Marine connectivity and fish length frequencies of selected species in two adjacent temporarily open/closed estuaries in the Eastern Cape Province,South Africa

The effects of timing, frequency and duration of mouth opening and marine overwash events on fish assemblages in two, adjacent temporarily open/closed estuaries were investigated. Sampling was conducted biannually over two years during summer and winter, using selective sampling gear to target estuarine-associated marine species. During this period the East Kleinemonde Estuary opened more frequently than the West Kleinemonde Estuary and it also experienced a greater number of bar overwash events when larval recruitment can occur. The timing of mouth opening and the frequency of marine overwash events did not influence species richness of marine-spawning species but had a pronounced effect on abundances (catch-per-unit-effort) of species. The species composition of both estuaries was similar, but the catch-per-unit-effort in the East Kleinemonde Estuary was more than three times greater than that of the West Kleinemonde Estuary. The East Kleinemonde also supported a greater proportion of immature individuals of Rhabdosargus holubi and Monodactylus falciformis, and the length frequency distributions of both these species differed significantly between the two estuaries. The larger fish sizes in the West Kleinemonde Estuary were attributed to the prolonged mouth closure that resulted in the trapping of larger juveniles and mature fish within the estuary.     

Ecology of southern African estuaries: Part XIII. The Palmiet River estuary in the south-western Cape

The Palmiet estuary is only 1,67 km in length, but has a relatively large catchment of 539 km². Rain falls largely during winter when it scours the estuary and widens the mouth, but by late summer the mouth narrows and, in some years, may close. The estuary never closes for more than a few months, and salinities are normal. The entire estuary has clear bottom water and high bottom salinities, but the surface waters are usually fresh and darkly stained with humic acid. This permanent stratification allows many marine species to penetrate the estuary.

Owing to the scouring in winter, the sediments are coarse, >98% consisting of sand and gravel, with a low organic content. In situ primary production is low, contributing only about one fifth of the organic material in the system, the rest being imported from the river and the sea. Species richness is low, only 28 species of invertebrates being recorded, but many of these occur in enormous numbers. Callianassa kraussi plays a crucial role, trapping fine particles around its burrows and locally enhancing the organic content of the sediments. Its faeces are an important vehicle for the concentration and turnover of organic matter.

Four of the 19 species of fish recorded breed in the estuary, the rest being represented largely by juveniles or small adults. Only three species occurred in the estuary year-round, the other species being absent during the period that the estuary is in flood.

Floods and a relatively high flow of river water are critical to keeping the estuary open. If, as proposed, a dam is built on the river, steps will have to be taken to ensure that the mouth is kept open. A related problem will be the reduction of organic material entering the estuary from the river and the sea.     

First record of freshwater fish on the Cape Verdean archipelago

The Cape Verdean islands form a distinct aquatic freshwater ecoregion characterized mainly by temporal water bodies with an adapted invertebrate community. Freshwater fish were not previously recorded from the archipelago. During a non-exhaustive survey of freshwater bodies on five islands of the archipelago, the first presence of a freshwater fish was recorded. Using barcoding sequences, the species was identified as the guppy (Poecilia reticulata), a highly invasive species alien to the Cape Verdean Islands.     

The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries

The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m² and 0 and 9.65 mg/dwt/m² in the West Kleinemonde Estuary and between 0 and 108 ind/m² and 0 and 0.318 mg/dwt/m² in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m² and 0 and 5.105 mg/dwt/m². Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly larger than females (P < 0.05). Sex ratios were skewed in favour of females in all three estuaries. Females were encountered carrying young from an overall length of 2.5 mm throughout the year     

Birds as major predators of fishes in the East Kleinemonde Estuary

This study provides a quantitative account of fish predation by piscivorous birds in the temporarily open/closed East Kleinemonde Estuary and represents the first global attempt to simultaneously relate such consumption to production by a fish community in the same estuary. Cormorants and herons were the dominant predators and seasonal variations in the avifaunal community composition were noted. Based on comprehensive counts over three years, the piscivorous bird population was estimated to have consumed a maximum of 4 414?kg of fish in 1994, 2 400?kg in 1995/96 and 2 960?kg in 2004/05. In 1995/96 fish production in the East Kleinemonde Estuary (55.89?g m^?2 a^?1) was estimated at 9 780?kg and maximum bird predation amounted to 25% of annual fish production within the system over the same period, assuming that all birds counted on the estuary foraged there and that the diet of these birds comprised only fish. The above 1995/96 figures, together with an estimate of fish predation by the dominant piscivorous fish Lichia amia of 696?kg suggests that birds are probably the single most important natural predator of fishes within this estuary. An unusual mass invasion by marine Cape Cormorants Phalacrocorax capensis during July 1994 was responsible for large-scale predation of fish (2 155?kg) and resulted in the population of estuary-associated marine fishes declining from approximately 63 300 to about 18 600 individuals during the 1994 closed phase. Given that little or no marine fish recruitment was possible while the estuary mouth was closed, piscivorous birds are likely to have a higher predatory impact on populations of juvenile marine fishes in small temporarily closed estuaries than in larger permanently open systems.     

Shallow-Water Trawling Off the Swartkops Estuary,Algoa Bay

Juvenile fish occurring in Algoa Bay off the mouth of the Swartkops estuary were collected using a 3-m beam trawl. Pomadasys ollvaceum, Engraulis capensis, Caffrogoblus agulhensls, Argyrosomus hololepidotus and Galeichthys feliceps were the most abundant species in the trawl catches. Despite the proximity of the Swartkops estuary the trawls failed to capture species which are abundant as Juveniles in the estuary and it is concluded that the estuary has little influence on the juvenile fish fauna outside the mouth.     

Disentangling the identities and distribution patterns of the introduced beachfleas Orchestia gammarellus and Platorchestia platensis (Crustacea: Amphipoda: Talitridae) in South Africa

Two introduced beachfleas, Orchestia gammarellus and Platorchestia platensis, have been recorded from South Africa, but have been misidentified by some earlier researchers and, prior to this study, each was also known from just a few, scattered observations, such that their true distributions remained obscure. We illustrate both species to clarify the features that identify and distinguish them and determine their true distributions by re-examining historical samples and by collecting new material from estuaries and lagoons along the west and south coasts of South Africa. Adult males of O. gammarellus have slender antennae and characteristic expanded, flattened, oar-like distal segments on pereopod 7. Adult males of P. platensis have the peduncle of antenna 2 strongly swollen and have bulbous, but not flattened, distal segments on pereopod 7. Both species occur under wrack and other debris along the banks of estuaries and sheltered lagoons. Orchestia gammarellus is found only along the south-west coast, in the Berg River Estuary, Langebaan Lagoon and the Diep River Estuary. Previous records from Knysna were misidentifications of P. platensis. Platorchestia platensis is found at one west coast site, Langebaan Lagoon, but is widely distributed from Cape Point eastwards to at least Algoa Bay. Both species share the same habitats as several other native beachfleas and competitive interactions between native and introduced species merit investigation.     

The ecology of two degraded estuaries on the north coast of Natal,South Africa

The biota of the Tongati and Mdloti estuaries were studied in relation to the environment and human interference. Results are compared with those obtained from a relatively undamaged estuary. The Tongati receives treated sewage effluent, is rarely closed from the sea, has low salinities and low oxygen tensions, but is rich in phosphorus and nitrogen. Energy values of benthic floe from Tongati were high and large quantities of water hyacinth (Eichomia crassipes) occurred. The zooplankton and zoobenthos were impoverished and dominated by freshwater species. The roots of Eichomia provided a habitat for many invertebrates, chiefly insect larvae and the crab Varuna iitterata. The fish fauna was poor and most species were confined to the lagoon near the mouth. Iliophagous species, mainly Mugilidae, were dominant. The Mdloti, frequently closed from the sea but often artificially opened, exhibited typical estuarine salinity patterns, was well oxygenated but relatively poor in phosphorus and nitrogen. Primary production and energy values of benthic floe were low. Zooplankton and zoobenthos were impoverished. The fish fauna, similar to that of Tongati, was dominated by Mugilidae.

The food chain from benthic floe to iliophagous fish remains viable in these degraded estuaries.     

Occurrence of Aeromonas salmonicida,Renibacterium salmoninarum,and Infectious Pancreatic Necrosis Virus in Ontario Salmonid Populations

Abstract

The results of samples collected from private and government fish farms and wild and feral fish populations in Ontario from 1981 to 1995 were synthesized to obtain prevalence estimates in salmonids at both the fish and site levels for three pathogens. Renibacterium salmoninarum and Aeromonas salmonicida were both detected on at least one site for every year investigated. Ontario Ministry of Natural Resources (OMNR) culture stations had the highest percentages of sites with infected fish for R. salmoninarum. Natural water bodies had the highest percentages of sites with infected fish for A. salmonicida. Infectious pancreatic necrosis virus (IPNV) was only detected sporadically on some commercial farms and never in OMNR hatcheries or in wild or feral fish. Although screening for any virus that would yield cytopathological effect was carried out during all the years surveyed, no virus other than IPNV was isolated. The low prevalence and “source-specific” presence of IPNV in Ontario demonstrates the necessity of representative sampling for the detection of rare pathogens. It was estimated that, overall, less than 1% of all fish in the sampled populations were infected with each of the three pathogens for almost every year studied. The importance of summarizing pathogen-testing data and the possible implications on disease control policy planning and assessment are discussed.     

Competition and niche partitioning in a floodplain ecosystem: a cladoceran community squeezed between fish and invertebrate predation

Seasonal floodplains occasionally comprise highly productive zooplankton communities which are exposed to rapid shifts in predator regimes, also between vertebrate and invertebrate predators.We recorded the impact of two co-occurring zooplankton predators, the notonectid Anisops sardea and 0+ fish fry of Tilapia rendalli (max gape size 1 mm), on a cladoceran community dominated by Ceriodaphnia reticulata (0.25–0.78 mm), Daphnia laevis (0.6– 1.8 mm) and Scapholeberis kingi (0.27–0.8 mm). Both predators strongly reduced abundance of all prey species, yet with a striking size-selective effect for Daphnia prey only, where fish showed a strong preference for small individuals, while Anisops preferred large Daphnia individuals. This contrasts with the general view of size selection in invertebrate versus vertebrate predators, but is logically caused by the feeding mode of the notonectid, and the gape size limitation of the fish fry. The two predators also showed a dietary niche differentiation in terms of both prey selection and habitat choice. T. rendalli fed preferably on small species and size classes, whereas predation from A. sardea concentrated on large prey. Competitive interference was indicated when feeding on Ceriodaphnia, and niche partitioning when feeding on the two other species. The predatory pattern suggests long-lasting coexistence in the system.     

The benthos of South Lake,St Lucia following a period of stable salinities

The invertebrate benthos of South Lake, St Lucia was monitored monthly from August 1981 to July 1982 following a period of stable salinities of approximately 35°/oo. The overall mean biomass for the year (dry mass) was 2,63 g m^-2 with mean values for muddy and sandy substrata of 4,19 g m^-2 and 1,07 g m^-2 respectively. The major contributors to standing stock were the bivalve Solen cytin-draceus and the polychaete Marphysa macintoshi. A total of 37 taxa were recorded compared with 23 in a previous survey in 1972-73. Present results are compared with those of 1972-73 and the differences discussed. The main changes were a decline in Assiminea, Nassarius and Prionospio and an increase in abundance of long-lived bivalves together with larger polychaetes. Species diversity at the sampling sites is analysed and discussed in terms of equitability of distribution.     

Detection of Infectious Pancreatic Necrosis Virus from the Leeches Hemiclepsis marginata and Hirudo medicinalis

Leeches have been reported to harbor several important fish pathogens, including spring viremia of carp virus, infectious hematopoietic necrosis virus (IHNV), and viral hemorrhagic septicemia virus (VHSV), and also may contain blood protozoa. In the present study, leeches were collected from water bodies located in Kurdistan province, Iran. The specimens were tested for IHNV, VHSV, and infectious pancreatic necrosis virus (IPNV) using the PCR method. The results showed that two different species of leeches, Hemiclepsis marginata and Hirudo medicinalis, were infected by IPNV among the seven species studied. The infected leeches were found in areas that were polluted with untreated sewage coming from upstream fish farms culturing Rainbow Trout Oncorhynchus mykiss. In addition, the fish at fish farms in the vicinity had been infected with IPNV 9 months previously. Our results showed that the virus causing infectious pancreatic necrosis is present in the leeches H. marginata and H. medicinalis, suggesting that leeches are a potential source of IPNV in fish farms.

Received October 14, 2015; accepted June 1, 2016 Published online September 29, 2016     

Host factors associated with the detection of Aeromonas salmonicida and Yersinia ruckeri in Ontario, Canada government fish hatcheries

This paper presents an epidemiological investigation of Ontario Ministry of Natural Resources Fish Health Laboratory data from 1981 to 1997, to determine whether fish species and age were associated with lot-level detection of Aeromonas salmonicida and Yersinia ruckeri in hatchery fish. In stepwise logistic regression, the species brook trout and back-cross (lake trout crossed with the hybrid “splake”) were more likely to test A. salmonicida-positive compared to all other species reared in the hatcheries. Similarly, the species brook trout was significantly more likely to test Y. ruckeri-positive compared to all other species. For both pathogens, the 1–5-month age group was associated significantly with detection. These findings suggest that purposive sampling of higher-risk fish lots could increase the likelihood of detecting both study pathogens.     

Fish community structures in Zostera and Non-Zostera regions of the Kromme estuary,St Francis Bay

Comparative seine netting for fish was performed quarterly during 1981 in the Zostera and non-Zosfera regions of the upper middle reaches of the Kromme estuary. Twenty-four fish and three crustacean species were recorded. The catches were dominated by the following species: Liza dumerili, Glossogobius glurus and Gilchristella aestuarius (Pisces). Only two fish species (Monodactylus falciformes and Rhabdosargus holubi) were recorded in significantly (P<0,05; P<0,05 respectively) higher numbers in the Zostera than in the non-Zosfera regions and community analyses (comparing numbers, species richness and diversity) revealed no significant (P>0,05) differences between the catches from the two regions. These results are contrary to findings of most other researchers and possible reasons for these differences are discussed.     

Feeding ecology of three inshore fish species at Marion Island (Southern Ocean)

The diets, morphological features and habitats of 258 specimens of the three inshore fish species Notothenia coriiceps, N. macrocephala and Harpagifer georgianus from Marion Island are described and compared. Correspondence analysis of the three diets shows the existence of three clearly defined feeding niches despite the occurrence of some common prey species. Inter-and intraspecific similarities and differences in the diets of small and large size classes of each species are also displayed by correspondence analysis. Size-limited predation by N. coriiceps of the limpet Nacella delesserti is described. Differences in the habitats occupied by the fish appear to be important in determining the species composition of their diets.     

Rights,Resources and Rural Development: Community-Based Natural Resource Management in Southern Africa — Christo Fabricius,Eddie Koch,Hector Magome and Stephen Turner (eds) 2004

Goats select some browse species more than others, given options. Seasonal trends of diet selection of Nguni goats indexed by intake were investigated in cafeteria-style experiments. The relationships between diet selection and plant chemical/physical traits of Vachellia nilotica, Vachellia robusta, Dichrostachys cinerea, Euclea crispa, Rhus lancea and Ziziphus mucronata, representing abundant species were studied in the dry and rainy seasons. Seasonal changes in browses affected diet selection. Selection of long shoot species, which were concomitantly broad-leafed, was higher than species with short shoots. Selection was higher for spineless than spinescent species. Diet selection correlated positively with increased leaf mass. In the rainy season, cellulose positively correlated with intake, number of bites and browsing time, whereas in the dry season, cellulose correlated with bite size. Diet selection tended to be driven more by shoot morphology and leaf mass than by either spinescence or plant chemistry. Plant chemical influence on diet selection was diverse in both seasons and showed no definite trend, whereas spinescence had no significant effect on short-term intake. The results represent important input to goat production and range forage species management.     

Meso-zooplankton movement through the newly constructed Mfolozi channel into and out of the St Lucia Estuary,South Africa

The historical canalization of the Mfolozi River resulted in the St Lucia Estuary losing its main freshwater source. This, combined with the recent drought, led to low water levels, hypersaline conditions and dramatic losses in biodiversity. The excavation of a beach spillway between the estuary and the Mfolozi River mouth in 2012, combined with the commencement of a wet phase in the preceding year, has alleviated the freshwater deprivation crisis. This study compares the meso-zooplankton composition within the channel on both flood and ebb tides, providing a preliminary understanding of the role of the Mfolozi channel in the migration and recruitment of organisms. Abundance was higher on ebb tides, while species richness was higher on flood tides. A total of 53 zooplankton taxa were recorded in the channel. Of these, one had never been recorded in St Lucia before, namely the gastropod Pterotrachea cf. hippocampus. Additionally, the ctenophore Pleurobrachia cf. pileus and the mysid Gastrosaccus gordonae were again recorded for the first time since the late 1970s. Results show that the beach spillway has facilitated recruitment into St Lucia from the ocean and the Mfolozi River. Further research is needed to ascertain what effect this recruitment has on long-term zooplankton community structure.     

Aphanomyces invadans and Ulcerative Mycosis in Estuarine and Freshwater Fish in Florida

Abstract

In the spring of 1998, the Florida Fish and Wildlife Research Institute received numerous reports of lesioned or ulcerated fish primarily from the St. Lucie Estuary on the southeast coast of Florida, an area known since the late 1970s for lesions of the ulcerative mycosis (UM) type. From these and archived reports, as well as others received from different areas of Florida, we documented that diseased specimens had randomly distributed skin ulcers (usually reddened or hemorrhagic) with raised irregular margins and, in some cases, deeply penetrating hyphae in the surrounding muscle tissue. Since 1998, 256 fish (comprising 18 species) with ulcerative lesions (from 15 different locations) were confirmed with hyphae in fresh squash preparation or by histological evaluation. Squash preparations revealed nonseptate, sparsely branching, thick-walled hyphae; histological sections revealed mycotic granulomas in the dermis that occasionally penetrated into the skeletal muscle. These pathological characteristics were consistent with UM caused by the oomycete Aphanomyces invadans in Southeast Asia, Japan, Australia, and the United States. For specific identification, six isolates from ulcerated fish were cultured and prepared for molecular characterization using established diagnostic methods. Ribosomal RNA gene sequence analysis identified three isolates as Aphanomyces invadans, one as the oomycete Achlya bisexualis, and two as the ascomycete Phialemonium dimorphosporum. A more extensive survey of 67 ulcerated skin samples from fish collected between 1998 and 2003 was performed using a polymerase chain reaction assay specific for Aphanomyces invadans. Of these, 26 (38.8%) samples from seven fish species and nine collection locations were positive. Confirmation of UM associated with Aphanomyces invadans represents new host records in Florida for the sheepshead Archosargus probatocephalus, striped mullet Mugil cephalus, white mullet Mugil curema, silver perch Bairdiella chrysoura, black drum Pogonias cromis, largemouth bass Micropterus salmoides, and American shad Alosa sapidissima.