2.1 Site and period of experiment The experiment was carried out in the Aquaponics laboratory at the Department of Aquaculture, Bangladesh Agricultural University (BAU), Mymensingh. The duration of the study was 60 days from 7th September to 6th November 2015.
2.2 Experimental design Fifteen plastic tanks of 30L capacity containing 20L water were used as fish rearing tanks. All the tanks were placed in two rows to facilitate better management such as feeding, cleaning and setting aerators for aeration. In this experiment four feeds were formulated replacing fish meal with wheatgrass powder of 100, 75, 50 and 25% respectively, which indicated as T1, T2, T3and T4and T5was control where no replacement of fish meal was done. All the experiments were carried out in triplicates. The experimental tanks were numbered as T1R1, T1R2, T1R3,T2R1, T2R2, T2R3, T3R1, T3R2, T3R3, T4R1, T4R2, T4R3,T5R1, T5R2, and T5R1, and the tanks were arranged in complete randomized block design. Plastic pipes of one foot long were placed at the bottom of the tanks for hiding and resting the fry. The tanks were covered with nets to prevent the fish jumping or predatory animals damage. Ten fry of stinging catfish was released per tank and acclimatized for a week with commercial feed before start the experiment.
2.3 Fry collection and acclimatization Stinging catfish fry was collected using oxygenated plastic bag from the Satota Matshya Hatchery, Digarkandha, Mymensingh. The fry was acclimatized to the laboratory condition and adapted with the small water tank at room temperature and kept for a period of 8 days prior to start the experiment. During this time aeration was provided using aerator and air stones, fry fed commercial powder feed containing 35% protein twice daily at 10 am and 5 pm.
2.4 Wheatgrass sprouting procedure The wheat was sprouted in galvanized trays (73×37×3cm3 ). At the beginning the trays washed with tap water and Sun dried and a thin layer of sand was spread on the trays. Then ½ kg wheat seed was taken in 4 separate plastic buckets each and cleaned, washed and soaked overnight in water. In the following morning the soaked wheat was washed again and sieved, wrapped with cotton bag and kept in cool and dark place for 24 hours. After that soaked and slightly germinated wheat was spread over each trays on sand and sprayed water on the seeds and covered with another tray for 3 days and watered twice daily uncovering the trays. After 3 days, the trays were uncovered when the wheat was sprouted fully and young wheatgrass looked yellowish and the trays kept in passive light but not direct sunlight and watered 3 times daily for another 4 days before harvest. In 7-8 days the wheat sprout became 6-7 inch long and dark green colors then the stems were cut down and weighed.
2.5 Blanching and powder preparation Blanching process was applied on wheatgrass to keep the color intact and all other contents as it is in wheatgrass. The water was boiled in a big tub at 75 to 105ºC temperature and harvested wheatgrass soaked in boiled water for 7minutes. After boiling wheat stems were put into an ice cold water where a pinch of sea salt was added to keep the water cooler. The process facilitated to stop the enzymatic activities, removed air and gases, kept the color green, improved texture, stopped changing flavor and leaching water soluble sugars from the wheatgrass. Following blanching the wheatgrass was kept spreading on a table in room temperature over night under fan to remove the excess water then dried in a homemade drier for 24 hours at 480Ctemperature. When the wheatgrass became crispy it was cut into small pieces with scissors and made powder by blender and kept in fridge at 40C before use in fish feed preparation.
2.6 Feed ingredients collection and analyze proximate composition The feed ingredients were collected from local market and analyzed proximate composition at the Fish Nutrition Laboratory at the Dept. of Aquaculture, BAU.
2.7 Feed formulation and feeding Prior to feed formulation, all the ingredients were ground and sieved through a sieve of 0.5 mm mesh size to have homogenous mixtures. Feed was formulated by giving emphasize on progressive replacement of fishmeal with wheatgrass powder. After sieving the ingredients they were weighted as per experimental design along with the vitamins and mineral premixes in an electronic balance (Electronic Precision Balance, EK 600i) and mixed well and add water to moisten the mixtures. The resultant dough sieved again with 1.0 mm mesh size sieve and kept in fridge in air tight plastic bags after Sun dried for feeding later. Some precautionary measures were taken such as Mustard oil cake soaked overnight and Soybean boiled before add in feed to abrogate glucocyanates growth inhibiting effect. The formulated feed Fed to the fry in all the treatments twice daily at the rate of 10% of their body weight at 10 am and 5 pm. The uneaten feed and faces were siphoned and 25%water was exchanged daily and all the water changed fortnightly to maintain good water quality in the containers.
2.8 Sampling of fish Sampling was done fortnightly. Six fries from each tank were randomly collected by scope net and length and weight were measured using millimeter ruler and electronic balance.
2.9 Growth performance of fish Several parameters were measured to evaluate the growth of stinging catfish fry.
Length gain (cm) = mean final length (cm) – mean initial length (cm)
Weight gain (g) = mean final weight (g) – mean initial weight (g).