THE REPRODUCTIVE BIOLOGY OF THE RABBITFISH IN HONG KONG

In vitro fermentation of Gracilaria lemaneiformis and its sulfated polysaccharides by rabbitfish gut microbes

This study intended to characterize the Gracilaria lemaneiformis (SW)-derived polysaccharide (GLP) and explore the fermentation aspects of SW and GLP by rabbitfish (Siganus canaliculatus) intestinal microbes. The GLP was mainly composed of galactose and anhydrogalactose (at 2.0:0.75 molar ratio) with the linear mainstay of α-(1 → 4) linked 3,6-anhydro-α-l-galactopyranose and β-(1 → 3)-linked galactopyranose units. The in vitro fermentation results showed that the SW and GLP could reinforce the short-chain fatty (SCFAs) production and change the diversity and composition of gut microbiota. Moreover, GLP boosted the Fusobacteria and reduced the Firmicutes abundance, while SW increased the Proteobacteria abundance. Furthermore, the adequacy of feasibly harmful bacteria (such as Vibrio) declined. Interestingly, most metabolic processes were correlated with the GLP and SW groups than the control and galactooligosaccharide (GOS)-treated groups. In addition, the intestinal microbes degrade the GLP with 88.21 % of the molecular weight reduction from 1.36 × 105 g/mol (at 0 h) to 1.6 × 104 g/mol (at 24 h). Therefore, the findings suggest that the SW and GLP have prebiotic potential and could be applied as functional feed additives in aquaculture.

Ginseng® as a reproductive enhancer agent for African catfish, Clarias gariepinus (Burchell, 1822)

Ginseng (Ge) is one of the most famous and precious consumed herbal medicines around the world. Ge plant roots have many advantages regarded as important in increasing fish production. Thus, the present study was conducted to investigate the possibility of using different levels (0.0, 100, and 200 mg/kg diet) of Ge as a reproductive enhancer agent for African catfish, Clarias gariepinus males. Results revealed that fish fed 200 mg Ge/kg diet significantly (P ˂ 0.05) increased growth performance, feed efficiency, gonado-somatic index, hematological parameters, serum follicle-stimulating hormone, total antioxidant capacity, sperm quality parameters, and ultrastructure of spermatozoa, as well as led to positively improved of the histological structure of the testes tissue compared to other treatments. Based on the obtained findings, it could be concluded that the effective use of dietary Ge at a level of 200 mg/kg as a promising reproductive agent for adult African catfish males consequently led to the sustainability of aquaculture for African catfish.

Hydroyeast Aquaculture® as a reproductive enhancer agent for the adult Nile tilapia (Oreochromis niloticus Linnaeus, 1758)

Tilapias are becoming increasingly popular culture fish because of their superior culture adaptability. In recent years, there has been a great interest in the use of probiotics in fish aquaculture. The objectives of the present study were to evaluate the effect of dietary graded levels (0, 5, 10, and 15 g/kg commercial diet, referred to treatments numbers T1, T2, T3, and T4, for males and T5, T6, T7, and T8 treatments for females) of a new probiotic Hydroyeast Aquaculture(®) on hematological and biochemical parameters, serum sex hormones, and the reproductive efficiency parameters of the adult Nile tilapia Oreochromis niloticus for 8 weeks. Results revealed that high levels of probiotics diet, 15 g (T4, ♂) and 10 g (T7, ♀) probiotic/kg diet, significantly (P ≤ 0.05) enhanced the physiological responses (hematological as well as serum biochemical parameters) together with, reproductive performances (sex hormones, testes and sperm quality parameters, absolute and relative fecundity, and ovarian measurements). Therefore, it could be conclude that Hydroyeast Aquaculture(®) is useful at levels of 15 g (T4) and 10 g (T7)/kg diet in improving the reproductive efficiency of adult O. niloticus males and females, respectively. Thus, the use of Hydroyeast Aquaculture(®) may be economically important for fish hatcheries.