Elsevier

Aquaculture

Volume 459, 1 June 2016, Pages 73-83
Aquaculture

Spawning, embryonic development and larval culture of redhead dottyback Pseudochromis dilectus Lubbock, 1976 under captivity

https://doi.org/10.1016/j.aquaculture.2016.03.017Get rights and content

Highlights

  • The Redhead Dottyback Pseudochromis dilectus was successfully bred under captivity for the first time and its courtship behaviour, embryonic and larval developments were documented.

  • The pairs laid ball-shaped egg mass which consisted of 400 to 500 spherical eggs/pair/spawning. Size of individual egg varied between 1743 and 1919 µm and incubation period lasted for 96h.

  • Larval rearing was carried out with different combinations of live feeds to standardize its larval rearing protocol.

  • The results revealed that naked ciliate Euplotes sp. is a promising starter live feed to overcome the critical period, and the brackish water cladocera, Diaphanosoma celebensis enriched with microalgae can be effectively utilized as a substitute in place of Artemia nauplii for its hatchery production.

Abstract

Reproductive behaviour, captive breeding, embryonic, larval development and suitable live feed for Pseudochromis dilectus were found out. Fishes ranging in total length 80–120 mm (male) and 70–80 mm (female) were reared in FRP tank (1000-L) for six months to develop pairs. The pairs laid ball-shaped egg mass (25 to 35 mm diameter) which consisted of 400 to 500 spherical eggs/pair/spawning (n = 18).The size of the individual egg varied between 1743 and 1919 μm and all the eggs were interconnected by fine sticky threads. The egg ball was white or transparent on the first and second day, black on 3rd day and silvery on 4th day of incubation. The hatching rate varied between 91 and 95%, and the peak hatching took place under complete darkness on completion of 96 h incubation. Total length of the newly hatched larvae varied between 5.1 and 5.3 mm with mouth gape 150 to 160 μm. First feeding started at 10 to 12 h after post hatch. The study concluded that Euplotes sp. (0 to 5 dph), enriched rotifer (6–15 dph) and microalgae enriched Diaphanosoma celebensis (16 to 30 dph) can be used as effective feed for high survival of larvae of P. dilectus. On 20 dph the metamorphosis initiated and became juvenile stage at 30 dph (82%). At 45 dph, all the larvae transformed to juvenile and shifted from pelagic to epibenthic in the aquarium with denser body having reddish colouration.

Statement of relevance

Pseudochromis dilectus (Family: Pseudochromidae) is a species of keen interest in marine aquarium trade and has distribution in the Western and Central Indian Ocean to Sri Lanka. As its males are colourful than the female, males are selectively exploited from the nature for aquarium trade which is also causing threat to natural population thereby reducing its availability. Hence captive production is a potential solution for reducing pressure on the natural stocks. However no scientific studies were conducted in P. dilectus with an objective to captive breeding. Hence the present study was aimed to generate baseline information on its reproductive behaviour, spawning, egg morphology, embryonic and larval development of P. dilectus and also to find out suitable live feed for higher survivability of larvae, their metamorphosis and juvenile production under captive conditions with a view to develop a reliable captive breeding and rearing techniques for its mass scale production.

Introduction

Marine ornamental fish plays an important role in interior decoration, and its culture is a rewarding industry as aquarium keeping has become the second popular hobby in the world. As a result, the ornamental fish trade is a global multi-million dollar industry with a world export value of US$ 362 million and corresponding imports valued US$ 362 million (FAO, 2014). Over the years since 1985, its international trade showed an increasing trend (Moorhead and Zeng, 2010) with an average growth rate of approximately 14% per year with an estimated wholesale trade of nearly US$ 1 billion and retail trade of about US$ 3 billion (Olivotto et al., 2005). However the marine aquarium trade relies predominantly on wild collected specimens (90%) by way of indiscriminate collection methods which created a negative repercussions on coral reefs and marine ecosystems (Olivotto et al., 2003), and most marine aquaria are stocked from the wild-caught specimens (Wabnitz et al., 2003). Increasing pressure on natural populations of reef dwelling organisms due to their expanding popularity in the aquarium trade has stimulated interest in the breeding and culture of marine tropical fish (Holt, 2003, Olivotto et al., 2003, Olivotto et al., 2011). Thus captive production of most demanded group would certainly help to relieve the fishing pressure on coral reefs (Tlusty, 2002; Pomeroy et al., 2006). Moreover, the hatchery produced juveniles are proved to be hardier, less susceptible to diseases and survive better in aquaria than their wild caught counterparts (Dawes, 1999; Ogawa and Brown, 2001, Ziemann, 2001, Olivier, 2003, Wabnitz et al., 2003, Wittenrich, 2007, Anon, 2011a). In the marine aquarium trade, the species under the genus Pseudochromis are the most sought-after group of dottybacks due to their contrasting colours, tiny size, hardiness and adaptability to live in aquaria (Thresher, 1984).

The redhead dottyback P. dilectus (Family: Pseudochromidae) is a species of keen interest in the marine aquarium trade. This family comprises 4 sub-families, 16 genera with over 120 species, and the subfamily Pseudochrominae alone consists of 5 genera with more than 70 species and are distributed throughout the tropical and subtropical Indo-West Pacific (Nelson, 2006). Though collection of these Indo-Pacific coral reef dwelling species from the wild is difficult due to their occurrence in crevices and deeper waters, the dottyback fish truly are a joy to keep in aquarium on account of their brilliant colour and intriguing personality (Debelius and Baensch, 1994). The prices are also very high when they are available in the market because of their rare availability. As a result currently there is a heavy reliance on wild caught Pseudochromids to satisfy the demand. Due to the importance of dottyback in aquarium trade, various research are ongoing in the aspects of their sex change (Wittenrich and Munday, 2005), reproductive behaviour, breeding and juvenile production of Pseudochromis fridmani (Brons, 1996; Moe, 1997) and Pseudochromis flavivertex (Brons, 1996, Olivotto et al., 2006a). In India and Sri Lanka, P. dilectus are exploited from their natural source for aquarium trade and due to heavy reliance on nature, it also showed a decline in its population from 2008 onwards (Jonathan, 1993, Anon, 2011b). Moreover scientific information on its reproductive behaviour and early development is scarce though it can be reliably reared in captivity in large quantities. Therefore, the present study was aimed to generate baseline information on reproductive behaviour, spawning, egg morphology, embryonic and larval development, metamorphosis and juvenile production of P. dilectus under captive conditions, and also to find out suitable live feed for higher survivability of larvae with a view to develop a reliable captive breeding and rearing techniques for its mass scale production.

Section snippets

Pair formation

The fishes (n = 30) ranging from 70 to 120 mm total length, of which 15 with greenish colour having total length 70–80 mm (presumptive female) and the rest having 80–120 mm total length with reddish-orange and greenish tinge (presumptive male) were collected from the pet shop, Mandapam, India, and stocked (1:1 ratio) in 1 ton FRP tank for pair formation. The experimental tanks were provided with biological filter and kept in the outdoor hatchery where an incident light intensity of 2500 to 3000 lx was

Pair formation and Broodstock developments

After a period of six months rearing in 1 ton FRP tanks, 6 pairs were formed. The males are reddish-orange with greenish tinge, and had elongate and slender body, while the females are dark greyish-green and smaller in appearance, with a plumpy abdomen. Most of the time, pairs were hiding in their respective hiding places except the intermittent patrolling by male. The pairs which exhibited territorial behaviour and aggression towards the other tank mates were chosen as pairs, then stocked in a

Discussion

Since, male dottybacks are colourful than female, they are selectively exploited from the nature for the trade which is also causing threat to natural population thereby reducing the availability (Jonathan, 1993; Anon, 2011b). A scientific study to understand the change in population of coral reef fishes in the Gulf of Mannar National Park, Mandapam, Tamil Nadu, India indicated significant decline in their population including P. dilectus from 2002 to 2008 (Anon, 2011b). Males of many coral

Conclusion

This study emphasized an important step for successful spawning, larval rearing and juvenile production of P.dilectus. Breeding and spawning were consistently obtained, but the larval survivability depends on the size of first food offered. Provision of Euplotes sp. during the initial phase (up to 5 dph); enriched rotifer B. rotundiformis (6–15 dph) and microalgae enriched D. celebensis (16–30 dph) are essential for obtaining significantly higher survival of larvae and healthy juveniles. D.

Acknowledgements

This study was undertaken with the funding from Indian Council of Agricultural Research (ICAR) ((MD/IDP/03)) in the marine hatchery of Central Marine Fisheries Research Institute, Cochin. Special thanks to the Director, CMFRI for the help at various stages of this study. The authors are also thankful to all staff of Marine Hatchery of CMFRI for their valuable support.

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