning site fidelity.     

Salinity tolerance of the guppy, Poecilia reticulata Peters

Experiments were conducted to determine the adaptability of the guppy to various salt concentrations. The guppy, Poecilia reticulata , (total length 11–40 mm) were subjected to abrupt and gradual changes from fresh water (salinity=0.1%) to various salinities (%). No mortality occurred when the fish were transferred from fresh water to 50% sea water (19.5%). Through gradual adaptation from 50% sea water to 80% of the fish were able to tolerate 100% (39%) sea water for 7 days. After a 7 day stay in sea water, fish were readapted to fresh water during a 3 h period. Through gradual adaptation fish were also able to tolerate salinities ranging from 39.0% (100% sea water) to 58.5%. After a 30 day stay in 150% sea water (58.5%), fish were readapted to fresh water over a 5 h period. The results indicate that they were well able to tolerate the abrupt change from 100 or 150% sea water to fresh water. Females that stayed in 150% sea water (58.5%) for 30 days had embryos in their gonads.     

The pathology and seawater performance of farmed Atlantic salmon infected with glochidia of Margaritifera margaritifera

The pathology of glochidial infection of the freshwater mussel Margaritifera margaritifera was examined in farmed Atlantic salmon Salmo salar in fresh water and for 150 days after transfer of salmon to sea water. Prevalence of infection in fresh water was 95%, mean abundance 134 per fish and mean infection intensity 140. Prevalence in sea water was 80–94% in the first 7 weeks after transfer but glochidia were absent, apart from remains, after 50 days in sea water. Glochidia on salmon in fresh water were associated with localized hyperplasia and fusion of secondary gill lamellae. Focally extensive epithelial hyperplasia and fusion of secondary lamellae were present 4–10 days after transfer to sea water. Twenty-three days after transfer, small nodules with a more discrete appearance were present suggesting partial resolution of tissue response; hyperplastic responses associated with glochidia were much reduced after 50 days. Plasma chloride in infected fish 10 days after transfer was 153 mmol. 1⁻¹, significantly higher than fish without infection, suggesting poorer adaptation to sea water. No mortalities due to glochidial infection in sea water were recorded and there was no significant difference in mean weight between infected and control fish.     

Salinity tolerance of the mosquito fish, Gambusia affinis (Baird and Girard)

Experiments were conducted to determine the adaptability of mosquito fish to various salt concentrations. Mosquito fish, Gambusia affinis , (total length (T.L.) 27–37 mm) were subjected to abrupt and gradual changes from fresh water to various salinities (S). Low mortality (10%) occurred when the fish were transferred from fresh water (S = 0·5‰) to 50% sea water (S = 19·5‰ Through gradual adaptation 65·0% of the fish were able to tolerate 100% sea water for 7 days. After a 7 -day stay in sea water, fish were readapted to fresh water during a 3-h period. The results indicate that they were well able to tolerate the abrupt change. Through a gradual adaptation fish were also able to tolerate salinities ranging from 39·0‰ (100% sea water) to 58·8‰     

A morphometric method for estimation of total lipid level in live Arctic charr: a case study of its application on wild fish

Linear body measurements were made on wild Arctic charr Salvelinus alpinus parr (100–200 mm L_F) from two populations in northern Norway during spring (May), summer (June and July) and autumn (October). To reduce handling stress, a method was developed were dorsal and ventral body measurements could subsequently be taken easily from a single picture of the anaesthetized fish. Multiple regression analyses investigated the possible correlation between the body measurements and both total and percentage lipid content of the fish. For both populations and during all seasons, the regression equations gave better estimates for total lipid than for percentage lipid. The regression equations for total lipid accounted for between 67·7 and 89·5% of the variance in lipid content for the different seasons within the lakes. The pooled data within each lake accounted for 62·9 and 81·0% of the variance in total lipid, while the pooled data for both lakes accounted for 67·7% of the variance. In general, the condition factor alone did not give a satisfactory estimate of lipid content of the Arctic charr (r² = 0·003–0·521). Shrinkage on validation values was high (0·20–0·52). Employing a ridge regression method resulted in models with lower r² values and lower shrinkage values (indicating more stable models). Published equations used for hatchery‐reared Arctic charr could not be used on wild fish from the same population. The close correlations between actual and predicted lipid levels found in this study show that morphometric measurements can predict total lipid levels in wild Arctic charr with reasonable accuracy. The most accurate results were obtained when equations were derived from each data set. Therefore, the method has the potential within a single study to estimate lipid levels in live fish as long as some fish can be sacrificed to develop a unique regression equation for each population or experiment.