African catfish (Clarias gariepinus ) is a widely cultivated freshwater fish species in the world . In addition to poor nutrition and adverse environmental conditions, the high variability and unpredictability of fish reproductive performance pose significant challenges to the mass production of fingerlings and overall productivity (Uedeme-Naa and Nwafili, 2017). To address these challenges, the use of plant and organic feed additives to improve gonadal maturation and egg viability has gained attention in aquaculture (Al-Khalaifah et al., 2020) . Cocoa (Theobroma cocoa) products have been shown to possess a wide range of health benefits and are rich in bioactive compounds , which have shown positive impacts on fish growth, health, and reproduction (Al-Khalaifah et al., 2020). There is a paucity of information on the effect of cocoa bean meal (CBM) on the reproductive development of catfish. Therefore, this study aimed to investigate the effect of varying dietary levels of CBM on the ovarian development of C. gariepinus.
Materials and methods
A total of 200 female C. gariepinus post-fingerlings, 9 weeks old and with similar body weights (23.12 ± 0.71 g), were procured from the Fish Multiplication Centre of the University of Nigeria, Nsukka, and used for the study. The fish were acclimatized in a concrete pond for 3 weeks and were then randomly divided into five treatment groups (T1, T2, T3, T4, and T5) in a completely randomized design with four replications. Each replicate was kept in a 100 L basin with 10 fish each. Five iso-nitrogenous (35% crude protein) and iso-caloric (2.51 Mcal/Kg) diets were formulated, with CBM at inclusion levels of 0, 10, 20, 40, and 50%, respectively, for T1, T2, T3, T4, and T5 diets. The fish received the diets for 9 weeks at the rate of 3.5% of the total biomass. The water was changed twice every week to ensure optimal quality. At the end of the study, fish samples were collected from each replicate, weighed, and taken to the laboratory for further processing. The fish were stunned, dissected, and the gonads were harvested, weighed, and fixed in Bouin’s fluid for 24– 48 hours before proceeding with histological analysis, as described by Cevaco et al. (1997). The Gonadosomatic index (GSI) was estimated as described by Çek et al. (2001 ). The fish ovarian developments were assessed on gross morphologically and histologically, as adopted and modified from earlier characterizations and classifications (Cek et al., 2001; Saka and Adeyemo, 2015). Body weights, ovarian weights, and GSI measurements were subjected to analysis of variance using IBM SPSS (Version 21), and mean differences were separated using Duncan’s New Multiple Range Test procedure, accepted at the 0.05 probability level.
The results of the study showed that feeding fish with CBM at 10% dietary inclusion (T2) resulted in a significant improvement (P<0.05) in body weight (BW), ovarian weight (OW), and GSI values compared to the other groups. The OW and GSI values in the control, T3, and T5 groups were similar (P≥0.05). The OW and GSI values in T4 were similar (P≥0.05) to T2 and those of the other groups. Moreover, the inclusion of cocoa bean meal in the diet of Clarias gariepinus catfish improved ovarian growth and development, as reflected in the gross morphology of the ovary. At week 9, the ovaries of the fish in T2 and T4 were observed to be better developed (stage IV) than those in the other treatment groups. The ovaries of the fish in the control group were in stage II of ovarian development, while those of T3 (20% CBM) and T5 (50% CBM) were in stage III of ovarian development.
The study observed a group synchronous type of ovarian development in the fish ovary. The results of the histology studies revealed that CBM caused a general improvement in the follicular development of the catfish ovaries. While oocytes in all developmental stages were observed in all groups, T1 showed the least development, with the secondary growth phase being predominant. On the other hand, the ovaries of T2, T3, T4, and T5 fish predominantly had oocytes in the maturation phase (stage 6). Additionally, ovaries of T2 (10% CBM) showed the optimum maturation, with sparse levels of oocytes in the secondary growth phase.
From the observation of this study, it can be suggested that CBM inclusion in fish feed can facilitate ovarian maturation. However, optimum ovarian maturation can be achieved with 10% CBM inclusion in fish meals.
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