Harvesting procedures, welfare and shelf life of ungutted and gutted shortfin pompano (Trachinotus falcatus) stored in ice

TL;DR: The asset of using AQUI-S™ was possibly better fish welfare during the stunning and euthanising phase since exposure to ice-slurry was associated with escape swimming behaviour and slow death.

About: This article is published in Aquaculture.The article was published on 2019-01-01 and is currently open access. It has received 6 citations till now. The article focuses on the topics: Aquaculture & Pompano.

Summary

1. Introduction

• Since pompano are most commonly traded as whole fish in the market, the external appearance of the fish is also important.
• In such a context, skin and eye color are relevant factors for the consumers perception of the product.
• Hence, emphasis was also put on color assessment throughout storage.

2.1 Fish harvesting and ice storage

• In case of both harvesting methods, vestibulo-ocular reflex, handling stress (blood pH and initial pH in white muscle), and body temperature were measured before the fish (n = 10) were subjected to analysis of skin and eye color.
• The fish were gutted in the traditional local way, that is, by removing the gill arches along with intestines through the throat (without opening the belly).
• Subsequently, the body cavities of gutted fish were thoroughly rinsed using bottled drinking water.
• All fish were repacked in EPS flight boxes filled with crushed ice before transport to the Research Institute for Aquaculture No. 1 (RIA-1) in Hanoi (15 h transport) where the fish were subjected to chilled storage.
• Melted ice was replenished with crushed ice and excess water was drained off daily.

2.2.2 pH in blood and muscle

• A shielded glass electrode (SenTix 41, WTW, Wilhelm, Germany) connected to a portable pH meter (model WTW 330i WTW) was used for the determination of pH in blood and white muscle.
• Just after sampling of fish from the AQUI-S TM bath or ice-slurry tub, gill arches were cut by using a scalpel before the pH electrode was brought in contact with the flowing blood to measure its acidity.
• A similar pHelectrode was inserted directly in epaxial white muscle in front of the dorsal fin after an incision had been made by a scalpel.
• The initial pH was recorded after some seconds when the fluctuating pH values had stabilized.
• The initial pH describes peri-mortem anaerobic white muscle activity (e.g. escape behaviour).

2.2.4 Body and core temperatures

• The body temperature of the fish was measured by using a Testo 110 thermometer (Testo AG, Lenzkirch, Germany) just after killing, between the dorsal fin and lateral line, next to the backbone in the thickest part of the fish.
• Core temperatures during ice storage were measured similarly.

2.2.5 Quality Index Method

• The authors chose to apply the QIM scheme intended for farmed sea bass (Dicentrarchus labrax) as shown in Seafish (2010) for their QI assessment of pompano.
• The sea bass scheme ranges from 0 -22 demerit points and includes assessments of fillet color (0-2) and viscera (0-2).
• Since pompano is normally traded as round fish, assessments of fillets and viscera were omitted.
• Accordingly, the modified total QI score ranged from 0 (very fresh fish) to 18 (spoiled fish).
• For gutted pompano, where gills and viscera were removed, the total attainable QI score became 11.

2.2.6 Mesophilic bacterial counts

• On each sampling day, approximately 10 g of fish white muscle of three fish from each treatment was excised with sterile scalpels and forceps.
• Before sampling, the skin around the sampling area was rinsed with 70 % ethanol.
• The skin of the sampled cube was removed aseptically before the samples were mixed with 90 mL of 0.1% peptone water.
• From the 10 -1 dilution, other decimal dilutions were prepared.
• Total viable mesophilic bacterial counts were determined using plate count agar (PCA, Merck) after incubation for 24 h at 29 o C.

2.3 Statistical analysis

• Initial pH and core temperature of ungutted and AQUI-S TM fish on Day 0 were compared by using Mann-Whitney U statistics since Shapiro-Wilk normality tests failed.
• The effect of storage time (Day 1 to 18) on flesh pH, rigor status, core temperature, skin color, TBC and QI was tested using a one-way ANOVA followed by a Holm-Sidak post hoc test when significance was indicated.
• Where normality tests or Levene Median tests of homogenity of variance failed, the Kruskal-Wallis One Way Analysis of Variance on Ranks method was applied followed by a Tukey post hoc test.
• The relationship between the quality index (QI) and storage time was analysed by linear regression.
• Unless otherwise stated, all data are presented as mean values ± standard error of mean (SEM).

3.1 Harvesting procedures and handling stress

• Frenzied burst of activity (escape behaviour) occurred immediately once the crowding process started as well as during transfer to the ice-slurry tub.
• After less than 5 min, practically all signs of movement had ceased.
• The fish were subsequently lying sideways on the bottom of the tub exhibiting weak and sporadic ventilation movements.
• No VORs altogether were observed for fish sampled from the ice-slurry tub as well as from the AQUI-S TM tub.
• The effect of excessive peri-mortem swimming activity was measured as low initial pH values in white muscle, pH 6.55, similar for both treatments (Table 1 ).

3.2 Ice storage and market quality

• Significant differences between the two treatments occurred on Days 10, 14 and 18.
• If demerit points related to gills were omitted from the ungutted and AQUI-S TM Quality Indexes, they would basically resemble the QI development of gutted fish.

4.1 Harvesting procedures and handling stress

• Fish from the volume confined by the sweep-net were collected by immersing a tub into the cage.
• Even though the fish became calm after AQUI-S TM was added to the tub it would not matter anymore since they were already severely stressed by crowding.
• As with the ice-slurry fish, the AQUI-S TM fish, with core temperature 29.2 o C, were also very stiff during sampling, strongly indicating vigorous muscle activity during crowding caused rapid depletion of ATP leading to early rigor onset.
• Thus, achieving rested harvest of pompano in cage cultures did not seem to be a feasible option.
• Absence of VORs of the AQUI-S TM fish in the present study indicated that good welfare was achieved during the stunning process per se.

5. Conclusions

• Due to the extreme excitability of shortfin pompano, the outlook for achieving rested harvest in floating cage systems seemed to be rather far-fetched.
• Since both ice-slurry and AQUI-S TM harvesting methods were preceded by very stressful fish crowding and transfer operations, all fish were harvested in an exhausted condition showing method of harvesting did not matter when the principles of rested harvest is considered.
• This effect was offset after ice storage for one day.
• In contrast, changes in eye color were more evident.
• The present study indicated that the shelf life of exhausted shortfin pompano stored in ice at constant low temperatures was about 18 d.

Figures

Fig. 1 811

Table 1 714

Table 4 769 Skin and eye color of shortfin pompano after ice storage for 18 days. 770

Table 3 751 Skin and eye color of shortfin pompano after ice storage for one day post mortem. 752