# Size-Related Quality Characteristics of Cage-Reared Butter Catfish (Ompok bimaculatus) in a River Basin

## TL;DR

This study shows that larger butter catfish from Thailand's Pak Phanang Basin have better nutritional quality and safer microbial profiles, which could help in GI certification.

## Contribution

The study establishes size-based quality markers for butter catfish to support GI certification and standardization.

## Key findings

- Larger fish had higher moisture, fat, energy, and better essential amino acid profiles.
- Medium and large fish showed healthier fat profiles with more polyunsaturated fats.
- Microbial safety improved with increasing fish size, with no harmful bacteria detected.

## Abstract

Butter catfish raised in cages in the Pak Phanang Basin (Nakhon Si Thammarat, Thailand) are sold in different market sizes, but it is unclear whether size can help verify product quality and support Geographical Indication (GI) certification. This study compared dorsal meat from small, medium, and large fish to link size with key quality traits. Larger fish had higher moisture, fat, and energy, while protein levels were similar across sizes. Small fish showed slightly higher flesh pH, and all groups had a pale whitish to slightly yellow color. Large fish contained more calcium and magnesium and higher levels of key essential amino acids, especially leucine and lysine, suggesting better protein quality. Medium and large fish also showed a healthier fat profile with more polyunsaturated fats. Total bacterial counts decreased with increasing size, and no harmful bacteria were detected in any group. These findings provide useful baseline markers to help describe, standardize, and document Pak Phanang Basin butter catfish for consumer confidence and GI requirements.

This study evaluated whether body size could serve as a quality and traceability marker for cage-reared butter catfish (Ompok bimaculatus) from the Pak Phanang Basin, Nakhon Si Thammarat, Thailand, in support of Geographical Indication (GI) certification. Fish were classified into three commercial size grades—small (12–15 fish/kg), medium (6–10 fish/kg), and large (3–5 fish/kg)—corresponding to fish harvested after 6, 8, and 12 months of rearing, respectively, with mean body weight and total length of 75 ± 7 g and 19.8 ± 1.1 cm (small), 120 ± 9 g and 25.8 ± 2.1 cm (medium), and 260 ± 10 g and 32.2 ± 2.8 cm (large). Dorsal muscle samples were comparatively analyzed to assess size-related differences in physicochemical properties, nutritional composition, and microbiological quality. Proximate analysis showed that moisture, lipid, ash, and total energy contents increased significantly with fish size (p < 0.05), whereas protein and carbohydrate contents did not differ significantly among size groups (p > 0.05). Small fish exhibited slightly higher muscle pH (7.02 ± 0.18) than medium and large fish (6.65 ± 0.11 to 6.66 ± 0.25) (p < 0.05). Flesh color was characterized by a pale whitish to slightly yellow appearance with high lightness (L*; p < 0.05), while redness (a*) and yellowness (b*) did not differ significantly among size groups (p > 0.05). Mineral composition varied with size, with large fish containing significantly higher levels of calcium and magnesium (p < 0.05). Amino acid profiling identified 17 amino acids, including eight essential amino acids (EAA) and nine non-essential amino acids (NEAA), with EAA being more abundant in large fish—particularly leucine and lysine—indicating improved protein quality, while NEAA were dominated by glutamic and aspartic acids across all size groups. Fatty acid analysis revealed higher proportions of polyunsaturated fatty acids (PUFA) and greater unsaturated fatty acid/saturated fatty acid (UFA/SFA) ratios (1.7–1.8) in medium and large fish. Microbiological assessment showed a decrease in total viable counts with increasing fish size, while Escherichia coli, Staphylococcus aureus, and Salmonella spp. were not detected in any size group, as these microorganisms are commonly used as key hygiene and food-safety indicators in fish products (E. coli for fecal/handling hygiene, S. aureus for human-handling contamination, and Salmonella spp. as a major foodborne pathogen). Overall, body size was associated with consistent variations in physicochemical characteristics, nutritional composition, and microbial quality of Pak Phanang Basin butter catfish. These findings provide baseline compositional and safety markers that can support product specification development and GI documentation.