Induction of gynogenesis and gonad development in the muskellunge

Muskellunge Esox masquinongy eggs activated with UV-irradiated yellow perch Perca flavescens sperm were subjected to heat shock at 31 ± 1° C for 6 min, 20 min after fertilization in three experiments. Survival at eyed stage was 1·7 ±1·6, 6·8 ± 4·8 and 2·3 ±0·5% in experiments I, II and III, respectively. After rearing the gynogenetic muskellunge in troughs and then in ponds, the sex ratio of gynogens in experiment I did not significantly (P>0·05) differ from the expected ratio 0:1 (male: female), however, one male and one intersex were observed. In experiments II and III, the sex ratio of gynogens differed significantly from expected (0 : 1). Three months after hatching, the growth of females did not significantly (P>0·05) differ among control and gynogenetic groups, whereas male growth was significantly (P<0·01) higher in the control v. gynogenetic group. The histological structures of the gynogenetic fish gonads in both sexes were similar to those described in the gonads of control muskellunge. After the overwintering period, signs of active spermatogenesis were observed in the testis of 1 + year old gynogenetic fish, whereas ovaries contained only oocytes at the perinucleolar stage. At this stage, plasma sex steroids testosterone (T) and oestradiol-17β (E2) cannot be used to discriminate the sex of gynogenetic muskellunge, as intersex, male and female fish had similar levels of T and E2.     

Plasma and ovarian thyroxine levels in relation to sexual maturation and gestation in female Sebastes inermis

Plasma T₄ (L-thyroxine) concentrations in the viviparous rockfish Sebastes inermis showed a peak (119·3±27·8 ng ml⁻¹) during the development of embryos. Ovarian T₄ concentrations increased during vitellogenesis and final maturation and decreased during embryogenesis.However, total T₄ content within the ovary increased continuously up to the larval stages. Plasma oestradiol-17β, (E₂) concentrations peaked at the final maturation stage and then recovered to the level seen during the non-reproductive periods. Plasma testosterone (T) concentrations showed a peak (5·33±1·08 ng ml⁻¹) at the embryo stage and high levels were maintained throughout the gestation period. Plasma T₄ concentrations during the embryo stage and ovarian T₄ content during vitellogenesis were much higher than the levels reported in oviparous fishes. These data suggest that in viviparous rockfish, T₄ may be required for sustaining gestation or embryo development within the maternal body. In addition, the high content of total T₄ in the ovary implies that there probably does exist a maternal-embryo relationship during gestation as well as during vitellogenesis.     

Reproductive biology of the mosquitofish in a permanent natural lagoon in south-west Spain: two tactics for one species

Introduced Gambusia holbrooki in a natural lagoon of southern Spain consisted of two age groups: 1992 cohort, 7-11 months old and 1993 cohort, <4 months old. In the 1992 cohort, females grew even during the gestation period at about 0·30 mm day^-1. In the 1993 cohort, females displayed a high growth rate (0·55 mm day^-1) and reached reproductive size in a few weeks, but stopped growing when they matured. All the 1992 cohort reproduced from mid-May to mid-June, but only 50% of the 1993 cohort reproduced, from mid-August to mid-September. Reproducing females were significantly larger in the 1992 cohort (39·8 mm) than in the 1993 one (34·8 mm). The largest 1992 females cohort had reproduced previously; the 1993 cohort had not. The mean dry weight of intra-ovarian embryos decreased to a minimum immediately before birth. These metabolic costs represented 29·8 and 31·4% of the initial weights of the 1992 and 1993 embryos, respectively. Mean dry weight of full-term embryo was significantly higher in the 1992 cohort (0·80 ± 0·129 mg; 95% CL) than in the 1993 one (0·70 ± 0·086 mg; 95% CL). With more females in 1992, cohort fecundity was considerably higher (number of embryos=7151; 63%) than in the 1993 (4193; 37%) cohort. The population completed two generations each year (spring and summer). The spring stock grew slower than the summer one but continued to grow during the gestation period, reaching larger final lengths, with more synchronous reproduction and clearer evidence of a second reproductive event. Each reproductive stock displayed its own life-history characteristics, with significant differences between mean length of reproducing females, growth rate, mean brood size, offspring size, standard fecundity and minimum length at reproduction.     

Effects of cadmium chloride on the development of rainbow trout Oncorhynchus mykiss early life stages

The sub-chronic (28–56 days) effects of exposure to low concentrations of cadmium (Cd; 0·05, 0·25, 0·50 and 2·50 μg l⁻¹) shortly following fertilization on embryos, larvae and juvenile rainbow trout Oncorhynchus mykiss were examined. Premature hatching occurred at lower concentrations (0·05 and 0·25 μg l⁻¹ Cd), however, delayed hatching was seen in the 2·50 μg l⁻¹ Cd group, with >90% of hatching occurring on the last day of the hatching period. Larval growth was negatively affected by Cd exposure in a concentration-dependent manner. Larvae exposed to 2·50 μg l⁻¹ Cd were 13·9 ± 0·8% shorter in total length ( L _T) and weighed 22·4 ± 3·5% (mean ± s . e .) less than controls at the end of the exposure period. Plasma sex steroid concentrations (oestradiol in juvenile females and 11-ketotestosterone in juvenile males) were elevated (four- to 10-fold over controls) in exposed fish in both males and females, following 28 days of exposure to 0·05, 0·25 and 0·50 μg l⁻¹ Cd, respectively. These results suggest that environmentally realistic concentrations (in the μg l⁻¹ range) of Cd can affect the development of O. mykiss impacting embryos, larvae and juvenile fish.     

Effects of light intensity and addition of carotene rich Dunaliella salina live cells on growth and antioxidant activity of Solea senegalensis Kaup (1858) larval and metamorphic stages

Senegal sole Solea senegalensis larval and metamorphic stages were exposed to a range of light intensities (200, 1000 and 2000 lx) in cultures with or without supplementation of β-carotene-rich live Dunaliella salina cells. Antioxidant biomarkers such as superoxide dismutase (SOD), catalase (KAT), total glutathione peroxidase (t-GPX) and malondialdehyde (MDA) were determined in larval and metamorphic stages. Growth was not affected ( P > 0·05) either by light intensity or D. salina supplementation. Survival after metamorphosis was also unaffected by D. salina supplementation (mean ± s . e . 81·0 ± 2·5% against 80·6 ± 2·9% those fed the control algal diet) or light intensity (mean ± s . e . 74·3 ± 4·9% for 200 lx, 85·1 ± 2·7% for 1000 lx and 82·8 ± 5·2% for 2000 lx, respectively). Light intensity affected ( P < 0·05) KAT and t-GPX throughout development. SOD was only affected in metamorphosing larvae. The highest KAT and t-GPX activities were detected when the lowest light intensity (200 lx) was used. Light had no effect ( P > 0·05) on MDA at any stage. Supplementing the diet with D. salina did not affect SOD, KAT or t-GPX and there was no interaction ( P > 0·05) with light intensity. MDA was the only biomarker whose activity was significantly ( P < 0·05) reduced when D. salina was supplemented to the larval rearing tanks. The effect of D. salina supplementation was only detected in metamorphosing larvae, whose MDA levels were noticeably higher than in earlier stages. These results are evidence of the antiperoxidative effect of β-carotene from live algae in the larval rearing process of marine fishes.     

Morphology and fine structure of the heart of the burbot, a cold stenothermal fish

The ventricle of the burbot Lota lota heart comprised 0·148 ± 0·006% of the body mass which is nearly two-fold heavier than the relative ventricular mass ( M _V) of other similarly sized teleosts. The shape of the ventricle is pyramidal and the wall is exclusively composed of spongious muscle without a distinct compact layer. The atrium forms 0·017 ± 0·002% of the body mass. Length, width, sarcolemmal surface area and volume of enzymatically isolated myocytes from burbot ventricle were 147·2 ± 10·2 μm, 6·3 ± 0·4 μm, 2440·8 · 251·5 μm² and 2356·8 ± 316·6 μm³, respectively. The myofibrils were peripherally located and their volume density was remarkably high: 65 ± 2 and 68 ± 3% in ventricle and atrium, respectively ( P >0·05). Although not particularly conspicuous, some nonjunctional and junctional sarcoplasmic reticulum (SR) was present in both atrial and ventricular myocytes. The SR formed peripheral couplings with the sarcolemma and the junctional clefts were frequently occupied by foot processes. These findings suggest that cold-adaptation is achieved by cardiac enlargement, high volume density of myofibrils and well-developed peripheral couplings in the SR in the heart of stenothermal burbot.     

Characteristics of sperm of polyploid Prussian carp Carassius gibelio

Wild-captured 16 diploid, five triploid and one tetraploid Prussian carp Carassius gibelio males produced motile haploid, aneuploid (1·5n) and haploid to aneuploid (> 2n) sperm, respectively, in similar concentration and with the lowest percentage of live spermatozoa in sperm for the tetraploid male (mean ± s . d . 83·03 ± 1·76%; P < 0·05) compared to diploid and triploid males (97·37 ± 1·11% and 96·70 ± 1·45%; P > 0·05).     

Effects of temperature on developmental performance, survival and growth of sea lamprey embryos

This study assesses the influence of thermal regime on the development, survival rates and early growth of embryos of sea lamprey Petromyzon marinus incubated at five constant temperatures (7, 11, 15, 19 and 23° C). The time from fertilization to 50% hatching and from hatching to 50% burrowing were inversely related to incubation temperature. All the embryos incubated at 7° C died at very early stages, while those maintained at 11° C did not attain the burrowing stage. Survival from fertilization to hatching was 61, 89, 91 and 89% at 11, 15, 19 and 23° C, decreasing to 58, 70 and 70% from hatching to burrowing at 15, 19 and 23° C, respectively. Larvae reared during the first 3 months of exogenous feeding in a common environment at constant 21° C, revealed maximum survival for an incubation temperature of 15° C (43% of burrowed larvae) decreasing strongly at 19° C (16%) and 23° C (one suvivor among 240 larvae). Body length at the burrowing stage was maximum for embryos incubated at 19° C, but body mass increased in the interval 15–23° C. Mean incubation temperatures experienced by 117 broods during the embryonic development in the source river were estimated in 15·3±2·30° C and 16·7±1·76° C (mean±1 s.d .) for the periods fertilization-to-hatching and hatching-to burrowing, respectively.     

Home range size and dispersion in the helmeted guineafowl (Numida meleagris galeata Pallas) of the Waza National Park, Cameroon

Field investigations of the home range size and emigration pattern of wild helmeted guineafowl ( Numida meleagris galeata Pallas) from 1992 to 1995 showed that home range size (±95% confidence limits (CL) ) varied with season from 3·6±1·5 km² for the dry seasons to 3·1±1·5 km² for the rainy seasons. Home range size varied depending on whether it was estimated with data for adult males, adult females or young birds, with a higher home range size for young birds, closely followed by adult males. Group size (±95%CL) varied by month, and was highest between March and April (47·0±8·1 birds/group) and lowest in August 9·0±5·1 birds/group). More young birds (±95%CL) (36·8±19·6%) dispersed than adult males (21·1±1·9%) or adult females (13·5±1·8%). There was a highly significant positive correlation between group size and the number of birds emigrating from the group. There was also a significant negative correlation between the weights of birds at tagging and the percentage that emigrated during the first year of study but not later. This is suggested to be linked to the high number of young birds emigrating, since they weigh relatively less than adults. The lack of correlation between body weight and number of birds emigrating a year or later after birds were tagged was thought to be due to the fact that birds tagged while young attained adult weight within a year.     

The effects of environmental factors on rainbow smelt Osmerus mordax embryos and larvae

Experiments were conducted to identify environmental factors that influence the survival of rainbow smelt Osmerus mordax during their early life stages. Developing rainbow smelt embryos and yolk-sac larvae were cultured under controlled conditions with different dissolved oxygen (DO; 1·09, 2·18, 4·37 and 6·55 mg l⁻¹, pH (4·0, 4·5, 5·0, 5·5, 6·0 and 7·0), nitrate ( 0·7, 3·6, 7·3, 14·6 and 29·2 mg l⁻¹), phosphate (0·04, 0·21, 0·42, 2·08 and 4·17 mg l⁻¹) and salinity (0, 5, 10, 15, 20 and 30) levels. Rainbow smelt embryos were also incubated with simulated tidal salinity fluctuations (2–28), ultraviolet radiation (irradiances of 2·8, 6·2 and 5·1 W m⁻²) and under natural conditions in two rainbow smelt spawning rivers. In the laboratory, hatch was only impaired under the lowest DO and pH conditions (0 and 13% hatch, respectively) and at highest constant salinity levels (0% hatch). Larval survival was only affected by pH levels ≤5·0. The experiment that compared hatch under natural conditions was terminated when embryos became covered with silt and fungus. These results suggest that water acidification, sediment and fungal growth may affect rainbow smelt survival during their early life stages.     

Control of seed development in Arabidopsis thaliana by atmospheric oxygen

Seed development is known to be inhibited completely when plants are grown in oxygen concentrations below 5·1 kPa, but apart from reports of decreased seed weight little is known about embryogenesis at subambient oxygen concentrations above this critical level. Arabidopsis thaliana (L.) Heynh. plants were grown full term under continuous light in premixed atmospheres with oxygen partial pressures of 2·5, 5·1, 10·1, 16·2 and 21·3 kPa O₂, 0·035 kPa CO₂ and the balance nitrogen. Seeds were harvested for germination tests and microscopy when siliques had yellowed. Seed germination was depressed in O₂ treatments below 16·2 kPa, and seeds from plants grown in 2·5 kPa O₂ did not germinate at all. Fewer than 25% of the seeds from plants grown in 5·1 kPa oxygen germinated and most of the seedlings appeared abnormal. Light and scanning electron microscopic observation of non-germinated seeds showed that these embryos had stopped growing at different developmental stages depending upon the prevailing oxygen level. Embryos stopped growing at the heart-shaped to linear cotyledon stage in 5·1 kPa O₂, at around the curled cotyledon stage in 10·1 kPa O₂, and at the premature stage in 16·2 kPa O₂. Globular and heart-shaped embryos were observed in sectioned seeds from plants grown in 2·5 kPa O₂. Tissue degeneration caused by cell autolysis and changes in cell structure were observed in cotyledons and radicles. Transmission electron microscopy of mature seeds showed that storage substances, such as protein bodies, were reduced in subambient oxygen treatments. The results demonstrate control of embryo development by oxygen in Arabidopsis .     

Autotriploid tench Tinca tinca (L.) larvae obtained by fertilization of eggs previously subjected to postovulatory ageing in vitro and in vivo

Eggs of diploid tench Tinca tinca were half-stripped out and stored for 0 (control batch), 1, 3 and 5 h at mean ± s . d . 17·0 ± 0·4 and 21·9 ± 0·5° C or for 0, 1, 2, 3, 4 and 5 h at 24·0 ± 0·0° C in vitro prior to fertilization. The eggs remaining in vivo in the fish kept at 17·0 ± 0·4 and 21·9 ± 0·5° C were collected and fertilized in the same time intervals. Fertilization rate and larval yield mostly decreased after 3–5 h storage of eggs both in vitro and in vivo and only the diploid larvae were found in all control batches. Triploid larval yields increased to a maximum 5·26% after 5 h in vitro storage at 24·0° C and 1·07 and 1·60% after 3 h in vitro storage at 21·9 and 17·0° C, respectively. Triploid larval yield during in vivo storage at 21·9° C reached a maximum 0·91% after 5 h. As the spontaneous autotriploid larvae arose solely from fertilized eggs previously subjected to postovulatory egg ageing by means of prolongated storage, the autotriploidy was probably caused by failure of extrusion of the second polar body.     

Freshwater adaptation during larval, juvenile and immature periods of starry flounder Platichthys stellatus, stone flounder Kareius bicoloratus and their reciprocal hybrids

The freshwater tolerance of starry flounder Platichthys stellatus , stone flounder Kareius bicoloratus and their reciprocal hybrids, produced by artificial insemination, were examined in the larval, juvenile and immature phases. Survival rate on being transferred to fresh water in the pre-settlement phase was 0% in stone flounder and hybrids and 16·7% in starry flounder. This rate in the post-settlement phase was elevated to >50% in starry flounder and hybrids but was still 0% in stone flounder and similarly in the immature period starry flounder and hybrids survived in fresh water, although stone flounder did not. The lamella chloride cells of the gill epithelium increased in starry flounder and hybrids in fresh water in all periods. Densities of lamella chloride cells increased from 1·6 ± 0·4 (mean ± s . e . number of cells per 1 mm filament) before the transferral (day 0) to 60·3 ± 6·2 on 14 days after the transfer to fresh water (day 14) in starry flounder in the immature period. These densities in hybrids were 0·6 ± 0·3 and 1·0 ± 0·3 on day 0, and, 35·3 ± 2·8 and 23·2 ± 4·6 on day 14, respectively. Stone flounder did not show a substantial change in chloride cell densities throughout the experimental period. These results suggest that low salinity tolerance was well developed in the settlement period in starry flounder and hybrids, and hybrids were also adapted to fresh water sufficiently regardless of the cross type.     

Poikilothermic traits and thermoregulation in the Afrotropical social subterranean Mashona mole-rat (Cryptomys hottentotus darlingi) (Rodentia: Bathyergidae)

When acclaimated for two months at 26 C the social Mashona mole-rat Cryptomys hottentotus darlingi (±S.D.) resting metabolic rate (RMR) of 0·98±0.·14cm²O₂g _-1 h_-1 ( n =21), within a thermal neutral zone (TNZ) of 28 31·5 C ambient temperature (Ta). The body temperature (Tb) of the mole-rat is very low. 33·3±0·5 C, and remained stable between 25 31·5 C ( n =28). Above 33 C. Tb increased to a mean of 34·±0· C (n=28) (Ta range 33 39 C). Below Ta 25 C. Tb showed strong poikilothermic tendencies, with Tb dropping to a mean of 26·8±1·16 C. whereas above Ta25 C. Tb varied in a typically endothermic pattern. The conductance is high 0·19±0·03 cm² O_2g¹ C ¹ (n=28) at the lower limit of thermoneutrality. The mean RMR at 18 C (the lowest Ta tested) was 2·63 ± 0·55 cm³ O₂g ¹ h ¹ (n=7) which is 2·6 times that of the resting metabolic rate in the TNZ.     

Effects of angling on feeding by largemouth bass

Angling practice significantly effected the time required for largemouth bass Micropterus salmoides to begin feeding. Mean ± s.e. time until feeding resumed was longest for fish that experienced a simulated tournament (15·6 ± 2·2 h) followed by fish that were caught and released (8·4 ± 2·2 h) and controls (0·3 ± 1·6 h). Effects on feeding related to angling practices were maintained throughout the 48 h observation period. Using multiple logistic regression and bioenergetics simulations, decreased growth in fish subjected to competitive or catch-and-release angling events was predicted. Fish subjected to multiple captures in a pond experiment had greater mass loss than those not captured, supporting model predictions.     

Bioassay of insulin activity of pancreatic tissue in active and aestivated African lungfish, Protopterus annectens (Owen)

The insulin activity of the pancreatic tissues of free-swimming and aestivated African lungfish, P. annectens (Owen), was bioassayed against standard insulin in rabbits. The hepatic glycogen content and plasma glucose concentration in free-swimming and aestivated lungfish were also estimated. The liver glycogen content was 64·47 ± 6·32 and 7·19 ± 2·68 mgg⁻¹ net wt and the plasma glucose concentration was 37·62 ± 4·22 and 6·39 ± 1·29% in free-swimming and aestivated lungfish, respectively.
Extracts of pancreatic tissue of the lungfish produced a dose-dependent decrease in the plasma glucose concentration in rabbits. The magnitude of the decrease in plasma glucose concentration produced by extracts from aestivated specimens was significantly smaller (about 26%) compared to that produced by pancreatic extracts from free-swimming active lungfish (about 37%). The insulin activity of the pancreatic tissue was 0·82 ± 0·02 and 1·27 ± 0·25 iu mg⁻¹ dry pancreatic tissue weight in aestivated and free-swimming lungfish, respectively.     

Cry (preservation of spermatozoa of the whitefish Coregonus muksun Pallas

The cryopreservation methods for whitefish, Coregonus muksun , spermatozoa were studied using six different extenders with -40°C and -196°C as storing temperatures. In 1980, the spermatozoa of individual fishes were frozen in dry ice, in vials containing three different media based on glycerol as cryoprotectant. The pure glycerol media resulted in a 20% average rate of fertilization when samples were stored at — 40°C. The thawing procedure did not affect fertilization. In 1981, the sperm of individual fishes was frozen in pellets and stored in liquid nitrogen. Cryopreserved semen thawed in 0·119M NaHCO₃ produced 29·6–87·7% eyed eggs. The differences were caused mainly by the type of extender. The highest rate of fertility was obtained using an extender consisting of 0·3 M glucose with 20% glycerol (87·7% eyed eggs; 98·6% eyed eggs when compared to the corresponding control). The same values, using the modified extender of Stoss (Stoss & Refstie, in press), were 38·7–82·4% and, on the average, 90% eyed eggs, respectively.     

Spermatozoa in triploids of the rosy bitterling Rhodeus ocellatus ocellatus

Artificially induced triploid male Rhodeus ocellatus ocellatus showed typical nuptial colorations, irrespective of spermiation. In milt from triploids, abnormal spermatozoa (malformation of the head and mitochondrion, excessive formation of the head, mitochondrion and flagellum, and no flagellum) occurred at 78°4% frequency. Spermatozoa with multiflagella were most common, often with a saccate-like organ. Many triploid spermatozoa moved actively as long as those of diploids (10·92±0·91 min=mean±S.D., P >0·05), but did not advance like diploids, spinning around until movement ceased. The sperm density in triploids was < 2% of that from diploids. In triploid testes, deformed and variously sized spermatids were often observed, and normal spermatids and spermatozoa were seldom recognized. The DNA content of triploid spermatozoa varied greatly, compared with that of diploids. Peak of sperm DNA content differed slightly between two triploid samples with two peaks at 1·5 n and 1·9 n ( P <0·0001 in both), respectively. Triploids had the greatest average sperm head diameter of 2·25±0·67 μm (mean±S.D.), while that of diploids was 1·83±0·15 μm ( P =0·002). In the fertilization test using the eggs of diploids ( n =1500, 30 trials), only one egg developed. The embryo chromosome number was 60 (2·5 n) and the ploidy of spermatozoa contributing to fertilization appears to be 1·5 n. The extremely low fertility of triploid R. o. ocellatus spermatozoa seems to be caused by the reduced motility and large head size of spermatozoa, and the low sperm density of the milt. The ploidy of spermatozoa that are successful in fertilization is likely to be related to the distribution pattern in the DNA content of cells.     

Growth, diet and metabolism of common wolf–fish in the North Sea, a fast–growing population

The von Bertalanffy growth parameters for common wolf–fish Anarhichas lupus in the North Sea were: male: L ∞=111·2 cm, t ₀=–0·43 and K =0·12; and female: L ∞=115·1 cm, t ₀=–0·39 and K =0·11, making this the fastest growing stock reported. Resting metabolic rates (RMR±S.E.) and maximum metabolic rates (MMR±S.E.) for six adult common wolf–fish (mean weight, 1·39 kg) at 5° C were 12·18±1·6 mg O₂ kg^–1 h^–1 and 70·65±7·63 mg O₂ kg^–1 h^–1 respectively, and at 10° C were 25·43±1·31 mg O₂ kg^–1 h^–1 and 113·84±16·26 mg O₂ kg^–1 h^–1. Absolute metabolic scope was 53% greater at 10° C than at 5° C. The diet was dominated by Decapoda (39% overall by relative occurrence), Bivalvia (20%) and Gastropoda (12%). Sea urchins, typically of low energy value, occupied only 7% of the diet. The fast growth probably resulted from summer temperatures approximating to the optimum for food processing and growth, but may have been influenced by diet, and reduced competition following high fishing intensity.     

Hypertension in Pagothenia borchgrevinki caused by X-cell disease

Approximately 15% of a population of the cryopelagic nototheniid fish Pagothenia borchgrevinki , found constantly swimming immediately beneath the annual fast ice, in McMudro Sound, Ross Sea, Antarctica, was affected by X-cell gill disease. This disease affected blood flow through the gill lamellae, and this in turn affected oxygen uptake. Exercise caused increases in heart rate and ventral aortic blood pressure. Heart rate increased from 15·1 ± 1·55 to 23·1 ± 0·93 beats min⁻¹ in healthy fish, with a similar increase (to 24·6 ± 0·26 beats min⁻¹) in X-cell-affected animals. In healthy fish, pressures rose with exercise (from 2·72 ± 0·11 to 3·75 ± 0·19 kPa) and then rapidly returned to resting levels during recovery. In X-cell fish pressures rose during exercise, but then continued to rise, to reach a high of 4·18 ± 0·13 kPa, close to the predicted maximum pressure able to be generated by these hearts. Recovery was rapid in healthy fish, but was prolonged in diseased animals. As they are constantly swimming, there is the potential that X-cell-affected fish suffer from chronic hypertension.