Abstract.-The effect on growth and survival of the initial stocking density (30, 20 and 10 eggs L -1 ) in larval rearing of spotted rose snapper (Lutjanus guttatus) was evaluated. The eggs were incubated in nine black fibreglass tanks with three replicates for treatment. Larvae were cultured in the same tanks using the green water technique. Larvae were harvested at 45 days post-hatch (DDE). Total length (LT), weight (PH) and survival rate (S) were determined. Initial stocking density did not affect growth and survival rates. Therefore, it is advisable to carry out larval culture of the spotted rose snapper using 30 eggs L -1 to maintain good growth levels.

Karyotypes of the purple snails Plicopurpura pansa and Plicopurpura columellaris (Gastropoda: Muricidae). The karyotypes of the purple snails Plicopurpura pansa (Gould, 1853) and P. columellaris (Lamarck, 1816) were established from 17 and 13 adults, respectively; and from eight capsules with embryos of P. pansa. In P. pansa were counted 59 mitotic fields in the adults and 127 in embryos; and 118 fields in P. columellaris. Chromosome numbers from 30 to 42 were observed in both species. Such a variation was notorious in each sample and there was no evidence of any relationship with tissue (gill, muscle and stomach). Both species has a typical modal number of 2n=36 chromosomes. Five good quality chromosome spreads were selected from adults of each species to assemble the karyotype. Classic cytogenetics statistics like relative lengths, arm ratio, centromeric index and the difference between long and short arms are presented. There were three pairs of metacentric and fifteen pairs of telocentric chromosomes in both species. This classification was not strong enough, so the chromosome complement by species was divided in four groups ("a", "b", "c" and "d") on the basis of relative lengths (p+q). A comparison of p+q in each chromosome pair was estimated within and between species by two ways analysis of variance and Tukey tests (P<0.05). Significant differences were identified among chromosome groups in each species; the differences between species were given by the first three pairs of chromosomes (group "a" biarmed) and the last two pairs (group "d" uniarmed). Deviations in chromosome number and relative lengths probably are given by chromosome rearrangements, related with chromosome polymorphism and presence of the atypical microchromosome "B". The fundamental number in both species was characterized by 42 chromosome arms. No sex chromosomes were identified.

Abstract.-The effects of different water temperatures (22, 25, 28 and 31ºC) and salinities between 0 and 60 psu (with intervals of 5 psu) on egg incubation of the bullseye puffer (Sphoeroides annulatus) were evaluated in this study. The embryos could not develop at 22ºC and the highest hatching rate for normal larvae was observed at 28ºC. At 0, 50, 55 and 60 psu larvae were unable to develop. Highest hatching rates were obtained at 25, 30 and 35 psu. It was concluded that water temperature and salinity affects the incubation period, embryo development stage and larval survival of the bullseye puffer.

Abstract.-The spotted rose snapper (Lutjanus guttatus) is one of the most commercially important fish species inMéxico. As it is considered a suitable candidate for culture, then it is necessary to identify its nutritional requirements in order to succeed. The aim of this study was to evaluate the effects of different protein and lipid levels on growth and survival of juvenile spotted rose snappers. Nine semi-purified diets were formulated with three protein levels (40, 45 and 50%) and three lipid levels (9, 12 and 15%). Hatchery-produced juvenile spotted rose snappers (2.2 ± 0.1 g) were used throughout the eight-week feeding experiment. Body weight, specific growth rate, condition factor, feed consumption, feed conversion rate, and survival were determined in each treatment at the end of the experiment. The highest weight gained and better feed conversion ratio were obtained in fish fed diets with 45 and 50% protein and their three lipids levels. Survival, feed consumption and condition factor were not affected by the treatments. These results indicate that juvenile spotted rose snappers require a minimum of 45% protein and 9% lipid for maximum growth and survival.

Abstract.-Three prophylactic treatments using three dosages each were used as surface disinfectants in bullseye puffer Sphoeroides annulatus eggs to study their effect on bacterial load reduction and hatching rate. Eggs were treated with proteolytic enzyme to remove stickiness. Tested treatments were: acriflavine