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Summary In line with current conservation efforts, some success in the captive breeding of the seahorse Hippocampus kuda (Teleostei: Syngnathidae) has been achieved. To evaluate the salinity tolerance of these hatchery-bred juveniles, 9-week-old H. kuda were transferred without prior acclimatization from ambient full strength seawater (32–33 ppt) to salinities ranging from freshwater to 85 ppt. Survival, growth, and total body water content were determined after 4 and 18 days of exposure. Juvenile H. kuda are able to survive in dilute seawater (15 ppt) for at least 18 days without any compromise in growth (both wet and dry body weight), survival, and total body water. Fish abruptly transferred to freshwater succumbed within 4–24 h, while survival of 5 ppt-reared fish decreased to ca. 65% in 18 days. Although 10 ppt-reared seahorses had growth and survival comparable with the control (30 ppt seawater), total body water was significantly elevated indicating reduced adaptability. The upper limit of H. kuda salinity tolerance was 50 ppt. Fish reared at salinities ≥55 ppt succumbed within 24 h. Like several other marine teleosts, growth and survival of juvenile H. kuda tended to peak in diluted seawater salinities of 15 and 20 ppt. These results indicate the possibility of growing hatchery-bred H. kuda in brackishwater environments. [ABSTRACT FROM AUTHOR]

Two populations of catarina scallop, Argopecten ventricosus (= circularis) (Sowerby II, 1842), were evaluated for their larval growth and survival responses to different stocking densities. Larvae from the Magdalena population had a significantly higher growth but equal survival at a density of 10 larvae ml-1 compared with 20 larvae ml-1 Larvae from the Concepcion population grew better at densities of 15 and 20 larvae ml-1 than at densities of 5 and 10 larvae ml-1, although survival was lower at higher densities. The differing response of these two populations to increased stocking densities is explained as a possible consequence of different population adaptations related to behavioural and physiological mechanisms. The importance of establishing optimum stocking densities for molluscan larvae is stressed in two contexts: maximizing growth and survival for different populations when artificially reared, and understanding the effects of stocking densities on phenotypic variance, especially during the course of genetic studies. [ABSTRACT FROM AUTHOR]