Sardinella longiceps

INTRODUCTION

• The Indian oil sardine (Sardinella longiceps) is a species of ray-finned fish in the genus Sardinella.

• It is one of the two most important commercial fishes in India.

• The Indian oil sardine is one of the more regionally limited species of Sardinella and can be found in the northern regions of the Indian Ocean.

• These fish feed on phytoplankton (diatoms) and zooplankton (copepods).

DIAGNOSTIC FEATURES

• The body of these Sardinella is particularly elongated even to the point of being sub cylindrical.

• They have a slightly rounded belly and have eight rays on their pelvic fins.

• They have a very large number of gill rakers and a faint golden spot behind the gill opening.

• They also have a faint golden midlateral line, as well as a black spot on the hind border of their gill covers.

GROWTH AND DEVELOPMENT

• S. longiceps typically reaches sexual maturity at around 15 cm in length and one year of age.

• While the lifespan of this fish is estimated to be about 2.5 years, it can be challenging to determine precisely due to the formation of annual rings in their scales.

• These rings may develop for various reasons other than yearly changes in the environment.

• After the first year, however, these rings become a more reliable indicator of age.

• They may form due to reduced feeding activity, which is often associated with plankton scarcity during the temperature rise in the summer environment.

REPRODUCTION

• In S. longiceps reproduction is influenced more by water conditions before and after the monsoon season than by seasonal patterns.

• This variability affects the spawning season, which can occur between June and December. Individuals typically spawn only once during this period. The timing of spawning is influenced by the size and age of the fish. Older, more mature adults (between 17 and 19 cm) tend to spawn earlier in the season, while juveniles arrive later.

• Commercial fishing peaks in June and July, coinciding with the period when juvenile fish have accumulated sufficient energy reserves for their first spawning season. Second spawning events are rare in S. longiceps, with females being more likely to exhibit this behavior.

• Ovary development is categorized into stages I-VI, with stages IV, V, and VI being capable of spawning.

• Fish at stage IV have ovaries that occupy two-thirds of their body cavity, while stage VI ovaries completely fill the cavity with large, transparent ripe eggs.

• Each spawning event yields approximately 75,000 eggs, which develop within 24 hours.

• These spherical eggs range from 1 to 4 mm in diameter and are characterized by an oil globule constituting a significant portion of the yolk, hence the term 'oil sardines'. Larval fish have 53 myotomes, but adults typically have 46-48 vertebrae.

• During the initial stage of development, movement is minimal, but larvae gradually begin serpentine swimming.

• By the end of the first day, the oil globule within the yolk disappears. On the second day, larval pigmentation stabilizes, and eye coloration becomes a silvery white sheen. By the third day, the yolk is completely absorbed.