Seed production of pearlspot, Etroplus suratensis, in recircualtory aquaculture system: An innovative approach for livelihood of aqua-farmers

Abstract

Pearlspot, Etroplus suratensis (Bloch, 1790) is commonly known as green chromide and is a popular brackishwater food fish in the western coast of India. Its firm meat texture and characteristic flavour makes it a favourite fish in the state of Kerala, which has recognized pearlspot as its state fish with the sole objective of conserving the natural stocks and enhancing its aquaculture production. Pearlspot fetches upto INR 250 to 500 in markets across the country and it sells for even higher prices in the niche markets. Recently, the fish has also started becoming popular among fish hobbiyists as an ornamental fish. Being a fish with an omnivores feeding habit, aquaculture of pearslpot is considered economical and highly adaptable to different culture systems like pond, pen and cages. A major bottle neck that is limiting the expansion of pearlspot farming is the insufficient availability of quality seed for stocking in different growout systems. Although, several studies report the breeding and seed production of pearlspot in earthen ponds, cement tanks and raceways, large scale seed production technology for the species is a challenging task due to issues such as pair formation and parental care among others. In order to overcome these issues as well as to carry out mass scale seed production, the Navsari Gujarat Research Center of CIBA (NGRC-CIBA) has developed a cage based mass spawning system for pearlspot and an RAS based Hatchery system (Incubation & larval rearing) at its research farm in Matwad, Navsari, Gujarat.Mass spawning of pearlspot in floating net cage installed in brackishwater pond Twenty four nos. (12 pairs) of pearlspot brooders comprising of both male (TL: 20.5 ± 0.201 cm & BW: 222 ± 4.33 g) and female fish (TL: 18.57 ± 0.44 cm & BW: 179.15 ± 10.97 g) were stocked in a floating cage (4 × 4 ×1.5 m) at a sex ratio of 1:1. The cage was installed in a brackishwater earthen pond. The brooders were segregated on the basis of the secondary sexual characteristics. Female fish were identified using the protruded pinkish enlarged ovipositor whereas, male fish were recognized with the presence of the whitish pointed genital papilla. The brooders were fed using formulated pellet diet containing 32% crude protein and 5% lipid @ 5% of body weight daily in two equal feeding rations. 12 circular clay bowls (Egg collectors) were placed in the cage at an interval of 1 m distance from each other as a substrate for laying the eggs. These egg collectors were suspended in the cage using nylon twine and tied to the cage collar for easy observation and collection of eggs. The number of egg collectors required depends on the number of breeding pairs released into the cage. A total of 27 spawnings were recorded within a span of 3 months, with an average of 2 - 3 spawnings/week. The number of eggs layed in each spawning ranged from 600 to 1,600 numbers, with an average fecundity of 900 nos./ spawning. The eggs were oblong, heavily yolked, light peach in colour and were adhesive in nature and attached to the substrate. Regular inspection of the egg collection bowls were carried out during morning and evening at 07:30 and 18:00 hours respectively, for presence of eggs. The physico-chemical parameters of the pond water during the spawning of pearlspot in the cage ranged as follows, temperature: 29 – 31o C, salinity: 9 – 17 ppt, Dissolved oxygen: 5 – 6 ppm and pH: 8.1 - 8.3