The seasonal cycle of condition in the pollan, Coregonus autumnalis pollan Thompson, of Lough Neagh, Northern Ireland

The length–weight relationship for Lough Neagh pollan was log W= 3·2 log L –2·24. Covariance analysis indicated that there were no differences between the sexes, with maturity, or between years. While a seasonal cycle in relative condition was in phase with gonad development during late summer and autumn, changes in somatic condition presented a more complex pattern. Somatic condition increased in spring, as did the quantity and diversity of food consumed. Despite good conditions for feeding and growth, there was an autumn fall in somatic condition, caused by the diversion of energy to gonad growth.     

The food of the pollan, Coregonus autumnalis pollan Thompson, in Lough Neagh, Northern Ireland

Stomach contents of pollan caught monthly throughout the year were examined. Stomach fullness was significantly correlated with water temperature. Adult pollan fed on bottom fauna, mainly chironomid larvae, in October-March, chironomid pupae in April and on Daphnia spp. in May-September. Immature (0+ and 1 +) fish also ate other cladocerans and copepods. While there is no evidence for selection of any benthic prey species, adult pollan appear to be highly selective feeders on Daphnia spp. in summer.     

The influence of light environment on depth of visual feeding by larvae and fry of Coregonus pollan (Thompson) in Lough Neagh

The depth limits for visual feeding by pollan larvae and fry, Coregonus pollan , were determined in Lough Neagh, Northern Ireland, by combining laboratory estimates of the minimum light threshold for feeding activity with field measurements of spectral, diurnal and seasonal changes in light penetration. Although feeding thresholds were lowest in the blue light (400–490 nm), the rapid attenuation of this region in the lake meant that the depth limits of feeding in situ were determined by response to the green region (490–595 nm). Effects of changes in irradiance and light penetration on the depth of feeding are considered during a seasonal study. Increased sensitivity, as the juvenile stages develop, may be offset by reduced light penetration due to algal growth. Over an annual period the maximum feeding depth for pollan varied between 2.6 and 4.1 m. In the juvenile stages of two other predatory species from the lake, perch, Perca fluviatilis , and pike, Esox lucius , the corresponding ranges were 1.1–1.9 m and 2.7–4.6 m respectively.     

Systematics of the Irish pollan (Coregonus pollan Thompson): an electrophoretic comparison with other Holarctic Coregoninae

Evidence is presented on the genetic relationships of 35 coregonine populations from Alaska, Britain, Ireland, Finland and Sweden. This evidence is derived from an electrophoretic analysis of 27 enzyme loci and additional 'general protein loci'. The Irish pollan C. pollan and the Alaskan C. autumnalis gave identical electrophoretic patterns for all proteins suggesting that they are conspecific and separated only since the last glaciation. C. peled, C. albula and the ' C. lavaretus' complex gave unique patterns for a number of proteins. The F_n C. oxyrhynchus X C albula hybrids, from a lake where no other coregonines occur gave a unique pattern for the enzyme phosphoglucose isomerase but all other enzymes were electrophoretically identical to the C. oxyrhynchus parent and the mean gill raker number was closer to this species than in the F₁ hybrid.     

Seasonal changes in the chemical composition of fish body and nutritional value of the muscle of the pollan (Coregonus pollan Thompson) from Lough Neagh,Northern Ireland

Studies on the chemical composition of adult pollan were carried out monthly from January to December 1977. Sex, weight of scaled fillet, and gonads were examined in 184 fish. Chemical composition which includes water, fat and ash content was analysed in the whole fish, muscle and gonads. This paper attempts to account for the fat and protein flow within fish of both sexes during gonad maturation. Extreme differences between males and females have been recorded in the fat deposition process during summer and spawning period. In spite of our fragmentary knowledge of spawning behaviour in pollan, an explanation is offered for these phenomena. The changes in fat content of female gonads were followed closely throughout the year and the cost of egg production was estimated as a percentage of the amount of fat deposited in the body. Since a similar growth pattern was found for both sexes of pollan, differences in feeding intensity might account for the difference in energy expenditure. Amino acid content was analysed in muscle and gonads and an Essential Amino Acid Index (EAAI) was calculated. There were some changes in EAAI which depended on sex and season. Finally, a new method for evaluation of muscle production expressed as fat and protein is used to determine the most suitable time for fish harvesting.     

The Irish pollan, Coregonus autumnalis: options for its conservation

The ecology of four relict Irish populations of pollan ( Coregonus autumnalis ) is compared with that of the species elsewhere, and used to advocate conservation. The threats to these populations from introduced/invasive species, habitat degradation, climate warming and commercial exploitation are summarized and the legislation governing conservation of the stocks is reviewed. Conservation options (legislation, habitat restoration, stock translocation and stock augmentation) are outlined and their practicality and efficacy considered. A preliminary search indicates that there are a number of lakes that appear to be suitable for pollan translocation.     

Synonymy of shape Proteocephalus pollanicola Gresson, 1952 (Cestoda: Proteocephalidae), a parasite of pollan,shape Coregonus autumnalis pollan,with shape P. exiguus La Rue, 1911

The systematic status of the tapeworm Proteocephalus pollanicola Gresson, 1952, a parasite of pollan Coregonus autumnalis pollan Thompson, was evaluated on the basis of freshly collected material from the type-locality (Lough Neagh, Northern Ireland). Comparison of morphological, biometrical and DNA data (RAPD method) from P. pollanicola and from P. exiguus La Rue, 1911, a very common parasite of coregonid fish, did not find any substantial differences between them to confirm the validity of P. pollanicola. Accordingly, P. pollanicola is considered to be a synonym of P. exiguus, a widely distributed parasite in the Holarctic.     

Myoglobin polymorphism in the pollan (Osteichthyes: Coregoninae).

Three electrophoretically separable phenotypes of heart and lateral line muscle myoglobin were found in the Irish pollan (Coregonus pollan). This polymorphism appears to be under the control of two co-dominant alleles. The allele frequencies were found to be virtually identical in samples from two lakes which have probably been isolated since the close of the last Ice Age. A significant excess of heterozygotes was found in samples from both lakes. This myoglobin polymorphism appears to be balanced, maintained due to heterozygote superiority.     

Myoglobin polymorphism in the pollan (Osteichthyes: Coregoninae)

Three electrophoretically separable phenotypes of heart and lateral line muscle myoglobin were found in the Irish pollan (Coregonus pollan). This polymorphism appears to be under the control of two co-dominant alleles. The allele frequencies were found to be virtually identical in samples from two lakes which have probably been isolated since the close of the last Ice Age. A significant excess of hetero-zygotes was found in samples from both lakes. This myoglobin polymorphism appears to be balanced, maintained due to heterozygote superiority.     

蒸发需求干旱指数(EDDI)在辽宁省干旱识别中的应用

蒸发需求干旱指数(EDDI)是从大气蒸发需求(E₀)角度出发建立起来的一种多尺度的干旱指标,具有不依赖降水量、适用于各种下垫面类型的特点,具备在不同时间尺度捕捉水胁迫信号的能力。本研究基于1961—2018年辽宁省52个气象站气象观测资料,逐日估算E₀,按年、生长季(4—10月)、春季、夏季、秋季、冬季分别计算EDDI,分6个时间尺度识别近58年辽宁省干旱发生的年际变化特征。结果表明: 研究期间,辽宁省EDDI年际变化阶段性明显,多个时间尺度的EDDI呈两个高值集中期。在20世纪60年代,年、生长季、春季、秋季和冬季5个时间尺度的辽宁省平均EDDI高值区相对集中,这一阶段辽宁省发生干旱的年数多、程度重;除冬季外,2014—2018年是其他5个时间尺度的EDDI高值另一个相对集中的时段;1981—1982年,辽宁省的年、生长季、夏季、秋季的EDDI值偏高。1963—1965年(除夏季外)、1972—1973年(生长季、夏季)、1989—1990年(年、生长季、春季、冬季)、1997—1998年(年、生长季、夏季)、2004—2005年(春季、冬季)和2013—2014年(年、生长季、秋季)都发生了干-湿或湿-干逆转事件。1985—1987、1993—1995和2005—2013年,辽宁省存在明显的干旱空窗期。     

Studies on the Feeding of Coregonus pollan (Thompson) Alevins and Fry in Lough Neagh

Pollan alevins and fry were collected in the open lake between March and July. Fish were measured in total length, upper (U_j) and lower (L_j) jaws and weighed. The gape-height was calculated according to two different formulae. For the examined fish the relationship between total length (L_t) and gape-height (D) was found to be D=0.092 L_t—0.306. The size of food in the gut content was measured, and this increased during fish growth, but amounted to 13.2–26.0 % of D. In the first food of pollan alevins, nauplii and copepodites dominated, but after the alevins had reached 20 mg, copepods appeared to be more frequent food items. In the middle of May, Daphnia longispina was found in the food of pollan fry with an individual weight over 45 mg. Benthic invertebrate fauna were taken after the fish weighed more than 1.4 g. Chironomus anthracinus and Chironomus sp. larvae were among the food item dominants.     

The Spawning and Early Life History of the Pollan (Coregonus pollan THOMPSON) in Lough Neagh,Northern Ireland

Studies had been carried out on the local non-migratory whitefish. Spawning behaviour and light conditions on the spawning ground are recorded. After artificial spawning, embryonal development took place under controlled conditions and the larvae were reared. Detailed characteristics of swim bladder creation and differentiation of the digestive tract are given. Distribution and number of pollan larvae near the spawning area and in the open lake were examined. Data are presented concerning the growth rates of larvae and fry in captivity and under lake conditions. Ecological data related to other coregonids are discussed and compared with the present study.     

The autecology of the chub, Squalius cephalus (L.), of the River Lugg and the Afon Llynfi

(1) Analysis of data from samples of chub taken at monthly intervals from two tributaries of the Herefordshire Wye revealed an annual cycle of scale growth with the formation ofa check during May or June. The frequency distributions of ages deter-mined from scale checks and the length-frequency distributions showed close simi-larities. It was concluded that age determinations based on an examination of the scales were valid, provided care was taken in the identification ofthe first scale cheek. The maximum age observed was 15 years. (2) Examination ofthe population structure revealed an overall sex ratio close to unity but there was a significant increase in the proportion of females in the 11 + and older age groups. Dominant year-classes were observed. The strongest was 1959, which was attributed to exceptionally warm, dry, sunny weather during the period May-September. (3) Female chub grew more rapidly and attained greater ultimate size than the males. Changes in the pattern of growth during the life-span were attributed to the attainment of sexual maturity, especially in the females. The length-weight relation-ships of the sexes diflFered slightly but were almost identical for the same sex in the two rivers studied. Seasonal variations in the growth-rate were followed. Most rapid growth occurred after check formation in May or June and continued until September.     

Relationship between scale growth checks, circuli formation rate and somatic growth in Rutilus rutilus (L.) a fish farm-reared cyprinid

Check formation on scales of roach Rutilus rutilus was examined during their production cycle at a fish farm in England through analysis of circuli patterns. Regular check formation was associated with the movement of fish from one type of grow-out facility to another; this resulted in a sudden shift in growth rate and the formation of a new check. As these had the characteristics of annual marks, their formation potentially invalidates their use as structures to determine the age of individuals during recapture events that may follow their introduction to the wild. At low growth rates, the number of circuli was constant throughout the year; this situation changed when fast growth rates were achieved. Five methods of backcalculation were also validated. When the proportionality between the body length and scale radii was weak, backcalculation methods were poor in determining length at check formation.     

The growth ofOreochromis andersonii (Pisces: Cichlidae) from the Okavango Delta,Botswana, and a comparison of the scale and otolith methods of ageing

Synopsis Otoliths and scales were used for age and growth determination ofOreochromis andersonii from the Okavango Delta, Botswana. Marginal increment analysis showed that an annulus was formed in both the scales and otoliths during the dry summer period. Using scales, the growth ofO. andersonii was described by L_t = 285.27(1-e^{-0.26(t+2.02)}) mm SL and using otoliths by the equation L_t = 267.48(1-e^{-0.25(t+2.18)}) mm SL. Maximum age estimates of 10 years using scales and 13 years using otoliths were obtained and the growth curves were significantly different (p < 0.01). Age estimation using scales tended to over-emphasise growth inO. andersonii resulting in larger predicted lengths-at-age. For this reason, otoliths are considered to be more reliable and suitable than scales in determining the age and growth of this species.     

Age,growth and reproductive biology ofNotothenia squamifrons gunther, 1880 from the Indian sector of the Southern Ocean

Summary The growth ofNotothenia squamifrons is analysed using scale reading of specimens from various isolated areas of the Indian sector of the Southern Ocean (Kerguelen, Crozet and Marion Islands; Ob, Lena and Kara-Dag seamounts). Studying reproductive biology reveals that spawning is annual and occurs during austral spring. Hatching takes place in summer. Scaling is set during the autumn. The smallest scaled fish measure 3.8 cm in total length. The data mentioned above, the check number on the scales and the sampling dates lead to the identification of the different age groups. Differences in growth rate appear between the studied areas. The fastest growth is observed around the Kerguelen Islands where the oldest specimens are 19 years old and reach 52 cm in total length. On the other hand, in the Crozet population,N. squamifrons does not live more than 12 years for a maximum length of 30 cm. Scale reading in fish from the Ob and Lena seamounts shows a minor decrease in growth during the winter season when compared to that in the other areas. The hydrographical conditions of this sector of the Southern Ocean may, in part, explain these differences: especially temperature and plankton biomass seem to effect growth rate. The cold antarctic waters and the highest plankton productivity, inducing the optimal growth rate, are found in the Kerguelen Islands.     

Growth, mortality, age composition and fisheries yields of fish from the Gulf of Aden

Tropical fish were collected by trawling in Yemeni waters. Age determinations were made on sections of vertebrae which were cross checked with scales. The values for the von Bertalanffy growth constants K were in the range 0.08–0.31. Total mortalities ( Z ) calculated from age compositions were in the range 0.31 to 0.67 for 11 species. The mean of 0.46 agreed closely with that derived from the formula of Pauly (1980 a ) of 0.45. Since the former included fishing mortality ( F ) in addition to natural mortality ( M ) it was suggested that a lower value be used in the Gulland (1968) yield formula: Y = 0.5 M Bo . Recruitment to the fishery for most species occurred by 3 years of age. The demersal fish stocks in Yemeni waters may not exceed 109×10³ tonnes at the present time. Using a value for M of 0.3, the annual sustainable yield may be in the region of 16×10³ tonnes.     

Age,growth and reproduction in creole perch (Percichthys trucha) in the Negro River,Argentinean Patagonia

Age, growth and reproductive characteristics of creole perch, Percichthys trucha, were investigated in the Negro River, southern Argentina from samples collected seasonally, December 1994–December 1995. Age was estimated via scale and whole otolith reading methods. Total length (n = 413) ranged from 103 to 432 mm, and weight from 12 to 1042 g. Significant differences between the length‐weight relationships of males and females were detected (P < 0.05). Isometric growth was observed in juveniles and males, whereas total population and females exhibited positive allometric growth. The marking pattern in scales and otoliths followed an annual rhythm, with the formation of only one annulus in scales and only one hyaline band in otoliths during autumn‐winter. The oldest males were 5 years old whereas maximum age in females was 12 years from scales and 15 years from otoliths. Because scales were found to underestimate age in individuals older than 4 years, otoliths were considered to be the best structures for creole perch age determination. Gompertz growth parameters based on otolith data were L∞: 428.0 mm, k = 0.46 and t₀ = 0.43 for total population (r = 0.90), L∞: 410.7 mm, k = 0.42 and t₀ = 0.46 for males (r = 0.91), and L∞: 434.1 mm, and k = 0.49 and t₀ = 0.43 for females (r = 0.91). Lengths at first maturity (TL₅₀) were 260 and 241 mm in males and females, respectively, both of which corresponded to ages between 1 and 2 years. Macroscopic gonad inspection and the high percentage of juveniles captured during summer indicated that spawning begins at the end of spring.     

The potential use of scales for estimating age and growth of Mediterranean albacore (Thunnus alalunga)

The ability to accurately estimate the age of fishes is critical for conducting stock assessments and developing fishery management policies. Scales were collected from albacore, Thunnus alalunga, caught in the Mediterranean Sea during the years 1989–1995 to estimate their age and growth. Ages, which ranged from 1+ to 6+ years, were estimated from the interpretation of the concentric rings on the scales of 473 individuals that ranged in fork length from 55.5 to 89 cm. Males reached a greater size and age than females. The relatively close agreement in the mean lengths at ages estimated by scales and other techniques constituted a preliminary verification of the method. The von Bertalanffy growth model was fitted to mean lengths at estimated ages, resulting in the following growth parameters for the combined sexes: L_∞ = 86 cm, K = 0.4, t_o = ?0.8 years. Parameter estimates were in agreement with what is known about life history of the species in the Mediterranean. Moreover, the growth rates were consistent with length increment observations from five tag returns, which lend support to our working hypothesis that the scale‐rings are annual structures. When the Mediterranean albacore growth parameters were compared with those of Atlantic Ocean albacore using scale age estimates, there were significant differences between the two populations, and Mediterranean albacore remain significantly smaller than Atlantic Ocean albacore.     

Dormancy of alpine and subalpine perennial forbs

Depth of dormancy of alpine and subalpine perennial forbs in autumn was investigated, which was judged by the number of days required for growth initiation at 24 °C. The depth of dormancy differed depending on Raunkiaer’s life-form and shoot habits. Chamaephytes with perennial shoot-axes showed shallower dormancy than hemicryptophytes with annual shoot-axes, and geophytes with annual shoot-axes showed the deepest dormancy. The results strongly suggest that the dormancy is more endogenously controlled in forbs less hardy to freezing stress. Potential growth ability of alpine herbaceous chamaephytes in autumn is an adaptive advantage, since they utilize the short vegetative period as long as possible. All of the species with annual shoot-axes had winter buds covered with scales. In plants with perennial shoot-axes, percentage of winter buds covered with scales increased with increasing depth of dormancy. The results indicate that the shoot apices are well protected by bud scales in forbs with a long endogeneous-dormant period.