Early Osteological Development of Larvae and Juveniles in Red Spotted Grouper, Epinephelus akaara (Pisces: Serranidae)

Ontogeny of skeletal ossification in Labeo calbasu (Hamilton, 1822) using differential fluorescence staining technique

The present study was carried out to study the larval skeletal development in Labeo calbasu by using a modified double skeletal staining technique with Alizarin red and Alcian blue. The larval samples were obtained after induced breeding of wild L. calbasu germplasm from the River Ganga. Samples from 2 to 20 dph (day post hatching) were preserved in 4% neutral phosphate buffered formalin solution. Alizarin red and Alcian blue were used to stain the bony and cartilage parts of the skeleton, respectively. The size of the specimens ranged from 6.6 ± 0.16 to 15.6 ± 1.15 mm. The development of skeleton was observed at very early stages. A straight notochord throughout its length and origin of caudal fin rays were seen on 2 dph. The ventral spines, unbranched caudal fin rays and hypurals at ventral side of notochord were clearly visible from 4 dph. Most of the head skeletal elements and vertebral column with vertebral centrum and neural spines started appearing at 4 dph. The dorsal and caudal fins with branched rays and the opercular and jaw bones started ossifying between 10 and 20 dph. The present study gives an idea about the skeletal development process as well as detects the skeletal abnormalities in Indian major carp, L. calbasu.

Effects of different light spectra on embryo development and the performance of newly hatched turbot (Scophthalmus maximus) larvae

Light is a key environmental factor that synchronizes various life stages from embryo development to sexual maturation in fish. For turbot, light spectra have the most influence at the larval and juvenile stages. In the current study, differences in the development of embryos and the performance of newly hatched turbot larvae exposed to five different spectra: full spectrum (LDF), blue (LDB, peak at 450 nm), green (LDG, peak at 533 nm), orange (LDO, peak at 595 nm) and red (LDR, peak at 629 nm), were examined. At 62.8 h post fertilization, a higher number of embryos exposed to short-wavelengths (LDG and LDB) had developed a heartbeat in comparison with embryos exposed to other wavelengths. Larvae exposed to the green spectrum had higher malformation rates than larvae exposed to the other spectra, indicating that larvae exposed to green light may have significantly reduced survival rates. The results of non-specific immunity parameters showed that the mRNA expression levels of cathepsin D (CTSD), cathepsin F (CTSF), catalase (CAT) and metallothionein (MT) in larvae exposed to LDB were significantly higher than those exposed to other spectra, but CAT activity in larvae exposed to LDB was significantly lower than larvae exposed to the other spectra. There was no significant difference in MT activity in larvae exposed to the five different spectra. The mRNA expression level of lysozyme (LZM) in larvae exposed to LDR was significantly higher than other spectra, while there was no significant difference in LZM activity observed in larvae exposed to LDR, LDG, LDB and LDF. The difference of the enzyme activity of total superoxide dismutase (T-SOD) was not significant among larvae exposed to the five spectra. mRNA expression of the heat shock protein 70 (HSP70) was significantly higher in newly hatched larvae exposed to LDB, LDR and LDG, indicating that larvae exposed to LDB, LDG and LDR exhibited a stress response. The mRNA expression level of the insulin-like growth factor-1 (IGF-1) and growth parameters in the newly hatched larvae exposed to the different spectra were not significantly different. The results of the present study indicate that LDO and LDF should be used for embryo incubation and newly hatched larvae when rearing turbot. This study provides a theoretical basis for optimizing the incubation light environment for fertilized turbot eggs, promoting immunity and reducing stress responses in newly hatched larvae.