Proximate composition and mineral contents of fishmeal prepared from fresh byproduct of the three fish species in Tekeze reservoir of Northern Ethiopia

Technical Summary: Proximate and Mineral Composition of Fishmeal from Tekeze Reservoir Byproducts

Problem Statement
In Ethiopia, low livestock productivity is frequently attributed to feed shortages, poor-quality feed resources, and inadequate animal nutrition. While the Tekeze reservoir in Northern Ethiopia supports diverse fishery resources with an estimated annual production potential of over 1,000 tons, a significant portion of the harvest (65–68%) consists of primary processing byproducts (heads, bones, skin, scales, fins, and viscera). Currently, these byproducts are often discarded, leading to environmental pollution, odors, and public health concerns, while representing a loss of valuable nutrients. Although fishmeal is a recognized high-quality feed ingredient, there is a scarcity of data regarding the proximate and mineral composition of fishmeal produced specifically from the byproducts of the dominant fish species in the Tekeze reservoir: Nile tilapia (Oreochromis niloticus), catfish (Clarias gariepinus), and barbus (Labeobarbus intermedius).

Methodology
The study was conducted at the Tekeze reservoir, utilizing byproducts collected from three harvesting stations. For each of the three target species, 30 kg of byproducts (viscera, heads, scales, skin, and bones) were collected, mixed to form composite samples, and transported to the Abergelle Agricultural Research Center.

The fishmeal preparation followed a standardized process:

1. Cleaning: Byproducts were washed to remove extraneous matter.
2. Cooking: 10 kg of cleaned byproduct per species was cooked in water at 95–100°C for 20–30 minutes.
3. Pressing: The cooked material was drained and pressed to remove oil and water to prevent oxidation.
4. Drying: The resulting press cake was dried in a raised rack solar tent dryer for three days.
5. Milling and Storage: Dried samples were ground to pass through a 60-mesh screen (0.25 mm) and stored in air-tight bags at 4°C.

Chemical analyses were performed using Association of Official Analytical Chemists (AOAC) methods. Proximate composition (moisture, crude protein, ether extract, crude fiber, and ash) and metabolized energy (ME) were determined. Mineral content (Calcium, Magnesium, Phosphorus, and Potassium) was analyzed using atomic absorption spectrophotometry, flame photometry, and colorimetric methods. Data were analyzed using one-way ANOVA and Duncan's multiple range test (p < 0.05).

Key Results
The study revealed significant variations (p < 0.05) in the nutritional profiles of the fishmeals based on the source species:

• Proximate Composition:

  • Crude Protein (CP): Barbus meal exhibited the highest CP content (55.36%), followed by tilapia (48.27%) and catfish (44.76%).
  • Ether Extract (EE) & Metabolized Energy (ME): Catfish meal had the highest lipid content (30.78%) and consequently the highest ME (4580.85 kcal/kg DM). Tilapia (18.94% EE) and barbus (15.51% EE) had lower values.
  • Ash Content: Barbus (28.91%) and tilapia (28.88%) meals had significantly higher ash content compared to catfish (24.30%).
  • Moisture: Catfish meal had the highest moisture (7.11%), while barbus had the lowest (5.86%).
  • Crude Fiber: No significant differences were observed among the species, with values ranging from 0.59% to 0.77%. Barbus meal had the highest crude fiber (0.77%), followed by tilapia (0.70%) and catfish (0.59%).

• Mineral Composition:

  • Calcium (Ca): Barbus meal contained the highest calcium (10.56%), significantly higher than tilapia (8.32%) and catfish (8.64%).
  • Magnesium (Mg): Tilapia meal showed the highest magnesium concentration (2.88%), while barbus and catfish were equal at 1.73%.
  • Phosphorus (P) and Potassium (K): No significant differences were found among the species. Phosphorus ranged from 4.70% to 5.46%, and Potassium ranged from 0.21% to 0.23%.

Significance and Claims
The authors conclude that fishmeal produced from the byproducts of Nile tilapia, catfish, and barbus in the Tekeze reservoir is a nutrient-rich ingredient suitable for supplementing conventional livestock and aquaculture diets in Ethiopia. The study highlights that these meals are particularly rich in protein, energy, and macro-minerals.

Specifically, the paper claims:

• Barbus meal is a superior source of crude protein and calcium.
• Catfish meal offers the highest energy density due to its high lipid content.
• Tilapia meal provides a high magnesium content.

The authors position this work as a contribution to sustainable feed development and resource-use efficiency, suggesting that converting these underutilized byproducts into fishmeal can reduce environmental pollution while addressing nutrient deficiencies in local animal feeds.

Limitations
The authors explicitly note that the study is limited to proximate composition and selected macro-minerals. It does not assess amino acid profiles, fatty acid composition, vitamin content, storage stability, processing yields, economic feasibility, or animal performance trials. Consequently, the findings are presented as preliminary nutritional data, and the authors advise caution when extrapolating these results to commercial production or practical feeding strategies without further investigation.