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    • Article

      Changes in plasma osmolality and chloride concentration during abrupt transfer of milkfish (Chanos chanos) from seawater to different test salinities 

      RP Ferraris, JM Almendras & AP Jazul - Aquaculture, 1988 - Elsevier
      Milkfish juveniles (40, 120 or 260 g) were acclimated to 32 ppt seawater, then abruptly transferred to water with salinities of 0, 16, 32 (control) or 48 ppt. Blood samples were taken 0, 1, 2, 3, 5, 7 or 14 days after transfer. Survival rate was 95% or greater in all salinities. Plasma osmolality in fish exposed to salinities other than 16 or 32 ppt deviated from control values immediately after transfer but were subsequently regulated to near normal levels after several days. Although these deviations were significant, they were relatively small (≤20% of initial) as plasma osmolality changed by less than 0.07 mOsm/kg per unit change environmental salinity. Plasma chloride values generally followed the same pattern of changes as plasma osmolality. When these deviations were integrated across time, summed deviations (mOsm·day kg−1 or mEq·day l−1) were proportional to the osmotic or ionic gradient but were inversely proportional to size. For 40-g fish, summed deviations were larger in 48 than in 0 ppt; for 120- or 260-g fish, these deviations were larger in 0 than in 48 ppt. These results indicate that small milkfish tend to adapt better to fresh than to hypersaline water while larger milkfish are more likely to find hypersaline water less stressful than freshwater. Like other organ systems previously studied in milkfish, these size-dependent adaptations in osmoregulatory mechanisms reflect natural habitat shifts during development.
    • Article

      Distribution pattern of shrimps and fish among Avicennia and Rhizophora microhabitats in the Pagbilao mangroves, Philippines 

      P Rönnbäck, M Troell, N Kautsky & JH Primavera - Estuarine, Coastal and Shelf Science, 1999 - Elsevier
      For sustainable management of mangrove ecosystems, there is a pressing need to increase our knowledge of fish and invertebrates associated with this system. This study sampled microhabitats (89–258 m2) inside the mangrove forest at Pagbilao, the Philippines, on two consecutive spring tides using stake nets. Distribution patterns of shrimps and fish were compared among four microhabitats that differed in dominant mangrove species (Avicennia marina, A. officinalis or Rhizophora apiculata), structural complexity of the root system, and proximity to open water habitat. A 5 to 6-year-old replanted Rhizophora microhabitat was also sampled to study faunal recolonization following replantation. The mean (±SE) density of the shrimp community was 1·5±0·2 shrimps m−2, dominated by Palaemonidae, followed by Acetes sp., Penaeus merguiensis and Metapenaeus ensis . The highest shrimp density was observed in the replanted Rhizophora habitat, which also had the highest structural complexity. The mean (±SE) density and biomass of the fish community was 5·1±2·0 fish m−2and 10·4±3·3 g m−2, respectively, dominated by Ambassis kopsi, A. urotaenia and Atherinomorus balabacensis. The fish community preferred the pneumatophore (Avicennia) microhabitats to the prop root (Rhizophora) habitats. Highest fish abundance and biomass were observed in the most inland habitat, which also lacked larger (total length >100 mm) carnivorous fish. The results demonstrate the extensive use of intertidal mangrove forests by vagile fauna, as well as the successful recolonization by shrimps and fish of replanted Rhizophora habitat. The role of mangroves as predation refuges, based on the distribution pattern of shrimps and fish, is discussed. Sampling strategies in mangrove intertidal habitat are also outlined.