Stress response of Nile Tilapia (Oreochromis niloticus L.) in different water temperatures [manuscript]
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Date
2018
Authors
Mark Joseph D. Dela Cruz
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Abstract
This study was conducted to assess the effect of different water temperatures (29-30°C; 33-34°C; 36-37°C; and 39-40°C) on the stress response of Nile tilapia (Oreochromis niloticus L.). To achieve this objective, 80 Nile tilapia were conditioned for 7 days and five were distributed in each aquarium. The four treatments were replicated trice. Feeding behavior of fish was observed and scored for 15 days using a scoring guide ranging from 0-3 points (o point - fish did not react or ate the feed; 1 point - fish ate only pellets that were directly put in front of it and did not move to eat the feed; 2 point - fish moved to eat the feed; 3 points - fish ate all feed items continously). Dominant fish in all treatments had the feeding response score (FRS) of 3 points while subordinate fish in all treatments had an FRS score of 2 during the first 5 days, and 1 during the 6th to 10th day. Eye color pattern (ECP), ventilation rate (VR) and skin color of the fish were monitored 0, 30 min, 1, 2, 6, 12, 24, 48, 72, 96 and 120 h after introduction to high temperature environment. The numbers of attacks in 10 minutes were observed daily. Subordinate fish in Treatment 3 (36-37°C) had a mean ECP of 5.54±0.12 followed by subordinate fish in Treatment 1 (29-30°C) with 5.36±0.61 and then by subordinate fish in Treatment 2 (33-34°C) with 5.31±0.13, but all of them were statistically comparable . Treatment 4 (39-40°C) had the significantly lowest (P<0.05) mean ECP of 3.06±0.23 in subordinate fish but was significantly higher compared to those in all dominant fish. Dominant in Treatment 3 (36-37°C) had a mean of 1.70±0.21 which was comparable to that in Treatment 2 (33-34°C) with 1.45±0.42 followed by Treatment 4 (39-40°C) 0.90±0.17 which was also comparable to that of Treatment 1 (29-30°) with 0.85±0.38. On VR, subordinate fish in Treatment 3 had the significantly highest mean of 2.06±0.13 buccal movements/sec but was comparable to those in subordinate fish in Treatment 4 (1.95±0.06 buccal movements/sec), subordinate fish in Treatment 2 1.89±0.03 buccal movements/sec), dominant fish in Treatment 3 (1.83±0.02 buccal movements/sec) and subordinate fish in Treatment 1 (1.72±0.02 buccal movements/sec). These mean VRs were followed by mean VR of dominant fish in Treatment 2 (1.56±0.02 buccal movements/sec) which was comparable to that of dominant fish in Treatment 4 (1.54±0.13 buccal movements/sec). Dominant fish in Treatment 1 had the significantly lowest mean VR of 1.36±0.05 buccal movements/sec. On number of attacks per 10 minutes during the first day up to the end of study, Treatment 1 had a highest mean number of attacks of 61.8±0.98 followed by Treatment 2 with 56.8±3.63; Treatment 3 with 47.9±6.84 and lastly Treatment 4 which had the lowest mean of 12.8±2.27. All four treatments were significantly different from each other. There was mortality of fish in all treatments. Four subordinate fish in Treatments 1, 2 and 3 died because they were more directly exposed to social stress. Only the dominant fish in Treatment 1,2 and 3 survived out of five fish stocked in the aquarium. However, Treatment 4 encountered 100% mortality after 5 hours exposure to very high temperature (39-40°C). On weight, there was decreased mean weight in Treatment 1,2 and and 3 while in Treatment 4, change in weight was not monitored because all the fish died due to high temperature. There was no change in the length of fish because of the short study period of 10 days. During the entire period of social interaction and exposure to different temperatures, subordinate fish in Treatments 1,2 and 3 changed the body color and ECP from pale to dark after the settlement of interaction while the dominant fish had pale body color and ECP. The body color of Nile tilapia subjected to thermal and social stresses became more intense when the fish was exposed to temperature higher than the ideal level. However, in Treatment 4 (39-40°C), the body color became paler and the mouth was reddish and the eye color was paler. It can be concluded that Nile tilapia can tolerate temperature up to 37°C, but they are stressed. Temperature above 32°C can influence the level of aggression during social interaction by reducing it and above 39°C the fish will die. The changes in ECP, VR and body color are indicators of the level of stress brought about by water temperature up to 37°C. As the fish became more stressed the ECP and body color became darker and the VR became faster. However when the fish is exposed at temperature above 39°C and the fish were about to die, these stress indicators are not reliable.