Influence of water pH and temperature on breeding and embryo development of Indian spiny loach (Lepidocephalichthys thermalis)

The Indian spiny loach (Lepidocephalichthys thermalis), a member of the Cobitidae family and small indigenous species (SIS), is an emerging candidate species for diversification in the Indian aquaculture sector due to its ecological adaptability and culture potential. However, the captive breeding and seed production protocols for commercial seed production of loach fish remain unexplored. Therefore, the present experiment was aimed at studying the effects of water pH and temperature manipulation on the natural spawning and embryonic development of L. thermalis. The study carried out two different experiments and in the first experiment, fish was released in three different pH regimes such as 6.0–6.5 (T1), 7.0–7.5 (T2), and 8.0–8.5 (T3) for a period of 60 days. A total of 9 experimental troughs (water holding capacity – 48 L) were used to stock the loach fish (average length - 5.77 ± 0.11 cm, average weight - 0.78 ± 0.06 g) at 1:2 sex ratio (female: male). Out of these three pH treatments, significantly higher (P < 0.05) spawning rate (1047.0 ± 71.33 eggs/g of female), fertilization rate (86.66 ± 6.42 %) and hatching rate (79.86 ± 5.57 %) were obtained in T2 treatment group which indicated better breeding performance of fish in that group. Further, the loach fish embryonic development was also recorded in T2 treatment group bred fish. In the thermal stimulation experiment, loach fish was kept at a constant water temperature of 26 °C and the fish were exposed to four different water temperatures such as T1 (25 °C), T2 (24 °C), T3 (23 °C) and T4 (22 °C) on 15th and 30th days. During this trial, no sign of breeding activity was recorded in different treatment exposed fish. However, the histological analysis of oocytes documented five different oocyte maturity stages such as chromatin nucleus stage (CNS), perinucleus stage (PS), vitellogenic stage (VS), ripening egg (RE), and hydrated oocytes (HYO) during the thermal stimulation experiment. Further, the study found significantly higher (63.24 ± 4.26 %) and lower (27.05 ± 2.14 %) final gamete maturation rates in T4 and T2 groups exposed fish, respectively. Based on the above results, it can be concluded that the pH of 7.0–7.5 is more suitable for successful captive spawning of loach fish. On the other side, temperature manipulation (sudden reduction of water temperature from 26 °C to 22 °C) had significantly improved the final gamete maturation of L. thermalis fish under captivity. These findings provide valuable insights for its inclusion in India’s aquaculture diversification strategies through captive seed production and also provide a promising solution for this species conservation at wild conditions.