# Evaluation of Different Terrestrial Oils as an Alternative to Dietary Fish Oil on Feed Physical Properties, Growth, Feed Utilization, and Fatty Acid Profile of Gangetic Catfish (Mystus cavasius)

## TL;DR

This study finds that terrestrial oils, especially mixed oils and black soldier fly larvae oil, can replace fish oil in the diet of Gangetic catfish without harming growth or feed quality.

## Contribution

The study identifies specific terrestrial oils as effective fish oil substitutes in catfish diets, with mixed oils showing the best performance.

## Key findings

- Mixed oil diets led to the best growth performance in Gangetic catfish.
- Fish oil replacement with terrestrial oils did not negatively affect feed efficiency.
- Black soldier fly larvae oil and palm oil showed good results in maintaining heart-healthy fats.

## Abstract

This study tested whether terrestrial oils (TOs) can replace fish oil (FO) in the diet of Gangetic catfish (Mystus cavasius). Over a 70-day feeding trial, fish were given five different diets: one with FO and four with TOs (soybean oil, black soldier fly larvae oil, palm oil, and a mix of black soldier fly larvae, soybean, and palm oils). The mixed oil diet led to the best growth, followed by the diets with black soldier fly larvae and palm oils. Soybean oil alone resulted in the poorest growth. While growth and body fat content varied, feed efficiency was not affected. Fish fed with FO had the highest levels of heart-healthy fats, while those fed with black soldier fly larvae and palm oils also showed good results. Linolenic acid was the lowest in the mixed oil diet, and lauric acid was the highest in the black soldier fly larvae oil group. Feed quality was best in the soybean and mixed oil diets. This study concludes that TOs, especially mixed oils, black soldier fly larvae oil, and palm oil, can successfully replace FO in the diets of Gangetic catfish.

The global demand for fish oil (FO) is increasing while its supply is decreasing, which has limited its use in aquafeeds. Research on alternative terrestrial oils (TOs) for commonly cultured fish species in Bangladesh is limited. This research involved a 70-day feeding experiment to assess the effectiveness of replacing FO with TOs in the diet of Gangetic catfish (Mystus cavasius). Five diets were formulated: a control diet (D1) with fish meal and FO, and four diets replacing FO with soybean oil (D2), black soldier fly larvae oil (D3), palm oil (D4), or a mixed oil combination (D5) of 50% black soldier fly larvae oil, 25% soybean oil, and 25% palm oil. A total of 675 fish (0.5 g each) were distributed in 15 100 L aquariums (45 fish/aquarium) and fed to satiation twice daily. Fish fed with Diet D5 showed significantly higher growth, followed by those fed with D3, D4, and D1, while D2 resulted in significantly lower growth. Fish on the D5 diet consumed the most feed, followed by those on the D3 and D2 diets, with similar feed intake levels for those on the D1 and D4 diets. FCR, FCE, and PER were not significantly affected by dietary oil sources. Whole-body lipid content (p < 0.05) was significantly lower in the D3 group and higher in the D2 group, while other groups showed intermediate values. The fatty acid composition in the fish reflected their diets: significantly higher n-3 LC-PUFA (EPA + DHA) content was observed in the D1 group, followed by the D4 and D3 groups, and fish fed with D2 and D5 showed significantly lower values. Alpha-linolenic acid C18:3n-3) was significantly higher in the D2 group, followed by the D3, D1, and D4 groups, with the D5 group having a significantly lower value. Total MUFA was significantly higher in D4, followed by D1, D5, and D3; the D2-fed group showed a significantly lower value. Lauric acid (C12:0) was significantly higher in D3, followed by D5; other groups showed significantly lower values. Feed physical properties were significantly influenced by oil type, with water stability, pellet durability, and palatability being significantly highest in the D2 and D5 diets, followed by D3 and D4, with D1 being the lowest. Fish on the D1 and D5 diets had a significantly higher condition factor (CF) compared to fish on the D2 diet. Considering the growth and overall performance in the current study, we concluded that under the current dietary composition, TOs can effectively replace FO in the diets of Gangetic catfish, with mixed oils, black soldier fly larvae oil, and palm oil being the most promising alternatives.