Captive breeding, embryonic development, and conservation of Horabagrus nigricollaris

[bekateen]

Again, I'm not a fan of using hormones to induce spawns, but this paper describes efforts to conserve an endangered species, and the article has helpful information about eggs and development:

C.P. Abhilash, Charan Ravi, Saikrishnan K.R., Sarath Varghese, Neethu Z., Chandana B.L., Ajith Kumar T.T., Uttam Kumar & Sarkar V. S. Basheer. 2025. Captive breeding, embryonic development, and conservation of the endangered catfish, Horabagrus nigricollaris (Pethiyagoda & Kottelat 1994): a first report. Aquaculture International, 33:121 https://doi.org/10.1007/s10499-024-01789-6

Abstract
Black collared yellow catfish,

Horabagrus nigricollaris

, an endangered endemic catfish of the River Chalakudy, Kerala, cherished by the locals is one of the most sought-after ornamental fish. Due to the limited range of distribution and rarity, H. nigricollaris needs to be conserved in situ. Captive breeding, embryonic development, nursery rearing, and restocking of the species were done for the first time ever as part of conservation efforts. A total of 10 breeding trials with a sex ratio of 1:1 was conducted between 2022 and 2023. Half of brooders spontaneously spawned after receiving an injection of WOVA-FH hormone (1.0 ml/kg body weight) with a latency period of 11.3 ± 0.37 h. Mean spawning fecundity was 1740 ± 193 with fertilization rate of 68.7 ± 2.4%, hatching rate of 71.3 ± 1.9%, and survival rate of 88.1 ± 3.2%. The fertilized eggs were adhesive and elliptical, golden yellow in color with a diameter of 2.1 ± 0.02 mm. The first mitotic cleavage occurs at 35 min post-fertilization (pf) and morula, blastula, and gastrula stages were completed at approximately 3.50 h, 6.15 h, and 10.30 h, respectively. The incubation period was 27 ± 3 h at a temperature between 26 and 28 °C. Newly hatched larvae were transparent and light yellowish, measuring 4.4 ± 0.2 mm, with a large oval-shaped yolk sac. Yolk absorption was completed within 3 days post-hatching. The larvae were fed a systemic and overlapping diet of live and artificial feed over 30 days, resulting in an average length and weight of 20.4 ± 0.2 mm, 1.3 ± 0.1 g, and a survival rate of 56.1 ± 3.2%. About 1500 fish of 120 days old with mean length 73 ± 3.0 mm and average weight 3.2 ± 0.2 g were reintroduced into the Chalakudy River at the Vettilapara region, which is the type locality of the species, to safeguard and increase the wild population.

Keywords: Endemic, Breeding, Restocking, Western Ghats, Black collared yellow catfish

[Bas Pels]

Producing 1500 fish from most likely 5 pairs of parents.

This does seam to be a good idea - BUT. But I wonder how much influence this has on the genetic diversity of the wild population.

As the population has a small area, and is endangerd, this population was not large. Say a thousand breeding pairs, which produced some 300 offspring each. After 120 day however, perhaps 1 percent of them is still alive - being 3000 fish.

I f you add 1500 fish to such a system, the added fish will influence the next generation largely - one in three fish will come from this group, being bred from only 10 fishes

The idea was good, but effectueally the genetic base of the whole species has dramatically been reduced.

[aquaholic]

Yes but it's easily possible to mix in as many males into a single spawn of eggs as you wish if genetic diversity is a factor. You could have fifty males to a female for example.

And hormonal inducement can double or triple gamete production if the total number of endangered specimens is a factor.

So a very useful process which is harder and more challenging than natural spawning. One still needs to condition brood fish, keep them happy, recognise which ones are likely to be receptive, when and how much hormone to deliver and if more is needed midway.

[edds]

The genetics of alleles in F1 organisms compared to the wild there is theoretically little loss of diversity, assuming a good range of genetics in the parents. However it could still have an impact as you suggest I. The genetics make up of the next generation if they substantially outnumber the other offspring.

It might come down to the survival rate of the introduced fish and whether they have any impact on the survivability of existing naturally spawned offspring.

[aquaholic]

Another aspect of injecting hormone and letting fish spawn by themselves is that adding these induced fish into a tank of non injected fish of same species is often enough to synchronise successful spawning of them all. It does help to adjust tank conditions favourably on top of hormone - lighting, temperature, dissolved oxygen, water movement, spawning sites etc.

Another interesting aspect is that inducing individual broodstock fish of difficult species several times or over several years makes natural spawning more likely to occur and indeed sometimes injecting with saline alone is enough to trigger spawning activity.

This applies to many fish species, not just catfish.