Morphological development, allometric growth and behaviour of hatchery-reared California halibut Paralichthys californicus were studied from hatching to metamorphosis (42 days post hatch, dph) at 18 C. Mean standard length (L S ) of larvae and juveniles increased from 2·1 mm at hatching to 10·5 mm at metamorphosis with the increase in length being approximately linear. Stages of morphological development were described using the alphabetic staging (A-I) used for other flatfish species. Organogenesis and differentiation were more rapid and complex in yolk-sac (hatching, stage A-3 dph, stage B), preflexion (3-19 dph, stages B-C), and flexion larvae (from 20 to 23 dph, stages D-E), as larvae developed most of their sensory, feeding, respiratory and swimming systems. After notochord flexion at 24-25 dph (stage F), most morphological changes were related to the progressive transformation from a bilateral symmetrical larva to an asymmetrical benthic juvenile (42 dph, stages G-I).

Establishment of hatchery breeding techniques for the threatened green sturgeon Acipenser medirostris is important for research and conservation hatcheries. Injections of either gonadotropin-releasing hormone analog (GnRHa) or GnRHa plus domperidone were used to induce ovulation in 13 female Klamath River green sturgeon and to induce spermiation in 19 males. Ovulated eggs were either rinsed in water or not rinsed before fertilization, and the eggs were fertilized with different milt dilutions and for different lengths of time. After fertilization, eggs either were allowed to adhere to the bottom of glass dishes or were silted for 1 h and then incubated in McDonald or upwelling jars. All broodfish ovulated or spermiated in all hormonal treatments, and the best treatment was GnRHa injected alone in a single dose of 10 lg/kg for males or in a 1lg/kg priming dose and a 19-lg/kg resolving dose for females. Females were held at 12-138C, and ovulation was observed 14 6 3 h (mean 6 SD) after the second injection. Domperidone was not required for successful ovulation and appeared to reduce the adhesion of ovulated eggs. From 49,000 to 115,000 eggs were collected from each female, and from 30 to 300 mL of milt were collected from each male. Sperm cell concentrations in milt ranged from 2.9 3 10 8 to 5.4 3 10 9 sperm/mL, and the sperm exhibited 90-100% motility for up to 5 min. In all experiments, egg rinsing improved fertilization success by 5-12%. Embryo survival to neurulation in the McDonald jars was lower (5-32%) than that in the upwelling incubators (60-82%). Green sturgeon eggs were sensitive to the high-impact rolling action at the bottom of the McDonald jars, probably due to the large egg diameter (mean 6 SD ¼ 4.33 6 0.14 mm) and thinner chorion (42 6 4 lm) relative to eggs of white sturgeon A. transmontanus (diameter ¼ 3.79 6 0.03 mm; chorion thickness ¼ 115 6 6 lm).

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This study evaluated weaning success of California halibut, Paralichthys californicus, larvae onto a microdiet at various stages of development utilizing growth, survival and digestive enzyme activity. Weaning onto a microdiet was evaluated at 16, 26, 36 and 46 days posthatch (dph). Alkaline and acid proteases and leucine aminopeptidase activities were measured after weaning and compared between the weaned treatment and Artemia‐fed controls. Survival was significantly lower in the microdiet‐fed treatments compared to the control groups. Growth was significantly reduced in all weaning treatments compared to the control, except for the 46 dph group. No differences in enzyme activities were detected between treatment and diet at 16 and 26 dph; however, activities were higher for the microdiet‐fed larvae at 36 and 46 dph. This study demonstrates that California halibut larvae possess a differentiated and effective digestive system early in development and can be weaned with relative success (>40% survival) before completion of the metamorphosis (i.e., 36 dph). The lack of weaning success at an early date cannot be entirely because of the absence of a functional stomach but could be related to, among other factors, the low‐microdiet ingestion rates observed and higher leaching of smaller microdiets.