The Effect of High Temperature on the Growth Performance of Hybrid Tilapia Oreochromis niloticus X Oreochromis aureus Juveniles Reared in a Recycling System

Tilapia juveniles live in littoral regions of freshwater ecosystems which have temperatures that may reach critical values for growth, especially in face of the onslaught of climate change. This study analyzes the effect of temperature (25, 30, 35, 40°C) on the growth and survival of hybrid tilapia juveniles in a re-circulating system. Duplicate groups of 30 juveniles were stocked in 200 L tanks in a closed, re-circulating system. Automatic heaters were used to establish the water temperatures, commercial food was supplied at 5% of their weight as daily ration. Fish were weighed and measured at 15-day intervals for a period of 3 months. Water temperature and dissolved oxygen were monitored daily. Ammonia, nitrates and dissolved reactive phosphorus were monitored every third day. Fish responses were estimated through variations in length, weight and inter-circuli space of fish scales. Average initial and final weight and length, Specific growth rate (SGR), Fulton Index (FI), Length-weight relationship and survival were used to assess tilapia growth performance. Weight, length, SGR and FI were significantly affected (P < 0.05) by water temperature. Growth of the fish reared at 30oC was almost one third greater than that at 25°C and one sixth greater than that at 35°C. Except for fish reared at 40°C, the other treatments showed a positive allometric growth, with the better results recorded for the 30 and 35°C treatments. The fish reared at 40°C survived only two weeks while the survival rate of 98, 90 and 88.3% for 25, 30 and 35°C, respectively.

Macroalgae as Soil Conditioners or Growth Promoters of Pisum sativum (L)

Mexico has long littorals that receive great amounts of marine algae that are wasted despite being potentially useful as growth promoters without the inconveniences of agrochemicals. Some macroalgae have been used with excellent results as soil conditioners and fertilisers in agriculture. In this study nine macroalgae from the coasts of Veracruz (Gulf of Mexico) and one from Guerrero (Mexican Pacific), Mexico, were tested. They were added to the soil in the form of fragments and of silage in liquid around Pisum sativum plants. A two-way random design with four replicas was followed. Two controls, hormones and water, were also used. Growth was recorded every third day. Results showed that four algae promoted growth (p<0.05) Ulva fasciata (ensiling treatment) and Ulva lactuca (ensiling treatment) and Gracilaria caudata (fragment treatment) and Palisada perforata (fragment treatment), compared with the hormones and water controls. The activity of Ulva fasciata and Palisada perforata is recorded for the first time. Since the control plants treated with hormones grew much less than those treated with the four algae, we conclude that the release of all algae compounds was responsible for the growth, and not the hormone mimetics.