Morphological and Allometric Changes in Anguilla japonica Larvae

Abstract

The freshwater eel Anguilla japonica is rapidly decreasing in number and has not yet been successfully mass produced. This may be at least partially attributable to the unique and long early life history of the eel. Therefore, we investigated its ontogeny of morphometry and growth pattern in larval stages to provide baseline information for understanding the early life history and improving seed rearing technology. This study was conducted for 200 days after hatching (DAH) and analyzed morphometry and allometry for eel larvae. The following cultured eel larval stages were identified: the yolk sac larvae stage (0–6 DAH, 3.23–6.85 mm total length (TL)), the pre-leptocephalus stage (7–30 DAH, 6.85–15.31 mm TL), and the leptocephalus stage (50–200 DAH, 15.31–60.06 mm TL). Cultured and wild eel larvae could be divided into characteristic larval stages at similar sizes. However, compared to wild eels, cultured eels had a slower growth rate and fewer preanal myomeres. Meanwhile, cultured eel larvae rarely had a mixed feeding period as the absorption of endogenous reserves was completed by 7 DAH. The lower jaw of eel larvae was significantly longer than the upper jaw from 50 DAH. In the pre-leptocephalus and leptocephalus stages, eel larvae showed continuous positive allometric growth at trunk height and tail muscle height with change to the willow leaf-like form. These growth characteristics may be the result of adaptation to the migration over long distances and to a diel vertical migration. The inflection point in the body parts growth patterns showed only before 30 DAH, and mass mortality appeared at this period. Therefore, to improve the growth and survival rates of cultured eel seed, it is necessary to focus on improving the feeding and rearing protocol until 30 DAH.

Allometric growth and larval development in Pacific red snapper Lutjanus peru under culture conditions

“…The allometry during larval period has been described in many species, including freshwater species like the golden dwarf cichlid Nannacara anomala Regan, 1905 (Kupren, Prusińska, et al ., 2014), the burbot Lota lota (L. 1758) (Kupren, Trabska, et al ., 2014), the catfish Lophiosilurus alexandri Steindachner, 1876 (Guimaraes de Mello et al ., 2015), the Eurasian perch Perca fluviatilis (L. 1758) (Kupren et al ., 2019); anadromous like the Siberian sturgeon Acipenser baeri Brandt, 1869 (Gisbert, 1999), catadromous like Anguilla japonica Temminck and Schlegel 1846 (Shin et al ., 2022); and marine species similar to the Pacific red snapper, like the spotted sand bass Paralabrax maculatofasciatus (Steindachner, 1868) (Peña & Dumas, 2009), the common dentex Dentex dentex (L. 1758) (Koumoundouros et al ., 1999) and the California halibut Paralichthys californicus (Ayres, 1859) (Gisbert et al ., 2002). In all the species the same growth pattern has been reported: a high allometric growth of head and tail sections during the early larval stages and a posterior reduction in allometry and a clear tendency to isometric growth during the end of the larval period (Fuiman, 1983).…”