Skipjack tuna were obtained from fishermen’s catch utilizing trolling line (pancing tonda) fishing gear during a one day fishing trip, including an operational duration of 8 to 10 hours and a fishing ground at Gulf of Bone (fishing ground shown in Figure 1) at the specified coordinates: Coordinates 4°13’57.66”S - 120°46’36.02”E, 4°24’5.26”S - 120°46’13.16”E, 4°24’30.75”S - 120°38’51.20”E, 4°29’21.21”S - 120°35’31.23”E, 4°36’11.12”S - 120°49’18.06”E, 4°41’16.97”S - 120°45’42.64”E, 4°44’1.35”S - 120°55’50.90”E, 4°50’19.47”S - 120°45’18.82”E, and 4°54’38.75”S - 120°53’33.85”E correspond to the Lamuru Village fish landing site, Bone Regency, South Sulawesi, Indonesia (04023°54.17’ S - 120019°59.13’ E) in July 2025.

Samples were acquired using purposive sampling methods. Skipjack tuna caught during the three one-day fishing events, with each fleet landing 1-2 fish weighing between 1.8 and 2 kg per fish, were aseptically processed and conveyed to the laboratory in insulated containers with a fish-to-ice ratio of 1:3 to sustain a temperature of . Laboratory examination was conducted within three hours of landing to mitigate alterations in quality parameters.

The organoleptic qualities of skipjack tuna captured by fishermen employing oneday fishing methods were assessed according to SNI 2346:2011 (BSN, 2011). The quality criteria evaluated in skipjack tuna include the eyes, gills, surface mucus, meat, odor, and texture using a fresh fish score sheet. Subsequently, six standard panelists evaluated the quality specifications. The data collected from the evaluation sheet were subsequently organized into a table, and the quality value was ascertained by calculating the average result for each panelist at a 95% confidence level. The quality value is determined using the following formula:

Where P is the confidence level, x is the sample mean, 1.96 is the standard deviation coeficient at the 95% level, μ is the population mean, s is the standard deviation of the quality value, and n is the number of panelists.

Temperature and pH evaluations as physical and chemical analyses on skipjack tuna were performed utilizing a Fluke 52 II Dual Probe Digital Thermometer, which has a temperature range of -40°F to 500°F with an accuracy of ±2.0°F. The thermocouple probe was inserted into the fish body or central location. The pH was evaluated using an HI981036 digital pH meter, which has a range of 0.00 to 12.00 pH, a precision of 0.01 pH, and an accuracy of ±0.05 pH. The probe tip was inserted into the fish flesh.

Total bacterial testing was performed according to SNI 2332.3:2015 (BSN, 2015). Bacteria were cultivated using the pouragar method and incubated at for 48 h, allowing for growth and multiplication, resulting in countable colonies. The analysis was conducted using 25 g of sample in 225 mL of Butterfield’s phosphate bufer solution, subsequently diluted from to . Then, 1 mL of each dilution was inoculated onto plate count agar via the spreading technique and incubated. The total bacterial count was determined using the following formula:

Information:

N = number of product colonies;

ΣC = total number of colonies counted on all plates;

n1 = number of plates counted in the first dilution;

n2 = number of plates counted in the second dilution;

d = first dilution counted

Histamine analysis was conducted using a spectrophotometric approach, as outlined in SNI 2354.10:2016 (BSN, 2016), based on the extraction of histamine from fish muscle tissue using methanol, while concurrently converting histamine into its hydroxyl form. Histamine was subsequently purified using ion exchange resin and transformed into its derivative with orthophthalic dicarboxylic acid (OPT) chemical. Histamine fluorescence was quantified using fluorometry at an excitation wavelength of 350 nm and an emission wavelength of 444 nm. The calculation was performed by inputting the concentration and fluorescence values of the working standard solution into a linear calculator application. The regression correlation coeficient (r), slope (b), and intercept (a) were used to determine the sample concentration. The fluorescence value of the sample was input into the conventional regression equation:

Information:

y = sample fluorescence;

a = intercept;

b = slope;

x = sample concentration to calculate

After obtaining the x value, it was multiplied by the dilution factor (fp) and converted back to the sample weight. The histamine value was expressed in µg/g or mg/ kg of the sample using the specified formula:

Information:

H = histamine concentration (μg/g sample)

A = concentration (X) derived from the computation in μg/mL

Data were examined using one-way ANOVA at a 95% confidence level (α=0.05). If the analytical findings indicated significant diferences, they were subsequently examined using Tukey›s HSD (High Significant Diference) test.

Skipjack tuna caught by the three one-day fishing fleets showed bright eyes, prominent eyeballs, and transparent corneas. The gills were vivid red and devoid of mucus, the skin was bright without any redness along the spine, and the abdominal wall remained intact. The fish had a distinctly fresh aroma, firm texture, elasticity upon finger pressure, and resistance to flesh separation from the spine. The organoleptic quality of skipjack tuna from the three one-day fishing fleets varied between 8.23 and 8.81, with a low coeficient of variation of 2.64%. The organoleptic value generated exceeds that of skipjack tuna caught using a purse seine, which is 7.8 (Sipahutar et al., 2019), and the organoleptic value of 8 for skipjack tuna taken with pole and line (Rossarie et al., 2019). Tukey’s HSD analysis results indicated significant diferences in the organoleptic qualities of skipjack tuna on each trip of each fleet (p<0.05). Figure 2 illustrates the quality and condition of the skipjack tuna, while Table 1 presents the organoleptic parameters of the fish caught in one day.

Table 1 presents the organoleptic characteristics of skipjack tuna obtained during a one-day fishing operation in Gulf of Bone, exhibiting superior quality. This results from the brief fishing operations lasting approximately 8-10 hours, the technique of capturing fish with trolling lines, and the utilization of ice for preserving the catch in storage holds. Ensuring fish quality postcapture relies on optimizing fishing techniques and post-harvest management practices. Reducing stress through the judicious use of fishing methods, along with eficient postharvest management practices, is crucial for enhancing the freshness and quality of fish, thereby promoting superior organoleptic characteristics (Svalheim et al., 2017; Uglem et al., 2020).

Fishing techniques significantly influence catch quality. Research indicates that methods that reduce stress on fish, such as trolling lines, yield superior quality catches compared with gill nets or trawls (Svalheim et al., 2017). Moreover, rapid fishing methods and the utilization of trolling lines enhance meat quality by reducing stress on fish (Digre et al., 2017; Rossarie et al., 2017). When coupled with prompt post-capture cooling, these techniques preserve the flavor, texture, and overall quality of fish (Tesfay & Teferi, 2017).

Measurements of physicochemical characteristics in skipjack tuna caught during a one day of trolling line fishing showed that fish meat temperatures ranged from 3.42 to except for one measurement point on vessel 2 (trip 1), which registered below the overall range seen throughout the fleets. The pH values of the fish meat ranged from 6.21 to 6.51, as indicated in Table 2. The physicochemical conditions of skipjack tuna caught by trolling lines were uniform among fleets, with parameter ranges consistent with the attributes of fresh fish. The consistency was due to the fishing grounds, fishing techniques, and onboard storage practices of the same vessels.

The consistency of the temperature and pH levels in skipjack tuna caught during this one-day fishing trip suggests that onboard treatment was relatively efective and uniform across fleets. The fish meat temperature of approximately at the landing site signifies that it was not subjected to extreme heat during catch or initial storage. This indicates that while 5°C is a permissible transition temperature, fish should preferably be maintained at refrigeration temperatures (0–4°C) to avert rotting (Tenyang et al., 2019; Wangtueai et al., 2021). Consequently, fishing vessel 2 indicates that temperature regulation requires enhancement to preserve superior fish quality by maintaining suficient ice utilization and limiting direct sunlight exposure. Eficient post-catch handling techniques substantially influence the quality and longevity of skipjack tuna, demonstrating that inadequate temperature regulation can lead to a dramatic deterioration in fish quality (Litaay et al., 2023).

Moreover, cold storage markedly postpones pH alterations, which are directly associated with microbial activity (Mu et al., 2017; Najih & Maskur, 2020). A pH value between 6.21 and 6.51 signifies that the fish is in the initial post-mortem stage, during which muscle glycogen has not been fully converted into lactic acid, indicating that the fish remains fresh (Tri et al., 2021). The pH of fresh fish muscle is typically near neutral, approximately 7.0; however, postmortem pH may decrease to an acidic range of approximately 5.5 to 6.5, impacting several quality characteristics, including flavor, texture, and spoilage rate (Castillo-Yanez et al., 2007; Hossain et al., 2020). Research indicates that 6–10 h after death, over 90% of fish attain peak rigor mortis when preserved under ideal conditions; however, this process may be postponed in cooler storage environments (0– (Rucinque et al., 2021). The correlation among capture techniques, stress levels, and pH stability in fish corroborates studies pertinent to optimal fishing practices and their impact on market quality (Petrik et al., 2020; Mujiyono et al., 2024). Tukey’s HSD analysis indicated that the physicochemical values of skipjack tuna exhibited significant changes alone in the temperature parameter throughout each trip of every fleet of vessels (p<0.05).

The TPC value in trolling line-caught skipjack tuna is approximately 10³ CFU/g, which is much lower than the maximum microbial contamination limit established by food quality regulations. The maximum TPC limit for fresh fish, according to national regulations (SNI 2729:2021) and international standards (International Commission on Microbiological Specifications for Foods), is typically CFU/g (Latifou et al., 2019). Consequently, all the tested fish samples were classified as very fresh and deemed safe for ingestion. The prompt implementation of cold storage methods after capture is crucial, as swift cooling can mitigate degradation processes linked to microbial proliferation and enzymatic reactions that lead to spoilage (Zou & Hou, 2016; Sardenne et al., 2021). In contrast, when fish are maintained at elevated temperatures, namely there is a notable escalation in the overall bacterial count, increasing from 4.61 to as much as 7.23 Log CFU/g within a 12-hour period (Ali et al., 2022).

lead to cross-contamination of the skipjack tuna catch. The results of Tukey’s HSD analysis showed that the total plate count values of skipjack tuna on each trip of each fleet were significantly diferent (p<0.05). The test results are presented in Table 3.

Microbiological analysis employing the TPC method on skipjack tuna caught within a one-day fishing trip revealed results between and CFU/g, accompanied by a low coeficient of variation of 3.01%, signifying uniformity in microbiological quality between fleets. This value somewhat exceeds that of skipjack tuna caught using pole and line, recorded at 2.5×10² (Harikatan et al., 2024), and purse seine, documented at (Sipahutar et al., 2019). The inadequate implementation of sanitation in the equipment used and the neglect of hygienic practices among one-day fishermen

The histamine levels in skipjack tuna caught in a one-day fishing trip were comparatively low, ranging from 3.46 to 4.22 mg/kg, with a coeficient of variation of 7.91%, suggesting a commendable degree of consistency between fleets and excursions. Tukey’s HSD analysis revealed significant diferences in histamine levels in skipjack tuna between trips 2 of each fleet . Table 4 presents the results of the histamine analysis of skipjack tuna.

The histamine levels in trolling linecaught skipjack tuna are well below the maximum limit established by international regulations. Histamine is a marker for evaluating fish freshness and quality. Histamine concentrations under 30 mg/kg in fish signify high quality; however, levels beyond 50 mg/kg denote degradation or impairment in fish quality (Chen et al., 2010; Besas & Dizon, 2012; Muscarella et al., 2013). All items examined, with levels ranging from 3.5 to 4.2 mg/kg, may be classified as safe, fresh, and of superior quality. The free histidine concentration in scombridae muscle tissue greatly influences histamine synthesis when fish are inadequately preserved (Hwang et al., 2010).

Factors that intensify histamine accumulation include temperature variations and extended storage without refrigeration, underscoring the necessity for rigorous monitoring protocols (Akbari-Adergani et al., 2012). Inadequate management and storage during the post-harvest process, including temperature misapplication, can lead to histamine production via the decarboxylation of histidine by bacteria in fish tissue (Visciano et al., 2014; Mahusain et al., 2016; Pertiwi et al., 2020). This can occur rapidly if fish are maintained at temperatures exceeding for extended periods, facilitating the proliferation of spoilage microbes that generate histamine (Chung et al., 2017). Maintaining fish at temperatures below 4.4°C is crucial to prevent histamine production by histamine-generating bacteria (Zou & Hou, 2016; Trevisani et al., 2019; Hiruma et al., 2020). Accumulated information from multiple studies highlights the necessity of stringent cold storage protocols to guarantee food safety and preserve the quality and freshness of caught fish.