Comparative assessment of egg and larval quality traits of progeny from wild-collected and captive-matured brooders of endangered golden mahseer, Tor putitora: A prelude to quality broodstock development and seed production

Abstract

In this study, we assessed the differences in reproductive outputs (fertilization and hatching rates); egg quality (egg size increase during hardening, biochemical composition, carotenoid content, and characteristics of ovarian fluid); and larval performance traits (growth, microanatomical development, survival, starvation response, and critical thermal tolerance) of progeny from captive-matured and wild-collected golden mahseer brooders. Fertilization and hatching rates were significantly higher in wild-collected brooders than in captive broodstock. Captive brooder eggs were significantly larger in size and weight but had significantly lower energy/nutrient (total protein, glucose, and triglyceride) reserves and total carotenoids. On the contrary, ovarian fluid from captive females had significantly higher levels of total protein, glucose, and triglycerides, possibly indicating weaker egg membrane and nutrient leakage due to membrane damage or lysis. During water hardening, the cumulative weight increase due to a higher water uptake rate was significantly higher in the wild origin eggs than captive brooder eggs. CTmax of larvae obtained from captive-matured brooders was lower during the early developmental stages (15 dph), but became similar to the CTmax of wild brooder's larvae at 35 dph. On the other hand, CTmin of captive origin larvae was higher than their wild counterparts at all examined stages. There were no differences in starvation tolerance of larvae between the two brooder types. Histological observations revealed that the intestinal nutrient absorption and hepatic nutrient accumulating efficiency during the early developmental stages was relatively lower in captive origin larvae, corresponding to the comparative growth metrics observed until 35 dph. Also, the survival percentage at 90 dph was lower in the larvae of captive brooders than their wild counterparts. Collectively, these findings indicate potential areas for improvement in the captive broodstock management of the endangered cyprinid, golden mahseer.