Keywords: Plant-based lipids, coho salmon, growth performance, fish oil reduction, sustainable aquaculture, smoltification.

Introduction

      The partial replacement of fish oil (FO) with vegetable oils (VOs), is a widely adopted strategy in salmon aquaculture to reduce dependence on marine resources and enhance sustainability [1-4].Projections under climate change scenarios indicate a progressive decline of up to 14% per decade in the biomass of Engraulis ringens (Peruvian anchoveta), the main global source of fish oil, further emphasizing the urgency of developing resilient lipid alternatives [5].In this context, canola oil (CO) has been used in salmonid diets for many years and has consistently demonstrated better growth performance than other VOs [2, 6]. For example, high levels of soybean oil have been associated with increased hepatic lipid accumulation, intestinal morphological alterations, and growth reductions of up to 15% compared to diets formulated with fish oil [7]. As a result, CO is now commonly included at levels ranging from 50% to 70% of the total lipid content in commercial salmon feeds, typically in combination with marine-derived oils [8, 9]. However, this replacement poses significant metabolic and digestive challenges, particularly during the juvenile stage, when physiological development and feed efficiency are critical [6, 10].

      In particular, VO-based diets typically contain lower levels of saturated fatty acids, exhibit a higher omega-6 to omega-3 ratio, and present reduced concentrations of long-chain polyunsaturated fatty acids (LC-PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Furthermore, they lack other bioactive compounds naturally found in fish oil, including phospholipids and cholesterol [4, 11].

      The imbalance in the lipid profile of high CO diets disrupts lipid metabolism, reduces digestive efficiency, and induces intestinal dysfunction [12]. In salmon fed diets high in soybean protein and canola oil, histopathological alterations such as mucosal atrophy, enterocyte vacuolization, and reduced villus height have been observed, compromising nutrient absorption and intestinal integrity [13]. These structural changes coincide with a higher proportion of unsaturated fatty acids, particularly oleic acid (18:1n-9) and linoleic acid (18:2n-6), the latter being a precursor of pro-inflammatory eicosanoids that contribute to intestinal inflammation and immune dysfunction [14]. Furthermore, diets rich in vegetable oils (VOs) with an unbalanced lipid profile have been shown to cause excessive intracellular lipid droplet accumulation in intestinal tissues, an effect less pronounced in FO-based diets [15].

      In contrast, strong evidence supports the essential inclusion of EPA and DHA in the diet to mitigate negative health effects in salmon and ensure optimal growth. According to Glencross et al. (2024), EPA+DHA requirements in Atlantic salmon vary by weight: for fish weighing 15-50 g, a minimum of 20 g/kg diet is recommended, while for 50-200 g, the requirement decreases to 18 g/kg diet. While EPA and DHA are essential for salmon growth and health, their synthesis from alpha-linolenic acid (ALA) is limited by enzymatic constraints and dietary availability. Studies on coho salmon (Oncorhynchus kisutch) established an optimal ALA requirement of approximately 10 g/kg diet. However, excessive supplementation (>25 g/kg diet) negatively affected growth [16].

      The limited availability of EPA and DHA from fish oil (FO) hinder their inclusion in salmon diets. Additionally, ALA conversion to omega-3 LC-PUFAs is insufficient to meet nutritional requirements. Therefore, it is essential to implement nutritional strategies that optimize lipid metabolism and enhance the absorption and retention of EPA and DHA in tissues. In this context, diets containing specific saturated fats have been shown to promote the conservation of omega-3 LC-PUFAs in Atlantic salmon [4]. This mechanism resulted in a higher specific growth rate (SGR) and increased EPA and DHA levels in tissues. Moreover, key metabolic pathways were activated, including the upregulation of the srebp1 gene, which enhanced omega-3 LC-PUFA biosynthesis and storage [4].

      Given these challenges, First Balance A & B (Patent Pending) were developed as strategic lipid blends combining vegetable oils, phospholipids, bioactive lipids and antioxidants to optimize lipid metabolism and feed efficiency in juvenile coho salmon (Oncorhynchus kisutch). Designed for early development, First Balance A contains ingredients that promote lipid absorption growth, and First Balance B, formulated for smoltification stage, can facilitate adaptation to seawater.

      This study evaluates their efficacy as partial and total FO replacements by analyzing their impact on intestinal morphology, lipid metabolism, and overall performance compared to common market FO and CO based diets [9].

Materials and Methods

 

Experimental Diets and Feed Manufacturing

      Six experimental diets were formulated to guarantee the nutritional requirements of juvenile coho salmon (Oncorhynchus kisutch). To ensure comparability across treatments, key macronutrient and additive levels were standardized, with all diets containing fish meal (obtained from MenhadenFish) (25%), marine protein (7%), land animal protein (18%), wheat (15.8%), wheat gluten (15%), soy lecithin (0.5%), vitamin/mineral/amino-acid premix (4.6%), and astaxanthin (0.1%). In addition, all diets contained 14% oil to maintain uniform lipid availability and facilitate direct comparisons.

      The first control diet contained 100% fish oil (FO), while the second control diet consisted of a 50/50 blend of fish oil and canola oil (FO+CO), a common formulation used in the aquaculture industry. The experimental diets incorporated two commercially available plant-based lipid blends (First Balance A and B), developed and distributed by Alianza. These blends were tested either as 100% replacements or 50/50 combinations with fish oil to assess their effects on fish performance and metabolism. While additional experimental diets were evaluated as part of a broader research initiative, this study focuses exclusively on formulations relevant to its objectives. Table 1 provides an overview of the lipid ingredient compositions of the six diets analyzed.

      All six diets were manufactured using identical commercial extrusion methods. The solid ingredients, including protein, starches, and mineral premixes, were weighed and transferred to a ribbon mixer (Patterson Equipment, Toronto, ON) to achieve homogeneity. The mixture then underwent particle size reduction in a hammermill (Prater-Sterling, Bolingbrook, IL) equipped with 0.033” screens. The processed feed mixture was extruded using an Extru-Tech E325 single-screw extruder (Sabetha, KS) to produce 2.5 mm floating pellets. The extruded pellets were dried with a conveyor oven (Colorado Mill Equipment, Canon City, CO) and sifted with a screener (Rotex Inc., Cincinnati, OH).

Table 1. Lipid fraction present in juvenile coho salmon experimental feed formulations.

Ingredients (%)	FO	FO+CO	FO+A	A	FO+B	B
Fish oil, Menhaden	14	7	7	–	7	–
Canola oil	–	7	–	–	–	–
First Balance A	–	–	7	14	–	–
First Balance B	–	–	–	–	7	14

      Prior to lipid coating, each oil source was preheated to 43°C in stainless steel containers to facilitate its absorption on feed pellets and ensure uniform distribution. The preheated oils were then added to dry pellets, which were divided into six batches according to lipid variation. The oil-coated diets were processed individually using a Phlauer vacuum coater (A&J Mixing, Oakville, ON), ensuring total lipid incorporation. The diets were then bagged and stored at room temperature until use, maintaining stability and preventing lipid oxidation. Once feed production was complete, finished feed samples were again analyzed for proximate composition (Table 2).

Table 2.  Proximate analysis of Pellets used for diets

Proximate Composition	FO	FO+CO	FO+A	A	FO+B	B
Protein (%)	50.6	50.7	50.7	50.7	51.1	50.6
Lipid (%)	20.8	20.5	19.7	19.8	19.8	20.0
Ash (%)	9.6	9.5	9.4	9.4	9.4	9.4
Moisture (%)	6.9	6.8	6.8	6.7	6.7	7.1

 

 

Fish Origin and Experimental Setup

      Coho salmon eggs were obtained from Riverence Brood (USA), hatched, and fed a starter diet until they reached an average weight of 3.9 ± 0.02 g. Twenty fish per tank were randomly stocked into 24 tanks (four replicates per dietary treatment), for a total of 480 fish. The initial tank biomass was 78 g with less than 10% variation (±5% of the mean), corresponding to a stocking density of 0.82 kg m⁻³. This low stocking density was selected to ensure sufficient space for optimal growth throughout the trial, minimizing potential crowding stress.

      Recirculating aquaculture systems (RAS) provide a controlled environment that minimizes external environmental variability, ensuring greater consistency and reliability in experimental conditions, which is critical for obtaining robust and reproducible data [17]. Given these advantages, this study was conducted in a 5,300 L RAS consisting of 24 cylindrical tanks, each with a volume of 151 L. Each tank was equipped with a subsurface recirculating drain, a central sludge drain, forced-air diffusers for oxygenation, a flow bar to regulate water current, and net covers to prevent fish escapes. Additionally, the system included a centrifugal water pump, a bead filter, a UV sterilizer, a biofilter, solids settling sumps, a clarifying sump, a water inlet float valve, and a heating/cooling unit.

      The RAS system was supplied with well water, and the following water quality parameters were maintained throughout the study: water flow of 6–7 L min⁻¹, temperature averaging 13.14 °C, dissolved oxygen at 9.63 mg L⁻¹, and a pH range of 7.2–7.6. Water temperature, dissolved oxygen, and pH were measured daily at 08:00. Ammonia (NH₄⁺), nitrite (NO₂⁻), and nitrate (NO₃⁻) levels were monitored weekly, ranging from 0.118 to 0.237 mg L⁻¹, 0.084 to 0.248 mg L⁻¹, and 21.7 to 39.2 mg L⁻¹, respectively.

Fish performance and physiological response

      The fish were not provided an acclimation period; instead, they were switched directly from their starter diet to their respective experimental diets on Day 0. Tanks were randomly assigned to dietary treatments, with four replicate tanks per treatment. Fish were fed manually to apparent satiation three times daily (08:00, 12:00, and 16:00 h) for 12 weeks. Satiation was determined when a small amount of uneaten feed remained in each tank.

      Tank biomass was measured at weeks 3, 6, 9, and 12 to follow growth performance. During each weighing event, feed containers were weighed to determine feed consumption and calculate feed conversion ratio (FCR) and specific growth rate (SGR), key metrics for assessing dietary effectiveness and fish performance. FCR, the ratio of feed intake to weight gain, reflects nutrient utilization efficiency, while SGR, expressed as the percentage of daily weight gain relative to initial body weight, provides a standardized growth measure. These indicators help evaluate the impact of dietary lipid sources on metabolic efficiency, nutrient absorption, and overall fish development.

These metrics were calculated using the following equations:

(Eq. 1) Feed Conversion Ratio (FCR):

(Eq. 2) Specific Growth Rate (SGR):

At the end of the 12-week trial, eight fish per treatment (n = 48) were randomly selected and euthanized using a lethal overdose of tricaine methanesulfonate (MS-222; 250 mg L⁻¹). Each fish was weighed and measured (fork length) to calculate Fulton’s Condition Factor (K). Blood samples were collected from the caudal vein using heparinized capillary tubes, and hematocrit values were determined by centrifugation (5 min at 10,000 × g).

The liver, spleen, viscera, and visceral fat were extracted and weighed to calculate organosomatic indices, which assess the relative size of these organs in relation to total body weight. These indices serve as indicators of metabolic status, organ development, and potential lipid accumulation, providing insights into the physiological effects of dietary treatments over the study period.

These metrics were calculated using the following equations:

Eq. (3) Hepatosomatic Index (HSI):

Eq. (4) Spleen Somatic Index (SSI):

Eq. (5) Visceral Somatic Index (VSI):

Eq. (6) Visceral Fat Index (VFI):

Eq. (7) Hematocrit (HMT):

      The remaining fish, with viscera removed, were pooled by treatment and stored at -20°C. Subsequently, the carcasses were homogenized, freeze-dried for 72 h using a FreeZone 2.5 L freeze dryer (Labconco, Kansas City, MO), and subjected to fatty acid profile analysis. Lipid extraction and fatty acid profiling of the homogenized samples were conducted using a protocol that included lipid extraction by the Bligh and Dyer method, saponification, methylation, and separation by gas chromatography using a capillary column [18]. The fatty acid profiles were determined following the AOCS Official Method Ce1i-07 [19].

Statistical Analysis

      All data were analyzed using one-way ANOVA to detect significant differences among treatments. When significant differences were identified, Tukey’s post hoc test was applied for pairwise comparisons (p < 0.05). Data are presented as mean ± SE, with four replicate tanks per dietary treatment (n = 4). Assumptions of normality and homogeneity of variances were verified prior to analysis.

Results and discussion

Productive Performance

      Final weight varied significantly among dietary treatments, indicating a significant effect of dietary lipid composition on weight gain. Figure 1 presents the average weight gain of fish across all dietary treatments. Fish fed FO+CO had the lowest final weight, reaching 51.0 ± 0.95 g, while those fed FO achieved the highest final weight at 58.4 ± 1.57 g, showing a significant difference between treatments (p < 0.001).

      All treatments containing First Balance A and B outperformed the FO+CO group in terms of final weight. Among them, fish fed First Balance A without FO supplementation exhibited the highest growth, with a 13.5% higher final weight compared to FO+CO, reaching 57.9 ± 0.92 g. The FO+A treatment, which had the lowest final weight among the First Balance groups, was still 7.1% higher than FO+CO, reaching 54.6 ± 2.69 g. Likewise, fish fed with First Balance B showed intermediate growth performance, with final weights between the 10.8% and 9.4% increase ranges.

      In line with these growth differences, previous studies have shown that the addition of canola oil to salmon (Salmo salar) diets reduces growth rates compared to diets formulated exclusively with fish oil [8, 20]. This growth reduction has been linked to the negative correlation between metabolic effects of CO and high-density lipoprotein (HDL) levels in salmon plasma. Specifically, fish fed CO based diets exhibit a decrease in total protein and fatty acid content within HDL particles, suggesting reduced efficiency in lipid transport and metabolism [20]. These findings suggest that First Balance A and B mitigate the negative impacts of FO+CO diet, preserving nutrient utilization efficiency and, consequently, growth performance. To better evaluate overall fish performance, SGR and FCR were analyzed together, allowing for a more integrated assessment of nutrient utilization and metabolic efficiency across dietary treatments.

Figure 1. Average weight per fish (g) based on total tank biomass (n=4, mean ± SE).

      Figures 2 and 3 present the specific growth rate (SGR) and feed conversion ratio (FCR) at the end of week 12 for the different dietary treatments. SGR was significantly lower in the FO+CO diet compared to FO, reaching 2.88 ± 0.02. In contrast, the First Balance diets resulted in higher SGR values. Notably, the A treatment achieved the highest SGR (3.04 ± 0.02), reflecting a 5.6% increase over FO+CO, while FO+B and B showed improvements of4.2% and 3.5%, respectively.

      In relation to FCR, lower values indicate greater efficiency in converting feed into biomass, which is critical for sustainable and cost-effective aquaculture production. In this study, feed conversion was more efficient in the First Balance diets compared to FO+CO, which showed the highest FCR at 0.80. The lowest value was observed in FO+B, with an FCR of 0.76, reflecting a 5.0% improvement over FO+CO. The A and FO+A diets followed, with reductions of 3.8% and 2.5%, respectively.

Figure 2. Specific Growth Rate (SGR) of juvenile coho salmon at week 12 for the different diets tested.

Figure 3. Feed Conversion Ratio (FCR) of juvenile coho salmon at week 12 for the different diets tested.

      The improvements observed in SGR and FCR may be attributed to multiple factors, as First Balance incorporates an optimized lipid profile with a specific balance of fatty acids, along with the inclusion of phospholipids, antioxidants, and other bioactive compounds. This formulation substantially alters the traditional composition observed in FO+CO mixtures, potentially enhancing metabolic efficiency in fish. For example, certain fatty acids such as oleic acid (18:1n-9) and lauric acid (C12:0) have been shown not to be incorporated in equivalent proportions into muscle lipids, particularly when present at high concentrations in the diet [21, 22]. This is due to their high rate of oxidation through β-oxidation, which limits their accumulation in tissues. In this context, high energy oils, such as those used in First Balance, are formulated to optimize energy production through fatty acid oxidation. This allows for a reduced reliance on amino acids as an energy source and, in turn, improves growth rates in fish [22].

      This metabolic advantage is also reflected in the differences between the First Balance A and B formulations. First Balance A contains a higher proportion of medium chain fatty acids (MCFA) and is designed to enhance energy availability and promote growth. In contrast, First Balance B was formulated to support smoltification by prioritizing oxidative stress mitigation, incorporating different sources of antioxidants and a lower content of MCFA. As a result, First Balance A achieved superior growth performance compared to First Balance B, highlighting the role of fatty acid distribution in modulating physiological outcomes.

      Among the functional components included in the formulation, antioxidants play a key role in mitigating oxidative stress by neutralizing reactive oxygen species (ROS), preventing cellular damage that could impair immune function and feed efficiency [3]. First Balance A contains specific tocopherols and ascorbyl palmitate, while First Balance B includes these along with rosemary-derived polyphenols. This antioxidant blend enhances oxidative stability and supports cellular integrity, which contributes to improved physiological responses and growth. In parallel, the inclusion of phospholipids supports membrane stability, facilitates lipid transport, and enhances nutrient absorption, all of which contribute to improved metabolic homeostasis and overall growth performance in fish [9]. This suggests that the synergy of these components in First Balance may help optimize energy metabolism and support physiological stability, ultimately contributing to improved growth performance in fish.

Physiological response

      The physiological parameter evaluation conducted through necropsy at the end of week 12 revealed significant differences in several key indices related to metabolic and nutritional health, as shown in Table 3. The hepatosomatic index (HSI) was determined as the percentage of total liver weight relative to the fish’s body weight, while the viscerosomatic index (VSI) and the visceral fat index (VFI) were calculated as the percentage of total visceral weight and visceral fat, respectively. These indices are closely related to lipid accumulation and distribution in the body and are recognized as key physiological indicators for assessing the metabolic status and overall health of the fish [23]. Variations in HSI and VSI have been widely used to detect changes in energy reserves, nutrient utilization efficiency, and to identify early signs of hepatic steatosis or metabolic stress, particularly under dietary regimes rich in plant-based ingredients [24]

Table 3. Necropsy results at the 12-week sampling point (n=8).

Test	HSI	VSI	VFI	SSI	HMT(%)
FO	1.42 ± 0.1	8.58 ± 1.01a	1.63 ± 0.13ab	0.10 ± 0.02a	49 ± 3.63a
FO+CO	1.58 ± 0.13	9.12 ± 1.42a	2.15 ± 0.35a	0.11 ± 0.02a	46 ± 4.99ab
FO+A	1.52 ± 0.07	8.45 ± 0.75a	1.50 ± 0.34b	0.10 ± 0.02a	47 ± 3.50ab
A	1.58 ± 0.08	8.41 ± 0.43a	1.87 ± 0.19ab	0.10 ± 0.03a	44 ± 3.17b
FO+B	1.42 ± 0.10	8.62 ± 0.67a	1.86 ± 0.17ab	0.10 ± 0.01a	46 ± 3.18ab
B	1.54 ± 0.10	8.73 ± 0.69a	2.00 ± 0.26ab	0.12 ± 0.03a	45 ± 1.79ab

*Superscripts of different letters within the same column denote significance (p<0.05). HSI: Hepatosomatic index, SSI: Spleenosomatic index, VSI: Viscerosomatic index, VFI: Voluntary feed intake, HMT: Hemocyte total (%).

      The FO+CO diet showed the highest HSI (1.58 ± 0.27), VSI (9.12 ± 1.42), and VFI (2.15 ± 0.35) values, suggesting increased hepatic and visceral fat deposition. In contrast, fish fed First Balance in blend with FO diets exhibited lower lipid accumulation indices. HSI values showed variation across treatments, with the lowest recorded in FO+B and FO (1.42 ± 0.10), representing a 10% reduction compared to FO+CO. The B and FO+A treatments exhibited intermediate values of 1.54 ± 0.10 and 1.52 ± 0.07, respectively. Notably, the A treatment showed a high HSI value (1.58 ± 0.08), comparable to FO+CO; however, this diet did not contain fish oil.

      This suggests that specific lipid composition in First Balance may have modulated the hepatic response typically associated with vegetable oil inclusion. This interpretation is supported by studies in Atlantic salmon, which have shown that higher dietary inclusion of canola oil can lead to increased hepatic lipid reserves, resulting in elevated HSI values [10, 25]. Among the main metabolic disruptions observed were reduced β-oxidation of fatty acids, accumulation of oleic and linolenic acids, impaired energy homeostasis, mitochondrial dysfunction, and increased inflammatory activity. Additionally, the inclusion of vegetable oils was associated with a reduction in the secretion of very-low-density lipoproteins (VLDL), which may impair hepatic lipid excretion and further promote lipid accumulation.

      Regarding VFI, the FO+A diet showed the lowest value at 1.50 ± 0.34, reflecting a 30% reduction compared to FO+CO. The FO + B and A treatments followed, with values of 1.86 ± 0.17 and 1.87 ± 0.19, respectively, representing reductions of approximately 13%. Finally, no significant differences were detected for SSI and HMT across treatments, suggesting that these physiological indicators remained stable regardless of dietary lipid composition.

      These findings align with previous studies in Atlantic salmon, where higher dietary inclusion of canola oil has been associated with increased lipid accumulation in hepatic and visceral tissues [10]. These metabolic changes have been linked to reduced expression of FABP11, a fatty acid-binding protein essential for lipid mobilization. Suppression of FABP11 impairs fatty acid transport and oxidation, promoting lipid accumulation in the liver and visceral tissues [26]. The lower VFI values observed in the present study with FO+A and FO+B suggest that the specific lipid composition of First Balance may counteract these typical effects associated with canola oil, possibly by preserving lipid mobilization pathways.

      These findings highlight the critical importance of maintaining a balanced lipid profile to support energy metabolism and growth performance [27]. Furthermore, the reductions observed in VFI and HSI may also be influenced by the synergistic metabolic effects of bioactive components included in the First Balance formulations, particularly antioxidants and phospholipids. In the case of First Balance B, the inclusion of polyphenols contributed to a further reduction in hepatic and visceral fat indices, likely through enhanced oxidative stress mitigation and improved regulation of lipid mobilization pathways. Specifically, antioxidants help reduce oxidative stress and stimulate β-oxidation, preventing hepatic triglyceride accumulation [13]. Meanwhile, phospholipids enhance the secretion of very-low-density lipoproteins (VLDL) and improve both lipid absorption and mobilization, contributing to better energy homeostasis and hepatic function [28].

Fatty acids availability

      The use of vegetable ingredients in aquaculture diets has been associated with a significant reduction in EPA and DHA levels in fish muscle, a trend that has been widely documented in various studies [18]. It is estimated that the concentration of these essential fatty acids in farmed salmon fillets has decreased by approximately 50% in recent years [21]. Additionally, the replacement of fish oil with vegetable oil blends has led to an increase in the proportions of oleic acid and linoleic acid, reflecting a shift in the lipid profile of fish fed with these formulations. Figure 4 shows the main unsaturated fatty acid profile of the whole body of the juveniles at the end of the trial.

Figure 4. Unsaturated fatty acid composition (% of total FA) of the whole‐body of salmon coho fed a control diet (FO) or diets containing CO, PMA and PMB for a period of 12 weeks.

      In this study, the FO+CO diet resulted in a total EPA + DHA concentration of 10.4% of total fatty acids in the whole body. Partial replacement of this blend with FO+A or FO+B led to improved omega-3 profiles, with higher EPA + DHA concentrations of 11.01% and 10.83%, respectively. These findings suggest that, in addition to supporting growth performance, the diets effectively preserved long chain omega-3 levels, ensuring the nutritional value of the final product for human consumption. However, diets formulated exclusively with First Balance (A and B), which still supported excellent growth performance, resulted in a marked reduction in EPA + DHA. However, considering that these diets did not include any fish oil, the resulting EPA + DHA concentrations of 4.13% in treatment A and 4.47% in treatment B still reflect a moderate level of omega-3 retention.

      In contrast to previous findings, the present study demonstrated that diets FA and FB, despite their lower content of EPA and DHA, were able to sustain excellent growth performance in juvenile salmon. This outcome differs from previous studies, which have consistently linked reduced dietary levels of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs) with impaired growth and diminished nutrient utilization. For example, a study by Glencross et al. (2024) reported that fish fed diets containing low levels of EPA and DHA (2.6% of total fatty acids) showed a 7% lower final weight compared to fish fed diets with higher EPA and DHA levels (9.2%).

      It is well established that, despite endogenous synthesis, the capacity to produce sufficient EPA and DHA is limited and cannot fully meet the physiological requirements of Atlantic salmon when using conventional diets such as FO+CO [13, 29]. Although a shift toward lipid profiles containing lower levels of marine-derived LC-PUFAs and higher levels of plant-derived precursors (such as ALA from canola oil) can activate hepatic desaturase and elongase enzymes in salmon, the overall synthesis capacity remains limited and often insufficient to maintain tissue LC-PUFA levels comparable to those achieved with fish oil-based diets [6].

      Nevertheless, the results obtained with First Balance demonstrate that efforts toward more sustainable solutions should not only focus on finding alternative sources of EPA and DHA, but also on optimizing the absorption, transport, and metabolism of these fatty acids to achieve a balance between growth performance and overall fish health. For example, the results obtained with A and B diets, fish were able to better utilize dietary nutrients despite the low levels of LC-PUFAs, as reflected by improved growth, reduced FCR, and enhanced lipid metabolism and distribution. These findings highlight a promising direction, but future studies are needed to better understand the underlying mechanisms and confirm their long-term applicability.

Conclusions

      The use of First Balance A and B as functional lipid blends significantly improved growth performance, feed efficiency, and lipid metabolism in juvenile coho salmon. Compared to the fish oil + canola oil diet (FO+CO), First Balance treatments increased final weight by up to 13.5%, improved specific growth rate (SGR) by 5.6%, and reduced feed conversion ratio (FCR) by 5.0%. Physiological indices such as VFI and HSI were also reduced, indicating enhanced lipid mobilization and metabolic efficiency. Blends with fish oil maintained EPA+DHA levels, while full replacement still supported growth despite lower tissue omega-3 content. These results demonstrate that First Balance supports growth performance and metabolic health in aquaculture species through improved lipid absorption, oxidation, and energy balance. Its formulation, which includes bioactive lipids, phospholipids, and antioxidants, enhances nutrient utilization, making it a viable strategy to reduce dependence on marine oils in aquafeeds.

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