In a ninety-day comparative aquaculture experiment conducted in Madyan Valley within the Swat district of Pakistan, researchers evaluated the growth performance and adaptability of newly introduced coho salmon (Oncorhynchus kisutch) alongside commercially established rainbow trout (Oncorhynchus mykiss). The experimental investigation demonstrated that while both salmonid species adapted successfully to raceway conditions and sustained continuous growth, rainbow trout achieved statistically superior developmental outcomes across all primary metrics evaluated during the trial. Specifically, fingerlings of rainbow trout exhibited significantly higher total weight gain and superior feed conversion efficiency percentages alongside significantly lower feed conversion ratios compared to coho salmon over ninety experimental days. These empirical findings confirm that although rainbow trout remains the more productive species under identical management and dietary regimens, newly introduced coho salmon displays viable biological potential for commercial rearing in northern Pakistan cold-water systems.

Aquacultural development represents a vital strategy for addressing global nutritional deficiencies and food insecurity, particularly as expanding human populations require accessible sources of high-quality animal protein and essential micronutrients. Fish meat provides a rich dietary supply of white meat containing essential amino acids, minerals, and polyunsaturated fatty acids, notably omega-3 fatty acids like eicosapentaenoic acid and docosahexaenoic acid, which reduce the risk of cardiovascular illnesses and improve life expectancy. In cold-water environments, intensive salmonid production depends on maintaining favorable conditions and formulating balanced feeds that satisfy the metabolic requirements of developing fish. However, diversifying regional aquaculture through the introduction of economically valuable species like coho salmon offers substantial commercial opportunities for local fish farmers seeking alternative high-value crops.

To ensure valid comparative observations, researchers assigned three raceways designated Raceway-1, Raceway-2, and Raceway-3 exclusively to rainbow trout, while assigning Raceway-4, Raceway-5, and Raceway-6 to coho salmon fingerlings. Each raceway was supplied with continuous freshwater delivered through a double inlet configuration designed to aerate incoming water through vertical drops and wooden splashing blocks, ensuring sufficient dissolved oxygen saturation. Furthermore, protective netting was securely installed over every raceway to shield fingerlings from external hazards, predatory disturbances, and physical damage throughout the study. Fingerlings of both species were chosen with comparable initial body masses, with rainbow trout starting at a mean initial weight of 12.7 plus or minus 0.73 grams and coho salmon starting at 12.1 plus or minus 0.14 grams.

To establish uniform stocking densities, exactly one hundred fingerlings of each salmonid species were graded from larger rearing raceways and transferred in water-filled containers before distribution into designated experimental units based on mean weight. The rainbow trout population of one hundred individuals was partitioned among three replicates by placing thirty-three fish in Raceway-1, thirty-three in Raceway-2, and thirty-four in Raceway-3. An identical distribution pattern was applied to the one hundred coho salmon fingerlings across Raceway-4, Raceway-5, and Raceway-6. Prior to initiating data collection, all fingerlings underwent a ten-day acclimatization period to adjust to raceway environments and minimize handling stress. For biweekly evaluations, representative random samples of ten fingerlings per species were selected, comprising three individuals from each of the first two replicates and four from the third replicate.

Throughout the ninety-day experimental timeline, both fish species were sustained on an identical formulated diet prepared on-site from fourteen dry ingredients purchased from a registered supplier. The feed components were dried, finely ground, passed through a meat grinder, and moistened to create uniform pellets that matched the developmental stage of the growing fingerlings. The processed feed pellets were subsequently dried at ambient room temperature, packaged into sealed plastic bags, and maintained under cool storage conditions at the Madyan facility. Laboratory analysis verified that the formulated ration provided a crude protein content ranging between thirty-five and forty percent, conforming to AOAC analytical procedures. The daily feeding ration was set at five percent of fish body weight, split evenly across two scheduled daily feedings at nine o’clock and sixteen o’clock. Total feed quantities were recalculated every fifteen days using an established feeding factor formula combining fingerling weight and observed water temperature.

Water temperature was systematically monitored using a digital Celsius thermometer at regular fifteen-day intervals within both rainbow trout and coho salmon raceways across the ninety-day experimental period. Recorded water temperatures followed a distinct seasonal cooling trend, registering 18.00 degrees Celsius on day fifteen, peaking at 19.50 degrees on day thirty, and then declining to 18.00 degrees on day forty-five, 17.00 degrees on day sixty, 16.00 degrees on day seventy-five, and terminating at 15.00 degrees on day ninety. Prior thermal research indicates that cold-water salmonids achieve favorable physiological performance within a temperature range spanning twelve to eighteen degrees Celsius, with optimal trout metabolism commonly documented between fifteen and seventeen degrees. Within the Madyan trials, fish demonstrated somewhat improved overall growth during periods when temperatures remained between fifteen and seventeen degrees compared to warmer phases. This observed temperature dynamic underscores the direct influence that surrounding water temperatures exert on salmonid feeding activity, nutrient assimilation, and energetic expenditure.

Growth progress was documented through biweekly sampling across all raceways, measuring weight gain defined as the difference between final and initial individual body weights. For rainbow trout, the periodic mean weight gain of sampled fingerlings advanced steadily across the six consecutive measurement intervals, recording 8.84 grams, 11.94 grams, 16.13 grams, 22.29 grams, and culminating at 25.05 grams at ninety days, rising from an initial fifteen-day baseline mean of 7.66 grams. This progression represented a net mean weight gain of 17.39 grams for rainbow trout across the three replicates. For coho salmon, mean weight gain similarly increased over time, recording 7.20 grams at day fifteen, followed by 8.03 grams, 11.66 grams, 14.88 grams, 20.48 grams, and reaching a final mean of 22.29 grams, yielding an overall net gain of 15.09 grams. Consequently, rainbow trout attained an extra net weight gain of 2.3 grams over coho salmon under identical conditions, a performance advantage confirmed to be statistically significant.

Feed conversion ratio, calculated as the dry weight of feed consumed divided by total wet weight gained, served as a crucial index of nutritional utilization efficiency throughout the trial. Lower feed conversion values reflect superior dietary conversion into animal biomass, whereas elevated values indicate that greater quantities of feed are required to produce equivalent weight gains. In the rainbow trout raceways, the mean feed conversion ratio declined progressively from an initial 1.79 at the first fifteen-day interval to 1.73, 1.39, 1.38, 1.33, and finally 1.25 on day ninety, yielding an overall treatment mean of 1.47. In comparison, coho salmon replicates recorded corresponding biweekly conversion values of 1.80, 1.78, 1.65, 1.41, 1.36, and 1.30, resulting in an overall treatment mean of 1.55. Statistical analysis revealed that the feed conversion ratio of rainbow trout was significantly lower than that of coho salmon at every measurement point, demonstrating that rainbow trout metabolized the formulated ration with greater metabolic efficiency.

Feed conversion efficiency, defined as the mathematical reciprocal of feed conversion ratio multiplied by one hundred, represents the percentage of feed mass converted into wet fish tissue. Consistent with the declining feed conversion ratios, the conversion efficiency of rainbow trout increased sequentially across each fifteen-day evaluation, progressing from 55.48 percent at the initial reading to 57.65 percent, 71.66 percent, 72.24 percent, 74.72 percent, and reaching 79.81 percent at day ninety. Coho salmon fingerlings demonstrated a parallel upward trend over the ninety-day trial, advancing from an initial 55.24 percent to 55.98 percent, 60.49 percent, 70.84 percent, 73.44 percent, and finishing at 76.88 percent. Comparative statistical testing confirmed that rainbow trout maintained significantly higher feed conversion efficiency percentages than coho salmon throughout the rearing period. Although both species demonstrated commendable efficiency gains as they matured, the consistently higher values exhibited by rainbow trout indicate superior nutritional assimilation under the specified dietary regimen and raceway conditions.

The findings from Madyan Valley align closely with earlier salmonid comparative literature examining growth divergence across cold-water species reared under controlled aquaculture environments. Similarly, historical research evaluating coho salmon alongside rainbow trout observed greater biomass accumulation in trout cohorts receiving identical dietary rations. Because coho salmon commands premium market pricing relative to standard commercial fish species, cultivating this newly introduced salmon represents a highly viable commercial venture for cold-water fish farmers in northern Pakistan.

Subject of Research: Comparative growth and feed efficiency of rainbow trout and coho salmon in Pakistani raceways

Article Title: Growth comparison of rainbow trout (Oncorhynchus mykiss) with newly introduced coho salmon (Oncorhynchus kisutch) species in Madyan Valley, Swat, Pakistan

Article References: Ahmad, T., Hasan, Z., Yahya, J., & Afridi, A. J. (2025). Growth comparison of rainbow trout (Oncorhynchus mykiss) with newly introduced coho salmon (Oncorhynchus kisutch) species in Madyan Valley, Swat, Pakistan. Aquaculture Science and Management, 2(1), Article 11. https://doi.org/10.1186/s44365-025-00017-3

Image Credits: AI Generated

DOI: 10.1186/s44365-025-00017-3

Keywords: aquaculture, rainbow trout, coho salmon, feed conversion ratio, fish growth, Swat Pakistan, raceway culture, fish nutrition, Growth, comparison, rainbow, trout