Netherlands Journal of Sea Research最新文献

The growth of juvenile Japanese flounder Paralichthys olivaceus (Temming et Schlegel) exposed to various feeding and temperature regimes was studied in the laboratory. The temperature limits for growth were estimated from about 9 to 32°C, and highest growth rate was observed at a temperature of 25°C. For fish of an initial total length of about 3 cm, exposed to temperatures between 10 and 30°C with unlimited food, the daily growth rate in length (dL; mm·d⁻¹) was described as a function of temperature (T,°C) by the equation: dL=0.005 T² − 0.0000046 T⁴ − 0.35. Fish fed with mussel meat or mysids displayed similar protein conversion efficiencies. The relationship between condition factor of the fish and the proximate body composition of the fish is reported.

Stomach contents were examined of 4527 adult individuals of 12 flatfish species collected during the 1982–1983 Bohai Sea Fisheries Resources Investigation. Their food habits, diet diversity, similarity of prey taxa, trophic niche breadth and diet overlap were systematically analysed. Ninety-seven prey species belonging to the Coelenterata, Nemertinea, Polychaeta, Mollusca, Crustacea, Echinodermata, Hemichordata and fish were found and five of them were considered to be principal prey for flatfishes: Alpheus japonicus, Oratosquilla oratoria, Alpheus distinguendus, Loligo japonicus and Crangon affinis. Among the flatfishes, Paralichthys olivaceus was piscivorous, whereas Pseudopleuronectes yokohamae and Pseudopleuronectes herzensteini both had polychaetes and molluscs as their main prey groups. Pleuronichthys cornutus was classified as a polychaete-mollusc eater, with a strong preference for crustaceans. Verasper variegatus, Cynoglossus semilaevis, Eopsetta grigorjewi and Cleisthenes herzensteini ate crustaceans. Kareius bicoloratus was classified as a mollusc-crustacean eater. Cynoglossus abbreviatus, Cynoglossus joyneri and Zebrias zebra were grouped as crustacean-fish eaters. However, Z. zebra also took polychaetes and C. abbreviatus and C. joyneri preyed on some molluscs. Trophic relationships among the flatfishes were complicated, but they occupied distinctive microhabitats in different seasons and selected their specific prey items, which was favourable to the stability of the flatfish community in the Bohai Sea.

Behavioural preference tests were used to determine if sediment selection played a role in habitat choice. Four species of juvenile pleuronectids were given a choice of eight sediments in a carousel and final choices were recorded after 20 h. Juvenile flatfishes demonstrated strong selection for sediments less than 500 μm. Juvenile starry flounder (Platichthys stellatus) selected larger particles with increasing fish size. Starry flounder under 25 mm in length chose mud, 50–80 mm fish chose mud and mixed mud sediments and larger juveniles (>150 mm) confined themselves to find sand. Juvenile halibut (Hippoglossus stenolepis) at 50–80 mm preferred a combination of mud and fine sand and were spatially segregated. Yellowfin sole (Pleuronectes asper) at 50–80 mm showed a slight preference for mud and mixed mud sediments over sand, a selection that became stronger in larger (>150 mm) fish. Juvenile rock sole (Pleuronectes bilineatus) at 50–80 mm preferred substrata of sand and mixed sand nearly 90% of the time. All species seldom selected sediments which were too coarse to allow the flatfishes to bury themselves, such as granular or pebble substrata. The results of these laboratory studies can be used to predict the distribution of juvenile flatfishes in a nursery area.

Juvenile flatfish were studied in a tropical estuary, Arquipélago dos Bijagós in Guinea-Bissau from October 1992 until April 1993. A total of eight flatfish species, belonging to the families Bothidae, Cynoglossidae, Psettodidae and Soleidae, were found. In comparison with other fish groups, flatfishes abundance was low with densities of less than 13 ind·100 m⁻². One species, Citharichthys stampflii, occurred in densities high enough to permit an analysis of distribution, growth and mortality. During the period of study, settlement of C. stampflii was observed in the estuary. Its distribution suggested a preference for offshore areas, densities decreasing towards the river systems. Repeated sampling in the intertidal area of Ilheu de Flamingos permitted a preliminary estimate of mortality and growth. Instantaneous mortality rates were about 0.03·d⁻¹, which is similar to estimates in temperate estuaries. Growth rates were slightly above 1 mm·d⁻¹, about the same as those measured in subtropical estuaries.