Size-dependent over-winter mortality of young-of-the-year roach, Rutilus rutilus

Over-winter survival of starved and fed young-of-the-year roach from two lakes in central Finland was examined in the laboratory between November 1992 and May 1993. The mortality rate of starving YOY roach (total length 38 ± 2 mm) from small (ca. 0.5 km²), eutrophic Lake Isojärvi was 50%, whilst roach (total length 32 ± 3 mm) from large Lake Päijänne (1106 km²) suffered 42% mortality. Mortality was size-dependent among roach from Lake Isojärvi, smaller individuals being more vulnerable. There was not strict size limit for survival as proposed previously. However, it seems that within populations approximately the same proportion of smallest roach died independent of the absolute lengths of the fish. Mortality of fed roach from both lakes was always < 5%. This good survival indicates indirectly the importance of energy reserves in wintering. Lipid and protein content of fasting roach from lake Isojärvi decreased during the winter. In the group of fasting roach from Lake Päijänne the amount of lipids stored increased between November and March and decreased thereafter. No change in protein content of fasting fish from Lake Päijänne was observed.     

Histochemical characterization of myotomal muscle in the roach, Rutilus rutilus (L.)

A histochemical study of the myotomal muscles in the roach revealed three main muscle regions: red, intermediate and white. These were distinguished on the basis of glycogen content, succinate dehydrogenase (SDH), and myofibrillar ATPase (mATPase) activity. Except for the red fibre region, none of these described regions is homogeneous. The principal new findings are the toniclike fibre, the presence of a transitional zone with two fibre types, and the mosaic organization of the white fibre region. The significance of this type of myotome architecture in relation to the locomotion of the species is discussed.     

Occurrence of an intersex condition in the roach Rutilus rutilus (L)

The roach, Rutilus rutilus , is normally a dioecius species. During an experimental study of reproduction in this species, a condition of apparently functional intersex was discovered. Anatomically the gonad was a testis, exhibiting various normal stages of spermatogenesis. A group of oocytes was found during the microscopical examination of the gonad, interspersed between lobules of normal testicular tissue. A few small oocytes were found to be in the chromatin-nucleolus stage, while the rest were in the perinucleolus stage. In addition, some large oocytes with an average diameter of 40 μm were randomly distributed among the lobules of the testis.     

Feeding migration of roach, Rutilus rutilus (L.), in Lake Arungen, Norway

In the period April–July 1980 we studied the feeding migration and food of roach in a small tributary of the eutrophic Lake Årungen, south-eastern Norway. Tagging experiments revealed a tendency in roach to utilize a specific tributary both for feeding and for spawning. The mean size of roach ascending the tributary in late June and July was significantly larger than the mean size of roach spawning 1–2 months earlier, probably due to higher water discharge in July than in May and June. The experiment indicates two separately motivated migrations involving homing. The roach fed more profitably in the tributary than in the lake, both in terms of food availability and predator avoidance.     

The morphology and histology of the pineal organ in roach, Rutilus rutilus (L.)

The pineal organ in the roach, Rutilus rutilus (L.), is covered by a semi-transparent area, the pineal window. Beneath this the pineal is attached to a long robust stalk, lying just under the parietal bone. The pineal is attached to the brain through the dorsal sac. Three cell types have been identified histologically. These are the sensory cells, supporting cells and the ganglia cells. The inner segment of the sensory cells respond to PAS and AF staining, while the remaining cells respond to Orange G, LG, or Acid Fuchsin. The evidence suggests that the roach pineal may have a dual photosensory and glandular function.     

Homing precision of roach Rutilus rutilus in Lake Arungen,Norway

Synopsis The present study tests the precision of repeat homing of roach, Rutilus rutilus, to two tributaries of a small Norwegian Lake, Årungen. A sample of 19 959 spawners was tagged or marked in the spawning area. After spawning the roach intermingled with other spawning demes in the lake. The year after marking, 2515 (12.6%) roach were recaptured during spawning in the five tributaries, 340 (13.5) of these were strayers. This straying is considerably larger than found in comparable autumn spawning species, but approximately the same as reported for other spring spawning species. The recapture rate was lower for females than for males, probably due to increased female mortality induced by the tagging manipulation.     

Sperm quality, secondary sexual characters and parasitism in roach (Rutilus rutilus L.)

According to sperm competition models, a male spawning in a disfavoured role should have spermatozoa with higher velocity but shorter longevity compared with a male spawning in a favoured role. Moreover, immunosuppressive androgens are needed to produce both secondary sexual characters and sperm cells. The 'sperm protection' hypothesis suggests that the immunosuppressive action of androgens has evolved to protect haploid spermatozoa, which are antigenic, from autoimmune attacks. Therefore, a male with high sexual ornamentation may be more susceptible to diseases but may possess better quality ejaculate than his less ornamented rival. We studied sexual ornamentation (breeding tubercles), ejaculation quality (sperm concentration, longevity and spermatozoal velocity) and intensity of parasitism in the cyprinid, Rutilus rutilus . Sperm longevity and spermatozoal velocity were positively correlated. Males having elaborated sexual ornamentation had longer-lived sperm and more Myxobolus mülleri parasites in the liver compared with males with low ornamentation. However, no difference was found between males with different degrees of ornamentation with respect to sperm concentration, spermatozoal velocity or other parasites. Since the highly ornamented males had higher sperm longevity, the present results are partly consistent with the predictions of the sperm competition models and the 'sperm protection' hypothesis.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 111–117.     

The induced spawning of roach, Rutilus rutilus (L.), with the antioestrogens clomiphene and tamoxifen

The induced spawning of gravid roach was investigated using the antioestrogens clomiphene and tamoxifen. Three dose levels ofeach were used: 0·1, l or 10 mgkg^-1, given twice with a 4-day interval to groups of eight fish with saline controls. Running males were randomly distributed. Tamoxifen, when injected at a rate of l mg kg^-1 was found to be most successful. This treatment induced ovulation in five of the six females, and profuse spawning on 3 consecutive days, 4 days after the first injection. Clomiphene induced ovulation and spawning in one of six females at 2 × 10 mg kg^-1, and two of eight females at 2 × l mg kg^-1, respectively 6 and 7 days after the first injection. The eggs produced showed normal devel-opment. No control fish ovulated or spawned. Both drugs probably act by indirect mechanisms, blocking sex steroid feedback inhibition of gonadotropin (GtH) secretion at the pituitary, thereby inducing a plasma GtH surge. The results of this experiment suggest that tamoxifen may be an effective substitute for pituitary preparations in the induced spawning of fish.     

Hypoxia increases intensity of epidermal papillomatosis in roach Rutilus rutilus

Hypoxia, which occurs frequently in aquatic ecosystems and is mainly due to increasing eutrophication can cause severe environmental stress in fish. We investigated experimentally the hypothesis that hypoxia could be one of the environmental stress factors that can induce papillomatosis in fish. Male roach Rutilus rutilus exposed to periodic oxygen deficiency and accompanied temperature increases (OT group) showed the highest increase in the intensity of papillomatosis, as measured by the number of scales covered by papillomatosis tumors. The second highest increase in disease intensity was among male roach exposed to periodical temperature increases. The incidence of such tumors was lowest in the control group, which was exposed to neither hypoxia nor increased temperature. The mortality of fish during the 17 d experiment was highest and the condition factor was lowest in the OT group, indicating this group experienced a higher level of stress. The apparent interaction of hypoxia and temperature suggests that these environmental stressors are among the multifactorial elements leading to papillomatosis in roach. Furthermore, these results provide experimental evidence to indicate that hypoxia may contribute to tumor development in fish.     

Consumption, growth and respiration of bleak, Alburnus alburnus (L.), and roach, Rutilus rutilus (L.), during early ontogeny

Three components of the energy budget, consumption ( C ), production ( P ) and respiration ( R ) in juvenile roach and bleak kept under controlled food ( Anemia salina , 2400 ind. l⁻¹) and temperature (20° C) conditions were measured in a study aimed at defining differences between the two species and elucidating the patterns of energy partitioning during ontogeny.
Daily food consumption rates (J day⁻¹ fish⁻¹) increased allometrically ( C =a W ^b) with body size ( W , mg dry weight) in both species. Covariance analysis indicated no differences in slope or intercept for the two regression lines ( P ≤ 0.05, n = 82). However, the two species grew at significantly different rates, roach faster than bleak.
The dependence of the respiration rate (μmol h⁻¹ fish ⁻¹) on body weight ( W ) can be described by an allometric function: R = a W ^b, where a ± 95% C.L. = 0.17 ± 0.15 for roach and 0.18 ± 0.20 for bleak. The slope for roach (b ± 95% C.L. = 0.78 ± 0.01) is slightly higher than that for bleak (0.69 ± 0.03).
Assimilation efficiency [AE = ( P + R ) C ⁻¹] was significantly higher in roach than in bleak. Different levels of AE correlated with differences in relative gut length (gut length as percentage of body length). Due to the shorter relative gut length above a weight of 5 mg, bleak has lower powers of digestion, which may explain lower production rates. These differences in energetic performance between the two species indicate mechanisms leading to niche differentiation in the early life history of the fishes.     

Wild intersex roach (Rutilus rutilus) have reduced fertility

Endocrine-disrupting chemicals, known to be present in the environment, have great potential for interfering with reproductive health in wildlife and humans. There is, however, little direct evidence that endocrine disruption has adversely affected fertility in any organism. In freshwater and estuarine fish species, for example, although a widespread incidence of intersex has been reported, it is not yet known if intersexuality influences reproductive success. The purpose of this study was, therefore, to determine gamete quality in wild intersex roach (Rutilus rutilus) by assessing sperm characteristics, fertilization success, and ability to produce viable offspring. The results clearly demonstrate that gamete production is reduced in intersex roach. A significantly lower proportion of moderately or severely feminized fish (17.4% and 33.3%, respectively) were able to release milt compared with normal male fish from contaminated rivers (in which 97.6% of the males were able to release milt), reference male fish (97.7%), or less severely feminized intersex fish (experiment 1: 85.8%, experiment 2: 97%). Intersex fish that did produce milt produced up to 50% less (in terms of volume per gram of testis weight) than did histologically normal male fish. Moreover, sperm motility (percentage of motile sperm and curvilinear velocity) and the ability of sperm to successfully fertilize eggs and produce viable offspring were all reduced in intersex fish compared with normal male fish. Male gamete quality (assessed using sperm motility, sperm density, and fertilization success) was negatively correlated with the degree of feminization in intersex fish (r = -0.603; P < 0.001) and was markedly reduced in severely feminized intersex fish by as much as 50% in terms of motility and 75% in terms of fertilization success when compared with either less severely feminized intersex fish or unaffected male fish. This is the first evidence documenting a relationship between the morphological effects (e.g., intersex) of endocrine disruption and the reproductive capabilities of any wild vertebrate. The results suggest that mixtures of endocrine-disrupting substances discharged into the aquatic environment could pose a threat to male reproductive health.     

Use of body-water content to assess the physiological state of roach Rutilus rutilus L. in natural conditions

It is shown that in natural conditions roach have two levels of water content in their organisms during their annual cycle which reflect different physiological states of the fish. During the feeding period, the body-water content is maintained at a low level of 72.6 ± 0.05%, determining the physiological state related to the growth of fishes. In winter, spring, and postspawning periods, the water content in the roach organism is high, 75 ± 0.06%, which reflects the physiological state of survival during periods of the year unfavorable for growth. The water content in the organism of fish is a convenient integrated parameter for assessing the general physiological state of fish in natural conditions.     

Histological differences in the lateral musculature of O-group roach, Rutilus rutilus (L.) from different habitats

The composition of the lateral muscles of first-year roach was studied using histological techniques. It was found that all samples had significantly higher levels of red muscles in the hindermost regions, and these levels rose as the fish became larger. Fish from a running water habitat contained significantly more red muscle than fish of the same age from still water, and it is suggested that this results from muscle development during natural'training'to water flow.     

Ontogenetic changes in haemoglobins in roach, Rutilus rutilus (L.) and rudd, Scardinius erythrophthalmus (L.)

The haemoglobins and globins of the roach, Rutilus rutilus (L.) and the rudd, Scardinius erythrophthalmus (L.) have been studied by starch gel electrophoresis. At all stages of development studied, the roach and rudd haemoglobins give a similar electrophoretic pattern, the young fish of about 2 cm standard length possessing three separate haemoglobins, of which two bands only persist in the adult. The evolutionary significance of multiple haemoglobins in fishes is briefly discussed.     

Epizootic cutaneous papillomatosis, cortisol and male ornamentation during and after breeding in the roach Rutilus rutilus

The prevalence of epidermal papillomatosis in roach is known to peak during the spawning period and to be higher in males than in females. The high occurrence of papillomatosis in polluted waters suggests that stress may contribute to the outbreak of the disease. However, little is known about breeding-induced stress in fish and its relationship with diseases. In this study, plasma cortisol concentration, hematocrit and the relative size of the spleen were determined in healthy and diseased male and female roach Rutilus rutilus during and shortly after spawning in a wild population. In addition, the sexual ornamentation (breeding tubercles on the lateral sides and on the frontal) of male roach during spawning was examined. Plasma cortisol concentration was higher during than after the spawning period, and higher in males than in females during spawning, indicating a spawning-induced stress and higher spawning stress among males. There was no correlation between cortisol concentration and the intensity of papillomatosis (number of scales under papilloma tumors) among the diseased fish. However, the significant interaction sex x disease status revealed by ANCOVA suggested that diseased males could be more prone to increased cortisol levels than diseased females or healthy males. Hematocrit values (ratio of the volume of red blood cells to total volume of blood) but not condition factor were lowered in papilloma-diseased fish after spawning. The relative size of the spleen was greater in males than in females. The number of frontal breeding tubercles correlated negatively with the intensity of papillomatosis. Experimental studies are needed to investigate the association of papillomatosis with stress and cortisol.     

The decline of a roach Rutilus rutilus (L.) population in Chew Valley Lake

A series of nettings for roach in Chew Valley Lake carried out by members of the Zoology Department, Bristol University, has revealed a marked decline in the population between 1965 and 1968. Fish from the main Lake were found to be heavily parasitized with Ligula intestinalis (L.) while those from the inflow pool (Herriott's Pool) were practically free from infection. It is considered that the decline of the roach can be linked to the incidence of Ligula , but that clean fish from the inflow pool may provide breeding stock and maintain the production of fry, which serve as food for the trout.