A technique for increasing ploidy in the blue tilapia, Tilupia nurea, was investigated for the purpose of determining its effect on standard length. Gametes of T. aweu were stripped from ripe adults and eggs were fertilized with donor sperm from several males. A description of the extra-oral incubation system used for the embryos is provided. This system resulted in a maximum of 90% successful hatch. Normal egg development was interrupted by immersion of newly fertilized eggs (15 min post-insemination) in cold or hot water for various durations. The reliability of these techniques for inducing polyploidy was examined using increased volume of erythrocyte nuclei as a criteria for success. A cold shock of from 32' C (ambient) to 11" C for a 1 h duration resulted in the largest incidence of polyploidy (75 %). Polyploid fish were found to be larger than diploid siblings when measured at 14 weeks of age.

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SUMMARYPlatyfish, Xiphophorus maculatus, are polymorphic for the patterns red-dorsal (Dr) and spotted-dorsal (Sd) fins, both controlled by closely linked loci on the X chromosome of Jamapa strain, Jp 163A. The intensity of red pigment looks the same in males and females, but spectrophotometric analysis of dorsal fin extracts showed that heterozygous intact males have significantly more red pigment (drosopterin) than homozygous or heterozygous females or castrated males. The mechanism of Dr expression in Jamapa is, thus, similar to the one present in the Belize stock, where a sex difference is readily apparent that is known to be under androgenic control. The Sd phenotype is identical in both sexes. Sd and Dr are not restricted to the X chromosome, and no evidence for gene dosage compensation has been obtained. Within the Jamapa stock the expression of Sd and Dr are best described in terms of dominance and recessiveness. Dr is strongly augmented by a testicular hormone. Dr and Sd have been separated by crossing-over. In natural populations both genes can occur by themselves, linked to each other or to other pigment genes. The development of the Sd macromelanophores is not contingent upon the presence of pterinophores (Dr) in the dorsal fin or elsewhere in the body.

Striped bass fingerlings of two sizes, 1.7 and 6.0g, were stocked in the fall of 1974 into floating cages placed in a sea water lagoon off of Shelter Island, New York. Duplicate stocking densities of 100, 200, 300 and 400 fish per 1.82m3 cage were established. Low water temperature (1.0 C) occurred in January and February 1975 and resulted in heavy mortality of the caged fish. In order to prevent the complete loss they were removed and overwintered in indoor pools from February until June at which time they were restocked in the floating cages at densities of 50 and 90 fish per cage. The mean growth rates by stocking densities indicated that fastest growth occurred with 100 fish per cage. Owing to mishaps which included escapes from the cages and mortalities, only 14% of the fingerlings stocked were harvestable as 0.25 and 0.5 Kg fish in the fall of 1975. The mean dress‐out weight of these 280 fish was 81%. Relative food conversion values were between 1.4 and 1.8:1.

Japanese aquaculturists have contributed greatly to the culture technology of Pacific puffer fish of the genera Fugu, which presently rank second only to the yellow tail (Seriola quinqueradiata) in total annual tons cultured in Japan. Culture of the Atlantic puffer fish of the genera Sphoeroides, however, has received little attention despite its high commercial value. Adult northern puffers (Sphoeroides maculatus) were collected from local waters in the spring and summer and maintained in both open and closed sea water systems. Eggs were stripped onto glass plates and fertilization was achieved using the wet method. One hundred percent fertilization and approximately 90% hatching were obtained when specially designed incubation chambers were used. The time from fertilization to hatching was 72 hours at 24 C and the newly hatched larvae were between 1.9 and 2.4 mm in length. Yolk sac absorption required 2–3 days at 24 C, during which time feeding was not observed. The larvae were maintained in 160–liter algal bloom systems using a Chlorella sp. and were fed marine rotifers, Brachionus plicatilis, as a first food. Newly hatched Artemia salina were provided 10 days post‐hatching. Thirty days posthatching the fish were given a prepared fish diet which they readily accepted and are presently being maintained. Cannibalism was observed to occur when the fish were approximately 20 days old and did not appear to be correlated to stocking densities or size. This behavior ceased when the fish were eating the prepared fish flesh diet.