Shinsuke Morioka

Otolith development and daily increment formation in larvae of the Kabyabya, a Malawian cyprinid, Opsaridium tweddleorum

Features of the sagitta, asteriscus, and lapillus of laboratory-hatched larvae of the Kabyabya, Opsaridium tweddleorum, were investigated until day 33 after hatching. The sagitta was round until day 17, subsequently becoming arrowhead-shaped with the development of anterior and posterior rostra. Increments in the sagitta increased at the rate of one per day before rostrum formation. However, they were occasionally overestimated in rostrum sections as a result of subdaily increment occurrence. Furthermore, both anterior and posterior rostra were fragile, being thin and platelike, and were often damaged during the extraction and grinding processes. The lapillus was also round until day 17, thereafter becoming fan-shaped. Increments in the lapillus were distinctive from the core to the margin, usually increasing at the rate of one per day after hatching. The asteriscus appeared in fish larger than 9.15 mm in standard length (from day 17), being oval with a somewhat ambiguous core, causing difficulty in discerning the first increment. These features indicated that the lapillus was the most appropriate otolith part for daily increment analysis in this species, although the sagitta was useful before rostrum formation.

Nutritional condition of larval milkfish,Chanos chanos, occurring in the surf zone

In order to clarify the nutritional conditions of larval milkfish in the surf zone, the following parameters were examined: 1) DNA and RNA content and RNA/DNA ratio of fed and unfed larvae collected from the surf zone and reared in the laboratory; 2) survival rate of the unfed larvae; and 3) total length, otolith increment counts and RNA/DNA ratio of wild larvae collected daily from the surf zone. The DNA and RNA content of the unfed larvae decreased, but increased in fed larvae. The RNA/DNA ratio decreased in unfed larvae, whereas in the fed larvae it decreased for the first three days after capture and increased thereafter. These results indicated that the values of DNA and RNA content and RNA/DNA ratio could be used as an indicator of nutritional condition of milkfish larvae after 6 days of starvation. Although total length of the wild-larvae did not show serial changes, their otolith increment counts showed continuous increases, indicating that the larvae sojourned in the surf zone for several days. In the same period, RNA/DNA ratios of the wild larvae decreased continuously, the ratios of larvae with fewer otolith increment counts being relatively higher than those of larvae with greater increment counts. Based on these results, the milkfish larvae remaining in the surf zone were concluded as being under insufficient nutritional conditions.

Development of 18 novel polymorphic microsatellite markers for the mysid crustacean Mesopodopsis orientalis

We have developed microsatellite DNA markers for Mesopodopsisorientalis (Tattersall 1908), a widely distributed mysid crustacean in shallow waters of the coastal and estuarine systems across India to Indonesia and the Philippines. A total of 18 novel polymorphic microsatellite markers were identified in 32 individuals from a sandy beach at Teluk Kumbar in Penang Island, Malaysia. The number of alleles per locus ranged from 3 to 17. The observed and expected heterozygosities varied from 0.031–1.000 to 0.092–0.938, respectively. These polymorphic markers could be available for future investigations of genetic diversity and structure of M.orientalis populations.

Development and characterization of 29 polymorphic microsatellite loci for Esomusmetallicus

Twenty-nine microsatellite loci were isolated and characterized from the genome of Esomus metallicus. Flanking polymerase chain reaction primers were designed and used to amplify these loci in 32 individuals. All loci were polymorphic; with allele numbers ranged from 2 to 27, observed heterozygosity from 0.031 to 0.969 and expected heterozygosity from 0.031 to 0.957. All conformed to Hardy–Weinberg equilibrium and no evidence of null alleles was observed. Pairwise comparisons between alleles did not detect any cases of linkage disequilibrium. The high level of polymorphisms observed in these microsatellite loci should enhance future investigation of the genetic differentiation and structure of populations of E. metallicus.