Chironomus Anthracinus Research Articles

İran’ın Açıklamalı Chironomidae (Diptera: Culicomorpha: Chironomoidea) Kontrol Listesine Yönelik Bir Ön Çalışma

This checklist deals with summarizing all the data on Iranian Chironomidae (Diptera). In total, 34 species from 5 subfamilies are listed as the fauna of Iran: Buchonomyiinae (single species), Chironominae (18 species from 24 genera with some unknown species), Diamesinae (unknown species within 4 genera), Orthocladiinae (8 species from 24 genera with some unknown species) and Tanypodinae (7 species from 10 genera with some unknown species). Three species, Chironomus anthracinus Zetterstedt, 1860, Cladotanytarsus (Cladotanytarsus) mancus (Walker, 1856) and Tanypus punctipennis Meigen, 1818 are new records for the fauna of Iran.

Stable isotope analysis provides fresh insights into dietary separation between Chironomus anthracinus and C. plumosus

We used stable isotope analysis to investigate dietary differences between 2 sympatric species of tubicolous chironomid larvae, Chironomus plumosus and C. anthracinus, from the profundal sediments of 6 eutrophic lakes in the UK and Germany. We found striking variation between lakes in both δ13C (−29.8 to −56.3‰) and δ15N (−7.8 to 14.7‰) in the 2 chironomid species. Moreover, C. plumosus was consistently depleted in both 13C and 15N relative to C. anthracinus. Our data support previous reports of interspecific dietary variations between the 2 species, which suggest niche separation partly on the basis of diet. However, reported differences in the feeding modes of the 2 species could not explain the extreme 13C- and 15N-depletion observed in chironomid larvae from several of the lakes. We suggest that the low δ13C signatures result from the ingestion of methanotrophic bacteria and subsequent incorporation of biogenic methane-derived C. Further, the chironomid larvae enhance methanotrophic activity via bioturbation of the surrounding sediment. Significant isotope differences between the 2 species may result from their variable tube morphologies or physiology.

Seasonal changes in the stable isotope values of lake‐dwelling chironomid larvae in relation to feeding and life cycle variability

Summary1. We studied seasonal changes in the carbon and nitrogen stable isotope ratios of larval Chironomus anthracinus and C. plumosus from the profundal sediments of four contrasting lakes.2. Pronounced seasonal changes in both δ13C and δ15N values were evident in chironomid larvae of both species from two summer‐stratified, eutrophic lakes: Esthwaite Water and Wyresdale Park. Changes were most marked in the larvae of C. plumosus and in larvae from greater depths. In contrast, neither C. anthracinus in summer‐stratified but mesotrophic Schöhsee, nor C. plumosus in polymictic Großer Binnensee, showed marked seasonality in larval stable isotope ratios.3. The particularly strong 13C‐depletion of larvae from the stratified, eutrophic lakes is attributed to a significant contribution of methane‐derived carbon to their diets. Feeding by larvae on isotopically light methanotrophic bacteria appears to occur mainly when autumn overturn of the water column restores oxygenated conditions to the sediment surface. At this time both δ13C and δ15N values of larvae decreased sharply.4. Changes in the mean stable isotope ratio of the larval populations can also occur when larger, more isotopically light, larvae pupate and emigrate from the population to hatch as imagos. This effect can induce seasonal changes in larval isotope values even in lakes in which there is no evidence of a significant involvement of methane‐derived carbon in their diets. Variations in emergence patterns between species and between lakes may generate differences in the seasonal pattern of change in stable isotope ratios in larval populations.5. Our results emphasise the importance of adequate seasonal sampling if stable isotope ratios are to be used as biomarkers to study the role of key groups, such as chironomid larvae, in the trophic structure of lakes.

High intraspecific variability in carbon and nitrogen stable isotope ratios of lake chironomid larvae

Stable isotope analyses of chironomid trophic interactions have recently indicated the potential importance of isotopically light biogenic methane as a carbon source. Mass balance of isotope ratios suggests that small proportional differences in ingestion of such an isotopically distinct basal resource by individual consumers can result in considerable intraspecific variability. To test this, we collected individual larvae of two closely related chironomid species (Chironomus anthracinus and Chironomus plumosus) from six lakes and analyzed their δ13C and δ15N. Intraspecific variability in larval δ13C and δ15N values was greater in lakes where chironomids were more 13C depleted. C. plumosus exhibited higher intraspecific variability relative to C. anthracinus. In two lakes, individual C. plumosus exhibited a range of 35‰ for δ13C and 16‰ for δ15N (equivalent to five trophic levels). There was a strong positive relationship between larval δ13C and δ15N, both between individuals from the same lake and also between lakes, suggesting that the underlying causative mechanisms are similar. Furthermore, larvae from deeper sites, which are more susceptible to prolonged anoxia, exhibited greater intraspecific variability, and larger larvae were significantly 13C depleted. Such high intraspecific variability can confound the interpretation of benthic food web stable isotope values. We advocate the reporting of more intraspecific isotopic variability as a means to further examine niche breadth and feeding behavior.

Diversity and structure of Chironomidae (Diptera) communities along a gradient of heavy metal contamination in a subarctic watercourse

Community structure of chironomid larvae was investigated along a gradient of heavy metal pollution in the subarctic lakes of the Pasvik watercourse, bordering Northern Norway and Russia. Sixty taxa were present in the four investigated lakes. Species richness was lower in Lake Kuetsjarvi, nearest the main source of pollution, relative to the more distant lakes, and Simpson's diversity index was similarly highest in the less polluted site with higher maximum depth. The number of orthoclad chironomid species was considerably higher at the least contaminated sites, whereas the relative abundance of Orthocladiinae was highest at the most polluted site. Chironomid density increased with increasing distance from the main source of heavy metal pollution, especially in the subfamilies Tanypodinae and Chironominae, and total chironomid biomass was significantly higher at the least polluted site. Canonical correspondence analysis revealed spatial patterns consistent with species-specific tolerance to the heavy metal concentrations. Protanypus morio, Monodiamesa bathyphila, Chironomus spp., Polypedilum scalaenum gr. and Sergentia coracina seemed to be tolerant to heavy metal contamination, occurring most commonly at the most polluted sites. In contrast, Heterotrissocladius subpilosus, Psectrocladius semicirculatus/sp. , Chironomus anthracinus, Pagastiella orophila, Cladotanytarsus iucundus, and Tanytarsus spp. appeared to be more sensitive taxa, being common at the least polluted sites, but rare or absent at the two sites close to the pollution sources. Densities of Procladius ( Holotanypus) spp., Tanytarsus spp. and Chironomus anthracinus were negatively correlated with heavy metal concentrations and these taxa appeared to be the best indicators of heavy metal contamination.

Silica and diatom growth in Lough Neagh: the importance of internal recycling

1. Lough Neagh is a large eutrophic lake with a high dissolved silica (SiO2) concentration arising from the basaltic rock in parts of the catchment and the normal winter maximum concentration is over 8 mg L−1. Based on frequent observations between 1974 and 1997, the annual cycles of SiO2 input, uptake and release are explored. 2. Large spring blooms of the planktonic diatoms Aulacoseira subarctica Haworth and Stephanodiscus astraea occur every year and are terminated by SiO2 depletion. Although there are periods when one diatom species has dominated the other, over the period as a whole, the two diatoms appear to be in a stable coexistence. 3. A model of the effect of river inputs on lake concentration shows that without SiO2 release from the sediment, the maximum spring dissolved SiO2 concentration (and hence diatom crop) would be only about one‐third of that actually observed. 4. It is concluded that within‐lake processes play a large role and are potentially more variable than catchment processes in determining the available SiO2 in Lough Neagh. 5. The role of benthic animals, especially Chironomus anthracinus, in the sediment SiO2 release process is discussed. Field data suggest the SiO2 release rate is highly sensitive to temperature, but this could be partly caused by an interaction between temperature and animal activity.

Survival and energy metabolism in an oxygen deficient environment. Field and laboratory studies on the bottom fauna from the profundal zone of Lake Esrom, Denmark

The three macroinvertebrate taxa, Potamothrix hammoniensis, Chironomus anthracinus and Pisidium spp. are permanent inhabitants of the regularly microxic/anoxic profundal zone in Lake Esrom. In situ and laboratory studies (10 °C) of metabolism (aerobic and anaerobic) and anaerobic survival in P. hammoniensis and Pisidium spp. are compared with previous results from C. anthracinus. The late summer microxic conditions in the lake lasts 2–2\( - \frac{1}{2}\) months, during which the three taxa display metabolic and behavioral strategies in order to survive. All three are respiratory oxy-regulators with critical oxygen levels at 1 mg O2 l−1 (P. hammoniensis and Pisidium spp.) or 2–3 mg O2 l−1 (C. anthracinus). The lethal time (LD50) in experimental anoxia follows a similar trend, with 150–170 days of survival in P. hammoniensis and Pisidium spp., compared to 2–5 weeks in C. anthracinus. The glycogen stores are almost (C. anthracinus) or fully exploited (P. hammoniensis and Pisidium spp.) during anaerobis and the animals finally enter a state of quiescence or dormancy. During the late phase of anoxia, their metabolism is down at (C. anthracinus) or below (P. hammoniensis and Pisidium spp.) 1% of normoxic metabolism. The populations in the lake behave rather similar in so far that the energy gain from anaerobic degradation of glycogen maximizes 1% of normoxic conditions regardless of species. Also, in Pisidium this appears to be the only energy source during dormancy. However, as previously presented in case of C. anthracinus, P. hammoniensis maintain a partly aerobic metabolism constituting 44% of normoxia during the microxic period, compared to the 12–19% obtained by C. anthracinus. It is thus demonstrated that P. hammoniensis and Pisidium spp. possess a remarkable ability to survive in situ severe oxygen depletion. P. hammoniensis can benefit from the presence of merely traces of oxygen, whereas C. anthracinus with poorer anaerobic survival is strongly dependent on minute oxygen supplies.

Importance of diffuse nutrient loading and lake level changes to the eutrophication of an originally oligotrophic boreal lake: a palaeolimnological diatom and chironomid analysis

The recent environmental history of Lake Lappajarvi in western Finland (63°00' N, 23°30' E, area 149 km 2 ), a humic, brown water lake with an average phosphorus content of ca. 20 µg l ‐1 , was studied from short core sediment samples taken from the two main basins of the lake. Based on the stratigraphy of diatoms and chironomids and the sediment quality it was possible to distinguish four developmental stages during the past century: (1) a pre-industrial stage covering the time up to about 1935; (2) a stage of increasing nutrient loading (ca. 1936‐1960); (3) a stage of pronounced erosion from lake level regulation and extensive ditching of the catchment area (ca. 1960‐ 1970); and (4) a meso-eutrophic stage from ca. 1970 onwards. Acidophilous Aulacoseira distans coll. and other species typical of dystrophic, nutrient-poor lakes characterized the diatom assemblages during the first stage, and the profundal zoobenthic assemblages, characterized by Heterotrissocladius subpilosus and Micropsectra, indicated good hypolimnetic oxygen conditions and a low sedimentation of organic matter (approximately less than 50 g m ‐2 a ‐1 ). The increased loading rapidly led to changes both in diatoms and chironomids (e.g., to an early extinction of H. subpilosus in the 1950s). The process finally led to eutrophication with a successive proliferation of diatom species such as Asterionella formosa followed by Aulacoseira ambigua, Fragilaria crotonensis, and finally Melosira varians. The relative proportion of alkaliphilous species reached a maximum in the final stage and the original profundal chironomid fauna was replaced by Chironomus anthracinus gr. and C. plumosus which are typical of profundal areas suffering from temporal oxygen deficit. It is notable that the considerable decrease in waste water loading from the point sources (80‐86%) during the past two decades has not led to a recovery in the lake. This highlights the importance of diffuse loading from agriculture, forestry and other human activities even to this comparatively large lake.

Bathymetric distributions of chironomid communities in ten French lakes: Implications on lake classification

Biological typology of lakes is commonly based on the analysis of profundal chironomid communities (THIENEMANN 1913, BRUNDIN 1949, SAETHER 1979, WIEDERHOLM 1980). In this study, ten French lakes were characterized using BRUNDIN and SAETHER's schemes of lake classification. The results showed that all these lakes were Chironomus anthracinus or eutrophic lakes, even though environmental factors (chiefly oxygen concentration and the amount of organic matter in the sediment) differed from lake to lake. We also compared the classification of these lakes as mentioned above with a new type of classification based on the analysis of bathymetric distribution of chironomid fauna. Taking the bathymetric distribution of chironomids into account seems to be more informative than relying only on an analysis of profundal communities. The lakes were classified according to bathymetric modifications of their communities related more to oxygen and organic matter than to chlorophyll-a concentrations. As these results were in disagreement with the trophic typology proposed by SAETHER (1979), we propose a hypothesis to explain the differences between the two types of classifications based upon the factors influencing chironomid communities.

Still-Waters Systems In and Around Eskişehir Chironomidae (Diptera) Larvae

During this study 25 species were found. Among these species, the ones showing highly widespread distribution were; 'Chironomus thummi K., Chironomus viridicollis K., Chironomus anthracinus (Zett.), Polypedilum scalaenum Schr. 7 species were found in Yukarı Kartal pound, while 2 were found in Kunduzlar dam. Countrary to these, none was found in Beylik pond. The fact that the samples of Ortocladiinae was found in the streams of that area (Şahin, 1987, a,c; Thieneman, 1954) and not in still-waters seems to support the old considerations on the subject.

Reproductive behaviour in Chironomus anthracinus (Diptera: Chironomidae), with a consideration of the evolution of swarming

Reproductive behaviour in Chironomus anthracinus Zetterstedt (Diptera: Chironomidae), one of the most ubiquitous species in cold‐temperate lakes of Northern Europe, was investigated in Lough Neagh, Northern Ireland. Aerial swarming is an indispensable part of mating in this species. It has been recognized that adults, emerging from offshore, travel to inshore resting sites for physical/sexual maturation, before gathering at lake margins to form swarms. After copulation, females immediately travel back to open‐water sites (up to 1000m offshore—the longest oviposition flight recorded for a chironomid species) for oviposition. Protandry was evident and sex ratios were completely reversed in the near‐shore swarming site and the offshore oviposition site. A sequence of mating behaviour was clarified, involving an initial grasp, landing, an end‐to‐end position, and separation. There was a high incidence of homosexual (male‐male) grasps, indicating that grasping is initiated with a fairly crude cue, and many (heterosexual) grasps failed to proceed to a correct mating position. This resulted in an estimation of only one out of eight grasps resulting in a proper copulation. More egg masses were found in the surface water farther offshore, together with spent females. An egg mass contained c. 1000 eggs and hatching occurred within one month of oviposition.Sexual differences in the pattern of reproductive migration between the emergence/oviposition site offshore, the inland resting site, and the near‐shore swarming site, and the modes of mating and mating success achieved, together point to a possibility that the conspicuous swarming behaviour in this species may have evolved primarily through mate selection on the part of females. A swarm occurring at the end of the males’ lives serves as an efficient mechanism for females to select the best‐quality mate, while males have no other strategy than to participate vigorously in a swarm if they are to attain a reproductive success with choosy females. Thus, two sexes apparently adopt different strategies in their reproductive life: males spend their energy in swarming, while females pass through the swarm site with a quick but guaranteed reward and spend their remaining energy in reaching offshore sites with muddy substrata which provide the best chance of survival for the offspring.

The role of glycogen during the ontogenesis of Chironomus anthracinus (Chironomidae, Diptera)

Large fluctuations in glycogen content were found in larvae, pupae and adults of Chironomus anthracinus (Zetterstedt) from the profundal zone of Lake Esrom, Denmark. In 2nd, 3rd and 4th instar larvae the glycogen concentration (expressed as percentage of dry weight) increased during periods of aerobic conditions to a maximum of 25%, but decreased in periods of hypoxia longer than two months to 10–12% in young larvae. A further decrease to about 5% took place, when moulting from 2nd to 3rd or from 3rd to 4th instar occurred after overturn. Prior to pupation the glycogen concentration was restored to 26–28%. The glycogen concentration approximated 22% in young pupae, but decreased during the pupal stage and newly hatched adults contained 12–15%. Finally, the glycogen store of both males and females was further reduced during the swarming period. Thus, glycogen seems to be an important energy source (1) during periods with hypoxic conditions, (2) during periods with high internal energy requirement such as ecdyses and metamorphosis, and (3) during the non-feeding adult life stage.

Effects of oxygen deficiency on survival and glycogen content of Chironomus anthracinus (Diptera, Chironomidae) under laboratory and field conditions

Growth and glycogen content of Chironomus anthracinus in Lake Esrom, Denmark was examined during summer stratification in 1992 and 1993. Simultaneously, effects of oxygen deficiency on glycogen utilization and survival were experimentally studied. The population consisted of almost fullgrown 4th instar larvae in 1992 and 2nd and 3rd instar larvae in 1993. Growth rate and glycogen content changed as hypolimnetic oxygen deficiency increased. During a 1st phase of stratification dry weight and glycogen content increased (2nd and 3rd instars) or was almost constant (4th instar) but decreased significantly during the following 2nd phase. This change from growth to degrowth and utilization of endogenous glycogen reserves correlated with a change in the thickness of the microxic layer (<0.2 mg O2 1−1) above the sediment surface. The layer increased from 2–3 m in phase 1 to 4–5 m in phase 2, and we suggest that this deteriorated the oxygen conditions and resulted in a change in larval energy metabolism from fully aerobic during the 1st phase to partly anaerobic in the 2nd phase. During the 2nd phase larval metabolism was estimated at less than 20% of normoxic rate. Experimental exposure of the larvae to anoxia indicated highly different survival of young larvae (2nd and 3rd instars) and older larvae (large 4th instars). The morality of young larvae was 50% after three days in anoxia at 10 °C, whereas only 25% of the older larvae had died after 3–4 weeks under similar conditions. Extending the treatment, however, resulted in increased death rate of the 4th instar larvae with only 10% surviving after seven weeks. The anaerobic metabolism of 4th instar larvae as estimated from glycogen degradation at 10 °C was 5% of normoxia in the interval from 0–5 days but 1.5% in the interval from 20–25 days. It is concluded that survival of C. anthracinus in anoxia is very limited, but traces of oxygen in the environment allowing for faint aerobic metabolism prolong the survival time of the larvae from a few days (2nd and 3rd instars) or a few weeks (4th instar) to probably 3–4 months.

Changes in the Benthic Macroinvertebrate Community of the Cleveland Harbor Area of Lake Erie From 1978 to 1989

The benthic macroinvertebrates of the nearshore zone of Lake Erie in the vicinity of Cleveland, Ohio, were sampled at 12 stations in October 1988 and May 1989 to determine the present pollutional status of the benthic community and to record changes over the past decade. The most abundant macroinvertebrates were, respectively, oligochaete worms, sphaeriid clams, and chironomid larvae. Of 75 taxa identified, 22 were oligochaetes, 16 were chironomids, and 11 were mollusks. Community composition in most of the harbor was suggestive of highly organically enriched sediments and was dominated by five tubificid worm species and pill clams ( Pisidium spp.). The open water community, representative of less enriched conditions, was dominated by the tubificid Limnodrilus hoffmeisteri as well as Pisidium spp. and midges of the Chironomus anthracinus? group. Improvement in the habitat quality of the study area, including the harbor, since the late 1970s was evident from a dramatic increase in the number of taxa at all sites, a reduction in the proportion of oligochaete worms, a large increase in the abundance of sphaeriid clams and midge larvae, and the widespread distribution though low abundance in open water sediments of caddisfiy larvae ( Oecetis sp.) which were absent in the late 1970s. Midges of the genus Chironomus remained largely absent from the harbor, and the abundance of the genus Procladius remained low around the mouth of the Cuyahoga River. The abundance of oligochaete worms has increased substantially around the river mouth over the decade. This increase may indicate an actual improvement of conditions overall, as might be expected with declining concentrations of toxic substances but continued organic enrichment of the sediments.

Evidence of Teratogens in Sediments of the Niagara River Watershed as Reflected by Chironomid (Diptera: Chironomidae) Deformities

Chironomids from two locations in an IJC “Area of Concern” in the Niagara River watershed and from one site in Lake Huron were sampled and classified as either normal or abnormal based on their menta (“teeth”) deformities. The two Niagara River sites were the King's Bridge reference site and the Kane Dock coal tar contaminated area. The latter site was immediately downstream of an abrasives company located about 800 m downstream of the King's Bridge reference site. Among the 739 chironomids sampled from the King's Bridge reference site, 3.1% (23) possessed menta with deformities. This deformity frequency was similar to the 2.8% deformity frequency observed in a clean water site in Lake Huron. Chironomids removed from the coal tar contaminated site displayed a deformity frequency of 14%. The dominant invertebrate in the coal tar (PAH) contaminated sediments was the midge ( Chironomus anthracinus), a non-biting fly larva referred to as a blood worm. Thus there was a significantly higher frequency of menta deformities downstream of the abrasives manufacturer's discharge than at the King's Bridge reference site (Student's “t” test, P < 0.05). The chironomids at the contaminated site were themselves contaminated with elevated levels of fifteen different PAHs. The PAH levels in the bodies of the deformed chironomids were higher than the levels in the undeformed chironomids collected at the same site. When over 200 chironomids with an average deformity frequency of 7.7% were taken from the PAH contaminated site and placed in clean (PAH uncontaminated) sediments taken from the King's Bridge Park reference site, the resulting F 1 generation displayed a mentum deformity frequency of 4%. These rearing experiments indicated that few, if any, of the observed C. anthracinus menta deformities were passed on to the next generation.

The fate of trace metals during the metamorphosis of chironomids (diptera, chironomidae)

The fate of the trace metals zinc, cadmium and copper during the metamorphosis of chironomids was studied under field and experimental conditions. Field observations demonstrated a significant decrease in the trace metal body burden of larvae and imagines of Stictochironomus histrio Fabricius. No such difference were noted between successive developmental stages of Chironomus anthracinus Zett. The exuviae of both species contained small amounts of trace metals. Experiments, in which larvae of S. histrio and C. riparius Meigen were individually exposed, showed that larvae of both species accumulated substantial amounts of zinc and cadmium. For these metals, a transfer to pupae and imagines occurred. However, pupae had a lower body burden than larvae, and imagines a lower body burden than the pupae. Copper was also accumulated in the larvae, but it was excreted almost completely before the pupal stage. Elimination pathways of the trace metals during metamorphosis and the ecotoxicological consequences of trace metal transfer are discussed.

Evidence of allergic hypersensitivity to chironomid midges in an English village community.

Some chironomid (non-biting) midges contain potent human allergens, principally in the form of insect haemoglobins. In view of previously demonstrated immunological cross-reactivity between some different midge species, the possible role of British midges in allergic disease was studied. The chosen site, Farmoor near Oxford, is a village that has been subject to several annual nuisance midge swarms since the construction of an adjacent water-supply reservoir in 1964, which was extended in 1975. The incidence and severity of hypersensitivity in the community was assessed by questionnaire survey, skin-prick testing, radio-allergosorbent tests (RAST) and RAST inhibition, and enzyme-linked immunosorbent assays (ELISA) and ELISA inhibition, using extracts of locally caught adult midges (Tanytarsus sylvaticus, T. bathophilus and Chironomus anthracinus) and laboratory cultured larvae (C. riparius). These tests revealed a low but significant level of midge-related hypersensitivity with skin-prick results showing seasonal fluctuations, but this seasonality was not confirmed with an IgE RAST. A correlation between IgE levels and relevant symptoms was found (P less than 0.01) using RAST, but not between IgE and skin-test results. Enzyme-linked immunosorbent assay results did not correlate with any other parameter measured. The incidence and severity of allergic reactions to the midges tested in this community was low.

Changes in behaviour, flight tone and wing shape in nematode-infestedChironomus (Insecta, Diptera)

The flight tones generated by wing beat frequencies of adult female and male non-biting midges,Chironomus anthracinus, infested by a species ofLimnomermis are very similar (mean values 219.9 and 228.9 Hz respectively), intermediate between normal females (205.1) and males (363.1), but closer to that of the uninfested females. Similarly, the wing shape of parasitized individuals appears intermediate resembling the female more than the male. Statistically wing width and surface area in the parasitized adults resemble those of females and differ significantly from those of normal males. The wing length of the parasitized midges, however, is more like that of males, but there is no statistically significant difference between the groups. Malnutrition of the larvae caused by competition with the parasite seems to result in wing shortening superimposed on sexual differences. All parameters of wing shape are negatively correlated with flight tones. Weight and musculature of the parasitized individuals have also been investigated, but only where worms were present in the thorax was a change found in the flight tones. The flight tone changes served no apparent biological function for the parasitized midges, but the worms apparently benefit from behavioural changes of the infected host, thereby reaching habitats where fresh hosts for its larvae may be available.

Studies on the Feeding ofCoregonus 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 (Uj) and lower (Lj) jaws and weighed. The gape-height was calculated according to two different formulae. For the examined fish the relationship between total length (Lt) and gape-height (D) was found to be D=0.092 Lt—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 life cycle of Chironomus anthracinus in Lough Neagh

Chironomus anthracinus generally had a one year life cycle at 8 m depth in Lough Neagh, during the study period. In spring 1975 however only a proportion of the population emerged as usual, the rest remaining a second year in the benthos to emerge in 1976. The mean dry weight of larvae just before emergence was 2.8 mg in 1971 and 2.6 mg in 1974 but only 1.6 mg in 1975, and it seems that larvae must reach a weight of at least 1.0 mg in the early spring to emerge that year. Considering temperature, oxygen saturation and standing crop of phytoplankton as factors influencing the life cycle, mean monthly chlorophyll a (phytoplankton) was weakly correlated with mean monthly increase in weight and % monthly weight increase could be related to temperature.