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Total mercury (THg) and organic mercury (OHg) concentrations were determined by cold-vapor AAS in ten species of fish, which were caught in the reservoir of a chlor-alkali plant in Tainan, Taiwan that had been abandoned for 22 years. The fishes, including Elops machnata, Pelates quadrilineatus, Gerres filamentosus, Leiognathus equulus, Thryssa hamiltonii, Orechromis spp., Nematalosa come, Liza macrolepis, Mugil cephalus and Chanos chanos, were sampled from September to October 2003. THg and OHg concentrations (μg/g flesh wt.) in fish muscles were 0.43±0.36 and 0.31±0.21, respectively, similar to values reported from various chlor-alkali plants worldwide. Of the OHg values, 37% exceeded the food safety limit of 0.3 μg/g set by the World Health Organization. Moreover, 77% of the tested OHg values were over 0.17 μg/g, which had been suggested for seafood safety limit in Taiwan. Finally, 100 g of fish muscle is the maximum allowable weekly consumption amount for the adult residents to avoid health treat that arise from ingesting toxic OHg.

Morphometric and meristic analysis of ladyfish, Elops machnata, were used to discriminate stocks along the Southeast and Southwest coast estuaries of India. Morphometric and meristic analyses showed a similar pattern of differentiation between E. machnata stocks and revealed a clear discreteness of two groups, an East coast (Marakanam, Parangipettai and Muthupettai) population and a West coast (Cochin) population. Higher total length (TL) (28.00 ± 7.043 cm), fork length (FL) (89.27 ± 2.201% TL) and standard length (SL) (81.77 ± 2.582% TL) were recorded in Cochin population and they were significantly different from the other three populations. Meristic counts were relatively homogenous in all the studied populations. No significant variation was found in counts of dorsal fin ray (DFR), anal fin ray (AFR), pectoral fin ray (PFR) and pelvic fin ray (PLFR). The first and second components (PCA analysis) accounted for about 92.2% of variation in all the morphometric characters. Among them, pre pectoral length (PPL) and pre dorsal length (PDL) showed high loading values in PC1 in all four populations. The overall random assignment of individuals to their original group was higher in morphometric than in meristic analysis. Such a presumption could be authenticated henceforth with molecular markers. Hence, further studies, using molecular markers are still required to precisely evaluate the genetic structure of E. machnata along the Indian coast.

Stomach content analyses were performed on eight carnivorous fish from four eastem Cape estuaries. Dietary importance was assessed by using three unrelated methods and by combining them to determine the index of relative importance of each food item. It was attempted to relate the percentage of fish with food in the stomach and the feeding intensity to the abundance of the fish in a particular estuary. In general fish consumed more food in estuaries where they were more abundant. The few exceptions that occurred could indicate that a particular estuary was selected for purposes other than food availability ego Tachysurus feliceps in the Krom estuary for spawning grounds or because of inter- or intraspecific competition for food ego T. feliceps and Monodactylus falciformis in the Krom and Argyrosomus hololepidotus in the Gamtoos and Sundays estuaries. Similarity analyses showed resource partitioning. Predators such as A. hololepidotus, Elops machnata, Lichia amia and Platycephalus indicus preferred teleost fishes such as mullets and Gilchristella aestuarius, whereas the stomach content of Pomadasys commersonni, T. feliceps and M. falciforrnis were dominated by Crustacea, particularly Upogebia africana. Most estuarine predators showed a diverse prey selection, but the

This study focused on ecosystem responses to the environmental perturbations caused by the 2004 Indian Ocean Tsunami in a small lake that was a freshwater body in 1996, prior to the tsunami. The physicochemical and biological characteristics of Kokilamedu Lake (KKM) revealed drastic changes, compared with pretsunami conditions. Monthly average observations on water quality indicated the electrical conductivity of the water increased steeply to 17.41 mS cm−1 in 2009, from the lowest pretsunami value of 1.83 mS cm−1 (range of 1.83–5.25 mS cm−1). Simultaneously, the nitrate + nitrite (NO3 + NO2) values increased significantly from 0.49 μmol L−1 in 1996 to 74.47 μmol L−1 in 2006. Silicate (SiO4-Si) exhibited a dramatic increase in concentration, from an average of 64.87 μmol L−1 in the pretsunami period to 309.71 μmol L−1 the post-tsunami period (2009–2010). Inorganic phosphate had increased to a maximum of 9.59 μmol L−1 from a pretsunami maximum of 1.09 μmol L−1. The chlorophyll-α concentrations did not respond to the increased nutrient stoichiometry of the lake. There was a decreased chlorophyll-α concentration under post-tsunami conditions. The recent infilling of the lake with sediment during the tsunami, associated with wind-driven resuspension reduced the light penetration. There was a significant improvement in dissolved oxygen concentrations (2006–2010 average of 8.27 mg L−1) in the lake, however, compared with the pretsunami values (1994–1995 average of 5.94 mg L−1). The algal component is now dominated by blue-green algae, while green algae had dominated in the pretsunami period. Pre- and post-tsunami observations from a control site did not exhibit such dramatic shifts from the 1995 and 1996 conditions, whereas a shift was apparent in the case of KKM. Certain marine fishes have adapted to this altered ecosystem. These marine species encountered (Elops machnata, Cociella punctata, Sphyraena jello, Platycephalus indicus, Glossogobius giuris) might have been recruited during the intrusion of the tsunami waves.

St Lucia is one of the largest estuarine systems in Africa, and attracts thousands of anglers each year. Catch card data from the National Marine Linefish System for the years 1986–1999 were analysed to determine catch composition, catch per unit effort ( cpue ) and seasonality of catches by recreational anglers. Because not all anglers completed catch cards, estimates of total catch were made using additional data on the number of private boat outings, the number of boat trailers at boat slipways and the number of boats recorded entering the campsite gates during 1992 and 1993. In all, 27 fish families, constituting 55 species, were recorded by recreational anglers. Dusky kob Argyrosomus japonicus , spotted grunter Pomadasys commersonnii , perch Acanthopagrus berda , Natal stumpnose Rhabdosargus sarba , springer Elops machnata and mini-kob Johnius dorsalis were the most prominent species caught in terms of numbers and mass. Catch rates expressed numerically (fish angler -1 h -1 ) peaked during the summer and early winter. However, in terms of mass, catch rates peaked during late winter and spring, when there were increased landings of large dusky kob. Fluctuations in cpue were linked to salinity and estuary mouth conditions (i.e. mouth closure). Despite annual fluctuations in cpue , regression analysis revealed an overall downward trend for the dominant species (dusky kob and spotted grunter) and a gradual increase for stumpnose, perch and springer, but with the exception of stumpnose, these trends were not significant. Socio-economic aspects of the fishery were also investigated by conducting an independent boat-angler survey. The value of the recreational fishery, in terms of accommodation and direct angler expenditure, was estimated to be in the region of R9 million during 1992. Angler attitudes towards fishing regulations were positive and anglers generally had a good knowledge of the regulations for target species. Based on this assessment, a number of suggestions are made regarding the future management of the recreational fishery at St Lucia. Keywords: catch and effort, management, recreational angling, socio-economics, St Lucia estuarine system African Journal of Marine Science 2002, 24: 263–279

The Random Amplified Polymorphic DNA (RAPD) technique was used to study the genetic diversity of four Elops machnata populations in South India . Elops machnata is considered as a least concern species (LC), categorized by the International Union for Conservation and Nature (IUCN). The population trends are currently stable in Indian Ocean , Eastern Africa , but are unknown throughout the rest of its expansive range, especially in Indian estuaries. Among the ten RAPD primers tested, eight primers got amplified and gave scorable bands. In total, 119 scorable bands were observed in all populations. The overall observed and effective number of alleles was found to be 2.000 ± 0.000 and 1.5307 ± 0.2503 respectively for the entire population. The overall polymorphic loci were 61.00% and the overall gene flow among the four populations was predicted to 0.1032. The genetic distance and geographic distance between the four populations showed a positive correlation. The highest genetic similarity (0.6824) was found between Parangipettai and Muthupettai population, which reflected the geographical relationship between them. Tow main clusters were obtained based on UPGMA dendrogram. This study proves that RAPD analysis has the ability to discriminate E. machnata populations in South Indian coastal waters.

The St Lucia estuarine system is the largest of its kind in Africa. Torrential rains from Cyclone Domoina during late January 1984, followed two weeks later by Cyclone Imboa, caused extensive flooding of the St Lucia system reducing salinities from a maximum of S=60 to S = 5 over a period of two weeks. The effects of this disturbance on the ichthyoplankton were monitored 3 km from the estuary mouth over the following ten months when physical conditions in the system began to stabilize. These data are compared with ichthyoplankton catch data collected at the same site immediately before the cyclones from March 1982 until January 1984. Results showed that flooding had relatively long-term effects on the distribution and numbers of some estuarine resident and marine migrant species which utilize the estuary as a nursery ground. The frequency of occurrence and proportional density of the estuarine resident Gilchristella aestuarius increased after the floods while that of Croilia mossambica and Gobius acutipennis decreased. No changes in the proportional densities of other estuarine resident species were noted. Increases were recorded in proportional densities of marine migrant species Elops machnata, Leiognathus equula, Johnius dussumierii and Pomadasys olivaceum, while proportional densities of Solea bleekeri and Rhabdosargus sarba decreased. The ecological significance of environmental disturbances in the St Lucia estuary by episodic flooding and its effect on the distribution and abundance of estuarine resident species and marine migrant species are discussed.

The aim of this study was to determine the effect of turbidity on the feeding strategies of fish in estuaries. Three species representing different feeding guilds were selected for the investigation. These were Elops machnata (representative piscivore), Pomadasys commersonnii (a macrobenthivore) and Atherina breviceps (a planktivore). The stomach contents of these fish were examined from a clear and a turbid estuary and some experimental work was carried out on A breviceps to test the hypothesis that turbidity affects feeding behaviour. Turbidity was found to have no effect on size selection of prey, but feeding rate, particularly of visual predators, was reduced at higher turbidity levels. This was caused by a decrease in the reactive distance of the fish. It would appear that in order to optimize the aquisition of food under different turbidity conditions fishes have the ability to change their feeding strategies. Visual predators are more affected by turbidity than are macrobenthic feeders.

The chemical body composition of ten marine migrants and one freshwater fish species caught in Eastern Cape estuaries was determined. Fish species were divided into three categories, taking fat/energy content as the criterion. Two species of mullet and Elops machnata had a high fat/energy content (>8 kJ·g−1; >8% fat), Pomatomus saltatrix, Liza tricuspidens, Diplodus sargus, Monodactylus falciformis, Labeo umbratus and Pomadasys commersonnii had medium values (5,5–8 kJ·g−1; 4–8% fat) and Lichia amia and Argyrosomus hololepidotus low values (

Catch per unit effort was obtained for the nekton of the Swartkops estuary near Port Elizabeth by means of gill netting. Fifty gill net catches were made in which 1 269 fish were caught in areas representative of the mouth, middle and upper reaches of the estuary. Pomadasys commersonni, already shown to be the most abundant angling species in the estuary, dominated gill net catches both in terms of mass (29%) and numbers (17%). The family Mugilidae (five species) comprised 25% of the mass and 42% of the numbers caught. Environmental factors and availability of food that might determine distribution offish in the estuary are discussed. The largest mean mass per individual was found in Chanos chanos (4 473 g), Elops machnata (1 656 g) and Valamugil buchanani (1 580 g). Lowest mean masses were recorded for Monodactylus falciformis (63 g), Rhabdosargus holubi (88 g) and Liza dumerili (94 g).

The biology of filter feeding teleosts in St Lucia, was studied for two years from 1976 to 1978. The three common species, Gilchristella aestuarius, Hilsa kelee and Thryssa vitrirostris were studied with the composition and cyclical nature of the zooplankton which formed their food. Stolephorus commersonii and Hepsetia breviceps which were rare were only briefly examined. The zooplankton was dominated by the calanoid Pseudodiaptomus stuhlmanni which formed > 70 % of the calorific value of the zooplankton for 70 % of the study period. The mysid Mesopodopsis africana was second in importance in terms of calorific contribution while the amphipod Grandidierella lignorum was relatively abundant. Larval forms, particularly post-veligers of Assiminea bifasciata were also important. There was a close correlation between the zooplankton cycles, both diel and annual, and the feeding, reproduction and recruitment of the three common filter feeding teleosts. G. aestuarius spent its whole life-cycle in the system and spawned in early summer when the resulting juveniles could feed on the summer zooplankton peaks. They grew at 0.5 cm month−1 and attained maximum size in one year. They were non-selective taking mainly P. stuhlmanni and post-veligers. H. kelee spawned in the sea and juveniles were common in St Lucia during 1978 when they fed non-selectively, chiefly on P. stuhlmanning the summer before disappearing over the winter. The resulting offspring went through a sequence of dietary changes which were closely related to zooplankton cycles. The importance of P. stuhlmanni in the pelagic food web of St Lucia is illustrated. The species supports not only the filter feeding teleosts but indirectly the predatory fish Argyrosomus hololepidotus and Elops machnata which feed on G. aestuarius and T. vitrirostris.

The food and feeding ecology of piscivorous fish in Lake St Lucia was monitored for two years. Piscivorous fishes feed predominantly on the planktivorous Gilchristella aestuarius and Thryssa vitrirostris but a wide range of prey species was recorded. Numbers of the predominant piscivores, Argyrosomus hololepidotus and Elops machnata, in an area appear to be related to the densities of their major prey, T. vitrirostris and G. aestuarius. Large piscivorous fishes are restricted to the deeper portions of the lake, whereas small piscivores such as Johnius belengerii and Terapon jarbua feed predominantly on small fishes in the littoral zone. The highly significant correlation between the composition of prey fish species in the lake and prey fish species in the diet of piscivorous fishes, indicates that piscivores are feeding in a density dependent manner. However, factors such as habitat, fish size and swimming speed of prey species are shown to be important in prey selection. Juvenile fish of species such as Sarotherodon mossambicus, Liza macrolepis and Acanthopagrus berda remain in shallow marginal areas, thus avoiding large piscivorous fishes. However by frequenting shallow areas these species become vulnerable to bird predators, especially egrets and herons.

The food and feeding habits of the three most important market fish in Hawaiian ponds (Mugil cephalus, Chanos chanos, and Elops machnata) were analyzed to ascertain the position of these fish in the food-chains and the food cycle occurring within the ponds. Mullet (M. cephalus) subsist primarily on littoral diatoms and blue-green algae, the presence of a unique pharyngeal filtering device prohibiting them from swallowing larger forms. No variation in food because of season or size of fish was found. Milkfish (C. chanos) are also herbivores; juveniles consume unicellular and other minute algae while larger fish take an increasing amount of larger filamentous algae. Competition for food between mullet and milkfish is greater than hitherto supposed and cannot be diminished under present operational procedures. An increased food supply for both species probably could be achieved by the application of inorganic fertilizers together with the construction of additional shallow areas in the ponds. Ten-po...