LABORATORY SPAWNING AND REARING OF A MARINE FISH, SILVERSIDE MENIDIA-MENIDIA MENIDIA

Adult silversides, M. menidia menidia (L.), were collected in early March 1974 and maintained in 3 recirculating seawater tanks in the laboratory. Respective groups were fed Moore-Clark Fry Fine at 3, 7 and 10% of their body weight per day. The photoperiod (light intensity approximately 2000 lx) was increased in increments of 10 min/day from 12 to 14 h light. The water temperature was increased by 1.degree. C/day from the ambient collection temperature, 14.degree. C, to 22.degree. C. Twenty-four days after beginning laboratory conditioning, fish in each tank were stripped. There was a significant increase (X2, .alpha. = 0.05) in the number of ripe males at all 3 feeding levels, compared to an initial field-collected group that was checked at the beginning of the conditioning period. Females also showed significant increases in ripeness at the 7 and 10% but not at the 3% feeding level. The gonadal indices (gonad weight expressed as percentage of body weight) of both sexes were significantly greater than those measured for the initial field-collected group, but did not differ from those of adults collected from the field at the time laboratory conditioning was terminated. Techniques for maintaining eggs from field-ripened adults in the laboratory were developed, and the effect of salinity on the percentage emergence of larvae determined. The highest emergence rate of larvae was 61% when eggs were maintained at 30% S. Emergence was 56% at 20.permill. S and 47.permill. S. The effect of delayed feeding on survival and growth of larvae was determined at 20 and 30.permill. S and 25.degree. C. Survival and growth was best for larvae fed Artemia sp. nauplii immediately after emergence at 30.permill. S.