I. John Hodgkiss

Role of fungi in freshwater ecosystems

There are more than 600 species of freshwater fungi with a greater number known from temperate, as compared to tropical, regions. Three main groups can be considered which include Ingoldian fungi, aquatic ascomycetes and non-Ingoldian hyphomycetes, chytrids and, oomycetes. The fungi occurring in lentic habitats mostly differ from those occurring in lotic habitats. Although there is no comprehensive work dealing with the biogeography of all groups of freshwater fungi, their distribution probably follows that of Ingoldian fungi, which are either cosmopolitan, restricted to pantemperate or pantropical regions, or in a few cases, have a restricted distribution. Freshwater fungi are thought to have evolved from terrestrial ancestors. Many species are clearly adapted to life in freshwater as their propagules have specialised aquatic dispersal abilities. Freshwater fungi are involved in the decay of wood and leafy material and also cause diseases of plants and animals. These areas are briefly reviewed. Gaps in our knowledge of freshwater fungi are discussed and areas in need of research are suggested.

Phylogenetic significance of morphological characters in the taxonomy of Pestalotiopsis species

There has been considerable disagreement regarding the relationships among Pestalotiopsis species and their delimitations. A molecular phylogenetic analysis was conducted on 32 species of Pestalotiopsis in order to evaluate the utility of morphological characters currently used in their taxonomy. Phylogenetic relationships were inferred from nucleotide sequences in the ITS regions and 5.8S gene of the rDNA under four optimality criteria: maximum parsimony, weighted parsimony, maximum likelihood, and neighbor joining. Phylogenies estimated from all analyses yielded trees of essentially similar topology and revealed 3 major groups that correspond with morphology-based classification systems. Molecular data indicated that the genus contains two distinct lineages based on pigmentation of median cells and four distinct groupings based on morphology of apical appendages. The analyses did not support reliability of other phenotypic characters of this genus, such as spore dimensions. Characters with particular phylogenetic significance are discussed in relation to the taxonomy of Pestalotiopsis.

Fungal communities on submerged wood from streams in Brunei, Hong Kong, and Malaysia

Fungi on submerged wood in streams are a diverse group, comprising taxa from various families. Fungal communities on submerged wood collected from Sungai Sitam in Brunei, Tai Po Kau Forest Stream in Hong Kong, and from a stream in Lipur Lentang Nature Reserve in Malaysia are reported. One hundred and forty-seven taxa were recorded. A higher species diversity including temperate and tropical species was recorded in Tai Po Kau Forest Stream in the subtropics. Ascomycetes and their asexual stages were dominant in tropical and subtropical freshwater habitats, while discomycetes were rare in these habitats. Distinct fungal communities are found on submerged wood in tropical, subtropical and temperate regions and these are discussed. Including the fungi identified in this study, over 1000 fungi has been recorded from freshwater habitats.

Longitudinal and temporal distribution of freshwater ascomycetes and dematiaceous hyphomycetes on submerged wood in the Lam Tsuen River, Hong Kong

Longitudinal and temporal distribution patterns of freshwater ascomycetes and dematiaceous hyphomycetes on submerged wood were investigated at 3 sites along the Lam Tsuen River in Hong Kong. Two-hundred-and-six species were recorded. Ascomycete genera were dominated by Annulatascaceae, Halosphaeriaceae, Lasiosphaeriaceae, Lophiostomataceae, and Magnaporthaceae; the most common taxa were Aniptodera chesapeakensis, Aquaticola ellipsoidea, Helicosporium griseum, Massarina purpurascens, M. thalassioidea, Ophioceras commune, and Sporoschisma uniseptatum. There were no significant differences (ANOVA, p > 0.05) in total number of species among the sites. However, the number of species of Halosphaeriaceae (p < 0.01) and Lasiosphaeriaceae (p < 0.05) was significantly higher at Site 3, and Annulatascaceae was dominant at Sites 1 and 2 (p < 0.05). Downstream changes in species composition were strongly correlated with elevated concentrations of NO3-N (r2 = 0.66), NH3-N (r2 = 0.66), and PO4-P (r2 = 0.73) resulting from human disturbance. The variation in species composition was also weakly correlated with other physico-chemical variables such as conductivity (r2 = 0.16) and aluminum (r2 = 0.11). Species diversity fluctuated temporally but did not change (ANOVA, p > 0.05) between dry and wet seasons. Species composition shifted and the frequency of occurrence of certain dominant taxa declined after heavy rainfall associated with El Niño, possibly because increased discharge washed away well-colonized woody substrata.

Reproductive biology of Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir, Hong Kong

SynopsisA 16-month study (August 1972 to November 1973) of Sarotherodon mossambicus in the Plover Cove Reservoir, Hong Kong revealed a sex ratio of 1:1 for small fish (below 19 cm standard length), but above this length males predominated in the population. Monthly sex composition also showed this approximately 1:1 ratio except during the months of August and September, when again males predominated. Males and females reached M50 at an average length of 17.8 cm and 16.2 cm respectively. Maturity and gonosomatic index studies showed that spawning occurred from May to October with peaks in June and August, and there were at least two spawnings each year. The relationship between fecundity and standard length of females collected during both spawnings was computed to be F = 118.49L–1150.91.

Age composition, growth and body condition of the introduced Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir, Hong Kong

SynopsisAge composition, growth and body condition of the Sarotherodon mossambicus (Peters) stock in the Plover Cove Reservoir were investigated. The fish in this reservoir have a relatively short life cycle; the stock consisted of mainly two to three age groups. Influx of recruits in September and October maintained a high proportion of O-age group fish in the stock. This percentage remained high until the following March or April when the I-age group attained dominance. Length-weight analyses indicated that S. mossembicus conform to the allometric formula W = aLn with ‘a’ and ‘n’ exhibiting marked seasonal variations. Growth was most rapid during the first 20 months of life and decreased noticeably after 30 months. In general growth was limited to those months when the water temperature was above 20° C. Both body condition and visceral fat content exhibited seasonal variations which were not correlated with each other or with variations in temperature. However, body condition appears to be directly related to feeding intensity. Mean body condition decreased with increasing age and also decreased progressively during this study. This progressive decrease was probably related to the progressive decrease in salinity of the water and also the carrying capacity of the reservoir rather than to the nutrient content of the water. Mean values for the body condition of females were in general higher than for males, suggesting that females are more robust than males.Maximum accumulations of fat occurred in June and July, corresponding to the breeding period. Such accumulations are thought to be a prerequisite before spawning.

Cheiromyces lignicola, a new chirosporous anamorphic species from Hong Kong

Cheiromyces lignicola sp. nov. is described and illustrated from a freshwater stream in Hong Kong. The species is characterized by chiroid, yellow- ish brown, distoseptate conidia that are composed of 3-5 arms, each terminating apically in an inflated cell. The developmental stages of the inflated apical cell are illustrated. Cheiromyces lignicola is compared with other Cheiromyces species, and other taxa that produce chiroid conidia with inflated apical cells. The taxonomic disposition of C. cubensis and C. wrightii in Cheiromyces is also discussed. Keys to spe- cies of Cheiromyces and to 26 anamorphic genera that produce chiroid conidia are provided.

A new species of Clohiesia from Hong Kong

Clohiesia lignicola sp. nov. (freshwater ascomycetes) is introduced based on a specimen collected on submerged wood in the Tung Chung River, Hong Kong. Ascomata are clypeate, asci are cylindric-clavate with a relatively massive apical apparatus and ascospores are fusoid-ellipsoidal.Clohiesia lignicola differs fromC. corticola in having wider asci and wider fusoid-ellipsoidal ascospores, and larger ascomata.Clohiesia lignicola is described and illustrated with light micrographs and is also compared with species in the genus,Annulatascus.

Stock density and mortality assessment of Sarotherodon mossambicus (Cichlidae) in Plover Cove Reservoir, Hong Kong

SynopsisTwo methods were used to estimate stock density and two to estimate mortality of Sarotherodon mossambicus (Peters) in Plover Cove Reservoir. The first method for density estimation (the capturemark-recapture method) involved tagging and pelvic fin clipping. The former technique was eventually abandoned in favour of the latter. Using the capture-mark-recapture method the population was estimated to be approximately 50,000. The number of fish recaptured was low (six recaptures out of 1590 fish marked) and undoubtedly led to underestimation of the density. The second method, using differences between catch per unit of effort values, gave a much more acceptable estimate of density—702,900.Mortality data were obtained by routine collections of dead fish and interpretation of ‘catch curve’ results. The former method revealed that whereas natural mortalities (that is, fishing mortality excluded) of all other stock and indigenous fish reach a maximum in May and June, Sarotherodon mortalities were at a maximum in February but with a smaller post-spawning summer peak between August and October. It is suggested that temperature is the major factor involved in these natural mortalities, though post-spawning mortality is thought to be responsible for the summer peak. Mortality data obtained by the second method, when compared with results of dead fish collections and gill net surveys, suggested that illegal fishing operations caused the greatest mortality and represented 97.75% of the overall mortality of Sarotherodon.

Cataractispora receptaculorum, a new freshwater ascomycete from Hong Kong.

A new species of Cataractispora, C. receptaculorum, is described from freshwater habitats. This species is characterized by triseptate verruculose ascospores and polar appendages that unfurl in water. The ascospores lack polar chambers that enclose the appendages as in C. bipolaris and C. viscosa. An ultrastructural study of this species revealed that the ascus wall and apical ring of this species is typical of the Annulatascaceae, while the ascospore wall with verruculose ornamentations and the ontogeny of the ascospore polar appendages are similar to the other species of Cataractispora. Cataractispora receptaculorum is illustrated with interference light, scanning and transmission electron micrographs.