Afghanistan’s aquaculture sector has grown quietly but steadily despite decades of conflict. National fish production rose from just 870 tons in 1980 to 11,107 tons by 2021, even though the country still records one of the lowest per capita fish consumption rates in the world, at just over 2 kilograms per person. Yet until now, no study had systematically assessed water quality parameters or documented the growth performance of rainbow trout under Afghan production conditions. That gap matters, because water quality is the single most powerful lever over fish health, growth, and farm economics. Poor water chemistry drives stress, disease outbreaks, and slower growth, translating directly into economic losses for farmers operating on thin margins.

The research team, led by scientists at Kabul University with a collaborator at Universiti Putra Malaysia, sampled two sites monthly between April and December: Site 1, the reservoir inflow that supplies the farm with water, and Site 2, the culture pond holding the fish. They measured temperature, dissolved oxygen, pH, total dissolved solids, ammonia, nitrite, nitrate, phosphate, sulfate, iron, and zinc, both in the field with calibrated meters and in the laboratory of the Ministry of Energy and Water using spectrophotometric methods following APHA protocols. Analytical blanks and duplicate analyses were run with each batch to guard against contamination, and the laboratory procedures met the quality standards required for water quality index calculations.

The spatial differences between inflow and pond were striking. Water in the culture pond was consistently cooler, with a mean temperature reduction of 3.02 degrees Celsius relative to the inflow, and the gap was widest in June, when the pond ran 5.8 degrees colder. Total dissolved solids were also significantly lower in the pond. More concerning were the substances that accumulated where fish were held. Ammonia concentrations averaged 110.8 percent higher at the pond site, peaking at a 275 percent increase in June, while zinc rose by 38.4 percent and iron by 31.2 percent on average. Phosphate, by contrast, fell by 61.5 percent in the pond, and nitrate and nitrite showed moderate increases. These patterns are consistent with the excretion and feed inputs typical of cultured systems, though the authors caution that the observational design means the correlations describe association rather than proven causation.

Dissolved oxygen emerged as the study’s most critical constraint. In April, oxygen levels fell to between 3.24 and 3.30 milligrams per liter at both sites, far below the threshold of at least 6 milligrams per liter generally recommended for trout culture. Cold-water salmonids like rainbow trout are notoriously sensitive to hypoxia, and such low concentrations are known to impair growth efficiency and physiological resilience. The oxygen deficit was most pronounced in spring, coinciding with the largest temperature differences between sites, and dissolved oxygen remained on average 15.1 percent lower in the pond than in the inflow throughout the monitoring period. The researchers suggest that biological activity and associated microbial processes in the pond likely contribute to the elevated oxygen demand, although confirming this would require controlled experiments.

One of the study’s most technically interesting findings came from comparing correlation structures between the two sites. At the inflow, nitrate and sulfate were strongly positively correlated, total dissolved solids were strongly negatively correlated with phosphate, and ammonia was strongly negatively correlated with zinc. In the culture pond, the web of relationships changed dramatically, with 18 statistically significant correlations, including 11 at the strictest threshold. The relationship between total dissolved solids and nitrite flipped from positive at the inflow to strongly negative in the pond, and the dissolved oxygen to iron correlation reversed from moderately positive to strongly negative. The authors interpret these reversals as consistent with changes in redox-related conditions under higher organic loading and oxygen consumption, a phenomenon they describe as nutrient-metal coupling, while emphasizing that correlation analysis alone cannot establish mechanistic control.

The fish themselves told a story of robust growth under imperfect conditions. Across 60 specimens sampled monthly and analyzed at Kabul University’s physiology laboratory, mean body weight climbed from 70.31 grams in April to 212.45 grams in December, a 202.2 percent increase, while body length rose 44.1 percent. The length-weight relationship revealed positive allometric growth, with the fitted power model yielding an exponent of 3.055, just above the isometric threshold of 3, meaning the fish gained weight disproportionately fast relative to length. Growth was strongest in the later months of the season, when thermal conditions were more favorable and feeding regimes likely optimized.

Organ-level indices added physiological nuance to the growth data. The hepatosomatic index, which reflects liver mass relative to body weight, peaked at 3.09 percent in May after a sixfold jump from April, suggesting heightened metabolic activity or energy storage during a period when oxygen was critically low. Liver weight itself peaked in June at 4.59 grams, more than a fifteenfold increase over April. The gonadosomatic index, by contrast, remained modest throughout the year, peaking at just 0.20 percent in May, and showed no significant relationship with the hepatosomatic index across individuals. This dissociation indicates that reproductive investment was decoupled from short-term hepatic energy reserves under current farming practices, a pattern the authors attribute to the fish’s reproductive cycle dynamics rather than direct water quality effects.

The study’s authors are careful about its limits. The work was conducted at a single farm, replication at the farm level was not feasible, and sampling from April to December did not capture the full annual cycle. Variables such as feed input rates, stocking density, sediment biogeochemistry, and microbial community structure were not directly quantified and may have shaped the observed patterns. Still, the practical implications are clear. April and May posed the highest risk to the trout because hypoxia coincided with rising temperatures, while autumn and early winter brought cooler but increasingly nutrient-rich water, signaling seasonal nutrient accumulation rather than immediate metabolic stress. The researchers recommend enhanced aeration to combat hypoxia, improved waste removal to mitigate ammonia and nutrient loading, careful monitoring of stocking densities, real-time water quality monitoring, and dietary supplements to bolster fish resilience.

For Afghanistan, where aquaculture is increasingly seen as a pillar of food security and economic development, the study provides something the sector has never had: localized, quantitative evidence linking environmental conditions to biological performance in a semi-intensive farming system. The message for farmers and policymakers alike is that trout production at Qargha is sustainable only with proactive water quality management. As global demand for farmed protein pushes aquaculture toward a projected 140 million tons of production by 2050, lessons from a fish farm beside a Kabul reservoir may prove unexpectedly relevant to the many semi-intensive systems worldwide where fish, water, and economics are locked in the same delicate balance.

Subject of Research: Water quality and rainbow trout growth performance at a semi-intensive aquaculture farm in Afghanistan

Article Title: Comparative assessment of water quality and rainbow trout performance between inflow and culture pond sites at Qargha Fish Farm, Afghanistan

Article References: Comparative assessment of water quality and rainbow trout performance between inflow and culture pond sites at Qargha Fish Farm, Afghanistan. (n.d.). https://doi.org/10.1186/s44399-026-00036-y

Image Credits: AI Generated

DOI: 10.1186/s44399-026-00036-y

Keywords: aquaculture, rainbow trout, water quality, Afghanistan, dissolved oxygen, ammonia, Qargha Fish Farm, hepatosomatic index, fish growth, hypoxia, nutrient loading, semi-intensive farming