EFFECT OF DIETARY LIPID LEVEL ON GROWTH PERFORMANCE, FEED UTILIZATION, AND BODY COMPOSITION OF TOTOABA, Totoaba macdonaldi

The totoaba (Totoaba macdonaldi) is a marine sciaenid native to the Gulf of California that has attracted people's attention as a candidate species for aquaculture. It stands out for being a legendary species that supported one of the most important fisheries in the Gulf of California at the turn of the 20^th century. Overfishing placed this species under the status of critically endangered, and a total fishing ban was imposed by the Mexican Law since 1975. However, breeding programs currently underway in Northwest Mexico have succeeded in the production of fry for the purpose of stock enhancement, as well as for the development of aquaculture. The development of aquafeeds for this species is in progress, as some qualitative and quantitative requirements are being determined. Nevertheless, its dietary lipid requirement is still unknown. Insufficient or excessive dietary lipid levels are detrimental to fish growth or carcass quality. Thus, the present work investigated the effects of dietary lipid level on growth performance, feed utilization, and body composition of T. macdonaldi.

An 8-week growth trial was performed in an indoor clear-water recirculating culture system at Kino Bay Experiment Station, University of Sonora, Mexico, consisting of 250 L circular tanks (0.71 cm diameter, 0.4 m²) equipped with biological and mechanical filtration, UV filter, and water aeration. Four juvenile fish with average individual mean body weight of 128.3 ± 9.9 g were stocked into each tank. A fixed dietary crude protein (CP) level of 46% was used to formulate diets containing 6, 8, 11, 14, 17, 20, and 22% dietary crude fat (CF). Each diet was randomly assigned to 5 replicate tanks. Fish were fed 3% of wet body weight daily, overfeeding was minimized while maintaining the feeding rate close to apparent satiation; the daily ration was divided into three equal portions offered at 08:00, 13:00, and 18:00 h. Total ammonia nitrogen, nitrite, and pH were monitored weekly, while dissolved oxygen, salinity and temperature were monitored daily.

Adequate and comparable growth of totoaba was observed over the 8 to 22% range of dietary CF. In contrast, growth was significantly reduced in fish fed 6% dietary CF, as evaluated by final weight, weight gain (g), percent weight gain, daily weight gain, thermal growth coefficient, and specific growth rate (Figure 1). These results were supported by measurements of the feed utilization indices. In response to increasing dietary lipid, lipid deposition in whole fish and liver increased significantly, while the moisture content was significantly reduced in these tissues. The CF content of fish muscle remained under 2% when fed up to 22% dietary lipid, it is therefore considered a lean-fish, although it is evident from these and other observations, that the muscle CF content of totoaba can be altered through dietary manipulation.